Luminescence investigations on sulfate apatite Na6(SO4)2FCl:RE (RE=Dy, Ce or Eu) phosphors

A new phosphor in the Cl-F system doped with Dy, Ce and Eu has been reported. Characterization of this phosphor using XRD, PL and TL techniques is described. Polycrystalline Na₆(SO₄)₂FCl:Dy; Na₆(SO₄)₂FCl:Ce and Na₆(SO₄)₂FCl:Eu phosphors prepared by a solid state diffusion method have been studied for their X-ray diffraction, photoluminescence (PL) and thermoluminescence (TL)characteristics. The PL excitation and emission spectra of phosphors were obtained. Dy³⁺ emission in the host at 475 and 570 nm is observed due to ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transition, respectively, whereas the PL emission spectra of Na₆(SO₄)₂FCl:Ce phosphor shows the Ce³⁺ emission at 322 nm due to 5d→4f transition of Ce³⁺ ion. In Na₆(SO₄)₂FCl:Eu lattice, Eu²⁺ as well as Eu³⁺ emissions are observed. The emission of europium ion in this compound exhibits the blue as well as red emission. The TL glow curves of the same compounds have the simple structure with a prominent peak at 150, 175 and 200 °C. TL response, fading, reusability and trapping parameters of the phosphors are also studied. The TL glow curves of γ-irradiated Na₆(SO₄)₂FCl sample show one glow peak indicating that only one set of traps is being activated within the particular temperature range each with its own value of activation energy (E) and frequency factor (s). The trapping parameters associated with the prominent glow peak are calculated using Chen’s half width method. The release of hole/electron from defect centers at the characteristic trap site initiates the luminescence process in these materials. The intensity of the TL glow peaks increases with increase of the added γ-ray dose to the samples.