Color Center in NaCl

Abstract

X-ray irradiation can produce color centers in alkali halide. Each compound irradiated with X-rays exhibits its own characteristic color. The color of crystals of NaCl changed to orange after X-ray irradiation at room temperature. It was still orange in a dark room, but the color changed to black after exposure to white fluorescent lamp. In addition, the color of NaCl changes to pale purple when irradiated with 405 nm laser after X-ray irradiation and to light brown when irradiated with 532 nm laser after X-ray irradiation. The color of the powder NaCl of 75 μm particle size became whiter after exposure to X-rays than that of 700 μm particle size. The single crystal NaCl turned orange after X-ray irradiation, but the color was returned to transparent after exposure to white fluorescent lamp. The NaCl of low purity (cooking salt) left under white fluorescent light after X-ray irradiation exhibited bluish color and violet.