A crystallochemical approach to determination of near-impurity exciton formation in alkali halide crystals containing extrinsic isovalent ions

A.N.Panova, B.V.Grinyov


Institute for Single Crystals, National Academy of Sciences of Ukraine, 60 Lenin Ave., 61001 Kharkiv, Ukraine

Received June 20, 1999

A crystallochemical approach has been developed to calculate the formation energy (Ed) of autolocalized excitons perturbed with extrinsic isovalent ions in alkali halide crystals (AHC). An equation has been proposed to calculate Ed taking into account the exciton absorption energy of the matrix crystal, the impurity ion interaction energy with the matrix lattice, the formation enthalpy and energy of the matrix and impurity crystals having common anions, as well as orbital electronegativity of metal components in those crystals. The calculated Ed values have been compared with maxima energy values of experimental extrinsic absorption bands (Em) for nine AHC types with extrinsic homologic cations (KCl-Na, KCl-Rb, KBr-Na, KJ-Li, KJ-Rb, KJ-Cs, CsBr-Na, CsJ-Na, CsJ-Rb) (Group I) and for seven AHC with Tl+ ion impurity (CsCl-Tl, CsBr-Tl, LiJ-Tl, NaJ-Tl, KJ-Tl, RbJ-Tl, CsJ-Tl) (Group II). The difference between Ed and Em has been shown to vary within limits from 0 to +-2.4 % for the Group I crystals. For the Group II ones, a satisfactory agreement qbetween Ed and Em has been obtained, too. A specific feature of the Group II crystals consists in that low-energy values of Ed correspond to Em ones for A absorption bands.

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