Environment-Dependent Eu²⁺-Activated Ba₃CaK(PO₄)₃ toward White-Light Emission by Chemical Cosubstitution of the (BO₃)^3– Anion Group

Investigating the phosphors doped with single activators in a single component to realize white-light emission is urgently desired for phosphor-converted white-light-emitting diodes. In this work, on the basis of the chemical unit cosubstitution strategy, the new borophosphate phosphors Ba₃CaK(PO₄)_3–x(BO₃)_x:0.02Eu²⁺ with a mixed anion group were prepared. Coupling structure refinement and photoluminescence analyses, Ba₃CaK(PO₄)_3–x(BO₃)_x consists of five different cationic sites with different coordination environments, with Eu²⁺ occupying the three sites for Ba²⁺. In the process of partial substituting (BO₃)^3– for (PO₄)^3–, because of the greatly distorted coordination field generated from the difference in the geometric configurations between the two anion groups, a red shift and broadening of the emission bands occurs, resulting in a color-adjustable emission from blue to white. A phosphor-converted light-emitting diode has been successfully fabricated with the incorporation of an as-prepared Ba₃CaK(PO₄)_2.6(BO₃)_0.4:0.02Eu²⁺ phosphor and a 405 nm near-ultraviolet chip, which exhibits Commission International de I’Eclairage chromaticity coordinates of (0.31, 0.37) and a correlated color temperature of 6295 K. As demonstrated in the present work, an approach adopted from phosphate to borophosphate is conducted to develop high-quality phosphors.