Optical properties and energy transfer of a novel KSrSc2(PO4)3:Ce3+/Eu2+/Tb3+ phosphor for white light emitting diodes.

A new langbeinite-type phosphate KSrSc2(PO4)3 has been synthesized by conventional high temperature solid state reaction. Rietveld structure refinement, a field emission scanning electron microscope, photoluminescence spectra, quantum efficiency as well as lifetimes were used to characterize the samples. Structure refinement reveals that KSrSc2(PO4)3 has two kinds of Sr(2+) and Sc(3+) sites for the doped ions to occupy, forming emission centers. The KSrSc2(PO4)3:Ce(3+) and KSrSc2(PO4)3:Eu(2+) phosphors both have broad excitation and emission bands due to spin- and orbit-allowed electron transitions. Phosphors with tunable blue to blue-green colors were obtained by codoping the Tb(3+) ions into the KSrSc2(PO4)3:0.03Ce(3+) and KSrSc2(PO4)3:0.03Eu(2+) phosphors with varying contents. The mechanism of Eu(2+)→Tb(3+) energy transfer is determined to be a dipole-quadrupole interaction in terms of the experimental results and analysis of photoluminescence spectra and decay curves of the phosphors by using the Inokuti-Hirayama theoretical model. Our prepared KSrSc2(PO4)3:Ce(3+),Tb(3+) and KSrSc2(PO4)3:Eu(2+),Tb(3+) phosphors are of potential value for UV excited WLEDs.