Nanocrystalline YAG powders doped with Er3+, Eu3+ or Tb3+ were synthesized through a citrate-nitrate sol-gel process. Thermal treatments were applied at successively increasing temperatures in the interval 600-1400°C. The structural transformations were monitored by XRD, FT-IR and optical spectroscopy. A pure garnet phase was observed for annealing temperatures higher than 930°C.

YAG:Eu nanopowders were synthesized by the nitrate-citrate sol-gel method. The morphologic modifications of the nanocrystallites produced by the thermal treatments at various temperatures are monitored by two parameters obtained from optical fluorescence spectroscopy: intensity ratio of the transition 5D0-7F2 and 5D0-7F1 and the maximum splitting of the 7F1 level. An abrupt change of both parameters is observed at the amorphous-crystalline phase

We present an analysis of the emission regimes of an Er:YLiF4 laser on the transition 4S3/2 - 4I15/2, under direct pumping and various upconversion pumping mechanisms. The analysis is based on the study of the steady-state solutions of a rate equation system. The thresholds of the various emission regimes are calculated. The influence of the pump mechanism and the excited-state absorption losses on the emission regime is discussed.