Rare earth-free high color rendering white light-emitting diodes using CsVO3 with highest quantum efficiency for vanadate phosphors

Abstract

We have developed a reliable water-assisted solid-state reaction for synthesizing CsVO₃, which is an excellent rare earth (RE)-free phosphor. The polycrystalline CsVO₃ had a large particle size of 4.3 μm and a very smooth crystal surface. The maximum internal quantum efficiency (IQE) value of CsVO₃ at 345 nm excitation was 95.8%, which is the highest value reported for vanadate phosphors. The IQE averaged for 10 samples was 92.3%, which was much higher than that of CsVO₃ prepared by the conventional solid-state reaction (84.4%). Moreover, the photoluminescence excitation band edge was red-shifted by 10 nm, resulting in the large increase of IQE in the near-ultraviolet range; the IQE at 400 nm remained at 85%. We prepared RE-free white light-emitting diodes (WLEDs) from the CsVO₃ powders and the red phosphor Mg₂TiO₄:Mn⁴⁺ for emission color tuning. The emission of the WLED was white at CIE (x, y) = (0.330, 0.382), the averaged color rendering index (CRI) was 91.1, and all CRIs exceeded 83. Thus, we fabricated high color rendering RE-free WLEDs by using polycrystalline CsVO₃ with an increased IQE.