Synthesis and Photoluminescence Properties of BaWO₄:RE³⁺ (RE = Eu or Sm) Phosphors

Abstract

BaWO₄:RE³⁺ (RE = Eu or Sm) phosphor powders were prepared with different doping concentrations of the activator ion by using the conventional solid-state reaction method. The dependences in the crystal structure, luminescence intensity, and morphology on the Eu³⁺ and the Sm³⁺ concentrations in BaWO₄ were investigated using X-ray diffraction (XRD), photoluminescence spectrophotometry, and scanning electron microscopy (SEM), respectively. XRD analysis showed tetragonal BaWO₄ structures for all the phosphors synthesized, regardless of the type and the doping concentration of the activator ion. SEM images indicated that as the concentration of activator ions was increased, the crystalline particles showed an increasing tendency to agglomerate irregularly. The room temperature excitation spectra of Eu³⁺- or Sm³⁺-doped BaWO₄ phosphors consisted of a broad charge transfer band in the ultraviolet region and several sharp 4f-4f transitions. When Eu³⁺-doped BaWO₄ phosphors were excited at 274 nm, the emission spectra exhibited sharp bands due to inner shell transitions occurring from the excited energy state ⁵D₀ to the lower energy levels ⁷F _J (J = 1, 2, 3, and 4). For Sm³⁺-doped BaWO₄ phosphors, three intense emission peaks at 568, 603, and 649 nm and a very weak line at 712 nm were observed. The highest asymmetry ratio-the intensity ratio of the ⁴G_5/2 → ⁶H_9/2 electric dipole to the ⁴G_5/2 → ⁶H_5/2 magnetic dipole transitions-was obtained for 1 mol% doping of Sm³⁺, indicating that the Sm³⁺ ions occupied the non-inversion symmetry sites.