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 ⁴G_5/2→⁶H_J (J = 5/2, 7/2, 9/2, and 11/2) transitions of Sm³⁺, in which the hypersensitive electronic dipole transition ⁴G_5/2→⁶H_9/2 (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⁺-O^2- group to Sm³⁺. The decay lifetime for ⁴G_5/2→⁶H_9/2 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.