R -Center Production in Alkali Halides

The suggestion that both the R₁ and R₂ bands in colored KCl crystals may be due to transitions of the F₂ center is considered. Formation mechanisms in support of this view are presented which are consistent with (1) the behavior of the R and M bands during F-light irradiation, (2) the observed decrease of the R bands and increase of the M band produced by heating, and (3) the photoconductivities measured for the R₁ and R₂ bands.