Improved Cooperative Emission in Ytterbium-Doped Oxyfluoride Glass-Ceramics Containing CaF_2 Nanocrystals

摘要

The effect of alumina content and heat treatment time, on microstructure and cooperative emission of oxyfluoride glass-ceramics were investigated. Two values (1.8 and 2.18) were selected for SiO_2/Al_2O_3 ratio. The results indicated that alumina content had a significant effect on the phase separation and the viscosity of the glasses. Although crystallization happened in the glass with SiO_2/Al_2O_3 ratio of 2.18 via spinodal decomposition phase separation, the other glass was crystallized in a homogeneous glass phase. Accordingly, the size and volume concentration of nano CaF_2 crystalline phase which precipitates during the heat treatment depends on the glass's alumina content. Furthermore, the crystal size was raised dramatically with duration of heat treatment time in the high-containing aluminum oxide. In the other glass specimen, i.e., in the glass with a SiO_2/Al_2O_3 ratio of 2.18, only a slight increase in the crystal size was observed by raising the heat treatment time. Increasing the time of heat treatment led to the incorporation of Yb~(3+) ions into CaF_2 crystalline phase. Moreover, cooperative emission coming from a pair of excited Yb~(3+) ions was obtained and increased significantly with the heat treatment time. The results showed that the optimum heat treatment time was 48 h.