Emitting-tunable Eu^(2+/3+)-doped Ca_(8−x)La_(2+x) (PO₄)_6−x(SiO₄)_xO₂ apatite phosphor for n-UV WLEDs with high-color-rendering

Currently, developing single-phased white light phosphors based on a single-doped activator is an efficient approach to blends of bicolor/tricolor phosphors for realizing phosphor-converted white light emitting diodes (pc-WLEDs) with a high color rendering index (CRI) and low correlated color temperature (CCT). Here, we present high CRI (R_a = 93-95) and low CCT (3500-6000 K) white lights by cosubstituting [Ca²⁺-P⁵⁺] for [La³⁺-Si⁴⁺] in the solid solution Ca_(8→2)La_(2→8)(PO₄)_6−x(SiO₄)_xO₂:Eu²⁺/Eu³⁺ (CLPSO_Eu). The results are attributed to the presence of multi Ca²⁺ sites due to possible mixing nanophases and the simultaneous occupancy of Ca²⁺ and La³⁺ sites by Eu, resulting in the mixing of blue (466 nm) and green emissions (540 nm) for Eu²⁺, and red emission (613 nm) for Eu³⁺, which were perfectly confirmed using X-ray Rietveld refinement, photoluminescence spectra and extended X-ray absorption fine structure. These findings not only imply that the as-prepared CLPSO_Eu are promising single-phased white light phosphor for near-UV based WLEDs but also offer a novel avenue to design high CRI white light phosphors based on a tunable Eu²⁺/Eu³⁺