Diffusion ofFCenters into Potassium Chloride Single Crystals

Diffusion of $F$ centers into potassium chloride crystals during an additive coloring process has been measured at various temperatures. A diffusion process which can be explained by a simple theory of volume diffusion seems to be predominant at higher temperatures. At lower temperatures, however, the occurrence of a disordered interfacial diffusion with an $F$-center concentration decreasing exponentially with the first power of penetration depth is confirmed.