抄録
Photochemical conversion and reorientation of V centers in KI crystals colored additively or electrolytically are studied at temperatures of 19–140 K. When V centers are dissociated at 19 K by irradiation with light in the 270 nm region, I2−-like centers are formed. The I2−-like centers begin to bleach at about 40 K forming centers of another type which possess ⟨110⟩ symmetry and give rise to absorption bands with peaks at 358, 430, 625 and 808 um. The V2 and V3 bands observed in quenched crystals are composed of absorption bands due to two kinds of V centers with ⟨110⟩ and ⟨111⟩ symmetries. Besides these centers, other V centers with ⟨100⟩ or near-⟨110⟩ symmetry are also formed by optical excitation; after the optical excitation, dipoles of V centers reorient into proper directions at a given temperature of the sample. Based on the model of the I3− molecule-ion bound to a cation vacancy, possible structures of the four kinds of V centers are discussed.
