Photoionization in Eu-doped barium fluorohalide crystals

The absorption, excitation, photostimulation spectra and thermoluminescence creation spectra of pure BaFX (X = Br, Cl) and BaFX: Eu2+ single crystals were studied in the vacuum ultraviolet region 5-10 eV at temperatures 6-300 K. The creation of a V-k-related thermoluminescence peak was observed when the BaFX : EU2+ crystal was illuminated with vacuum ultraviolet (VUV) phot ons with energy above 6 eV. Band-to-band transitions begin above 8-9 eV. Lo w temperature photostimulation spectra for Eu2+ luminescence created by 6-7 eV photons showed new bands in the infrared region, the intensities of whi ch were directly proportional to the Eu2+ concentration. However, the same infrared photostimulation bands for exciton luminescence were observed also in undoped crystals after X-ray irradiation. The results show that trapped electrons and self-trapped holes were created by VUV photons in BaFX : Eu2 + crystals. It was concluded that Eu2+ ions assist in creation of free elec trons and holes by photons with energy 2-3 eV lower than those of band-to-b and transitions. (C) 2001 Elsevier Science Ltd. All rights reserved.