Absorption Bands of Paired-Ion Centers (Ga⁺)₂, (In⁺)₂ and (Tl⁺)₂ in KI

Abstract

Absorption spectra of KI containing high concentrations of Ga⁺ and In⁺ impurity ions are obtained at 2°K. New absorption bands which are due to the (Ga⁺)₂ and (In⁺)₂ paired-ion centers are observed at 4.04 and 4.51 eV in KI:Ga and at 3.75 and 4.25 eV in KI:In. The low-energy bands A′ are unambiguously related to the A band and the high-energy bands C′ to the C band. Trials have been made to understand the electronic structure of the paired-ion center in terms of the electronic structure of the single-ion center. The paired-ion-center absorption bands related to the C band are unambiguously assigned as follows: the C′ band is due to the transition ¹∑_g⁺(¹A_1g)→¹∑_u⁺(¹T_1u), and the band due to the transition ¹∑_g⁺(¹A_1g)→¹Π_u(¹T_1u) under- lies the C band. As for the paired-ion-center absorption bands related to the A band, two possible assignments are suggested.