EXCITONIC AND RECOMBINATION PROCESSES IN CAWO4 AND CDWO4 SCINTILLATORS UNDER SYNCHROTRON IRRADIATION

Excitation spectra of intrinsic (IL) and extrinsic luminescence (EL) f rom CaWO4 and CdWO4 crystals, measured using synchrotron radiation (4- 30 eV) at 8 K, have been analysed. In CaWO4 the IL (2.9 eV) is efficie ntly excited by photons of 5.5-7.0 eV at the creation of molecular exc itons. The EL is efficiently excited in interband transitions (hv > 6. 8 eV). The energy threshold for the multiplication of electronic excit ations is E-t approximate to 15 eV in CaWO4 and E-t approximate to 10 eV CdWO4. In CdWO4, a fraction of the molecular excitons undergoes aut oionization due to an overlap with the continuum of the interband tran sitions. Fast emission (<2 ns) is found at 80 K under the pulse excita tion by electrons with an energy of 300 keV. The continuous temperatur e-independent emission of CaWO4 crystals in the region of 2-5 eV is in terpreted as an intraband luminescence. The emission at 5.5 eV is ascr ibed to a metastable molecular excitons. (C) 1998 Elsevier Science Ltd . All rights reserved.