The effect of melt-homogenization and heat-treatment on the optical properties of the rare earth doped oxyfluoride glass-ceramics

We prepared four Er³⁺-Yb³⁺ co-doped oxyfluoride precursor glass (PG) samples with the same chemical composition at different melt-homogenization temperatures (T_homo), respectively, at the same melt-quenching rate. We investigated the effect of T_homo and heat-treatment (HT) on the crystallization, structure, and optical properties of the four samples. The results show that the structural heterogeneity in the PG sample increases with lowering T_homo, and this promotes phase-separation, and hence, formation of Ba₂LaF₇ crystals. Consequently, the light transmittance of PG samples is decreased, but the up-conversion (UC) luminescence is enhanced. Moreover, the crystallinity of the four PG samples was increased by HT, and this altered the light transmittance, and greatly enhanced the UC luminescence. The mechanism of these discovered phenomena was discussed in terms of structure and crystal evolution. This work provides an effective way to optimize the optical and photonic performances of the rare earth doped oxyfluoride glass-ceramics.