The Eu3+ fluorescence line‐narrowing (FLN) results, used to estimate the Eu3+ occupation at given sites  in the host crystal , reveal that the Eu3+ ions have a twin distribution in both the A and B sites with high asymmetry ratios of ΛA = 9.7 and ΛB = 10.7, respectively. More interestingly, at lower Eu3+ doping levels, the ions are predominantly located at the B sites (≈75%), indicating that the high color purity of Ca3WO6: is mainly caused by the high asymmetry ratios of the Eu3+ sites. Rietveld refinement combined with the FLN technique provides more reliable results for increasing the Eu3+ substitution at the A site with Eu3+ and K+ doping concentrations, which lower the lattice energy of Ca3WO6:. The structural distortions owing to K+ co‐doping in terms of the quadratic elongation and bond‐angle variance exhibit good correlations with the Ca(Eu)O12 A‐site cuboctahedra and Ca(Eu)O6 B‐site octahedra, partially accounting for the higher Λ values.In this study, Eu 3+ positioning and local site distortion in Eu3+ and K+ co‐doped Ca3WO6 double perovskites, elucidating their high‐color‐purity red photoluminescence and a twin distribution of Eu3+ ions at sites A and B. The computational approach is also adapted to validate the estimations.In this study, synchrotron X‐ray diffraction, Rietveld refinement, and high‐resolution photoluminescence spectroscopy are combined to reliably estimate Eu However, the former type of LEDs are not ideal for indoor illumination because they have a lower color‐rending index (Ra < 80) owing to insufficient red‐luminescent components. Conversely, for the latter type of LEDs, the red‐component luminescence intensity of red phosphors excited by NUV LEDs, such as Y2O2S:Eu3+ and Y2O3:Eu3+, is much lower than that of other color components, such as green‐luminescent ZnS:Cu+,Al3+, and blue BaMgAl10O17:Eu2+ phosphors, which cause the white light to deviate from natural light. Therefore, new red phosphors that are cost‐effective, have high emission intensities under NUV‐blue excitation, high color purity, and satisfactory chemical stability are required. A relatively new application of red phosphors has been developed in artificial plant factories, where red illumination is used to grow a variety of plants in well‐organized in‐house environments free from diseases and unaffected by unexpected weather conditions.Ultraviolet (UV) or blue‐light‐excited phosphor‐conversion‐type light‐emitting diodes (pc‐LEDs) have attracted increasing attention as third‐generation white‐light illumination devices owing to their high efficiency, high brightness, long lifetime, and environmental protection.1 Comm3+‐adopted molybdate and tungstate compounds have attracted significant attention as potential red phosphors owing to the energy transfer from MO42−  tetrahedra or MO66− octahedra to Eu3+ ions, as molybdate and tungstate have a broad, strong charge‐transfer band (CTB) in the NUV‐blue region. Among them, double perovskite oxides A2BMO6 , Eu3+, AA'BMO6 , and Eu3+ systems with an MO6 octahedral framework have been widely investigated.6− octahedra exhibit a broad PL peak caused by CT centered at 2.91 eV (≈426 nm). However, at room temperature (R.T.), the PL intensity originating from [WO6]6− is very low because of thermal quenching. Additionally, such a broad PL from [WO6]6− was not observed in this study. Therefore, the PL contribution from [WO6]6− in our compounds appears to be negligible.The tungstate ion is well‐known as a luminescence center in inorganic materials. In the case of the Ca≈426 nm).39 How3+ and K+ concentration dependence of the emission intensities of Ca3‐2xEuxKxWO6 (x = 0.025–0.275) at 615 nm excited at 320 nm (CTB), 395 nm, and 465 nm (direct excitation of Eu3+). The evolution of the latter two direct excitations (395 and 465 nm) is almost identical. They displayed a rapidly increasing intensity up to x = 0.075, followed by a moderate increase, and thereafter, an intensity decrease owing to concentration quenching in a concentration region higher than x = 0.175. By contrast, the CTB excitation induced a different evolution that continuously increased up to x = 0.175 and thereafter showed a moderate enhancement. This can be explained by the difference in the local structures of Eu3+ ions, which are excitable at their respective excitation wavelengths: when using the CTB excitation wavelength, Eu3+ ions at the B site should be excited because the corner sharing via oxygen between WO6 and the neighboring EuO6 at the B site allows energy transfer from the WO6 octahedra to Eu3+ ions by an exchange mechanism; consequently, the emission of the B‐site Eu3+ ions is more easily induced than that of the A‐site Eu3+ ions in double‐perovskite host materials. Moreover, the different evolutions shown in Figure 3+ ions occupy two different sites (A and B) in the Ca3WO6 structure.Figure 3‐2xEuxKxWO6 as a function of Eu3+ and K+ concentrations is shown in Figure 5D0 – 7F1 and I5D0–7F2  are the emission intensities of 5D0–7F1 (MD) and 5D0–7F2 (ED), respectively. The asymmetry ratio Λ might be useful for discussing the magnitude of the degree of distortion of the Eu3+–O2− coordination polyhedron. The tendency of the symmetry ratio of Ca3‐2xEuxKxWO6 as a function of Eu3+ and K+ concentration differed between the CTB and Eu3+ direct excitations, as shown in Figure 3+ ions occupying sites A and B have different asymmetry ratios, particularly at concentrations lower than x = 0.125. In the present Ca3‐2xEuxKxWO6 system, the asymmetry ratio increased with the concentrations of Eu3+ and K+ up to x = 0.1 and 0.125, respectively, at CTB and direct excitations of Eu3+; thereafter, a drop was observed, and the Λ value was maintained. Zhao et al. reported an increase in the asymmetry ratio with K+ ion doping. They attributed this to the difference in the radii of Ca2+ (148 pm) and K+ (178 pm) ions. Indeed, the different radii of the host and charge‐compensation ions induces lattice distortion, increasing the asymmetry ratio. Conversely, the decrease in the asymmetry ratio exceeding x = 0.1 and 0.125 indicates that significant doping of the charge‐compensation ion with different ionic radii would relieve the distortion in the lattice , YVO4:Eu3+ nanopowder (Λ = 8.3), BaTiO3:Eu3+ (Λ = 6.5), and BaZrO3:Eu3+ (Λ = 7.8). These values resulted from the distortion induced in the nanoscale particles and/or by the presence of defects such as oxygen vacancies.In addition, the asymmetry ratio shown in the system excited by CTB was found to be sufficiently high, i.e., Λ = 7.2 at x = 0.1; this was a higher value in comparison with other red phosphor candidates for pc‐LEDs, such as YΛ = 6.3),22 YVO3+ and K+ concentrations of 320 and 395 nm, respectively, were estimated, as shown in Figure f−f) excitation, concentration quenching of PL occurs due to energy killer sites that capture the excitation energy transferred among Eu3+ ions. Nevertheless, the increasing concentration of Eu3+ ions compensates for the decrease and thus the PL intensity remains high. Notably, the IQE and EQE excited at 320 nm (CTB) were quite low compared with those excited at 395 nm at maxima of 2.9% (x = 0.2) and 1.9% (x = 0.2), respectively. In the quantum‐efficiency experiment, the absorption ratio at the corresponding wavelength, defined as the number of absorption photons divided by the number of incident photons, was estimated, as shown in Figure f−f direct) excitation. Nevertheless, the quantum efficiencies (IQE and EQE) for the 320 nm excitation were much lower than those for direct excitation. It should be noted that Eu3+ PL incited under 320 nm excitation required energy transfer from O2p electrons to Eu3+ ions, indicating the possibility of an energy trap for defects during the energy‐transfer process and/or non‐radiative relaxation of O2p electrons. Moreover, energy loss may occur within Eu3+ ions after receiving excitation energy from O2p electrons; consequently, Eu3+ ions would relax to the ground state nonradiatively. Host absorption is also possible because the reported bandgap of the Ca3WO6 crystal is 3.82 eV, corresponding to the absorption edge wavelength of ≈325 nm; therefore, this is one of the loss processes of the absorbed photons.The internal quantum efficiency (IQE) and external quantum efficiency (EQE) at Euu3+ ions.49 Nev the critical distance for PL concentration quenching was estimated as follows:V is the unit cell volume, cx is the critical concentration for PL quenching, and Z is the number of cation sites in the unit cell. At x = 0.225 and 0.175, the PL intensity was maximized in the CTB and direct excitation, respectively, and thereafter decreased with a further increase in the concentration. The cR values were estimated as 11.0 and 11.5 Å. Blasse suggested multipole and exchange interactions as the mechanisms of energy transfer for Rc > 5 Å and Rc < 5 Å, respectively. The Rc values exceed 5 Å, indicating that the mechanism between Eu3+ ions in the CaWO3 double perovskite was likely caused by multipole interactions.Using the Blasse equation,51 the3‐2xEuxKxWO6 are shown in Figure Table 3+ and K+ concentrations results in the color coordinates approaching the ideal red chromaticity  for the National Television Standard Committee (NTSC) system. The CCT values ranged from 2000 to 3000 K, except at x = 0.025 and 0.05. To assess the effect of Eu3+ and K+ co‐doping, the color purity (C.P.) was calculated as follows:dx, dy) are the coordinates of the dominant wavelength,  are the coordinates of the sample point, and  are the coordinates of the illuminant point. In this study,  =   and  =   for a dominant wavelength of 615 nm. The calculation results are listed in Table 1‐2xEuxLixTiO3 red phosphors. As observed in the PL spectra  phosphors exhibited 5D2 and 5D1 emissions at lower Eu3+ concentrations, which reduced the purity of the red color  chromaticity coordinates of Caa Figure , the Eu3r Figure . Figure C.P. values of various Eu3±doped phosphors, as a function of the asymmetry ratio, as shown in Table Figure 3WO6:, which will provide more insight into the correlation of the C.P. value with the asymmetry ratio. As indicated by the linear correlation coefficient (0.750), the correlation is not linear but semi‐logarithmic (correlation coefficient: 0.917) according to C.P.  =  82.04  +  15.59  ×  log10(Λ) for 0.2 < Λ < 10. Nevertheless, this plot clarifies the reason for the higher color purity of the Eu3+ red luminescence with an increase in local asymmetry around the Eu3+ ions. It can be seen that the C.P. values do not always fall on the regression line, which is due to their spectral shapes, PL peak shift, and line broadenings of the 5D0‐7FJ signals  in the red‐orange region. Other previously reported values, for instance, C.P. = 82.9%, Λ = 4.61 for YVO4:2%Eu3+, and C.P. = 94.2%, Λ = 1.04 for Y2O2S:0.5%Eu3+, deviate significantly from the regression line (not plotted in the figure) owing to the influence of blue‐green luminescence from 5D1,2, as discussed above. Alternatively, these reported values might have been calculated in the limited spectral region of longer wavelengths (orange‐red).Here, we attempt to assess the CIE coordinates and hosphors,68 as + ions acting as charge compensators. To further investigate the structural factors influencing the PL properties, high‐resolution PL spectroscopy was performed, and the obtained data were used for the crystallographic analysis of the Rietveld refinement to clarify the effect of the local structures on the macroscopic PL properties. The next section describes the methodology and provides insights into the development of phosphors with high color purity.Moreover, the PL color properties observed in this study could be derived from structural modifications or distortions caused by the co‐doping of large monovalent K2.33‐2xEuxKxWO6 (x = 0.025–0.275) and the deconvoluted PLE spectrum of Ca2.95Eu0.025K0.025WO6 obtained via the FLN technique at 615 nm are shown in Figure 7F0–5D0 transition range of 577 (≈17 330 cm−1) and 581.4 nm (≈17 200 cm−1). In the case of Eu3+ in a lattice site, the 7F0–5D0 transition should give rise to a peak because 7F0 and 5D0 are nondegenerate levels. As shown in the figure, two different peaks appear at λA = 579.1 nm (peak A) and λB = 580.3 nm (peak B). The multiple peaks appearing in the 7F0–5D0 transition indicate the presence of a corresponding number of Eu3+ lattice sites. Moreover, the peak positions indicated that the different excitation energies were affected by the intensity of each site in the crystal field. Specifically, it was established that the red shift of the Eu3+f–f transition occurs in crystals, as opposed to the Eu3+ species existing as free ions. Jørgensen explained this as the “nephelauxetic effect,” indicating an energy shift of the excitation level by crystal fields. Therefore, the Eu3+ ions occupy two different lattice sites, as evidenced by the spectra of the two 7F0–5D0 transition peaks. The two Eu3+ lattice sites must be Ca2+ sites in the Ca3WO6 structure, where the Ca2+ ions occupy the A (12‐coordinate) and B (6‐coordinate) sites in the perovskite structure. Each excitation peak was identified by comparing the A‐ and B‐site crystal‐field potentials, as the excitation peak shift is dependent on the depth of the crystal‐field potential via the nephelauxetic effect. The electrostatic potentials at the A and B sites were estimated as −1.44 and −1.77 eÅ−1, respectively, considering only the nearest neighboring anions in the A‐ and B‐site polyhedra. As a result, the peaks at λA and λB were assigned to A‐ and B‐site Eu3+ ions, respectively. Deconvolution was applied to the other samples, and the results are shown in Supporting Information. For lower x concentrations, the two main peaks were deconvoluted to determine the integrated intensities of peaks A and B, with a slight background band . Moreover, when x  ≥  0.175, additional broad bands separated by spectral deconvolution, as shown in Figure −1) and ≈577.7 nm (≈17 310 cm−1). These bands seem to be attributed to Eu3+ in the impurity crystal phase, Ca9Eu2W4O24, as the peak position corresponded to the excitation bands spanning from ≈578.7 to ≈581.4 nm in the high‐resolution PLE spectrum of Ca9Eu2W4O24 previously reported by Qin et al.The PLE spectra of Ca00 cm−1).31 In 3+ and K+ concentrations. This implies a diversification of the electrostatic potential in the A‐site Eu3+ owing to two possible factors: the presence of oxygen vacancies and varied atomic positions in the unit cell. As discussed previously, oxygen vacancies are common in perovskite structures. In addition, according to Shannon et al., the radii of 12‐coordinate Ca2+ and K+ ions are 148 and 178 pm, respectively, corresponding to a size difference of 30 pm. Thus, the atomic positions of the constituents around the K+ ions were affected by K+ doping. Based on these two factors, the B‐site polyhedron was tilted while maintaining its shape via strong covalent bonding with oxygen, whereas distortion of the A‐site polyhedron was induced owing to its ionic bonding nature. Thus, we believe that the diversification, particularly at the A site, is caused by slightly different local environments around Eu3+ ions, that is inhomogeneous broadening of Eu3+ PL. This is attributed to the introduction of oxygen vacancies and the alteration of oxygen positions through Ca2+ substitution with K+ ions of different ionic radii  indicated that the A‐ and B‐site symmetries have a lower site symmetry (1C) and an inversion center (iC), respectively. Thus, the 5D0–7F1 and 5D0–7F2 transition peaks split into a triplet and pentet, respectively, as observed in each spectrum (marked ↓), corresponding to the degeneracies of the final levels of 7F1,2. Low site symmetries were found to disrupt the degeneracies via the crystal‐field effect. The difference between the A and B sites for the Eu3+ ions was reflected in the shape of the site‐selective spectra.3‐2xEuxKxWO6 (x = 0.025–0.275) as a function of the Eu3+ and K+ concentrations. The B‐site asymmetry ratio was higher than that of site A for all samples. The highest Λ value was 10.7 and 9.7 for sites B and A, respectively. The asymmetry ratio tended to increase with x, particularly at site B. When the concentration increased to x = 0.125, the site‐selective asymmetry ratio decreased for both A and B sites. This agrees with the asymmetry ratio evolution estimated from the conventionally obtained PL spectra  as a function of the Eu3+ and K+ concentrations. The following Equations 3+ distribution at sites A and B based on the high‐resolution PLE and site‐selective PL spectra.NEu denotes the total number of Eu3+ ions; NA site and NB site denote the number of Eu3+ ions at the A and B sites in the Ca3WO6 structure, respectively; PA and PB denote the Eu3+ ratios at the A and B sites, respectively; and CA and CB denote the calibration factors for the A‐ and B‐site PL peak areas and Speak A and Speak B in the PLE spectra, respectively. Notably, the PLE spectra were recorded with a larger slit width (Δλem) of ≈15 nm to collect more 5D0−7F2 emissions. As the integrated intensity of the 7F0–5D0 excitation band for 5D0−7F2 emission depends on the transition probability W0 − 2 and the number of Eu3+ ions at each site, the number of Eu3+ ions in the A and B sites should be estimated by eliminating the influence of the transition probabilities W0 − 2 of each Eu3+ ion from the integrated intensity. The calibration factors in Equations  are the branching ratios of the 5D0−7F2 emission, W0 − 2/(W0 − 1 + W0 − 2), under the approximation of negligible 5D0−7F0 and 5D0−7F3‐4 emissions. Thus, the quotient of the integrated 5D0–7F2 intensity (Speak A or Speak B) divided by the branching ratio was proportional to the number of Eu3+ ions at a specific site (see Supporting Information for a detailed derivation). Based on the aforementioned considerations, the Eu3+ distribution was analyzed, and the results in Figure 3+ was ≈77–54% for site B in all samples. The highest B‐site occupation of Eu3+ is 77.0% at x = 0.075, decreasing to 54.0% at x = 0.275.