Hydrogen-mediated manipulation of luminescence color in single-component Eu doped CaYAlSiO4 by defect passivation

Abstract

Multivalent rare-earth ions in a single host allow color-tunable or white-color phosphors but controlling their valence states to manipulate luminescence color has been challenging. Here we experimentally demonstrate the activation of Eu2+ dopants and the resulting luminescence color tuning in CaYAlO4 by hydrogen incorporation via the defect passivation of Si substitution. Eu doped CaYAlO4 without Si substitution exhibits only red emission attributed to Eu3+, and post-heat treatment under hydrogen enhances Eu3+ 4f-4f excitation as the signature of oxygen vacancy formation. However, the Si substitution impedes the formation of oxygen vacancies against the post-hydrogen treatment and enables the hydrogen incorporation in CaYAlO4 to activate Eu2+ ions. The fading of the Eu2+ emission by subsequent heat treatment under an inert atmosphere directly indicates the hydrogen-induced Eu2+ activation. The ratio of Eu2+ and Eu3+ emissions and consequent luminescence color in the Si-substituted CaYAlO4 are tunable with post-heat treatments under different conditions. The finding here sheds new light on hydrogen as a factor determining luminescence in oxide phosphors.