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

Abstract

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)₃:0.03Ce³⁺ and KSrSc₂(PO₄)₃:0.03Eu²⁺ 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.