Thermally stimulated luminescence studies of a LiYF4:U4+ crystal

The present paper gives the first detailed report on trap level spectroscopic studies of gamma irradiated lithium-yttrium tetrafluoride single crystals doped with tetravalent natural uranium. The work carried out includes the growth of single crystals followed by thermally stimulated luminescence (TSL) and electron spin resonance (ESR) studies on the gamma irradiated crystal. The TSL studies in the 300-600 K temperature range have revealed the presence of four glow-peaks. The trap parameters have been calculated for the two prominent peaks. The predominant radiation-induced colour centre has been identified as an F centre and its growth and annihilation behaviour has been studied in detail. ESR studies on the gamma irradiated crystal at 300 K have shown formation of U5+ ions in small amounts. Further, the spectral character of the glow-peaks revealed the presence of a strong emission group at 690 nm, characteristic of tetravalent uranium ions. It has been suggested that U4+ ions play an important role in TSL, taking part in the (U4+↔ U5+) process. (author)