ΛA1+ΛACB=ΛB1+Λ3+ distribution estimated using this method was verified by comparing the reliability factors Rwp and FR obtained via Rietveld refinement for Eu3+‐doped ions substituted only at site A, only at site B, and at both sites, with a distribution estimated by the FLN spectra, as shown in Figure Rwp and FR are reliability factors that indicate the degree of agreement between the fitting and calculation validity of a structural model. The Rwp and FR results show that the FLN distribution model is more reasonable than the A‐ or B‐site substitution models.The Eu3+ concentration  to Eu3+(A). This is evidenced by the presence of Eu3+–Eu3+ interactions that improve color purity by reducing 5D1,2 emissions via cross‐relaxation between neighboring Eu3+ ions with increasing Eu3+ concentration, as explained in Section To explain the observed PL properties as a function of Eun Figure , additioe A site.78 Fors Figure ; therefo3+ ions distributed among the A and B sites, and why is a selected lattice site (A or B) not used for Eu3+ ions in the Ca3WO6 crystal? According to Van Gool and Piken, the chemical composition and crystal structure are determined by the thermodynamic energy reflected by Madelung's electrostatic potential. Hoppe demonstrated that the enthalpy of formation of solids was reflected by the Madelung electrostatic potential, and Glasser showed that the total lattice energy and Madelung electrostatic potential had a linear relationship in ionic solids. Based on these fundamentals, the Madelung lattice energies (EM) were calculated for the Ca3‐2xEuxKxWO6 (x = 0.025–0.275) crystal structure models obtained via Rietveld refinement of Figure i) and EM of the crystal structure were calculated using the following equations in the VESTA program,Zj denotes the valence of ion j, ε0 is the permittivity of a vacuum, and lij is the distance between ions i and j.Wi=(occupancy)×.In this study, the following questions arise: Why are the Eund Piken,79 the3+ and K+ at the Ca site (A and/or B) in the Ca3WO6 lattice stabilized the lattice energy; however, increasing the doping levels was found to induce different behaviors for the A‐site only, B‐site only, and Eu3+ A/B distributions obtained from the FLN analysis. The FLN distribution model clearly exhibited the most stable energy compared with the other models. When Eu3+ ions were substituted at both A and B sites with the distribution shown in Figure EM was stabilized by Eu3+ and K+ doping. The reason for this stabilization is explained in the next section.In all cases, the co‐doping of Eu33.13 compounds. As defined in Equation EM) is influenced by the site potential, ϕi. Therefore, the reason for the stabilization of EM by Eu3+ and K+ doping can be elucidated by comparing the site‐potential evolutions at each lattice site as a function of the Eu3+ and K+ concentrations. The site potentials shown in Figure 3+ occupation determined using FLN spectroscopy  and distance (ijl) between Eu3+(W6+) and neighboring j‐th ions, as shown in Equation 2+ with Eu3+ and K+ affect the lattice site valence.Changes in the charge distribution of the structure induced by the substitution of CaChanges in the number of cation or anion vacancies affect the lattice site valence.2+ with Eu3+ and K+ affect the distance between the ions.Changes in the atomic positions of all ions by substituting CaYoshimura and Sardar showed that the structural stability of a crystal can be described by Madelung electrostatic site potentials and lattice energies, which are applicable to perovskite‐structured ABOompounds.37 As y Figure , the chey Figure , as disc3+ occupation parameters at sites A and B, chemical compositions, and atomic positions in the unit cell were considered and are listed in Table 2+ + Ca2+(A) → Eu3+ + K+(A). To avoid the vacancy effect, atomic positions were obtained from the database (JCPDS 22–0541). The second set of parameters, denoted cal‐2, reflects the evolution of scenarios I and II. Accordingly, scenario II could be extracted by subtracting ϕi, obtained from the cal‐1 parameter set, from the ϕi of cal‐2, where the structure of Ca3WO6 from the database was used to simplify the calculation. The final set of parameters  reflects scenario III, whose atomic positions were taken from those obtained via Rietveld refinement as a function of the Eu3+ and K+ concentrations.To formulate scenarios I–III, a series of EuA), B‐site Ca(Eu) (ϕB), and W (ϕW) are shown in Figure A . The evolution of cal‐1 appeared to be linear, whereas that of cal‐X and cal‐2 was more complex. By contrast, cal‐3 exhibited a slight destabilization trend. Notably, the cal‐X and cal‐2 results resembled the evolution of ϕA with an increase in Eu3+ and K+ concentrations, i.e., ϕA evolution was strongly dependent on the change in charge distribution, as observed in scenarios I and II. To determine which scenario was more likely to occur for ϕA, we compared the correlation coefficient of the experimental result  with those of scenario I  and scenario II , which was assessed by subtracting the evolution in cal‐1 from that in cal‐2. The correlation coefficients were estimated to be 0.78  and 0.99 . In conclusion, the ϕA stabilization must be caused by the introduction of vacancies.The calculated site potentials for the A‐site Ca  – ϕA) were calculated to determine which defective vacancies of oxygen or cations influenced ϕA stabilization. Robust negative correlations of −0.96 and −0.94 were estimated for cal‐2 and cal‐1, respectively. In addition, the change in charge distribution owing to Eu3+ substitution at the A or B sites might affect ϕA. The evolution of ϕA for the case of complete Eu3+ substitution at the A or B sites, as well as K+ substitution at the A site  → Eu3+(A) + K+(A)). Moreover, ϕA was stabilized when Eu3+ ions were situated at the B site. Significantly, an increase in the B‐site valence together with a decrease in the A‐site valence (Ca2+(B) + Ca2+(A) → Eu3+(B) + K+(A)) can reduce the site potential for Eu3+. According to Yoshimura and Sardar, the site A potential destabilizes with decreasing valence of the A‐site cation from A3+ to A+ for an ideal cubic perovskite structure, i.e., AIIIBIIIO3. The dissimilar behavior of ϕA is thought to arise from the different perceptions of the Ca3WO6 structure. On the one hand, it is believed to be a monoclinic double perovskite with locally distorted A and B sites; however, Yoshimura et al. assumed a simple cubic ABO3 perovskite structure. Based on the above discussion, ϕA stabilization is caused not only by the introduction of oxygen and cation vacancies but also by the charge distribution of the decreasing (increasing) average valence of A(B)‐site ions in the double perovskite host crystal.Moreover, the correlation coefficients reflecting the amount of oxygen (or cation) vacancies (mol%) and site potential ϕB O6, and WO6 polyhedra obtained via Rietveld refinement, which enables a better understanding of how the Ca3WO6 lattice is geometrically changed, particularly in relation to ϕB and ϕW. Focusing on the average bond length, the B‐site Ca lengthened and the W‐site Ca shortened with increasing Eu3+ and K+ concentrations. In addition, the expansion of the Ca(Eu)O6 polyhedra and shrinkage of the WO6 polyhedra are shown in Figure 3+ concentration because the concentration of Eu3+ ions at the B‐site exhibited a higher correlation coefficient (0.92) with the B‐site bond length. Therefore, ϕB destabilized and ϕW stabilized with increasing Eu3+ and K+ concentrations.3+ and K+ doping, the A‐site polyhedron volume decreased with doping. Based on the results, the volume change appears to be caused by a change in corner oxygen position followed by a change in W‐ and B‐site polyhedra volumes, keeping with Ca(A)−O bond length.Interestingly, although the average bond length of site A was almost unaffected by doping and only slightly increased with EuEM calculated using cal‐X and cal‐1–3 are shown in Figure EM was estimated using cal‐X and cal‐1,3 stabilized with Eu3+ and K+. The contribution to EM was significant, decreasing in the order ϕW > ϕA > ϕB because the formal charge of W6+ was triple that of the B‐site Ca2+, whereas the A‐site Ca2+ ions occupied double the equivalent positions of B‐site Ca2+. Thus, even though ϕB was destabilized by the expansion of the B‐site polyhedron, EM was stabilized because the ϕW and ϕA potentials were significantly stabilized by the shrinkage of the WO6 polyhedron and change in charge distribution by doping and oxygen defects. In conclusion, because EM stabilization is caused by ϕW and ϕA stability induced by Eu3+ substitution at site B, B‐site substitution is dominant in the Eu3+ distribution. Furthermore, increasing the concentration of K+ at the A sites induces the destabilization of ϕB by the expansion of the B‐site polyhedron, which can be compensated for by decreasing the ϕA site potential.The lattice energies 3+ ions will be discussed in relation with the Eu3+ asymmetry ratio obtained from the luminescence data. Thus, it is worth mentioning the question of which structural model is most convincing for the Ca3WO6:Eu3+,K+ phosphors. It should be noted that the atomic ratios, including Eu3+ and K+ ions, were experimentally determined though EDS measurements. The distribution of Eu3+ ions between the A and B sites was estimated using the high‐resolution PLE technique of FLN, which demonstrated high reliability even for the low concentration x = 0.025, as shown in Figure Rwp and RF) were observed in both cases, indicating that the refinement using the Eu3+ distribution successfully reproduced the observed synchrotron XRD patterns of the samples. This practical model provides an explanation for the structure of the respective sample and will be used in the next section.In the following section, the geometrical evolution of A and B site structures for Eu3.25D0−7F2 ED transition of Eu3+ ions can be allowed for Eu3+ ions at lattice sites without inversion symmetry. To the best of our knowledge, parameters that appropriately describe the ED transition intensity have not yet been proposed for Eu3+‐doped phosphors. A geometrical parameter reflecting the asymmetry ratio Λ would help screen a variety of potential phosphors for the design of high‐color‐purity red phosphors. In this study, the representative geometrical distortion parameters of coordination polyhedra, namely quadratic elongation <λ> and bond angle variance (BAV) σ2, were proselytized by Robinson et al., who investigated the correlation using the asymmetry ratio defined by Equation 2 were calculated using Equations n denotes the