Remarkably Enhancing Green-Excitation Efficiency for Solar Energy Utilization: Red Phosphors Ba₂ZnS₃:Eu²⁺, X^– Co-Doped Halide Ions (X = Cl, Br, I)

Abstract

Eu²⁺-activated Ba₂ZnS₃ has been reported as a red phosphor with a broad emission band peaking at 650 nm under blue excitation for white-LED. In this study, Ba₂ZnS₃:Eu²⁺, X^- (X = F, Cl, Br, I) phosphors doped with halide ions were prepared by traditional high-temperature solid-state reaction. Phase identification of powders was performed by X-ray powder diffraction analysis, confirming the existence of single-phase Ba₂ZnS₃ crystals without dopant. The corresponding excitation spectra showed an additional broad band in the green region peaking at 550 nm when the phosphor was halogenated except by the smallest F^-. It was proved that the green-excitation efficiency successively strengthened from Cl^-, to Br^-, to I^-, which suggested larger halide ions made a greater contribution to the further splitting of the t_2g energy level of the doped Eu²⁺ ions in the host Ba₂ZnS₃, and the optimized formula Ba_1.995ZnS_2.82:Eu²⁺_0.005, I^-_0.18 showed a potential application in solar spectral conversion for agricultural greenhouse and solar cell. Defect chemistry theory and crystal field theory provided insights into the key role of halide ions in enhancing green-excitation efficiency.