Intense red upconversion emission of Yb/Tm/Ho triply-doped tellurite glasses.
By conventional melting and quenching methods, 3Yb2O3-0.2Tm2O3-xHo2O3 (wt%, x=0.2~1.2) was doped into an easily fiberized tellurite glass with composition of 78TeO2-10ZnO-12Na2O (mol%) to form YTH-TZN78 glasses. Under 976 nm excitation, the direct sensitizing effect of Yb ions (Yb→Ho) and indirect sensitizing and self-depopulating effects of Tm ions (Yb→Tm→Ho) were found to present intense red upconversion emission at 657 nm (Red, Ho:5F5→5I8) and were responsible for the absence of the usually observed 484 nm emission (Blue, Tm:1G4→3H36). Regardless of the dopant concentration of Ho ions, the intensity of the red emission at 657 nm (Red, Ho:5F5→5I8) is about three times stronger than that of the green one at 543 nm (Green, Ho:5S2→5I8). For this certain red emission at 657 nm, 0.4 wt% Ho2O3-doped YTH-TZN78 glass was found to present the highest emission intensity and is therefore determined as a promising active tellurite glass for red fiber laser development.
Luminescence of erbium doped tellurite glass containing silver nanoparticles
Enhancing the optical properties of rare-earth doped inorganic glasses by embedding metallic nanoparticles (NPs) of controlled sizes and examining the mechanism of enhancement are important and challenging. A series of Er3+ doped zinc tellurite glasses with and without silver NPs of molar composition (74.5- x)TeO2-25ZnO-0.5Er2O3-xAgCl with 0 = x = 1.0 mol % were prepared by meltquenching technique. They were characterized by X-ray diffraction, transmission electron microscopy, differential thermal analysis (DTA), and Fourier transform infrared (FTIR), ultraviolet-visible-near infrared and photoluminescence spectroscopy. The thermal, structural, and optical properties of these glasses were determined and analyzed. The XRD pattern confirms the amorphous nature of all samples. The high resolution TEM reveals the presence of silver NPs of average diameter 24 ± 2 nm with measured lattice constant of 2.09 A and a Gaussian size distribution. The observed glass density ranges from 5.481 to 5.697 g cm-3 and the refractive index evaluated using Sellmeier’s equation varies between 2.16 to 2.27. Thermal parameters such as glass transition temperature (Tg), crystallization temperature (Tc), melting temperature (Tm) and thermal stability ?T (Tc-Tg) were determined from DTA analyses. A wide and stable glass formation range around 87oC-105oC was found. The structural properties measured by using FTIR show that as the AgCl content increases, the sharp infrared (IR) absorption peaks were consistently shifted from 675.13 cm-1 to 679.03 cm-1 which were assigned to the structural changes between the stretching vibration mode of TeO4 (trigonal bipyramids) and TeO3(trigonal pyramids). The absorption peaks around 1600 cm-1 and 3400 cm-1 are related to the stretching vibrations of the hydroxyl group participating in the strong metal and hydrogen bonding, respectively. The absorption spectra consist of eight absorption peaks centered at 1510, 975, 799, 655, 586, 523, 489 and 447 nm corresponding to transitions from ground state to 4I13/2, 4I11/2, 4I9/2, 4F9/2, 4S3/2, 2H11/2, 4F7/2, and 4F5/2 excited states, respectively. From PL spectra, excitation at 786 nm and 470 nm for up and down-conversion exhibits strong green and red emission comprised of three emissions band at 501, 548 and 634 nm. The significant enhancement in the luminescence with the increase of AgCl is ascribed to the local field enhancement induced by Ag0 surface plasmon resonance and the energy transfer from fluorescent Ag0?Er3+ ions. The improved optical and structural properties suggest that the studied glasses are potential candidates for nanophotonic devices.
1.6μm emission and gain properties of Ho3+ in selenide and chalcohalide glasses
Spectroscopic properties and the gain of the 1.6μm emission in selenide and chalcohalide glasses doped with Ho3+ were investigated. Intense 1.6μm emission with high quantum efficiency was observed from both glasses. Tb3+ ions were codoped to depopulate the Ho3+:I75 level and resulted in the population inversion between the I55 and I75 levels. Estimation of the gain coefficient indicated that a positive gain over the entire U-band window is possible in Ho3+/Tb3+-codoped selenide glasses. Selective energy transfer from the selenide host glass to the Ho3+:I75 level resulted in a strong 2.0μm emission.