초록
$CaWO_4:Sm_x$(x = 0, 0.5, 1.0, 1.5, 2.0 mol%) white phosphors with different concentrations of $Sm^{3+}$ ions were synthesized using the hydrothermal method. The crystal structure, surface, and optical properties of the $CaWO_4:Sm_x$ phosphors were investigated using X-ray diffraction(XRD), field-emission scanning electron microscopy(FE-SEM), photoluminescence(PL) and photoluminescence excitation(PLE). From the XRD results, the crystal structure of the $CaWO_4:Sm$ phosphors was found to be tetragonal. The $CaWO_4:Sm$ phosphors became more cohesive with increasing $Sm^{3+}$-ion concentration. The photoluminescence excitation(PLE) peak of the phosphors, at around 250 nm, was ascribed to the transition from the 1A1 ground-state to the high-vibration level of 1T2 in the $WO{_4}^{2-}$ complex. The maximum emission spectra of the phosphors were observed when the $Sm^{3+}$ concentration was 0.5 mol%. The luminescence intensity of the $CaWO_4$ phosphors was decreased for $Sm^{3+}$ concentrations greater than 0.5 mol%.
