Rapid addition of iodide causes the optically excited low-temperature donor acceptor luminescence from AgBr1-xIx (x<0.4) microcrystals to shift to approximate to580 nm whereas this luminescence is observed from 530 to 540 nm in microcrystals with homogeneous iodide incorporation. The band-gap energy in rapid iodide addition microcrystals is approximate to0.1 eV smaller than the measured band-gap energy for iodide concentrations near the maximum solubility (approximate to40%) even when the total iodide content is only a few percent. Low-temperature photoluminescence and excitation spectroscopy, transmission electron microscopy (TEM) and computational methods have been applied to determine the structure responsible for this behavior. The data generated indicated that nanoregions of fcc rocksalt AgBr1-xIx (x>0.9) are integrated into these microcrystals. These nanoregions of high iodide are strained and can engender the characteristic dislocations observed in the TEMs. Some dislocation features are removed by annealing (200degreesC). Heating also causes the luminescence and band-gap energy to return to the values characteristic of the crystals with a homogeneous distribution of iodide.

Rapid addition of iodide causes the optically excited, low-temperature donor-acceptor luminescence from AgBr1-xIx (x < 0.4) microcrystals to shift to approximate to580 nm, whereas this luminescence is observed between 530 to 540 nm in microcrystals with homogeneous iodide incorporation. The band-gap energy in rapid iodide addition microcrystals is approximate to0.1 eV smaller than the measured band-gap energy for iodide concentrations near the maximum solubility (approximate to40%), even when the total iodide content is only a few percent. Low-temperature photoluminescence and excitation spectroscopy, transmission electron microscopy (TEM), and computational methods have been applied to determine the structure responsible for this behavior. The data generated indicates that nanoregions of fcc "rock salt" AgBr1-xIx (x > 0.9) are integrated into these microcrystals. These nanoregions of high iodide are strained and can engender the characteristic dislocations observed in the TEMs. Some dislocation features are removed by annealing (200 degreesC). Heating also causes the luminescence and band-gap energy to return to the values characteristic of the crystals with a homogeneous distribution of iodide.

The formation of point defects in alkali halides by monochromatic radiation was investigated over a wide range of photon energies from the near UV exciton region to the hard X-ray region near the K-edge of bromine (from about 5 eV to 14 keV). The spectral dependence of the production efficiency was measured using monochromatic X-rays and VUV radiation as well as turnable monochromatic beams of synchrotron radiation. F center production efficiencies of the order of one keV/F-center were obtained for KBr and KCl. The yield dropped sharply in regions of strongest absorption such as in the exciton bands. An increase in F-center production efficiency was observed for KBr at the K-edge of bromine (13.4 keV). In the soft X-ray region (50-1500 eV) the F-center generation curves were strongly influenced by the X-ray absorption depth and proximity of the surface.

The formation of $F$ centers by monochromatic soft x-ray radiation was studied in the range of photon energies 50 to 1500 eV by use of a sensitive laser-induced luminescence technique. Production efficiencies of the order of $\frac{1 \mathrm{keV}}{(F \mathrm{center})}$ are obtained throughout the upper end of the above energy range in KCl and KBr at 77 K. Saturation densities of about ${10}^{18}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ occur, with the total number of centers depending upon the depth of penetration of the radiation. Reduced efficiency is noted at the lowest energies and highest absorption coefficients, and is possibly related to the observed photodesorption of neutral and ion species from the surface.

The spectral dependence of the F-center production efficiency was observed 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 several alkali halides. Evidence of a definite increase at the core threshold was observed as well as a significant wavelength dependence of the F-center production efficiency in the near-uv region. These studies were made possible by the development of an extremely sensitive method of detecting F centers in ultralow concentrations, which utilizes the luminescent properties of these centers.