Abnormal Visible Luminescence Mechanism of Tb^3＋-Yb^3＋ Codoped SiOu-Al2O3-CaF2 Glass Studied by Time-Resolved Spectra

The upconversion energy transfer mechanism in Tb^3＋-Yb^3＋ co-doped SiO2-Al2O3-CaF2 glass is investigated by time-resolved spectra. The effect of donor ion Yb^3＋ is involved in the dynamic decay behavior of acceptor ion Tb^3＋, which provides direct proof for the energy transfer from Yb^3＋ to Tb^3＋. The pump power dependence curves show that the upconversion luminescence is a two-photon process. The measured decay curves of the 5D4 state （Tb^3＋） contain two parts： a slow decay process corresponding to its radiation, and a fast one with a decay parameter approximately twice the lifetime of the ^2F5/2 state （Yb^3＋ ）. The fast decay process is contradictory to the generally accepted cooperative sensitization upconversion rate equation model. Since the effect of the host environmental is excluded by comparative experiments, we believe that there should be another energy transfer mechanism in Tb^3＋-Yb^3＋ co-doped SiO2-Al2O3-CaF2 glass in addition to the cooperative sensitization process.