Thermostimulated Luminescence, Exoelectron Emission and X-Ray Induced Luminescence Studies in CaSO4 : Eu and CaSO4: Eu, Na
✍ Scribed by Lakshmanan, A. R. ;Tomita, A.
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 310 KB
- Volume
- 173
- Category
- Article
- ISSN
- 0031-8965
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✦ Synopsis
X-and UV radiation induced thermostimulated luminescence (TSL), thermostimulated exoelectron emission (TSEE) and X-ray induced luminescence (XIL) studies in CaSO 4 : Eu and CaSO 4 : Eu, Na reveal that the X-ray induced TSL peaks exhibit Eu 2+ (blue) and Eu 3+ (red) emissions ± ± but their relative ratio varies with the peak. In contrast, UV induced TSL peaks exhibit only Eu 3+ emission. Even in the CaSO 4 : Eu sample, which contains both Eu 2+ as well as Eu 3+ , no Eu 2+ 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 explained by the charge transfer model. In CaSO 4 : Eu, the X-ray induced TSEE peak coincides exactly with the 400 K TSL peak whereas the UV induced TSEE is negligible. This indicates an Auger-like decay of electrons following the self-absorption of 400 nm Eu 2+ emission due to the 400 K TSL peak. Intense XIL in CaSO 4 : Eu occurs mainly due to Eu 2+ emission which decreases with increasing irradiation temperature from 100 K perhaps due to thermal quenching. But the significant variation in XIL intensity in the temperature interval 350 to 450 K is attributed to Eu 2+ 3 Eu 3+ oxidation. XIL in CaSO 4 : Eu increases with X-ray intensity but is nearly independent of X-ray exposure time. These results suggest that XIL emission is probably caused by metastable Eu 2+ centers formed during X-irradiation.