Phototransferred Thermoluminescence of CaWO4 Crystals

The PTTL of CaWO4 crystals was studied after exposure to X or β radiation at RT, and subsequent illumination with UV light at LNT. The main PTTL peaks appeared at 195 and 280 K, while TL peaks recorded at 165, 280, 340 and 400 K. TL could be excited only by band to band transitions, but PTTL could also be stimulated with photon energies smaller than the band gap. The trap responsible for the 340 K TL peak acts as a reservoir for the phototransfer. The PTTL and TL emission spectra showed a main broad 500 nm band composed of components at 490 and 520 nm. The XL and PL showed maxima at these wavelengths, indicating that the same luminescence centres are responsible for the PTTL as for TL, XL and PL emissions. The dependences of the PTTL intensity on the β dose and on that of the stimulating UV were both sub-linear. (author)