Crystallization and spectroscopic properties investigations of Er3+ doped transparent glass ceramics containing CaF2

Transparent oxyfluoride glass ceramics with composition of 45SiO2–25Al2O3–5CaCO3–10NaF–15CaF2–0.5ErF3 (in mol%) were developed through controlled crystallization of melt-quenched glass. Non-isothermal crystallization kinetics investigation showed that the average apparent activation energy Ea and Avrami exponent n are about 283 kJ/mol and 2.22, respectively, indicating the crystallization a three dimensional crystal growth process controlled by the diffusion with a decreasing nucleation rate. X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM) observation revealed the precipitation of CaF2 crystallites sized about 15 nm among the glass matrix after heat-treatment at 650 °C for 2 h. For as-made glass, no upconversion signals were detected when excited with a 30 mW diode laser at 980 nm, while strong upconversion emissions at 545, 660 and 800 nm were obtained for transparent glass ceramic under similar excitation condition.