number of all coordinate oxygen bonds with the center cation in the polyhedron; il denotes the length from the center cation to the i‐th oxygen; l0 denotes the center‐to‐vertex distance for an octahedron with Oh symmetry, whose volume is equal to that of the strained or distorted octahedron with bond length il; m denotes the number of angles consisting of nearest‐neighbor oxygen–cation bonds in the polyhedron; θi denotes the i‐th O–M–O angle, and θ0 denotes the O–M–O angle of the corresponding regular polyhedra. Figure 3‐2xEuxKxWO6, with the correlation coefficient r. For both the A‐site cuboctahedron and B‐site octahedron, <λ> and σ2 were linearly plotted, where rAsite = 0.42 and rBsite = 0.97, respectively. Robinson et al. demonstrated a strong linear correlation between <λ> and σ2 on the tetrahedra and octahedra of eight and five types of compounds, respectively. Another study on a variety of compounds revealed a strong relationship between the two parameters. Specifically, a strong linear correlation between <λ> and σ2 was confirmed for the B‐site octahedra of the double‐perovskite‐type compound Ca3‐2xEuxKxWO6. To determine whether <λ> or σ2 was affected by the structural components, 2D plots of <λ> and σ2 in the A‐ and B‐site polyhedra and K+ ion concentrations were obtained via EDS measurements, as shown in Figure 2 for sites A and B are shown in Figure 2 and the K+ ion concentrations were found to be strongly positive or negative and linear at the A and B sites, respectively, indicating that K+ doping increased the distortion of the A‐site Ca(Eu)O12 cuboctahedra and decreased the distortion of the B‐site Ca(Eu)O6 octahedra. A similar trend was observed in previous studies on Eu3+‐doped double‐perovskite‐type phosphors, where the evolution of the asymmetry ratio of Eu3+ 5D0−7F1,2 transitioned with increasing concentrations of K+ ions, which were co‐doped in the host compound.In general, the n et al.,83 who2) are well correlated with the asymmetries of the B‐site octahedra, although there is no correlation between <λ> (or σ2) and Λ for the A‐site cuboctahedra. Notably, <λ> and σ2 are structurally averaged parameters representing the features of the MO6 and MO12 polyhedra (M = Ca and Eu (or K)), whereas Λ is a spectroscopically obtained parameter that reflects the local environment around the Eu3+ ions. Thus, the correlation coefficients for the A‐site cuboctahedra and B‐site octahedra can be interpreted as the degree to which MOn polyhedral distortion coincides with that contributing to the luminescence of Eu3+. The linear correlations in Figure 2 of the Ca(Eu)O6 octahedra appropriately describe the distortion of the B‐site EuO6. Conversely, no correlation between <λ> (or σ2) and Λ of the A‐site cuboctahedra was observed. The difference in the tendencies of the A‐ and B‐site polyhedra resulted from their rigidity, which arises from the strength of the bond between oxygen and the center cation of each polyhedral site. If the bond is covalent, the polyhedral shape is easily maintained. Conversely, if the bond is weak, the polyhedral shape is likely to change via Eu3+ substitution at the Ca sites. In other words, <λ> and σ2 of Ca(Eu)O6, estimated via Rietveld refinement, were similar in evolution to the Λ values spectroscopically determined for the EuO6 octahedra; however, the polyhedron distortion of Ca(Eu)O12 appeared to differ from that of the EuO12 polyhedron. Although further investigations using expansive compounds are required, it is noteworthy that the geometrical distortion parameters <λ> and σ2 could be helpful in reflecting the distortion around the Eu3+ ions when exploring new Eu3+‐doped red phosphors.Figure + co‐doping on the asymmetry ratio, quadratic elongation, and bond angle variance were discussed in the final part of this study. The evolution of luminescence properties with varying concentrations of Eu3+ and K+ was carefully tracked, and it was found that the luminescence evolution is influenced by both Eu3+ and K+ doping concentrations, encompassing all substitution effects. Therefore, an attempt was made to statistically separate and analyze the doping effects of each element. The correlation coefficient between the fraction of each element in the samples and the quadratic elongation or bond angle variance was examined. The element fractions, including Eu3+ and K+ ions, were experimentally evaluated through EDS measurements, as shown in Table B) and the quadratic elongation or bond angle variance at the B site  exhibited weaker correlations with the quadratic elongation or bond angle variance at the A site  were systematically investigated. The basic luminescence properties can be summarized as follows. All the samples exhibited a pure red emission with CIE coordinates of , which approaches the ideal red color with the help of effective Eu3+–Eu3+ interactions with an increase in x, reducing 5D1,2 emissions. The highest asymmetry ratio was 7.2 at x = 0.1 when excited at 320 nm, whereas the highest IQE was 12.3% at x = 0.1 when excited at 395 nm. Site‐selective PL spectroscopy was used to estimate the microscopic asymmetry ratios. The A‐ and B site‐selective asymmetry ratios were found to be significantly high, with values of 9.8 and 10.7 at x = 0.075 and 0.125, respectively. Peak splitting was also observed in the spectra based on the local symmetries of C1 and Ci around the Eu3+ ions at the A and B sites, respectively, with a break in the inversion symmetry. The high‐resolution PLE spectra revealed that Eu3+ had a twin distribution at sites A and B. The Eu3+ occupation at the B site was quantitatively estimated to be 50–75 atm%, and that at the A site increased with increasing Eu3+ and K+ concentrations. The validity of the distribution was confirmed using Rietveld refinement, and lattice energies (EM) were compared for a variety of Eu3+ distributions, following the results of the FLN spectra and 100% A‐ or B‐site substitution models. The Eu3+ site distribution was explained by the site potentials (ϕi). The B‐site substitution of Eu3+ ions was dominant for lower Eu3+ and K+ concentrations despite the dopant‐induced ϕB destabilization by the expansion of the B‐site polyhedron because the simultaneous substitution of K+ at the A site effectively stabilized the ϕA potential. Further doping caused an increase in the A‐site Eu3+ occupancy and reduced the EM energy owing not only to the stabilization effect but also the decrease in ϕW, resulting in well‐structured WO6 frameworks. Based on these results, it was concluded that two factors of the Eu3+ lattice site endowed Ca3‐2xEuxKxWO6 with an extremely high asymmetry ratio and red PL color purity: 1) the lower symmetry (higher asymmetry ratio) and higher Eu3+ distribution at the B site compared with those of the A site, and 2) Eu3+–Eu3+ interactions, which reduced 5D1,2 emissions. The methodology demonstrated here can be applied to Eu3+ crystalline phosphors with multiple Eu3+ sites to elucidate the structural origins of their luminescence properties and is promising for accelerating the development of new Eu3+ phosphors.The optical properties and structural parameters of Ca53‐2xEuxKxWO6 (x = 0.025–0.275) were prepared using a conventional solid‐state reaction method. The raw materials were CaCO3 , WO3 , Eu2O3 , and K2CO3 . All the raw materials were mixed in stoichiometric amounts for 20 min in an agate mortar. The mixed powders were then placed in an aluminum crucible and calcined at 1200 °C in air for 12 h.Powdered samples of Ca The Madelung electrostatic site potential and lattice energy were calculated from the crystal structure using MADEL, a Madelung potential calculation software built into VESTA. The Eu3+ concentrations of the samples were estimated using energy‐dispersive X‐ray spectroscopy (EDS) using a JEOL JSM‐6010LA scanning electron microscope (SEM) with an acceleration voltage of 10 kV. The photoluminescence (PL) and photoluminescence emission (PLE) spectra were measured using a Hitachi F‐7000 fluorescence spectrophotometer. In addition, the quantum efficiency was assessed using a spectrophotometer with a BaSO4‐coated integration sphere. The FLN spectra were obtained using a tunable dye laser (rhodamine 6G:566–640 nm) pumped by an Ar+ laser . The dye laser with a linewidth of ≈1 cm−1 could site‐selectively excite Eu3+ ions within the inhomogeneous absorption width of the 7F0–5D0 transition. During the acquisition of the PLE spectra, a larger slit width corresponding to ≈15 nm was used to collect the widest possible 5D0‐7F2 luminescence component, which ranged from 600 to 630 nm.XRD patterns were obtained to confirm the crystal phases of the samples using an X‐ray diffractometer  with Cu Kα radiation (λ = 1.5418 Å) at a tube voltage of 45 kV and tube current of 40 mA. Synchrotron XRD measurements of the samples were performed to obtain the crystal structure parameters at the BL5S2 beamline of the Aichi Synchrotron Radiation Center . The X‐ray wavelength was 0.8002 Å. Rietveld refinement was performed using the RIETAN‐FP.86 TheThe authors declare no conflict of interest.T.O. contributed in conceptualization, data curation, formal analysis, investigation, wrote – original draft, and visualization. R.O. contributed in writing‐review and editing, investigation, methodology, and validation. T.H. contributed in conceptualization, methodology, software, resources, investigation, writing‐review and editing, visualization, supervision, funding acquisition, validation, and project administration.Supporting InformationClick here for additional data file.


