Thermal decay of photochromic color centers in CaF2, SrF2, and BaF2 crystals doped by La and Y impurities
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The absorption spectra of photochromic centers in CaF2, SrF2, and BaF2 crystals doped by La and Y impurities and thermal decay of the centers in the temperature range 80–600 K are investigated. Under low-temperature x-ray irradiation, ionized photochromic color (PC+) centers are generated in La- and Y-doped CaF2 crystals and in a La-doped SrF2 crystal. It is revealed that, upon heating of the CaF2-LaF3 crystal, PC+ centers are transformed into photochromic color (PC) centers. In the SrF2-YF3 crystal irradiated at room temperature, photochromic color centers are generated as well. All color centers decay at a temperature of approximately 600 K. After irradiation of the BaF2-YF3 crystal at a temperature of 80 K, absorption bands are observed at energies of 2.25 and 3.60 eV, which are related to neither PC centers nor PC+ centers.
PACS numbers78.70.-g 78.70.Dm
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