Crystal Structure Refinement of BaCaSiO4:Eu2+/Mn2+ and Its Tunable Luminescence

Abstract

Color-tunable phosphors have been widely developed to enhance the luminous efficiency of phosphor-conversion white light-emitting diodes using near ultraviolet chips. For this application, the Eu2+ and Mn2+ ions are typically used as sensitizers and activators, respectively. One of suitable host materials is a (Ba,Ca)SiO4 system. For example, the tunable luminescence of Eu2+/Mn2+ co-doped Ba1.55Ca0.45SiO4, Ba1.3Ca0.7SiO4, and Ba1.2Ca0.8SiO4 compounds has been reported. However, the luminescence of BaCaSiO4:Eu2+/Mn2+ has rarely been studied. In this study, BaCaSiO4:Eu2+/Mn2+ powders were prepared by a solid-state reaction process. And then the phase formation, the crystal structure, and tunable luminescence were investigated. The starting mixtures were fired at 1100−1300 °C for 4 h under a 5% H2 (+ 95% N2) atmosphere. Rietveld refinement was performed to verify the crystal structure. The crystal system of BaCaSiO4 is a hexagonal structure. It was most probable that both of the Eu2+ and Mn2+ ions were incorporated into the Ca2+ sites. The PL spectra exhibited two emission bands: green (A-band) and red (B-band) assigned to the Eu2+ and Mn2+ ions, respectively. The B-band occurred through an energy transfer (ET) from Eu2+ to Mn2+. The intensity ratio of the A- to B-band closely depended on the Eu/Mn ratio, resulting in a change in CIE chromaticity coordinates. Fluorescence lifetimes, multipolar interactions and critical distances between Eu2+ and Mn2+, ET efficiencies, and the evolution of the PL spectra were estimated and discussed.