The development of novel phosphor materials with excellent performance and modification of their photoluminescence to meet the higher requirements for applications are the essential research subjects for luminescent materials. Multi-site luminescent materials with crystallographic sites for the activator ions that broaden the tunable range of luminescent spectra and even enhance the luminescent performance have attracted significant attention in the pursuit of high-quality luminescence for white light-emitting diodes. Here, we summarize multi-site luminescence characteristics based on the different kinds of host and activator ions, introduce the identifications of multi-site activator ions via optical analysis, provide a structural analysis and theoretical calculation methods, and introduce the regulation strategies and advance applications of multi-site phosphors. The review reveals the relationship between crystal structure and luminescent properties and discusses future opportunities for multi-site phosphors. This will provide guidance for the design and development of luminescent materials or other materials science. The Nobel Prize in Physics was awarded to Isamu Akasaki, Hiroshi Amano and Shuji Nakamura “for the invention of efficient blue light-emitting diodes (LEDs) which has enabled bright and energy-saving white light sources” in 2014. The white LEDs (wLEDs) have been widely used as the fourth generation of green solid-state lighting sources in general lighting, displays and other advanced applications ,4. Nowad3Al5O12:Ce3+ were restricted to low color rendering index (CRI) Ra < 80 for advanced and healthy applications  dodecahedrons, [DO6] octahedrons, and [EO4] tetrahedrons are illustrated in 3+ is generally dominated at a single crystallographic site, and even Eu2+ is difficult to introduce into the garnet lattice; this can be attributed to the significant differences in the crystallographic environment among the A, D and E sites and the rare appropriate divalent crystal sites in the garnet lattice. As a result of the research and development of the garnet-structure phosphor, increasing numbers of multi-composition materials are synthesized and studied, as the A, D and E cationic sites can be occupied by various divalent, trivalent or tetravalent ions, including Y3+, La3+, Gd3+, Lu3+, Mg2+, Ca2+, Sr2+, Ba2+, Al3+, Ga3+, Sc3+, Zr4+, Hf4+, Si4+, Ge4+, etc. The garnet lattice possesses various cationic crystallographic sites with different valence states, which provide significant possibilities to construct numerous multi-site luminescence opportunities. The design of phosphors based on the typical structural model is an effective strategy . To achi2+ doping, the {Y2Mg}[MgAl](AlSi2)O12 (YMAS) is designed via the substitution of Mg2+-Si4+ for Y3+-Al3+ and Al3+-Al3+ in YAG, whose structure model is illustrated in 2+, exhibits a broad band that can be divided into two Gaussian bands peaked at 461 nm and 503 nm due to the Eu2+ ions dominated at eight-coordinated and six-coordinated crystallographic sites, respectively  is changed from 80 to 105 nm with the Eu2+ doping level from 0.01 to 0.10 due to the crystal field splitting and nephelauxetic effect. Similarly, the Mn2+ doped YMAS phosphor is synthesized, which exhibits the multiple emissions. As shown in 2+ ions occupy Mg2+ site of [AO8] dodecahedron to form red emission peaked at 635 nm (Mn1), replace Mg2+ site of [DO6] octahedron to form deep red emission peaked at 735 nm (Mn2) and dominate the Al3+ site of [EO4] tetrahedron to form green emission peaked at 536 nm (Mn3) , , [Ga2/Mg2] and [Ga5/Ge1] sites, respectively. Furthermore, the concentration quenching of different emissions shows different speeds (CrI > CrII > CrIII > CrIV) which also causes energy transfer. Based on the above, the FWHM of Mg7Ga2GeO12:Cr3+ phosphor can be broadened from 101 to 226 nm by changing the Cr3+ doping concentration. Similarly, some Cr3+-doped multi-site NIR phosphors are summarized and shown in Recently, many Cr3+ emission exhibits a series of sharp emission bands whose peaks barely shift with changes in the local surrounding. However, the multi-site regulation of Eu3+ can achieve the modification of color coordinates, luminescence efficiency and thermal stability. For instance, the SrLu2O4 (SLO) compound with an orthorhombic structure provides two inequivalent crystallographic sites of Lu3+ that can be dominated by Eu3+ activator ions, forming the two types of (Lu1/Eu1)O6 and (Lu2/Eu2)O6 octahedrons  and the enlargement of the [WO6] octahedron, as shown in 2+ to W6+ sites and results in the effective Mn4+ emission, as illustrated in As with Eu ions, Mn ions with two types of valance state can be used as the activator of phosphors, including Mnthe host . MgGa2O4ectively . Incorpo3+-activated phosphors with strong near-ultraviolet absorption and efficient emission have been developed for high-quality pc-LEDs. Based on the multi-site luminescence strategy, a broadband cyan-emitting K2Ca2Si2O7:Bi3+ phosphor is designed and synthesized  polyhedron, as illustrated in The regulation strategy can also be used to improve the luminescence performance of multi-site phosphors, including emission intensity, quantum efficiency, thermal stability, etc. The unique borosilicate Baectively . With th9Lu2Si6O24:Eu2+ lattice can improve the thermal stability because the Eu2+ ions prefer to dominate the Ba2 site with higher rigidity, gradually increasing the Sr-substituted concentration from 0 to 0.3 [2+ ions are induced to partially occupy the Ba3 site with lower rigidity, which results in lower thermal stability. As for the multi-site phosphors, different crystallographic sites for the activator ions exhibit different local structure characteristics, meaning the regulation of local structure affects thermal performance. As for Eu2+-activated Ba2Ln(BO3)2Cl, their emission spectra are centered at 526, 548 and 511 nm, as shown in 3+ in Ba1.2Ca0.8SiO4 can be improved by 30 times due to the co-doping of Ce3+ and Tb3+ [3+ in the lattice induces the energy transfer from Ce3+ to Tb3+, which significantly enhances the luminescence performance of the co-doped phosphors.Thermal stability is an essential parameter to consider when evaluating the application performance of phosphors. It is determined by the structure rigidity, band gap, crystal defects and other local structures of the luminescent materials . The evo0 to 0.3 . Howeverand Tb3+ . The mul3+, Ho3+, Tm3+, Sm3+, Yb3+, Dy3+, Gd3+, Nd3+, etc. [2+, Ce3+, Cr3+, Mn2+ or other kinds of activators that are susceptible to the external crystal field gradually attracted more attention [Besides high-quality lighting for wLEDs, multi-site luminescence has also been applied in non-contact optical thermometric technology for temperature measurements in thermally harsh, corrosive or intracellular environments . Initial3+, etc. . Howeverttention ,82. Henca) and relative sensitivity (Sr) can represent the optical thermometric property of the phosphors [9NaZn(PO4)7 is an multi-site structure for luminescence 7 phosphor exhibits an asymmetric broad emission band with peaks at around 415, 490 and 570 nm due to the 5d-4f transition of Eu2+ at Ca3, Ca1/Ca2 and Na sites, respectively. The Mg2+-substitution in the Ca9NaZn(PO4)7:Eu2+ phosphor adjusts the emission from yellow to warm white via an increased red-emitting component; this achieves good optical properties for wLEDs. The three sub-emissions of the multi-site luminescence shows different temperature-dependent performance, as shown in 2+ in Na site decreases significantly, and the Eu2+ at Ca3 site changes slightly. This might be attributed to the local crystal structure of each crystallographic site. According to the FIR calculation, the maximum Sa is 0.0228 K−1 at 498 K and the maximum Sr is 0.81 K−1 at 398 K (as shown in 9NaZn(PO4)7:Eu2+ phosphor for optical thermometry. Interestingly, the Ca9NaZn(PO4)7:Eu2+ phosphor is sensitive not only temperature, but also pressure, as shown in 2+ in Ca1/Ca2 sites are enlarged gradually. With an increase of pressure from 6.12 to 16.48 GPa, the emission bands and their intensities for Eu2+ in three luminescence centers are regulated significantly. In addition, the peaks shift from 410 to 423 nm, 502 to 552 nm and 580 to 627 nm for Eu2+ in the Ca3, Ca1/Ca2 and Na sites, respectively. The reduced symmetry, an increase in generated defects and increased phonon energy caused by pressure increasing lead to the broadening of FWHMs, as the larger nephelauxetic effect and stronger crystal field splitting due to structural shrinkage by pressure increase results in the red-shift of emission peaks. The Ca9NaZn(PO4)7:Eu2+ phosphor shows a better pressure sensitivity (5.21 nm/GPa) and exhibits very close CIE chromaticity parameters under the same pressure during the compression and decompression processes. This demonstrates its potential application for optical pressure sensors.According to the requirements of the non-contact optical thermometric technology, multi-site luminescence should be characterized by fast response, high precision and high spatial-temporal resolution ,103. Bashosphors ,98. The hosphors . The tem2+, Ce3+, Cr3+, Eu3+, Mn2+, Mn4+, Bi3+, etc. Second, identification of the preferential occupation for the activator ions is difficult but essential to reveal the structural characteristics and modify the optical performance for the multi-site phosphors. Using optical analysis, structural analysis and theoretical calculations, several measurements and methods are evaluated and elucidated to clarify the multi-site luminescence. Third, based on the clear understanding of the structure and optical properties, the regulation strategies of multi-site luminescence and their representative work are introduced and discussed in terms of modification of emission spectrum, enhancement of luminescence performance, applications on advanced fields, etc. According to the review of various experimental, theoretical and applied results, we conclude that there are still several important and necessary challenges for multi-site luminescence that must be investigated and developed in future, including but not limited to the following:Our review describes the construction, identification and regulation of the multi-site luminescence based on research and investigations conducted over the past 20 years. First, several types of host materials with various crystallographic sites for activator ions to construct multi-site phosphor are introduced in detail, and multi-site luminescence characteristics of different activator ions are summarized, including Eu(1)Design of a novel multi-site phosphor with excellent luminescent performance is still an ongoing mission. Achieving delicate control of emission color during the design process is essential for the material science. Recently, several approaches have been carried out to discover new materials based on known or unknown crystal structures that can be used to find multi-site hosts, such as solid-state combinatorial chemistry, single crystal growth, single-particle-diagnosis, etc. Furthermore, materials genome engineering and big data computing can be introduced to design a novel multi-site phosphor. Based on a high-quality material database and using scientific and accurate criteria, high throughput screening and experimental verification can effectively achieve the development of new luminescent materials. In the above approach, the mineral structure model, phase diagram, thermodynamics, energy band theory and other basic theories can guide the screening and optimization of new materials.(2)Optimization of luminescence properties of multi-site phosphors is still an important challenge. An excellent phosphor material should have strong absorption, strong emission, high luminous efficiency, high stability, etc. Generally, delicate compositional tailoring is a valid strategy to modify the surrounding crystal environment of activator ions to enhance luminescence performance, such as cation substitution, anion substitution, solid solution substitution, constructing energy transfer, etc. However, the origin of multi-site luminescence is complicated; as such, accurate directional regulation is difficult. The first principles calculation equipped with high-throughput computation and machine learning will be helpful to effectively analyze the relationship of structure and properties, which could be a promising strategy for optimization of multi-site luminescent materials.(3)Achieving wider and deeper advanced applications of multi-site phosphors is an eternal goal. Multi-site luminescent materials have been used in high-quality full-spectrum lighting due to their broad and tunable emission. Many multi-site NIR phosphors have been developed for use in security monitoring, food composition analysis, bio-sensing, etc. Recently, the applications in non-contact temperature testing have attracted significant attention and have been summarized specifically. The emission intensity and material stability of these applied phosphors must be improved further. Multi-site phosphors with better performance will obtain wider and deeper advanced applications, and could be customized according to the specific multi-site luminescence characteristics.With the higher requirements of applications, the study and research of multi-site luminescence will never stop. We hope our review will provide some inspiration for the design and modification of the multi-site phosphors, even in the wider field of luminescent materials or other materials science.


