Photoluminescence properties of a double perovskite tungstate based red-emitting phosphor NaLaMgWO6:Sm3+

In this work, the conventional solid-state method was applied to synthesize a series of red-emitting NaLaMgWO6:Sm3+ phosphors. The crystal structure, phase purity, morphology, particle size distribution as well as elemental composition of the as-prepared phosphors were investigated carefully with the aid of XRD, SEM, EDS, FT-IR analyses, indicating the high-purity and micron-sized NaLaMgWO6:Sm3+ phosphors with monoclinic structure were prepared successfully. The spectroscopic properties of Sm3+ in NaLaMgWO6 host including UV–vis diffuse reflection spectrum, photoluminescence excitation and emission spectra, decay curves, chromaticity coordinates and internal quantum efficiency were investigated in detail. Upon excitation with UV (290 nm) and n-UV (406 nm), NaLaMgWO6:Sm3+ phosphor presented red emission corresponding to the 4G5/2→6HJ (J = 5/2, 7/2, 9/2, and 11/2) transitions of Sm3+, in which the hypersensitive electronic dipole transition 4G5/2→6H9/2 (645 nm) was with the strongest emission intensity because Sm3+ ions were located at a lattice site with anti-inversion symmetry. The optimal concentration of Sm3+ was different for the given excitation wavelength such as 290 nm and 406 nm, which was interpreted by the extra effect of the energy transfer from W6+-O2- group to Sm3+. The decay lifetime for 4G5/2→6H9/2 transition of Sm3+ was very short (< 1 ms) and decreased with the increasing Sm3+ concentration. The present investigation indicates that NaLaMgWO6:Sm3+ phosphor could be a potential red component for application in w-LEDs.