Luminescence and up-conversion mechanism of Er3+/Ho3+ co-doped oxyfluoride tellurite glasses and glass-ceramics

Transparent oxyfluoride tellurite glasses with composition of TeO2-SiO2-AlF3-CaO-NaF-ErF3-HoF3 were prepared by a conventional melt-quenching method. Hexagonal β-NaCaAlF6 nano-crystal phase was formed after heat-treatment. Er3+ and Ho3+ ions remain in the residual glass phase after crystallization. Luminescence properties and up-conversion emission mechanism were investigated. Luminescence intensity of Er3+ at 1.53 μm reduced gradually along with the increase of Ho3+ ions concentration both for glasses and glass-ceramics. The green and red up-conversion emissions were observed under 980 nm excitation. With the increase of the Ho3+ ions concentration, the green emission intensity decreased monotonously and the red emission intensity increased obviously, there existed energy transfer between Er3+ and Ho3+ ions, (1) Ho3+(5I8) + Er3+(4I11/2) → Ho3+(5I6) + Er3+(4I15/2), (2) Ho3+(5I6) + Er3+(4I11/2) → Ho3+(5F3) + Er3+(4I15/2), (3) Ho3+(5I6) + Er3+(4I13/2) → Ho3+(5F5) + Er3+(4I15/2). The decrease of red emission intensity at 3.0 mol% of Ho3+ ions was mainly due to the cross-relaxation among Ho3+ ions, Ho3+(5F3) + Ho3+(5I8) → Ho3+(5F5) + Ho3+(5I6).