Thermostimulated luminescence, exoelectron emission and X-ray induced luminescence studies in CaSO4 : Eu and CaSO4 : Eu, Na

X- and UV radiation induced thermostimulated luminescence (TSL), thermostim ulated exoelectron emission (TSEE) and X-ray induced luminescence (XIL) stu dies in CaSO4:Eu and CaSO4:Eu, Na reveal that the X-ray induced TSL peaks e xhibit Eu2+ (blue) and Eu3+ (red) emissions - but their relative ratio vari es with the peak. In contrast, UV induced TSL peaks exhibit only Eu3+ emiss ion. Even in the CaSO4:Eu Sample, which contains both Eu2+ as well as Eu3+, no Eu2+ emission is seen in all the TSL peaks produced by UV irradiation. These results confirm that the X-ray induced TSL in these phosphors is best explained by the energy transfer model while UV induced TSL is best explai ned by the charge transfer model. In CaSO4:Eu, the X-ray induced TSEE peak coincides exactly with the 400 K TSL peak whereas the UV induced TSEE is ne gligible. This indicates an Auger-like decay of electrons following the sel f-absorption of 400 nm Eu2+ emission due to the 400 K TSL peak. Intense XIL in CaSO4:Eu occurs mainly due to Eu2+ emission which decreases with increa sing irradiation temperature from 100 K perhaps due to thermal quenching. B ut the significant variation in XIL intensity in the temperature interval 3 50 to 450 K is attributed to Eu2+ --> Eu3+ oxidation. XIL in CaSO4:Eu incre ases with X-ray intensity but is nearly independent of X-ray exposure time. These results suggest that XIL emission is probably caused by metastable E u2+ centers formed during X-irradiation.