Color Centers Produced in KCl and KBr by Prolonged X Irradiations at Low Temperatures

Abstract

A 893where e= ~iE«(5u-Sn)T; S n and Su, are the elastic compliance constants, T is the applied stress and E w is the shear-deformation-potential constant of the conduction-band minima. Also, 6A C = chemical splitting of the ground state. The ls(E) and ls(Zi) states are assumed to be degenerate. The solutions to the secular equation are e-A c (3 roots), -2e-A c , andThe variation of the ground states with strain is shown in Fig. 15. It is seen that the two states described by the first two types of roots vary with strain in a manner which is identical to that of the p states.The following linear combinations of the effectivemass wave functions permit the selection rules of Fig. 12 to be deducedThe principal purposes of this study were to observe the effect of an x irradiation of extended duration on the production of color centers in KC1 and KBr at low temperatures and to examine the implications with regard to possible color-center models. Growth curves were determined at 5°K for the F, K, M, and H bands in KC1 and KBr and for a new band at 245 m/i in KC1 and at 278 m/j in KBr, called the W band. Growth curves were determined at 80°K for the F, K, and M bands in KC1 and KBr. The growth of the F 4 band in KBr and of a band having its absorption maximum at 240 nut in KC1, designated as the 7(240) band, was also followed at 80 C K. The ratio of the absorptions at the peak of the F and K bands was found to remain constant indicating that both of these bands arise from transitions in the same center. The concentration of M centers was found to depend quadratically on the F-center concentration. This result gives conclusive support to the model proposed by van Doom and Haven that the M center consists of a pair of associated F centers. The F-to-TI ratio was observed to be constant for short x-ray exposures, supporting the viewpoint that the two centers are produced as complementary defects; however, for prolonged exposures, this ratio is no longer constant. The number of F centers is in constant ratio to the combined concentrations of H and H' centers provided that the oscillator strength of the E' band is suitably chosen. The linear dependence of the generation of both Vi centers in KBr and 7(240) centers in KC1 on F-center concentration suggests that the F 4 and 7(240) centers, rather than V\ centers, are fundamentally related to the mechanism of formation of F centers near liquid-nitrogen temperature for a prolonged irradiation.

OH− Dissociation and U2 Decomposition in Hydroxide‐Doped KCl and KBr Crystals

“…This is observed a t 4.5 'K as well as a t 77 OK. The H band peaks a t the same wavelength as does the band which arises after X-irradiation a t lowest temperatures [23], the half-width however being 10% smaller in our experiment than observed after X-raying. There is always an absorption present after X-irradiation due to V, centres [ 2 2 ] , this being responsible for the broader H band reported in that case.…”

Theory of tunneling recombination of defects stimulated by their motion I. General formalism

“…However, in describing deeply non-steady bimolecular reactions, discussed in Sections 2 and 3, one should keep in mind the restrictions of (3.27)) (3.28) as well as (3.21), (3.24). I n particular, these equations are incapable of describing formation of irradiation-induced loose aggregates of similar defects a t high doses, which has been observed experinientally in alkali halides even at low temperatures where defects are certainly immobile [95,96]. (Defect mobility greatly stimulates such an aggregation.…”

Physics and Current Understanding of X-Ray Storage Phosphors

“…It is caused by forbidden transitions of the V K centre, which become dipole allowed due to the loss of the inversion symmetry by slow oscillations [79]. Since the known H centre bands at 3.26 eV and 2.50 eV [80] are 370 S. Schweizer: Physics and Current Understanding of X-Ray Storage Phosphors [63] superimposed by the intense bands of the F and V K centre, respectively, no MCDA band can be clearly assigned to the H centre. Due to the strong overlap of the H centre bands with those of the F and the V K centre, respectively, the identification of H centres by MCDA-EPR turned out to be difficult.…”