Luminescence and electron-phonon interaction characteristics of radiation-induced point defects in magnesium fluoride nanocrystals

Nanocrystals of magnesium fluoride have been irradiated by γ-rays at 77 K or electrons at room temperature. Three types of radiation-induced defects (color centers) with previously unknown characteristics, such as luminescence and excitation luminescence spectra, luminescence lifetime, and Huang-Rhys parameters, have been observed and studied in these nanocrystals. It has been established that the luminescence excitation spectra of these centers contain two closely spaced bands with slightly different intensities. It was shown that pre-irradiation annealing of nanocrystals at temperatures above 823 K for one hour leads to the impossibility of observing all three new types defects in irradiated samples. It has been found that during the post-radiation annealing of samples, one of the new types of color centers is transformed into a well-known defect described earlier in the literature. It is concluded that new types of defects are generated near the nanoclusters which are formed during nanocrystals production. It has been found that defects previously known and referred to as M (C1) consist of two modifications which differ in luminescence and excitation luminescence spectra, and in dependencies of their concentrations upon temperature annealing.