Characterization, photoluminescence, and X-irradiated thermoluminescence studies of rare-earth-doped calcium sulfate
摘要
Rare-earth (Eu3⁺ and Tb3⁺)-doped calcium sulfate (CaSO₄) phosphors were synthesized using a simple and cost-effective high-temperature recrystallization method. The structural, morphological, and optical properties of the prepared samples were systematically investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), diffuse reflectance spectroscopy, photoluminescence (PL), and thermoluminescence (TL) techniques. XRD analysis confirmed the formation of a single-phase orthorhombic structure of CaSO₄ with good crystallinity, while SEM studies revealed microcrystalline particles with sizes ranging from submicron to micrometer scale. FTIR spectra confirmed the presence of characteristic sulfate vibrational modes with slight shifts upon rare-earth doping, indicating successful incorporation of Eu3+ and Tb3+ ions into the host lattice. Diffuse reflectance analysis showed a red shift in the absorption edge for doped samples, and the optical band gaps were estimated using the Tauc relation, yielding values of 6.26 eV for undoped CaSO₄, 5.89 eV for Tb3+-doped CaSO₄, and 5.30 eV for Eu3+-doped CaSO₄. Photoluminescence studies revealed characteristic emissions of Eu3⁺ ions in the red region (~ 618 nm) corresponding to 5D₀ → ⁷F₂ transitions and strong green emission (~ 545 nm) from Tb3⁺ ions due to 5D₄ → ⁷F₅ transitions. Thermoluminescence measurements indicated enhanced glow peak intensity in doped samples, suggesting improved trapping and recombination processes. The results demonstrate that rare-earth doping significantly enhances the optical and luminescent properties of CaSO₄ phosphors, making them promising candidates for applications in optoelectronic devices and radiation dosimetry.