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

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 Y₃A_l5O₁₂: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.