UV-induced photoluminescence and thermally stimulated luminescence of CaSO4:Eu and CaF2:Tb3+ phosphors

Ultraviolet radiation induced changes in photoluminescence (PL) and thermally stimulated luminescence (TSL) of europium activated calcium sulphate (CaSO4:Eu3+, Eu2+) and terbium doped calcium fluoride (CaF2:Tb3+) phosphors have been studied. PL measurements suggest conversion of Eu3+ to Eu2+ on 254 nm irradiation corresponding to charge transfer band of Eu3+ ions and reduction of Eu2+ ions with 365 nm illumination representing a f-d transition of Eu2+ ions. Similar studies carried out on CaF2:Tb3+ phosphor, however, do not show any significant wavelength specific changes. The integrated TSL output appears to be rate-dependent for both phosphors. The wavelength dependent changes in TSL output observed for CaSO4:Eu phosphor have been correlated with those obtained in PL studies. The changes in TSL and PL characteristics of CaF2:Tb3+ phosphor have been explained on the basis of stabilisation of traps based on matrix specific charge similarities. (C) 2000 Elsevier Science Ltd. All rights reserved.