Evolution of highly efficient rare-earth free Cs(1−x)RbxVO3 phosphors as a single emitting component for NUV-based white LEDs

Abstract

Since the commercialization of white light-emitting diodes (WLEDs) in 1996, they are rapidly replacing conventional lighting sources and have become an essential commodity for day-to-day human life. At present, most of the WLEDs existing in the market are rare-earth based, which are very limited, expensive and often not available due to monopolistic supply conditions. Hence, there is a serious demand for novel rare-earth free phosphors to achieve cost-effective and energy-efficient WLEDs with excellent luminous efficacy for general illumination. Herein we report on highly efficient rare-earth free Cs_(1−x)Rb_xVO₃ phosphors as a single emitting compound for near UV-based WLEDs manufactured by the citrate sol–gel method for the first time. Rietveld refinement is performed for the X-ray diffraction patterns of the CsVO₃ host and CsVO₃:0.25Rb phosphors to reveal their orthorhombic pyroxene structure. The difference in the ionic radii of Rb⁺ and Cs⁺ ions led to a more distorted VO₄³⁻ tetrahedron with a broken T_d symmetry, which allows spin forbidden transitions for CsVO₃:0.25Rb phosphors, resulting in enhanced internal and external quantum efficiencies of 94.7% and 84.5% along with superior luminescence properties compared to the CsVO₃ host. When varying the input current from 20 to 200 mA, the fabricated WLED exhibited a good color rendering index of 69.7–81.5 and an extremely high luminous efficacy of 94.8–58.7 lm W⁻¹, which are among the highest values for the same host lattice. These rare-earth free CsVO₃:0.25Rb phosphors with a single emitting center may emerge as a new class of advanced inorganic phosphors for near UV-based WLEDs in the lighting industries.