Opposite to other immunoglobulin (Ig) classes and subclasses, there is no consensus on the definition of normal levels of serum total IgE. However, longitudinal studies on birth cohorts produced growth charts of total IgE levels in helminth-free and never atopic children and defining the normal ranges of total serum IgE concentration at the individual, rather than population, level. Accordingly, very ‘low IgE producers’  became atopic while keeping their total IgE levels in a range considered ‘normal’ if compared to the general age-matched population but ‘abnormally high’ if projected on the tIgE growth chart against the trajectory of that child’s own percentile levels. In ‘low IgE producers’, the IgE-specific activity, i.e., the ratio between allergen-specific and total IgE, is more important than the absolute specific IgE levels to confirm causality between allergen exposure and allergic symptoms. Patients with allergic rhinitis or peanut anaphylaxis but low or undetectable allergen-specific IgE levels must therefore be reconsidered considering their total IgE levels. Low IgE producers have been also associated with common variable immunodeficiency, lung diseases, and malignancies. A few epidemiological studies have shown a higher risk of malignancies in very low IgE producers, leading to a debated hypothesis proposing a novel, evolutionistic-relevant function for IgE antibodies for antitumor immune surveillance. Immunoglobulin E (IgE) was discovered in the 1960s . Tests tThe normal range of IgG serum levels is kept narrow, being limited to a three-fold factor only (from 600 to 1800 mg/dL) in humans . In contConsidering that helminths are, by far, the most potent inducers of IgE , differeAs mentioned above, the apparent lack of constraints in the upper and lower limits of serum IgE levels greatly hampered the use of this parameter in the diagnostics of IgE-mediated allergic diseases ,9. On thThe evolution of total IgE levels was examined at the individual level in the Multicenter Allergy Study (MAS), a large birth cohort born in Germany in 1990 and examined until 2020 . A hallmBy defining the normality of total serum IgE values at the individual level, the definition of ‘abnormally high’ tIgE levels would change as well. The MAS also disclosed that, at the onset of the first atopic response, a child’s trajectory deviates upwards from the ‘normal trajectory’ of the patient’s own percentile . TherefoStudies in the MAS birth cohort have also led us to speculate that, in Westernized and virtually ‘helminth-free’ children, tIgE levels derive largely from two distinct pools: IgE spontaneously produced  and IgE produced during atopic responses to environmental allergens  ,20. The The concepts exposed so far may be of help in understanding those infrequent, but not rare, clinical cases of patients with IgE-mediated allergic manifestations but very low allergen-specific IgE levels. This category includes the patients with no genetic predisposition toward producing high levels of IgE but with a genetic predisposition toward producing allergen-specific IgE responses . AccordiIgE-specific activity is one of the four crucial parameters for the effective degranulation of mast cells and basophils . It is s‘Local Allergic Rhinitis’ (LAR) has been defined as a form of allergic rhinitis, confirmed by Nasal Allergen Provocation Tests (NAPT) in patients with no positive skin prick test (SPT) or IgE test against the offending allergen ,30. The The existence of a deficiency in immunoglobulin E production has been hotly debated since the discovery of this Ig class. Given their very low levels, very close to the lower limit of detection of most immunoassays, it has been difficult to find an operative definition for such an immunodeficiency . Levels A possible link between low or undetectable IgE levels and primary immunodeficiencies, with a particular focus on antibody deficiencies, was soon suspected after the discovery of IgE themselves . IgE levThere is still no report of genetic defects leading to isolated IgE deficiency . However, a family with a cluster of cases of IgE deficiency, associated with chronic bronchitis and fibrotic lung disease, has been reported . Beyond Whether these associations are genuine or spurious, i.e., due to parallel defects in other immunoglobulin classes, remains a matter of debate . In a seThe evolutionistic origin of IgE is extremely old, dating back several hundred million years , suggestMultiple epidemiological studies have described inverse associations between allergic diseases and malignancies ,49 and lNevertheless, it has been proposed that FcεRI, whose expression is upregulated by IgE, mediate through IgE themselves antibody-dependent cellular phagocytosis (ADCP) and antibody-dependent cellular cytotoxicity (ADCC) against tumor cells which membrane antigens are recognized by IgE antibodies . AccordiIf IgE antibodies really do participate in immune surveillance mechanisms against tumor cells, then low IgE producers should be at risk of developing malignancies. Indeed, a few reports in the last decade have associated IgE deficiency with malignancies. Among 63 patients with IgE deficiencies, a significantly high rate of prior malignancy was found  compared to those without IgE deficiencies, independently from the presence of CVID . In a laFive decades of investigation on IgE and allergic diseases have been mostly dedicated to investigating the pathologic effect of having too many of these immunoglobulins. For a few years now, scientists and clinicians have also been studying the other side of the coin. These investigations are opening new perspectives not only on the understanding of ‘low-IgE-producers’ and allergic patients but also on the search for the still-elusive function and evolutionistic meaning of this intriguing antibody.


Ice discharge from Greenland’s marine-terminating glaciers contributes to half of all mass loss from the ice sheet, with numerous mechanisms proposed to explain their retreat. Here, we examine K.I.V Steenstrups Nordre Bræ (‘Steenstrup’) in Southeast Greenland, which, between 2018 and 2021, retreated ~7 km, thinned ~20%, doubled in discharge, and accelerated ~300%. This rate of change is unprecedented amongst Greenland’s glaciers and now places Steenstrup in the top 10% of glaciers by contribution to ice-sheet-wide discharge. In contrast to expected behaviour from a shallow, grounded tidewater glacier, Steenstrup was insensitive to high surface temperatures that destabilised many regional glaciers in 2016, appearing instead to respond to a >2 °C anomaly in deeper Atlantic water (AW) in 2018. By 2021, a rigid proglacial mélange had developed alongside notable seasonal variability. Steenstrup’s behaviour highlights that even long-term stable glaciers with high sills are vulnerable to sudden and rapid retreat from warm AW intrusion. From 2018 to 2021, KIV Steenstrups Nordre Bræ, a marine-terminating outlet glacier of the Greenland Ice Sheet, retreated ~7 km, thinned ~20%, doubled in discharge, and accelerated ~300%. This rate of change is unprecedented in the observational record. Between a half and two-thirds of loss since the 1990s has been attributed to acceleration in ice discharge from marine-terminating outlet glaciers3, a process initiated through interactions between the ocean and the glacier terminus6. Understanding these interactions is a critical component of understanding future sea level contributions from the Greenland Ice Sheet6.The Greenland Ice Sheet is the dominant contributor to global sea-level rise from the cryosphere, losing 222 ± 30 billion tonnes of ice per year between 2012 and 20178, initiating calving loss by submarine melt and undercutting of the ice front12. The second is terminus melt initiated by near-ice circulation and plumes from fresh subglacial discharge14, which enable heat transfer between the ocean and ice. Discharge is sourced from the surface melt of the ice sheet, leading to both oceanic and atmospheric influences on terminus melting15. The third mechanism is the acceleration of the calving rate via the breakup rigid ice mélange21, the backstress of which acts to inhibit calving24. All three mechanisms have the potential to trigger rapid retreat in previously stable glaciers, sustained by positive feedback arising from retrograde bedslopes25 and dynamic thinning27.Forcing at the ice–ocean interface is understood to occur via three primary mechanisms. The first is the submarine melting of glacier termini by the transport of warm, deep Atlantic water (AW) through fjords to glacier calving fronts3, even when directly adjacent30. This variability has been attributed to fjord geometry31, glacier geometry33, subglacial hydrology34 and the distribution of oceanographic currents35. None of these, however, can consistently explain spatiotemporal heterogeneity in glacier response, suggesting that such variability is a complex combination of multiple conditions. For instance, some have argued that deep termini, susceptible to buoyant flexure and losing mass through full-thickness calving, are controlled by seasonal18 and interannual19 mélange variability, whilst retreat of shallow glaciers, calving primarily through small-magnitude serac failure, is driven primarily by subglacial melt21. Conversely, others have suggested that the deep termini are forced by AW intrusion, whilst shallow, well-grounded glaciers are protected by their proglacial bathymetry36. The former has been supported by glacier-scale studies of deep outlets such as Sermeq Kujalleq (Jakobshavn Isbræ) and Kangerlussuaq37, which conclude that retreat was initiated by the destabilisation of rigid winter mélange. Meanwhile, other studies have found deep outlets, such as Zachariae Isstrøm29 and Helheim5, to be forced primarily by AW. Sermeq Kujalleq (Store Glacier) has been found to be susceptible to both processes38, destabilising entirely in response to either a doubling of frontal melt or a complete loss of mélange. This is problematic for larger-scale modelling exercises, which frequently choose only one mode of ice–ocean interaction to parameterise8. Being able to better differentiate the controls on tidewater glacier vulnerability is important as many glaciers that contribute significantly to Greenland’s cumulative ice discharge are less well studied than the few that dominate the literature2.However, glaciers exhibit highly heterogeneous responses to relatively uniform ocean forcing12, corresponding with the latitudinal extent of the warm subtropical waters carried by the Irminger Current35. Retreating glaciers were typified by deep fjords  and retrograde bedslopes31. However, a more recent synchronised retreat in response to atmospheric warming began across the sector in 201639, including at Kangerlussuaq40. Studies of ocean reanalysis data concluded that this response was not due to AW, which experienced no anomaly in 201639. Instead, it was proposed that the retreats occurred in response to either (1) atmospheric forcing leading to a high cumulative meltwater input, resulting in the increased submarine melt at the front39; or (2) surface-level ocean forcing resulting in a loss of winter rigid mélange, leading