Synthesis, structure and optical properties of europium doped calcium barium phosphate – a novel phosphor for solid-state lighting

A new phase, Ca₆BaP₄O₁₇, was found in the CaO–BaO–P₂O₅ phase diagram and its Eu²⁺-doped derivative was evaluated as a possible phosphor for solid-state lighting. Ca₆BaP₄O₁₇ was prepared by conventional solid-state synthesis and its structure was solved ab initio from high-resolution, synchrotron X-ray powder diffraction data. The bandgap of Ca₆BaP₄O₁₇ was estimated to be 5.79 eV. Under excitation with UV to blue light, Ca₆BaP₄O₁₇:Eu²⁺ shows strong yellow emission with the peak position at 553 nm. A white LED, which was fabricated with an InGaN blue chip and Ca₆BaP₄O₁₇:Eu²⁺, achieved a luminous efficacy of 31 lm W⁻¹ with a color-rendering index of 78 around the correlated color temperature of 6500 K.