Luminescence characterization of gamma-ray-irradiated rare-earth doped BaSO4 and MgSO4 phosphors

Photoluminescence (PL), thermoluminescence (11) and mechanoluminescence (ML) of rare-earths (RE) doped BaSO4 and MgSO4 phosphors were studied. Undoped and doped phosphors containing different concentrations of dopant were synthesized by solid-state reaction method. X-ray diffraction (XRD) pattern of the samples matched well with their standard data of Joint Committee on Powder Diffraction's (JCPD) file. In the PL spectrum of Dy doped samples, peaks around 470 and 580 nm were observed due to transition of Dy3+ ion. Eu doped BaSO4 showed PL peak at 380 nm due to transition of Eu2+ ion, however, in the PL spectrum of MgSO4:Eu phosphors, transition of Eu3+ was also observed along with transition of Eu2+ ion. Dy doped gamma-ray-irradiated BaSO4 and MgSO4 phosphors showed at least two distinct peaks in their TL glow curves. The first peak occurred in range 120-150 degrees C and the second peak was observed in the range 20-230 degrees C. The TL glow curve of gamma-ray-irradiated BaSO4:Eu contained a distinct peak at 170 degrees C. Two distinct peaks, one at 110 degrees C and another at 220 degrees C were observed in the U glow curve of gamma-ray-irradiated MgSO4:Eu phosphors. TL spectra showed that RE ions act as luminescence centre in BaSO4 and MgSO4 system. When the ML was excited impulsively by dropping a load on to the gamma-ray-irradiated samples, only one sharp peak was observed in the ML intensity versus time curve of Dy doped samples, however, two peaks were observed in the ML intensity versus time curve of Eu doped BaSO4 and MgSO4 phosphors. The ML spectra of samples showed the characteristic emission of rare-earth impurities. Experimental results suggest that although almost similar states are responsible for PL, TL and ML, the luminescence efficiency of the phosphors depends on the mode of excitation. (C) 2011 Elsevier Ltd. All rights reserved.