Lithium fluoride crystals are irradiated at various doses by gamma rays at 77 K. The time evolution of photoluminescence signals from aggregated F 2 +, F2, F3 + and F 3 color centers, and of the absorption intensity of primary F centers are measured at various annealing temperatures. The lifetimes of anionic vacancies υa and F2 + centers, the characteristic times of concentration growth of F2, F 3 + and F3 centers, and also the activation energies of diffusion of vacancies and F2 + centers together with various processes of aggregation are determined. It is found that lifetime decreases for vacancies while increases for F2 + centers by increasing the irradiation dose. It is also shown that, after irradiation during annealing, vacancies are formed as a result of the reaction F2 ++H→υa+Fl-, where Fl- is a fluorine ion in a lattice site and H is a fluorine interstitial atom. Then these vacancies participate in color centers aggregation kinetics. The presence of F- centers in the irradiated crystal is established, and the processes which lead to the formation of F2, F3 + and F3 centers after irradiation, are unveiled. © 2013 Elsevier B.V.
Color centers aggregation kinetics in lithium fluoride after gamma irradiation
Montereali, R.M.
2013-01-01
Abstract
Lithium fluoride crystals are irradiated at various doses by gamma rays at 77 K. The time evolution of photoluminescence signals from aggregated F 2 +, F2, F3 + and F 3 color centers, and of the absorption intensity of primary F centers are measured at various annealing temperatures. The lifetimes of anionic vacancies υa and F2 + centers, the characteristic times of concentration growth of F2, F 3 + and F3 centers, and also the activation energies of diffusion of vacancies and F2 + centers together with various processes of aggregation are determined. It is found that lifetime decreases for vacancies while increases for F2 + centers by increasing the irradiation dose. It is also shown that, after irradiation during annealing, vacancies are formed as a result of the reaction F2 ++H→υa+Fl-, where Fl- is a fluorine ion in a lattice site and H is a fluorine interstitial atom. Then these vacancies participate in color centers aggregation kinetics. The presence of F- centers in the irradiated crystal is established, and the processes which lead to the formation of F2, F3 + and F3 centers after irradiation, are unveiled. © 2013 Elsevier B.V.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
