Pressure Induced Color Centers in CaF2 and BaF2

The effect of pressure to 52 800 atm has been studied on x-irradiated CaF2 and BaF.. The three bands discovered by Smakula are little affected by pressure or bleaching. There are two new bands induced by pressure, which are greatly enhanced by any change in pressure. These bands show a marked blue shift with increasing pressure. Each can be bleached by light of its own frequency, and restored by reapplication of pressure. It is suggested that the pressure-induced bands are due to electrons associated with pressure-induced lattice defects, while the bands discovered by Smakula are associated with colloidal deposits or impurities.