Temperature characteristics of NaY(MoO4)2: Sm3+ and effect of Li+ doping on luminescent properties of phosphors

Intense orange phosphors NaY(MoO4)2: Sm3+ were successfully synthesized by means of a conventional solvothermal process in the presence of disodium ethylenediamine tetraacetate (EDTA-2Na) as a surfactant. The dependence on the phase structure, particle morphology, photoluminescence property and thermal quench behavior of the as-prepared phosphors were studied in detail. The molar ratio of EDTA-2Na/Re3+(Re = Y and Sm) played significant roles in the selective preparation of NaY(MoO4)2 microcrystals with various regular uniform shapes. With increasing molar ratios of the two composite, the morphology of the products changed from octahedron, truncated octahedron, microcube to thin plate, namely, truncation degree was positively correlated with molar ratios. The possible formation mechanism of NaY(MoO4) microplates was explained from the effects of EDTA-2Na on adsorption for (001) planes. NaY(MoO4)2: Sm3+ phosphors exhibit the orange fluorescence and the optimal single dopant contents of Sm3+ was 3.0 mol%. In addition, the markedly high enhancement of Sm3+ characteristic emission about 25.72% was achieved by co-doping with Li+ ions, and the introduction of Li+ ions had no obvious impact on the phase as well as morphology of NaY(MoO4)2: Sm3+. By optical analysis, it can be inferred that the improvement of the emission intensity was the result of the cooperative effects of ion electronegativity and the crystal field environment. The emission intensity at 543 K was as high as 60% of that at ambient temperature, meanwhile, the thermal activation energy was obtained to be 0.30344 eV on the basis of the temperature-dependent mode through means of charge transfer state, which make the phosphors a promising candidate for some temperature sensitive devices.