A.N.Panova, B.V.Grinyov
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.