DYNAMICS AND MECHANISMS OF UP-CONVERSION PROCESSES IN YB3-DOPED AND HO3+-DOPED FLUOROZIRCOALUMINATE GLASSES( SENSITIZED TM3+)

The efficient upconversion fluorescences corresponding to the (1)G(4) --> H-3(6) (480 Mn) and F-3(4) --> H-3(6) (805 nm)) transitions of Tm3 + and the S-5(2) --> I-5(8) (545 nm) transition of Ho3+ were observed in Yb3+/Tm3+ and Yb3+/Ho3+ doubly doped fluorozircoaluminate glass, re spectively under 980 nm excitation. The dependences of these upconvers ion fluorescences upon the pumping intensity and the doping concentrat ions were interpreted with a rate equation model which takes into acco unt of Yb3+ reversible arrow Tm3+(Ho3+) energy transfers. The energy t ransfers from Yb-3t to Tm3+(Ho3+) only occur within those yb(3+) ions which are closer to the Tm3+(Ho3+) ions, and the more distant Yb3+ ion s must transfer their energy to the closer Y6(3+) ions through the gla ss with a diffusion-limited regime. The back transfers from Tm3+(Ho3+) to Yb3+ were also demonstrated in both the Yb3+/Tm3+ and Yb3+/Ho3+ sy stems. They account for the concentration quenching of the up-conversi on fluorescences at higher doping concentrations.