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

By cosubstituting [Ca2+-P5+] for [La3+-Si4+] in the Eu-doped Ca(2 -> 8)La(8 -> 2)(SiO4)(6-x)(PO4)(x)O-2 (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.