Optical, electron spin resonance and electrical studies of coloured KCl crystals doped with cadmium

In additively coloured cadmium-doped crystals an ultra-violet band at 310 nm is observed in addition to the F band at 565 nm. The absorption of the F band is found to decrease and the absorption at the 310 nm band is found to increase with the increase in the cadmium concentration. The F-aggregate centres and alkali metal colloids cannot be formed by optical and/or thermal bleaching of the F band in these crystals. On heating the crystals to 350-600 °C, the 310 nm band and the F band disappear and a new band at 275 nm with a half-width of 0·70 ev appears. The centres responsible for the 275 nm band give an electron spin resonance absorption line of Lorentzian shape and a g value of 1·999 and seem to be metallic colloidal particles of cadmium. The conductivity ratio σ c /σ n (σ c is the conductivity of the coloured crystal and σ n that of an identical uncoloured crystal) remains less than unity from room temperature to about 500 °C. In x-irradiated crystals the V 3 band observed at 218 nm in pure crystals shifts towards the longer-wavelength side and the band half-width increases with the increase of cadmium concentration. The growth of the F-band absorption is found to increase with the increase in the cadmium concentration up to about 1%. For larger cadmium concentrations the growth rate is found to decrease.