Luminescence from Sodium Chloride

The x-ray-induced luminescence from NaCl has been studied in the range from 2.1 to 5.2 ev and in certain cases correlated with optically induced luminescence. The intensity and spectral distribution of the x-ray-induced luminescence was found to be dependent on the previous heat treatment received by the crystal. Before heating, bands are present at 2.25, 3.1, and 5.0 ev; afterwards, strong new bands appear at 2.45 and 3.5 ev and the intensity of the 5.0-ev band is increased. Prolonged x-irradiation reduces most of the effects of heat treatment; however, following such prolonged x-irradiation, a relatively strong band is present at 2.9 ev.In the heated crystals, it was found possible to induce the 2.45- and 3.5-ev bands by irradiating x-ray-colored crystals with light absorbed in the F band; thus indicating that these bands are probably due to electronic transition from the conduction band into lower lying levels. An afterglow due to the thermal ejection of the electrons from traps was found and studied in conjunction with the optically induced luminescence. The same bands were present in the optically induced luminescence as in the afterglow.