Thermoluminescence of MgSO4 Doped with Eu and P Impurities

CaSO4:Eu, MgSO4:Eu and MgSO4:Eu,P phosphors have been prepared and their thermoluminescence (TL) characteristics were studied. A main glow peak due to Eu2+ ions is seen at ~146 oC and 440 nm and glow peaks at ~145 oC, ~190 oC, ~260 oC and ~360 oC for 590 nm and 625 nm wavelengths are identified as Eu3+ ion emissions in MgSO4:Eu. Emission spectra in MgSO4:Eu and the MgSO4:Eu,P show that the MgSO4:Eu3+ glow peak at 260 oC for 590 nm and 625 nm shifts to 280 oC with enhanced intensity while the Eu2+ ion glow peak at 146 oC remains but with reduced intensity. The main glow peak at ~146 oC and 440 nm from Eu2+ ions shows significant difference from the characteristic glow peaks of Eu3+ ions. It is observed that the wavelength of the Eu2+ ion glow peak is inversely proportional to the radius of the cation of the host sulfate in alkaline-earth sulfate phosphors. By contrast the wavelengths of the Eu3+ ion glow peaks remain unchanged in different sulfates. Besides, the glow curve at ~146 oC obtained using a conventional blue sensitive reader shows simply the first order kinetics. It is concluded that the luminescence centers and distribution of traps related to Eu2+ ions are different from that of Eu3+ ions in MgSO4:Eu and MgSO4:Eu,P phosphors.