Effect of alkaline earth metals on luminescence characteristic in Eu-Doped oxynitride phosphate glasses

Highlights: • Eu³⁺ captures the electron released from NHC and POHC and is reduced to Eu²⁺. • The introduction of N promotes the self-reduction of Eu³⁺ ions. • Under large alkaline earth metal ion radius, Eu ion tends to coordinate with N³⁻. • Tunable luminescence realized by doping with different alkaline earth metals. In this article, a series of Eu-doped oxynitride phosphate glass samples are prepared. It is shown that the photoluminescence of Eu can be tuned through different alkaline earth metal ions (M²⁺). The luminous intensity of Eu²⁺ decreases with increasing ionic radius in the order of MgCaSrBa. And with the increased mismatch degree of radius between M²⁺ and Eu ions, the luminescence of Eu³⁺ gains intensity. The effects of M²⁺ on structure and luminescence characteristics of glass are mainly due to the following three factors: the field strength of M²⁺, the degree of mismatch between M²⁺ and Eu ions, and the influence of alkaline earth metals on the coordination tendency of N³⁻ and O²⁻ with Eu ions. The reduction mechanism is explained by combining the unequal substitution of Eu³⁺ ions for divalent alkaline earth metal cations with the reduction of Eu³⁺ by O²⁻ and N³⁻ ions. Our work provides a new perspective for studying the luminescence characteristics and mechanism of Eu ions in oxynitride Phosphate Glasses.