Thermally Induced Aggregation of Color Centers in Sodium Fluoride
The aggregation of F or F′ centers or both in NaF was studied via the changing optical absorption spectra observed during warming to 344°K immediately following low-temperature (80°K) X-irradiation. The extensive X-irradiation causes the formation of a large F'-center absorption (OD > 3) which has a peak at 470 mµ. Thermally induced bleaching of F' centers is accompanied by the formation of M centers, which were found to reach a maximum concentration at 318°K. A new band with a peak at 725 mµ was observed to grow in, reach a maximum at 283°K, and then disappear. Standing at room temperature, after thermal treatment, causes a decrease in the F and M1 bands and increase in the R2 (440-mµ) and Rl (400-mµ) bands and in bands at 570 mµ and 870 mµ. F-center aggregation in NaF is not great, nor is aggregation enhanced by allowing the crystal to stand at room temperature as happens in KCl
KeywordsOptical Absorption Spectrum Color Center Sodium Fluoride Band Light Triangular Point
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