  The photophysical properties of Bi82+ and Bi53+ polycations stabilized by
[AlCl4]- have been studied experimentally and theoretically. The obtained
product was thoroughly evaluated by powder X-ray diffraction and
photoluminescence spectroscopy, making it clear that both Bi82+ and Bi53+
contribute to the observed broad near-infrared emission. Furthermore, it was
revealed that Bi82+ polycation mainly results in the emission peaking at ca.
1180 nm, while Bi53+ the longer-wavelength emission. The following quantum
chemistry calculation on Bi82+ polycation helps us attribute some observed
excitation bands in the visible spectral range to specific electronic
transitions of bismuth polycations. It is believed that systematical
investigation of structural and luminescent properties as well as detailed
quantum chemistry calculation of molecular crystals containing such kinds of
bismuth units allows us to obtain a clearer picture on bismuth-related
photophysical behaviors, which not only serve to solve the confusions on the
luminescence origin of bismuth in other material systems such as bulk glasses,
glass fibers and conventional crystals, but also is helpful to develop novel
applicable broadband tunable laser mediums.
