Upconversion dynamics in Yb3+-Ho3+ doped fluoroindate glasses

The mechanisms and dynamics of the upconversion emissions in Yb3+-Ho3+-doped fluoroindate glasses by exciting at 975 nm have been analysed. The upconversion efficiencies have been measured as a function of temperature in the range from 12 to 295 K. The temporal evolution of the 545- and 650-nm upconversion emissions obtained under flash excitation at 975 nm in codoped samples with 2.25 mol.% of Yb3+ and 0.75 mol.% of Ho3+ cannot be described using the energy migration model. This indicates that at this concentration of Yb3+ the rapid migration regimen between these ions has not been reached. A model is proposed in order to explain the temporal evolution of these emissions taking into account energy migration between donors and backtransfer processes. (C) 1998 Elsevier Science S.A.