Fabrication and enhanced photoluminescence properties of $\hbox {NaLa}(\hbox {MoO}_{4})_{2}$: $\hbox {Sm}^{3+}$, $\hbox {Bi}^{3+}$ phosphors with high efficiency white-light-emitting

Abstract

The tetragonal scheelite-type $\hbox {Sm}^{3+}\hbox {/Bi}^{3+}$ ions co-doped with $\hbox {NaLa}(\hbox {MoO}_{4})_{2}$ phosphors were synthesized by a facile sol–gel and combustion process using citric acid as complexing agent. The crystal structure and morphology of these as-prepared samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Furthermore, UV-absorption and the photoluminescence (PL) properties of these phosphors were systematically investigated and the PL of the phosphors shows strong white light emissions. Efficient energy transfer from the $\hbox {MoO}_{4}^{2-}$ group or $\hbox {Bi}^{3+}$ ions to $\hbox {Sm}^{3+}$ ions was established by PL investigation excited at 405 nm. The PL intensity of the studied materials was investigated as a function of different $\hbox {Sm}^{3+}$ and $\hbox {Bi}^{3+}$ concentrations. The PL investigations revealed that the phosphors exhibit apparent characteristic emissions, which is ascribed to the transition from the ground state energy level $^{4}\hbox {G}_{5/2}$ to excited state energy levels $^{6}\hbox {H}_{\mathrm{J}}$ ($J= 5/2, 7/2, 9/2$) and the $\hbox {NaLa}(\hbox {MoO}_{4})_{2}$: 4 mol% $\hbox {Sm}^{3+}$ and $\hbox {NaLa}(\hbox {MoO}_{4})_{2}$: 4 mol% $\hbox {Sm}^{3+}$, 8 mol% $\hbox {Bi}^{3+}$ present white emissions with the CIE coordinates of (0.350, 0.285) and (0.285, 0.229), respectively. The absolute quantum efficiencies of the phosphors are 40% ($\hbox {NaLa}(\hbox {MoO}_{4})_{2}$: 4 mol% $\hbox {Sm}^{3+}$) and 52% ($\hbox {NaLa}(\hbox {MoO}_{4})_{2}$: 4 mol% $\hbox {Sm}^{3+}$, 8 mol% $\hbox {Bi}^{3+}$), respectively.