to increased calving19. Once again, understanding controls on tidewater glacier vulnerability is necessary for both identifying the climate and ocean conditions that lead to past retreats and for predicting future change.Diverse forcing has typified Greenland’s southeast sector. A notable increase in ice discharge beginning in ~2001 that extended as far as 69°N was attributed to AWHere, we examine recent changes at K.I.V Steenstrups Nordre Bræ  , where ~0.8–1.0 km of retreat occurred. This temporary retreat generally began in June but recovered, often overwinter but always within ~2 years. For instance, between early June 2016 and the 16th of January 2017, Steenstrup’s calving front retreated by ~1.3 km before recovering ~0.7 km between January and June 2017.Prior to 2018, Steenstrup’s calving front had been stable for decades, with an average 2015 front position only ~200 m from the average 1985 front position Fig. . The ave−1) Fig. , with anIn contrast, 2018 saw more significant and sustained retreats. This began in mid-May, totalling ~3.2 km by the 12th of January when the annual winter advance began. This pattern repeated in 2019, retreating ~3 km between mid-May and early February. After a relatively short advance period relative to 2018, an additional ~2.1 km of retreat occurred between early May and November 2020. At this point, the front began advancing, far earlier than in previous years and lasting much longer into July 2021. By 4th July 2021, the terminus had advanced to the annual maxima, ~2.4 km from the November minima, and only ~0.3 km beyond the 2020 maxima. This advance was matched by a significant late-summer retreat of 2.9 km by early December, ultimately losing ~0.5 km relative to the annual minima of the previous year. In total, Steenstrup retreated ~7.1 km between 2018 and 2021, resulting in the creation of a new fjord ~6 km long.−1 in August 2020 (an increase of more than 270%). However, alongside the front advance between November 2020 and July 2021, Steenstrup’s speed greatly reduced, declining to ~12.8 m d−1 at the frontmost point by early July. At the point closest to the glacier front, acceleration occurred coincident with the retreat of the glacier calving front and continued for the rest of the year, reaching a maximum of 15.0 m d−1 in the last observation of the year (2021-10-22). However, it took time for this acceleration to propagate inland, with the two points further inland not accelerating until late August/early September, whilst the point furthest from the terminus showed no clear late-season acceleration. The total increased flow speed resulted in a doubling in the rate of ice discharge by 2021, reaching 6.37 Gt a−1 and placing Steenstrup in the 93rd percentile of Greenland’s outlet glaciers by contribution to total ice discharge, up from 3.34 Gt a−1 and 82nd percentile in 20163.Steenstrup’s retreat occurred alongside an associated increase in glacier speed. After exhibiting no change between 1985 and 2016 Fig. , speed i−1 in 2016 to 2.1 m d−1 in 2021. On average, speed increased over 100% within 19 km of the 2016 front position, over 50% within 27 km, and over 20% within 40 km. This acceleration was limited to the main glacier trunk: both distributaries exhibited statistically significant slowdowns, the northernmost distributary from ~0.5 m d−1 to ~0.2 m d−1, and the southernmost from ~4.4 m d−1 to ~0.9 m d1  surface melt product41 models the maximum annual melt at Steenstrup for the 2018–2021 period between 5.0 and 7.6 m a−1, suggesting surface elevation change is far greater than could be attributed to increased surface melting and hence likely related to ice thinning under increased along-flow strain rates . By 2021, a combination of surface elevation loss and retreat along a retrograde bedslope resulted in ~1 km of the tongue being at or near flotation by 2021, as indicated by the ice surface height relative to flotation . Full recovery took one or two winter seasons. These ephemeral retreats occurred alongside modelled periods of positive surface temperature anomalies in climate reanalysis datasets. This is true in oceanic and atmospheric products, with warm surface waters in the proximal continental shelf zone from the Copernicus Marine Environment Monitoring Service (CMEMS) Arctic Ocean Physics Reanalysis monthly mean data42 Fig. , and hig42 Fig. .Fig. 5Un43  was observed in a small embayment on the southwest side of the terminus only, negating the ability of the mélange to modulate the timing and magnitude of calving, and relatedly, ice discharge.The second mechanism is attributable to the loss of rigid mélange in response to warm surface waters, leading to a loss of backstress or impediments to calving and a subsequent increase in ice discharge. This mechanism was observed at Kangerlussuaq, with a significant retreat following a lack of mélange development in the winters of 2016/17 and 2017/1829. OMG MBES observations  is rare compared to the front of Sermerlik and Kangerlussuaq Fjords, which have deep canyons to aid AW transfer55 . The vulnerability of Steenstrup, which was relatively shallow and well-grounded at the ice front, to AW rather than mélange destabilisation or surface melt contrasts with expectations that AW is least effective at initiating retreat in shallow, well-grounded glaciers21. Indeed, Steenstrup is identified as a stable ‘calving ridge’ glacier12, raised above the level of AW by a sill and having only a small floating section. It is of note, however, that this interpretation may be skewed by the poor topographic reconstruction of the terminus region  between 2018 and 2020 down a retrograde bedslope  mélange in the 2021 mosaic but not 1985–2020  will be controlled by the full extent of dynamic thinning and ocean forcing.The next ~8 km of the retreat will be influenced by the collapse of the two tidewater distributaries, which are already thinning rapidly Fig. . As thesctor see , but visctor see  suggests37. Meanwhile, sensitivity to warm AW intrusions will continue, especially if the collapse of the two northeastern distributaries provides new pathways for AW entry through the deeper northern fjord . Steenstrup should be a priority for ongoing in situ data collection, particularly the collection of in-fjord CTD data  and better basal topography (to better understand the future evolution of retreat). Aided by more comprehensive in situ data, Steenstrup is a good candidate for numerical modelling experiments: providing both the opportunity to test the ability of models to replicate complex changes and forcings and to provide future projections that will be falsifiable on a timescale of years.12 that AW around the GrIS is becoming progressively warmer in recent decades5, providing increasing opportunities for warm waters to penetrate to the front of marine-terminating glaciers that are relatively more protected from incursions by proglacial bathymetry54. Steenstrup has shown that the stability of glaciers is hard to predict using our current knowledge of smaller, stable, and data-sparse glaciers, especially given the apparently poor reconstruction of the geometry of the ice–ocean interface at Steenstrup and elsewhere. There may be many more well-grounded and mélange-deficient glaciers that, whilst resistant to warm surface waters and subglacial discharge, are primed to retreat and increase their contribution to total GrIS ice discharge in the face of increasing AW incursion.Model reanalysis presented here and elsewhere35.Calving front positions were manually digitised along the centreline between 1985 and 2021 using Landsat 4–8, ASTER, and Sentinel-1 data, a continuation of the dataset previously presented by Walsh et al.67. Between 1985 and 2015, we downloaded annual mosaics of velocity provided by the ITS_LIVE project  and annual velocity maps . To do this, we make use of ITS_LIVE velocity dataect Fig. . Beyond ect Fig. , we downTo present a time series Fig. , ITS_LIVAs updated annual mosaics between 2019 and 2021 were not available at the time of writing, we calculated our own annual mosaics to produce difference maps between 2016 and 2021 for visualisation Figs. b, 4a. Frt-test is used to assess whether differences between the mosaic pixels are significant  image patches using a combination of speckle and feature tracking of the textured mélange surface. Here, we measure only the extent of rigid mélange, or regions of icebergs and sea ice that can be tracked from one image to the next because they maintain coherence, using the intersection of the rigid melange patch with an extended centre flowline  mode from the Sentinel-1 A and B. Velocity maps over rigid mélange-occupied regions of the fjord and surrounding margin were processed following GrIMP workflows69 and surface displacement mapping using SETSM70, as well as SAR products from Terra/TandemSAR-X. The velocity time series from King et al.3 were further appended through 2021 using velocities from GrIMP Sentinel 1 A & 1B71. Temporal data gaps are filled using a Kalman filter approach72 based on estimating a median seasonal variability computed from detrended available observations superimposed on the multiyear time series trend. Velocities are smoothed using a moving filter weighted by observational errors, which arise due to noise-to-pixel ratios and co-registration quality between paired images, and resampled at uniform monthly time steps. Ice thicknesses were obtained from differencing surface elevations from historic DEM data (ranging from AeroDEM through ArcticDEM) with bathymetry from BedMachine v4. Total ice thickness errors include the combined spatially variable and systematic errors from the BedMachine product with an estimated random error of 5 m from surface elevation data. Monthly ice discharge estimates were calculated by summing the product of ice thickness, velocity, and ice density (910 kg m-3) at each 250 m along-gate bin , respectively.To explore the potential for floatation at the calving front, we estimate the theoretical floatation thickness (H_f) based on basal topography extracted from BedMachine v4 as42. We convert potential temperatures to thermal forcing (the difference between the in situ temperature and freezing point of seawater), using pressure and salinity to calculate the freezing point as−3, −4, and −4)76. We calculated monthly anomalies in the thermal forcing over the continental shelf in front of Steenstrup  Arctic Ocean Physics Reanalysis monthly mean datarup Fig. . Here, w77, lacking eddy resolution and not optimised to match the depth of the thermocline. As a result, we evaluate the CMEMS product by comparing the monthly average data to all available OMG CTDs that fall within zone CE1 between 2016 and 2020  bathymetry data from the Oceans Melting Greenland (OMG) project43.Bathymetric data  basin-integrated monthly subglacial melt, assumed constant, from Karlsson et al.80. Constants 4), α (0.39), 10. The output, 12.The rate of undercutting  is parameterisedSupplementary Information


