Effect of annealing on the photoluminescence and thermoluminescence properties of Eu²⁺ doped BaSO₄ microgravels

The quest for developing phosphors emitting intense ultra violet (UV) rays and thermoluminescence (TL) occurring in the temperature range between 180 and 250 °C is on the progressive surge as the phosphors are highly desirable for phototherapy lamps and X-ray dosimetry. For this work, strong UV and TL emitting Eu²⁺ doped BaSO₄ gravels of sub-micro size were synthesized by acid-assisted co-precipitation method. The as-prepared phosphors were annealed at different temperatures (300–700 °C) for 10 h to enhance the UV and TL emissions. The influence of annealing on the crystallite size, morphology, vibrational bands, PL and TL were studied by X-ray diffraction (XRD), Field emission gun scanning electron microscopy (FEGSM), Fourier transform infrared spectroscopy (FTIR), Photoluminescence (PL) and TL spectroscopies, respectively. From XRD, it is noticed that the crystallite size and crystal quality increase when the annealing temperature is raised from 300 to 500 °C, whereas they are found to be decreasing at 600 °C and the trend continues till 700 °C. FEGSEM images show that all the phosphors have similar gravel morphology with inhomogeneous sub-micro size distribution. Formation of clusters is also noticed for phosphors while annealing in the range 300–500 °C. The vibrational bands related to the phosphor have been identified from the FTIR spectra. From PL and TL studies, the prominent emission intensity is found to be the maximum for 500 °C annealed phosphor revealing optimization. PL spectra also exhibit a strong UV emission at ~ 374 nm. The TL glow curve of the phosphors shows the first deconvoluted peak in the temperature range 198–210 °C and the second peak in the range 240.3–259.1 °C. The activation energy for the first peak is in the range 1.02 to 1.30 eV, whereas the second peak is in the range 0.72 to 2.98 eV. Thus the optimized multi-utility phosphor could be beneficial for phototherapy lamps and X-ray dosimeters.