On the Nature of X‐Centres in NaCl Crystals with Anionic Impurities

Abstract

The effects of heat treatment and light on the conversion of Finto X-centres have been investigated in specially treated NaCl crystals with hydroxyl impurities. The mechanism of the stimulating action of the impurity in the F -+ X conversion is analysed. The results of the work are treated from a viewpoint of a new model of X-centres, according to which these centres are "quasicolloidal" formations, occurring a t the initial stage of F-centre coagulation. Suggestions are presented about the mechanism of a direct formation of quasicolloidal centres (X-centres) in crystals under high-dose y-irradiation.I n speziell behandelten NaC1-Kristallen mit Hydroxyldefekten wurde der EinfluD einer Temperung und Belichtung auf die Konversion von Fin X-Zentren untersucht. Der Stimulierungsmechanismus des Defekts auf die F -+ X-Konversion wird analysiert. Die Ergebnisse der Arbeit werden vom Standpunkt eines neuenModells fiir X-Zentren behandelt, wonach diese Zentren ,,quasi-kolloidale" Gebilde darstellen, die im Anfangszustand der F-Zentren-Koagulation auftreten. Fiir den Mechanismus einer direkten Bildung quasikolloidaler Zentren (X-Zentren) in Kristallen unter y-Bestrahlung hoher Dosis werden Vorschliige gemacht.

Effect of irradiation parameters on defect aggregation during thermal annealing of LiF irradiated with swift ions and electrons

“…34,35 Additive coloration produces F centers without the complementary hole centers as Schottky anion vacancies. Illumination of additively colored KCl crystals in the F-center absorption band ͑564 nm͒ at temperatures 500-770 K creates a new absorption band at 730 nm 35,36 which remains stable after quenching to RT. Subsequent illumination at 730 nm restores the F-center band.…”

Spatially resolved optical studies ofF-center diffusion in KBr crystals

“…[2][3][4] The concentration of the X centers is determined mainly by the concentration of the nucleation sites related to dislocations. 3,8,9 Under appropriate conditions ͑Sec. III B͒ F→X reaction occurs with no change in the area under the absorption curves, and the X-band width and the height at saturation are close to those of the initial F band.…”

“…5,7 X centers are most widely regarded as quasicolloids consisting of several hundred, or thousand F centers with a quasimetallic binding. 4,5,8 X centers are produced by F-center aggregation. [3][4][5]8 The migration process of F centers which leads to their aggregation can be considered as a diffusion influenced by illumination, internal electric fields, and mechanical strains.…”

“…4,5,8 X centers are produced by F-center aggregation. [3][4][5]8 The migration process of F centers which leads to their aggregation can be considered as a diffusion influenced by illumination, internal electric fields, and mechanical strains. 4,8,9 The growth of the spectral X band is due to the ripening of X centers rather than the growth of their concentration.…”

“…[3][4][5]8 The migration process of F centers which leads to their aggregation can be considered as a diffusion influenced by illumination, internal electric fields, and mechanical strains. 4,8,9 The growth of the spectral X band is due to the ripening of X centers rather than the growth of their concentration. [2][3][4] The concentration of the X centers is determined mainly by the concentration of the nucleation sites related to dislocations.…”