Luminescence properties of CsI crystals grown from the melt treated by metals-getters
The processes of purification of CsI melt from admixtures by metals-getters (Ti, Ta, and Zr) are studied through two ways: investigation of change in concentration of oxide-ion entering from the getter into the melt and investigation of luminescence properties of CsI single crystals grown from the treated melt. The treatment by Ti does not lead to the removal of oxide-ions; however the growth melt is polluted by Ti species (Ti2O3). This causes drastic changes in the luminescence properties of CsI crystals. Their radioluminescence spectra do not contain the band caused by fast 7 and 30 ns components (maximum at 308 nm) and there arises a band (maximum 418 nm) corresponding to slow microsecond component. The enterance of Ta leads to removal of oxide ions, but the interaction products (Ta2O5 or CsTaO3) are partially dissolved in CsI melt that leads to appearance in the radioluminescence spectrum of the intense band (maximum 416 nm) caused by the slow component together with less intense band (maximum at 305 nm) due to the fast components. Only treatment by Zr allows to suppression of the slow component completely. The radioluminescence spectrum of CsI crystals grown from the Zr-treated melt includes only one band (maximum at 306 nm), whereas the luminescence at wavelengths more than 410 nm is absent. For this crystal two parameters describing its performance are determined. The effective time of luminosity of the fast components is equal to 14 ns and the ‘Fast/Total’ ratio is 0.88. So, the treatment of CsI melt by Zr allows obtaining an extremely fast scintillation material.