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 beta-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 mu m 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+(I-5(8)) + Er3+(I-4(11/2)) -> Ho3+(I-5(6)) + Er3+(I-4(15/2)), (2) Ho3+(I-5(6)) + Er3+(I-4(11/2)) -> Ho3+(F-5(3)) + Er3+(I-4(15/2)), (3) Ho3+(I-5(6)) + Er3+(I-4(13/2)) -> Ho3+(F-5(5)) + Er3+(I-4(15/2)). The decrease of red emission intensity at 3.0 mol% of Ho3+ ions was mainly due to the cross-relaxation among Ho3+ ions, Ho3+(F-5(3)) + Ho3+(I-5(8)) -> Ho3+(F-5(5)) + Ho3+(I-5(6)). (C) 2013 Elsevier B.V. All rights reserved.