A novel Mn4+-activated Li3CsGe8O18 red phosphor and cation substitution induced photoluminescence improvement

Abstract

Nowadays, non-rare-earth Mn4+-activated red phosphors have emerged for improvement of the lighting quality of phosphor-converted white light-emitting-diodes (pc-WLED), owing to the low cost and the admirable luminescence properties. In this work, a novel narrow-band red-emitting Li3CsGe8O18:Mn4+ phosphor was synthetized based on the component substitution from Li3RbGe8O18, which exhibits the red luminescence centered at 668 nm upon 466 nm excitation. By further designing [Cs+-Rb+] cation substitution, the photoluminescence intensity and luminescence efficiency are obviously improved. The photoluminescence intensity enhanced 1.75 times than Li3RbGe8O18:Mn4+ phosphor, while the corresponding internal quantum efficiency (IQE) increased by 1.57 times. According to the Rietveld refinement results, the corresponding mechanism of luminescence enhancement is attributed to the smaller distortion degree of the [Ge(1)O6] octahedron. The pc-WLED device is fabricated by the optimal Li3Cs0.5Rb0.5Ge8O18:1%Mn4+ red phosphor, yellow phosphor with Y3Al5O12:Ce3+ and 460 nm InGaN chip, showing a warm white light emission with low correlated color temperature (4474K) and high color rendering index (90.8). The result implies that the Li3Cs0.5Rb0.5Ge8O18:1%Mn4+ phosphor can be used as a potential red phosphor for pc-WLED application.