  A comparative first-principles study of possible bismuth-related centers in
TlCl and CsI crystals is performed and the results of computer modeling are
compared with the experimental data. The calculated spectral properties of the
bismuth centers suggest that the IR luminescence observed in TlCl:Bi is most
likely caused by Bi--Vac(Cl) centers (Bi^+ ion in thallium site and a
negatively charged chlorine vacancy in the nearest anion site). On the
contrary, Bi^+ substitutional ions and Bi_2^+ dimers are most likely
responsible for the IR luminescence observed in CsI:Bi.
