Tendentious multiple sites occupation towards white light emission in single-phase Ba2(1-y/3)Ca(1-y/3)SryB2Si4O14:Eu2+ phosphors

Abstract

Site preferences of Eu2+ ions on the Ba2+ sites and the Ca2+ sites were discovered in the mixed cation borosilicate Ba2CaB2Si4O14 (BCBSO). Eu2+ ions are more likely to locate on the Ba2+ sites over the Ca2+ sites according to the Density Functional Theory (DFT) calculation and the photoluminescence spectrum analysis. The emission band centered at 408 ​nm was confirmed to be generated from the Eu2+ ions located on the Ba2+ sites, while the emission band centered at 548 ​nm was considered to be generated from the Eu2+ ions on the Ca2+ sites. Dual sites occupation results in a collective emission band covering 380 ​nm–780 ​nm in BCBSO:Eu phosphors. By further doping with Sr2+ ions, crystal environment of the luminescence centers could be well modulated, resulting in the tunable emission from yellow to white under UV excitation. The photoluminescence quantum yield was significantly improved from 17.9% to 36.8%. Finally, a series of white LEDs with tunable CCT (from 5132 ​K to 3402 ​K) and high Ra (reach up to 89.6) were obtained using the Ba2(1-y/3)Ca(1-y/3)SryB2Si4O14:0.03Eu single-phase white light emission phosphors.