Controllable Eu valence for photoluminescence tuning in apatite-typed phosphors by the cation cosubstitution effect

Abstract

By cosubstituting [Ca²⁺–P⁵⁺] for [La³⁺–Si⁴⁺] in the Eu-doped Ca_(2→8)La_(8→2)(SiO₄)_6−x(PO₄)_xO₂ (0 ≤ x ≤ 6) system, Eu³⁺ ions are controllably and gradually transformed to Eu²⁺. Thus, the emission colors consecutively changed from red to blue/green light. Furthermore, excellent warm-white lights with the low correlated color temperature (CCT) range of 3500–3800 K and a high color rendering index (R_a) (88.4–93.2) have been achieved by mixing the as-prepared phosphors at different cation cosubstitution ratios.