Abnormal Visible Luminescence Mechanism of Tb³⁺-Yb³⁺ Codoped SiO₂-Al₂O₃-CaF₂ Glass Studied by Time-Resolved Spectra

The upconversion energy transfer mechanism in Tb³⁺-Yb³⁺ co-doped SiO₂-Al₂O₃-CaF₂ glass is investigated by time-resolved spectra. The effect of donor ion Yb³⁺ is involved in the dynamic decay behavior of acceptor ion Tb³⁺, which provides direct proof for the energy transfer from Yb³⁺ to Tb³⁺. The pump power dependence curves show that the upconversion luminescence is a two-photon process. The measured decay curves of the ⁵D₄ state (Tb³⁺) 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 ²F_5/2 state (Yb³⁺). 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 Tb³⁺-Yb³⁺ co-doped SiO₂-Al₂O₃-CaF₂ glass in addition to the cooperative sensitization process.