Changes in the dynamic architecture of podocytes, the glomerular epithelial cells, lead to kidney dysfunction. Previous studies on protein kinase C and casein kinase 2 substrates in neurons 2 (PACSIN2), a known regulator of endocytosis and cytoskeletal organization, reveal a connection between PACSIN2 and kidney pathogenesis. Here, we show that the phosphorylation of PACSIN2 at serine 313 (S313) is increased in the glomeruli of rats with diabetic kidney disease. We found that phosphorylation at S313 is associated with kidney dysfunction and increased free fatty acids rather than with high glucose and diabetes alone. Phosphorylation of PACSIN2 emerged as a dynamic process that fine-tunes cell morphology and cytoskeletal arrangement, in cooperation with the regulator of the actin cytoskeleton, Neural Wiskott–Aldrich syndrome protein (N-WASP). PACSIN2 phosphorylation decreased N-WASP degradation while N-WASP inhibition triggered PACSIN2 phosphorylation at S313. Functionally, pS313-PACSIN2 regulated actin cytoskeleton rearrangement depending on the type of cell injury and the signaling pathways involved. Collectively, this study indicates that N-WASP induces phosphorylation of PACSIN2 at S313, which serves as a mechanism whereby cells regulate active actin-related processes. The dynamic phosphorylation of S313 is needed to regulate cytoskeletal reorganization. Mammalian cells are highly complex self-organizing structures whose dynamic build is determined by numerous parameters such as size, shape, position and polarity, as well as internal and external signaling. The signaling mechanisms by which cells maintain this structure depend on the coordination between the cytoskeleton and proteins at the cell membrane. Podocytes, the glomerular visceral epithelial cells, perfectly illustrate the importance of the cytoskeleton in maintaining optimal cell function. In vivo, podocytes form interdigitating projections, called foot processes. The inter-cellular junctional structure joining adjacent foot processes is called the slit diaphragm. The slit diaphragm contains proteins typical of adherents and tight junctions ,2 as welHere, we sought to investigate the role of the actin-binding protein PACSIN2  in regulating podocyte morphology and cytoskeletal arrangement and establish the biological relevance of its phosphorylation at S313 in podocytes. Recent reports link PACSIN2 to angiogenic sprouting , epithelRelying on a rat model for obesity, diabetes and severe DKD, along with human nephrectomy samples and serum samples from individuals with type 2 diabetes (T2D), we show that the phosphorylation of PACSIN2 at S313 associates with increased circulating free fatty acids (FFA) and kidney dysfunction. Using cultured podocytes, we demonstrate that, in cooperation with N-WASP, PACSIN2 orchestrates architectural changes in podocytes, which can be influenced by the phosphorylation status of S313 and in turn impact the response of podocytes to injury.The isolation of glomeruli from ZDF rats (RRID: RGD_12859287) was performed using graded sieving with 250/150/75 µm sieves  as previously described . Human g® CLx Imager  and quantification with Image Studio Lite 5.2 (LI-COR). The following antibodies were used: α-tubulin , β-actin , PACSIN2  and Rac1  from Merck , N-WASP , RhoA  and phospho-PKC Substrate  from Cell Signaling Technology , PACSIN2  from ABGent  and PKCα  from Abcam . Antibodies for ubiquitin , FilaminA  and Dynamin2  were purchased from Santa Cruz Biotechnology . IRDye 800CW anti-rabbit IgG  and IRDye 680RD anti-mouse IgG  were from LI-COR . The antibody specific for PACSIN2 when phosphorylated at serine 313  was described in reference [Podocyte and glomerular lysates were analyzed by Western blotting as previously described , followeHuman podocytes, shown to be negative for mycoplasma, were maintained as described . ShortlyProliferating podocytes were transiently transfected with flag-PKCα  or GFP-NCells were lysed in NP-40 or RIPA-buffer supplemented with protease and phosphatase inhibitors as described in ,15.Origin, maintenance, sacrifice and metabolic measurements of 8 and 34 weeks old lean and obese male ZDF-Leprfa/Crt rats have been previously described . The FFA5 cells were detected in each sample.Proliferating podocytes were transfected with GFP-ev (empty vector), PACSIN2-wt, PACSIN2-S313E or PACSIN2-S313A using Lipofectamine 2000 . After 75 cells were seeded to each well and incubated for 30 min at 37 °C. The wells were washed by means of immersion into a plastic tray containing PBS. Adhered cells were fixed with methanol and stained with Crystal Violet for 30 min . After intense washings, cells were solubilized in 0.5% Triton X-100 and the number of cells was determined by measuring the absorbance at 595 mm using Hidex .PACSIN2-wt or S313E/A cDNAs, described in , were suPACSIN2-wt or S313E/A were transiently transfected into proliferating human podocytes. Cells were lysed in NP-40 buffer supplemented with protease and phosphatase inhibitors. Lysates were precleared with protein A-Sepharose  and incubated at 4 °C for 16 h with anti-N-WASP antibodies or rabbit IgG (Invitrogen) as a control. The immune complexes were bound to protein A-Sepharose, washed with lysis buffer and immunoblotted as described above.https://cellprofiler.org/ accessed on 10 January 2023) [PACSIN2-wt or S313E/A were transiently transfected into proliferating human podocytes. Cells were fixed with 4% PFA, permeabilized with 0.1% Triton-X100 and stained when mentioned with CellMask Blue , Hoechst , anti-β-tubulin III IgG , phalloidin-488  to stain filamentous actin (F-actin), c-myc  and paxillin  to stain focal adhesions. Alexa Fluor 594 anti-rabbit IgG  and Alexa Fluor 488 anti-mouse IgG ) were used as secondary antibodies. Imaging was carried out using the Opera Phenix HCS system  with a 20× air objective (NA 0.4), followed by processing with CellProfiler 3.1.8 (ry 2023)  to correhttp://www.cellclassifier.org/ accessed on 12 December 2019) [Advanced Cell Classifier (er 2019)  was usedp-value of 0.001 or smaller was considered statistically significant.The statistical significance was calculated with GraphPad version 8.4.2 software  and data were presented as mean ± SD. To compare differences between groups, we performed a Mann–Whitney test (two groups) or a one-way ANOVA test with Bonferroni post hoc test (multiple groups). For high-content analyzes, only a We observed that pS313-PACSIN2 was increased in the glomeruli isolated from obese ZDF rats at the age of 8 weeks compared to the glomeruli obtained from lean controls, but the ratio of pS313-PACSIN2 to total PACSIN2 was not increased A–D. In tNext, we explored whether the phosphorylation of PACSIN2 at S313 was an early feature of diabetes, preceding the onset of albuminuria. We used human glomeruli isolated from individuals with T2D without DKD . Transient overexpression of PACSIN2-S313E in proliferating human podocytes induced an increase in N-WASP levels in comparison to empty vector A,B, withBased on the observation that phosphorylation of PACSIN2 at S313 regulates N-WASP levels in podocytes, we reasoned that N-WASP could regulate the phosphorylation of PACSIN2 in return. Overexpression of N-WASP in cultured podocytes increased PACSIN2 expression  but did Analyses of wiskostatin-treated podocytes showed differences in cell size in podocytes overexpressing PACSIN2 without any treatment G. AdditiWe then tested whether the phosphorylation status of PACSIN2 at S313 would affect the response of podocytes to actin-related injury. We altered the actin cytoskeleton using cytochalasin D, which inhibits actin polymerization and assembly causing cells to retract. We then monitored the recovery after the washout E. We fouWe speculated that the decreased cell spreading observed so far when overexpressing mutated forms of PACSIN2 in comparison to wt-PACSIN2 could be explained by differences in actin arrangement. We overexpressed in proliferating human podocytes myc-PACSIN2-wt, -S313E and -S313A; then we trained Advanced Cell Classifier to recognize their altered morphology (examples are shown in Our study shows that PACSIN2 is phosphorylated at S313 in DKD. We found that pS313-PACSIN2 increased with FFA accumulation, PKC activation and N-WASP inhibition. Our experiments highlight the reciprocity of the relationship between PACSIN2 and N-WASP as they coordinate to regulate cell architecture. Dynamic phosphorylation at S313 emerged as a regulatory mechanism during cytoskeletal reorganization. Since minor imbalances in podocyte cytoskeleton can disrupt the structural integrity of the glomerular filtration barrier, our data suggest that PACSIN2 could, via its phosphorylation at S313, be able to fine-tune the structure of the glomerular filtration barrier.Previous studies have already linked PACSIN2 and N-WASP showing that PACSIN2 can directly interact with N-WASP and facilitate its recruitment to specific cellular locations, such as actin polymerization sites . This ulOn the other hand, we found that N-WASP was able to regulate PACSIN2 phosphorylation as well. Pharmacological inhibition of N-WASP distinctively increased pS313-PACSIN2 and upregulated PKC activity A–E. SincIn our investigations, it was clear that phosphorylation of PACSIN2 at S313 was not required for all PACSIN2 functions. For instance, N-WASP inhibition altered the localization of all three forms of GFP-PACSIN2 F and phoA few mechanisms could explain how PACSIN2 and its phosphorylation at S313 can regulate podocyte architecture. Primarily, our experiments emphasize the interconnection between N-WASP and PACSIN2. Although we show that non-phosphorylatable PACSIN2 increases cell shrinkage with wiskostatin treatment G, more sIn the context of diabetes, our study presents new links in the signaling pathways regulating the development of DKD. Our experiments suggest that FFA accumulation triggers the phosphorylation of PACSIN2 at S313 via PKC and that pS313-PACSIN2 associates with the progression toward kidney disease. Given that PKCα activation is largely dependent on glucose concentrations in podocytes ,40, it wOur study has limitations. Cell transfections were performed in proliferating podocytes as opposed to differentiated podocytes; as in our experience, modulations of PACSIN2 expression in differentiated cultured podocytes are quickly abolished. Therefore, some of the differences seen in our study could be connected to differences in podocyte proliferation, which could affect the present results.Our study shows that PACSIN2 is phosphorylated at S313 in diabetes and DKD. By overexpressing PACSIN2 in cultured podocytes, we show that PACSIN2 could play a protective role in DKD, by decreasing apoptosis and reinforcing matrix adhesion. Phosphorylation of PACSIN2 at S313 emerged, in a complex interplay with N-WASP, as a dynamic process that could fine-tune the ability of PACSIN2 to modulate podocyte architecture. Our findings suggest that even mild cytoskeletal effects may have a substantial impact on the response of podocytes to injury, further emphasizing the complexity of the balancing forces behind cytoskeletal regulation. Future studies using knockout or transgenic PACSIN2 mice with experimentally induced DKD are needed to confirm whether changes in PACSIN2 levels affect podocyte survival and foot process effacement in vivo and understand the connection between PACSIN2, N-WASP and PKC.