  Temperature behavior of the Bi+ center emission, excitation bands and
luminescence decay law in KAlCl4 crystal are investigated. Abrupt changes of
the monocation optical properties are observed at phase transitions of the
host. The observed optical transitions are assigned to the specific energy
states of Bi+ ion. It is shown that two thermalized levels are responsible for
the luminescence. The experimental temperature behavior of the emission and
excitation bands are in agreement with theory of electron-phonon interaction of
impurity centers in solids; the effective-phonon frequencies and Huang-Rhys
parameters are estimated. The configuration coordinate diagram is determined
for the Bi+ center in KAlCl4 crystal.
