Synthesis and luminescence properties of Sm3+ doped NaKLaMO5 (M = Nb, Ta) red-emitting phosphors

A series of Sm3+ doped NaKLaMO5 (M = Nb, Ta) phosphors were successfully synthesized via high temperature solid-state reaction. The X-ray diffraction results indicated that the as-prepared phosphors crystallized in pure phases with tetragonal structure. The obtained photoluminescence spectra revealed that these phosphors can be excited by near-UV (406 nm) and they emit red light due to the predominant (4)G(5/2) -> H-6 (9/2) transition (664 nm) of Sm3+. The optimal doping concentration of Sm3+ was found to be 0.03 (3 mol%), based on which the critical energy transfer distance of Sm3+ ions in NaKLaMO5 (M = Nb, Ta) phosphors was calculated, and the concentration quenching mechanism was determined. The measured decay curves indicated that these phosphors had short decay lifetime ( < 1 ms), which decreased with the increase of Sm3+ concentration. As to NaKLa0.97Sm0.03Ta1-xNbxO5 series, with the Nb5+-contents (x) increase, the emission intensity gradually increased up to the complete replacement of Ta5+ by Nb5+. So, among all as-prepared phosphors, the phosphor NaKLa0.97Sm0.03NbO5 has the optimal luminescence performance, and its internal quantum efficiency, CIE coordinates, and temperature-dependent luminescence properties were investigated in detail. The research in this work provides a reference for choosing appropriate red phosphor for white light-emitting diodes.