  Plexciton is the formation of new hybridized energy states originated from
the coupling between plasmon and exciton. To reveal the optical properties of
both exciton and plexciton, we develop a classic oscillator model to describe
the behavior of them. Particularly, the coupling case, i.e., plexciton, is
investigated theoretically in detail. In strong coupling, the
electromagnetically induced transparency is achieved for the absorption
spectra; the splitting behaviors of the modes are carefully analyzed, and the
splitting largely depends on the effective number of the electrons and the
resonance coupling; the photoluminescence spectra show that the spectral shapes
remain almost unchanged for weak coupling and change a lot for strong coupling;
the emission intensity of the exciton is strongly enhanced by the plasmon and
can reach to the order of $10^{10}$ for a general case. We also show the
comparisons between our model and the published experiments to validate its
validity. This work may be useful for understanding the mechanism of the
plexciton and for the development of new applications.
