Energy Transfer Mechanism in Pr-Doped SrF$_{2}$ Crystals
Results of investigation of energy transfer mechanism in SrF2 crystals doped with Pr3+ ions are presented. Temperature dependences of 5d-4f and exciton emission in this material under X-ray excitation, and thermostimulated luminescence (TSL) in temperature range 80-300 K are studied. It has been established that in SrF2-Pr3+ crystals the consecutive electron-hole capture mechanism of energy transfer takes place. Also we found that hole centers made a contribution to energy transfer from primary electrons and holes to Pr3+ ions.
Study of Nd 2 þ absorption in x-irradiated CaF 2 , SrF 2 , BaF 2 crystals
The absorption spectra of x-irradiated alkaline-earth fluoride (CaF2, SrF2, BaF2) crystals doped with Nd3þ ions have been investigated. X-irradiation results in creating the absorption bands of inter-configuration 4fne4fn 1e5 d1 transitions of Nd2þ. The charge reduction of the neodymium by irradiation is not temperature-stable and the ions reoxidation (Nd2þ / Nd3þ) occurs under heating to 570 K in CaF2, 520 K in SrF2 and 470 K in BaF2. © 2016 Elsevier Ltd. All rights reserved.
Photoionization processes in barium fluorohalide crystals doped with Eu2
The absorption, excitation and photostimulation spectra and thermoluminescence creation spectra of pure BaFX (X = Br, Cl) and BaFX:Eu2+ single crystals were studied in the vacuum-ultraviolet (VUV) region 5-10 eV at temperatures of 6-300 K. Creation of a VK thermoluminescence peak was observed when the BaFX:Eu2+ crystal was illuminated with VUV photons with energies above 6 eV while band-to-band transitions begin above 8-9 eV. Low-temperature photostimulation spectra for Eu2+ luminescence created by 6-7 eV photons show new bands in the infrared region, with intensities directly proportional to the Eu2+ concentration. However, the same infrared photostimulation bands for exciton luminescence were also observed for undoped crystals after x-ray irradiation. Therefore, a trace concentration of the shallow electron traps is present in each undoped and Eu-doped BaFBr and BaFCl crystal. The results show that self-trapped holes and electrons are trapped on different non-europium centres, created by VUV photons in BaFX:Eu2+ crystals at low temperature. It was concluded that Eu2+ ions assist in the creation of free electrons and self-trapped holes by photons with an energy 2-3 eV lower than those of band-to-band transitions.