Energy transfer in PbO-Bi 2 O 3 -Ga 2 O 3 glasses codoped with Yb 3+ and Er 3+

concentrations. The measured luminescence decay curves of the donors are used to determine the experimental transfer rates; the best fittings for them are obtained with single exponentials. The microparameters are calculated and used to determine the theoretical rates. The real migration mechanism, involved in the energy transfer of each sample, diffusion, or hopping, is determined by means of the experimental transfer rates and the theoretical ones; fast excitation diffusion among donors, followed by a direct donor to acceptor energy transfer, predominates. A comparison is made with the energy-transfer mechanism of ZBLAN glass codoped with Yb 3+ and Er