Preparation and up-conversion characterization of CaF2:Yb3+, Ho3+/BaF2:Yb3+, Ho3+ co-doped glasses and glass–ceramics

• New oxyfluoride tellurite glasses were prepared successfully.
• CaF2 and BaF2 nano crystals were formed by heat treatment.
• Up-conversion emission properties and mechanism were investigated.

Oxyfluoride tellurite glasses with compositions of TeO2–Al2O3–CaF2/BaF2–NaF–YbF3–xHoF3 (x = 0.1, 0.3, 0.5, 1.0, 1.5, 2.0 mol%) were prepared by conventional melt-quenching method. Effect of heat-treatment schedules on crystallization behavior and microstructure were analyzed by differential scanning caborimetry, X-ray diffraction, infrared spectra and scanning electron microscopy. Cubic CaF2 and BaF2 nano-crystal phases were formed by controlling heat-treatment schedules. Up-conversion emission properties and mechanism of Yb3+ and Ho3+ ions in glasses and glass–ceramics were investigated. The green and red up-conversion emissions were observed under 980 nm LD excitation. Up-conversion luminescence intensity in glasses was obvious higher than that in glass–ceramics. And there existed concentration quenching effect among Ho3+ ions resulted from cross-relaxation.