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

Abstract Transparent oxyfluoride tellurite glasses with composition of TeO 2 –SiO 2 –AlF 3 –CaO–NaF–ErF 3 –HoF 3 were prepared by a conventional melt-quenching method. Hexagonal β-NaCaAlF 6 nano-crystal phase was formed after heat-treatment. Er 3+ and Ho 3+ ions remain in the residual glass phase after crystallization. Luminescence properties and up-conversion emission mechanism were investigated. Luminescence intensity of Er 3+ at 1.53 μm reduced gradually along with the increase of Ho 3+ 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 Ho 3+ ions concentration, the green emission intensity decreased monotonously and the red emission intensity increased obviously, there existed energy transfer between Er 3+ and Ho 3+ ions, (1) Ho 3+ ( 5 I 8 ) + Er 3+ ( 4 I 11/2 ) → Ho 3+ ( 5 I 6 ) + Er 3+ ( 4 I 15/2 ), (2) Ho 3+ ( 5 I 6 ) + Er 3+ ( 4 I 11/2 ) → Ho 3+ ( 5 F 3 ) + Er 3+ ( 4 I 15/2 ), (3) Ho 3+ ( 5 I 6 ) + Er 3+ ( 4 I 13/2 ) → Ho 3+ ( 5 F 5 ) + Er 3+ ( 4 I 15/2 ). The decrease of red emission intensity at 3.0 mol% of Ho 3+ ions was mainly due to the cross-relaxation among Ho 3+ ions, Ho 3+ ( 5 F 3 ) + Ho 3+ ( 5 I 8 ) → Ho 3+ ( 5 F 5 ) + Ho 3+ ( 5 I 6 ).