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 Sr2+ and Sc3+ sites for the doped ions to occupy, forming emission centers. The KSrSc2(PO4)(3):Ce3+ and KSrSc2(PO4)(3): Eu2+ 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 Tb3+ ions into the KSrSc2(PO4)(3):0.03Ce(3+) and KSrSc2(PO4)(3):0.03Eu(2+) phosphors with varying contents. The mechanism of Eu2+ --> Tb3+ 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):Ce3+, Tb3+ and KSrSc2(PO4)(3):Eu2+, Tb3+ phosphors are of potential value for UV excited WLEDs.