Spectroscopy of gadolinium gallium garnet crystals doped with Y b3 + revisited
The optical spectroscopy measurements of gadolinium gallium garnet (GGG) crystals doped with Yb show evidence of the presence of non-equivalent optical centers with very similar radiative decay rates. The energy level schemes of those centers have been determined on the basis of optical absorption, luminescence and Raman experiments. Crystal field fitting resulted in two sets of slightly different crystal field parameters for two non-equivalent Yb centers. Both sets of parameters describe perfectly the experimentally detected Y b3 + energy levels. Correlation between systematic trends in the experimental energy level schemes and crystal field parameters is discussed.
Low-temperature high-pressure spectroscopy of lanthanum lutetium gallium garnet crystals doped with Cr 3+ and Nd 3+
Low-temperature luminescence measurements under high pressures in diamond-anvil cell of nonstoichiometric lanthanum lutetium gallium garnet (LLGG) doped with Cr 3 + ions and nonintentionally with Nd 3 + ions are reported.Three nonequivalent Cr 3 + centers were found in the crystal using this technique. The results also reveal information about the electronic structure of different Cr 3 + centers in those crystals. Cr 3 + ions in a LLGG crystal experience a very low crystal field strength. The energy differences between the 4 T 2 and 2 E levels are negative, and equal to about - 1100 cm - for two of those centers and about -1500 cm - 1 for the third one. The spectral results were corroborated by a theoretical analysis of the luminescence decay times as a function of pressure, which allowed one to establish the exact values of the crystal-field parameter Dq at ambient pressure for those centers. The crystal exhibits a large inhomogeneous broadening of the R lines, associated with nonstoichiometry. In addition to the Cr 3 + luminescence also luminescence of Nd 3 + ions was detected in the LLGG crystals. One of the Nd 3 + luminescence lines, associated with the 4 F 3 / 2 4 I 9 / 2 transition. is strongly dependent on pressure, with a pressure coefficient equal to 0.96′0.02 cm - 1 /kbar, which makes this system interesting as a pressure gauge in the infrared region.
Fluorescence quenching of Nd3+ in LaF3 studied by direct measurements on pairs
The self-quenching of the Nd 3+ infrared fluorescence in LaF 3 has been studied by the direct measurement of the transfer rates for various classes of Nd 3+ pairs. Using weakly doped samples, the pairs are isolated and their behaviour is intrinsic. The results obtained at 1.2 K are used to predict the properties of concentrated crystals. From the difference between the predicted behaviour and the experimental results reported by others, it is concluded that migration of the excitation among the donors plays a prominent part. This situation, unusual at low temperatures, is discussed. Other results as existence of a short range interaction, transfer rates inside (Pr, Nd) pairs, efficiency of three ions processes are also discussed Etude de l'autoextinction de la fluorescence IR de Nd 3+ dans LaF 3 par mesure directe des vitesses de transfert pour plusieurs types de paires d'ions Nd 3+ . Isolement des paires en utilisant des cristaux tres dilues pour observer leur comportement intrinseque. Mise en evidence du role important de la migration de l'excitation parmi les donneurs; discussion de cette situation inhabituelle a basse temperature (1,2 K). Discussion d'une interaction a courte portee, des vitesses de transfert pour des paires (Nd, Pr), du rendement des processus a 3 ions