NONRADIATIVE DECAY PROCESSES AND MECHANISMS OF FREQUENCY UP-CONVERSION OF ER3-BAF2-LAF3 GLASS( IN ZRF4)

We have investigated the decay processes of the Er:S-4(3/2) and F-4(9/ 2) states and the mechanisms of frequency upconversion under 800 nm ex citation of Er3+ in ternary ZrF4-BaF2-LaF3 glasses. The decay processe s of the Er:S-4(3/2) and F-4(9/2) states are discussed on the basis of the Er concentration dependence of the fluorescence lifetime. The qua ntum efficiencies of emission of the S-4(3/2) and F-4(9/2) states are 73% and 25%, respectively. The difference in the quantum efficiencies between these states can be explained from the difference in the multi phonon decay rates: the multiphonon decay rate of the S-4(3/2) state i s much smaller than that of the F-4(9/2) state. The multiphonon relaxa tion is a dominant nonradiative decay process of the F-4(9/2) state. A dominant nonradiative decay process of the S-4(3/2) State is self-que nching at high Er concentrations, The upconversion mechanisms under 80 0 nm excitation are also investigated from the dependence of upconvers ion luminescence on excitation wavelengths (800 and 980 nm), excitatio n laser power, and Er concentration. The mechanism of upconversion fro m 800 to 660 nm is mainly due to the energy transfer between the I-4(9 /2) --> I-4(13/2) and F-4(9/2) <-- I-4(11/2) transitions. We also show that the upconversion from 800 to 550 nm is due to excited-state abso rption. (C) 1997 American Institute of Physics.