Study of theF′Center in Several Alkali Halides

Abstract

The F' hand has been produced and measured in the following alkali halides: NaCl, KCl, KBr, KI, RbCl, Rbl, CsBr, and Csl. The spectra consisted of a single main peak and either a shoulder or a distinct second peak to the high energy side of it. The main peak in NaCl had a syrrnrrietric bell shape, whereas in the remainder of the salts it showed some structure The potassium and rubidium salts showed a shoulder located on Che high energy side of the main peak. .The cesium halides showed a more complex structure. The structure in the main peak may be attributed to difference in band structure between the sodium halides and the other alkali halides. The shoulder, or second peak, to the high energy side of the main peak has been assigned tentatively to F'center absorption where the F center is left in an excited 2p state. A semicontinuum model variational calculation has also been carried out using a correlated Hylleraas wave function. The F' binding energies * were calculated in a self-consistent priori fashion for m m and O.om . (m is the conduction band effective mass.) Generally good agreement with experimental binding energies was achieved for the * m = O.om case. Also the potential well was adjusted to force agreement * with experimental binding energies for the m = m case. The resulting wave functions were used to calculate the absorption coefficients for the F' centers. Generally good agreement was obtained concerning the position and sizes of the main peaks and their half-widths. The second absorption edges, corresponding to leaving the F center in an excited 2p state, were calculated. Good agreement with the experimental second edges was