SPECTROSCOPY AND FLUORESCENCE DYNAMICS OF (TM3-CRYSTALS FOR 1.5-MU-M LASER OPERATION(, TB3+) AND (TM3+, EU3+) DOPED LIYF4 SINGLE)

Fluorescence dynamics of the H-3(4) and F-3(4) energy levels of Tm3+ i ons in LiYF4 single crystals codoped with Tb3+ or Eu3+ ions were exper imentally investigated and confronted with classical energy-transfer m odels: direct cross-relaxation-type energy transfers between donor D a nd acceptor A, where D = Tm3+ and A = Tb3+ or Eu3+ (static Forster-Dex ter model extended by Inokuti-Hirayama) as well as energy migration be tween Tm3+ ions (hopping and diffusion models by Burshtein and Yokota- Tanimoto), The fluorescence decays were accurately described in the: c ase of Tb3+ codoping because of resonant energy transfer, thus of more precise estimations of energy transfer parameters from the absorption and emission spectra, In the case of Eu3+ codoping, the Tm3+ --> Eu3 energy transfers need to be phonon-assisted to compensate for the red uced overlap between the Tm3+ emission and Eu3+ absorption spectra and the models, though giving satisfactory results, appeared less powerfu l. Based on these results, optimized values for the dopant concentrati ons were finally derived to keep high the fluorescence quantum efficie ncy of H-4(4) and to shorten the lifetime of the F-3(4) energy levels of the Tm3+ ion in order to alleviate the problem of self-termination of the H-3(4) --> F-3(4) laser transition occuring around 1.5 mu m.