  In order to reveal the relaxation mechanism of photogenerated charge-transfer
excitations in quasi-one-dimensional halogen-bridged diplatinum complexes, we
calculate the low-lying adiabatic potential energy surfaces of a
one-dimensional extended Peierls-Hubbard model. High-energy excitations above
the electron-hole continuum may relax into polarons, while excitons pumped
within the optical gap are self-localized and then either decay by luminescence
or divide into solitons. Neutral solitons, charged solitons, and polarons may
be simultaneously photogenerated in a diplatinum-halide chain, which has never
been observed in any conventional platinum-halide chain. Optical conductivity
is also simulated along the decay paths for experimental verification.
