Synthesis and enhancement of photoluminescent properties in spherical shaped Sm3+/Eu3+ co-doped NaCaPO4 phosphor particles for w-LEDs

A series of Sm3+ doped and Sm3+/Eu3+ co-doped NaCaPO4 phosphors have been successfully synthesized via molten salt method. The structural, morphological, optical, photoluminescence and decay properties of the synthesized phosphors were investigated. Sm3+ doped phosphor exhibits excellent emission properties in the orangish-red region under n-UV excitation (403 nm), and the optimized doping concentration of Sm3+ was found to be 1.0 mol%. The excitation spectrum confirms that Sm3+/Eu3+ co-doped NaCaPO4 phosphors can be efficiently excited by both n-UV and blue LED chips. In the co-doped NaCaPO4:Sm3+/Eu3+ phosphors, the intensity of main characteristic emission peaks of Sm3+ decreased and Eu3+ increased with increasing Eu3+ ion concentration. The energy transfer (ET) from Sm3+ to Eu3+ was demonstrated to be quadrupole-quadrupole in nature by applying Dexter's ET formula and Reisfeld's approximation. Commission Internationale de l′Eclairage (CIE) chromaticity coordinates for co-doped samples lie in the red region. The decay time for the 4G5/2 level of Sm3+ decreases with increasing Eu3+ concentration, which also indicate the energy transfer from Sm3+ to Eu3+. These results indicate that Sm3+/ Eu3+ co-doped NaCaPO4 multifunctional phosphor is a promising and an attractive potential candidate for n-UV and blue excitation based w-LEDs.