Defect Production in Alkali Halide Crystals by Monochromatic X and Ultraviolet Radiation

The spectral dependence of the F-center production efficiency of several alkali halides was observed in diverse parts of the electromagnetic spectrum. Using low flux monochromatic sources, this efficiency was measured in the hard x-ray region at the K-edge of bromine in KBr and in the near ultraviolet part of the spectrum corresponding to the exciton region of the alkali halides. A significant increase in the production efficiency was observed at the K-edge, indicating a new F-center production mechanism. In the ultraviolet, maxima in the F-center production efficiency were observed in the long wavelength tail of the first exciton peak and even in the region of the alpha band, providing the first direct measurements of the F-center production efficiency in this region. These studies were made possible by the development of an extremely sensitive, new method of detecting F-centers in ultralow concentrations, which utilizes the luminescent properties of these centers. This Laser-Induced Luminescence method enables us to detect concentrations of F-centers that are five orders of magnitude smaller than can be detected by optical absorption measurements. Thus, we were able to investigate a new regime of F-center production, the early part of the so-called stage I region, and observe that it is linear for about four orders of magnitude. The effects of the presence of moderate concentrations of hydroxyl dopant in KBr were also investigated with this method to clarify the role it plays in F-center production. The photochemical reactions of this impurity induced by irradiation into its ultraviolet absorption band were studied and luminescent emission from one of the hydroxyl dissociation products was observed for the first time.