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

Abstract

By cosubstituting [Ca(2+)-P(5+)] for [La(3+)-Si(4+)] in the Eu-doped Ca(2→8)La(8→2)(SiO4)6-x(PO4)xO2 (0 ≤ x ≤ 6) system, Eu(3+) ions are controllably and gradually transformed to Eu(2+). 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 (Ra) (88.4-93.2) have been achieved by mixing the as-prepared phosphors at different cation cosubstitution ratios.