A single Eu2+-activated high-color-rendering oxychloride white-light phosphor for white-light-emitting diodes

Abstract

Single-phased, high-color-rendering index (CRI) white-light phosphors are emerging as potential phosphor-converted white-light-emitting diodes (WLEDs) and as an alternative to blends of tricolor phosphors. However, it is a challenge to create a high CRI white light from a single-doped activator. Here, we present a high CRI (Ra = 91) white-light phosphor, Sr5(PO4)3-x(BO3)xCl:Eu2+, composed of Sr5(PO4)3Cl as the beginning member and Sr5(BO3)3Cl as the end member. This work utilized the solid-solution method, and tunable Eu2+ emission was achieved. Color-tunable Eu2+ emissions in response to structural variation were observed in Sr5(PO4)3-x(BO3)xCl solid solutions. This was further confirmed using X-ray Rietveld refinement, electron paramagnetic resonance spectroscopy, and in the photoluminescence spectra. The color-tunable emissions included the white light that originated from the combination of the blue emission of Sr5(PO4)3Cl:Eu2+ and an induced Eu2+ yellow emission at approximately 550 nm in the solid solution. Importantly, the white-light phosphors showed a greater R9 = 90.2 under excitation at 365 nm. This result has rarely been reported in the literature and is greater than that of (R9 = 14.3) commercial Y3Al5O12:Ce3+-based WLEDs. These findings demonstrate the great potential of Sr5(PO4)3-x(BO3)xCl:0.04Eu2+ as a white-light phosphor for near-UV phosphor-converted WLEDs. These results also provide a shortcut for developing a high CRI white-light phosphor from a single Eu2+-doped compound. A white light-emitting diode with a very high colour rendering index is made using a phosphor based on a europium-doped oxychloride material. A team of scientists from China, Switzerland and the USA investigated the white-light phosphor Sr5(PO4)3−x(BO3)xCl:Eu2+. Its structural and electronic properties were characterized by X-ray diffraction analysis, photoluminescence spectroscopy, and fluorescence decay analysis of the phosphor. When excited by ultraviolet light (365 nanometres) from a light-emitting diode, the phosphor emitted broadband photoluminescence with peaks in the blue (446 nanometres) and yellow (550 nanometres) regions. These emission characteristics resulted in high-quality white light with a very high colour rendering index that was significantly better than those of existing commercial white light-emitting diodes based on the phosphor YAG:Ce3+, indicating the potential of this new phosphor.