Beschreibung:
<jats:title>Abstract</jats:title><jats:p>The self‐trapping of the exciton component of the polariton is considered in the adiabatic approximation. The possibility of the coexistence of self‐trapped (STP) and coherent (CP) polaritons is demonstrated. Such coexistence is possible even for a large effective mass of the exciton component, if the exciton—photon coupling is sufficiently strong, as it is in the case of core polaritons. The self‐trapping barrier of polaritons depends essentially on the frequency of the exciting source, the character of relaxation processes, and some other factors. The shape of the adiabatic surfaces obtained allows one to suggest an explanation of a number of peculiarities observed in the optical spectra of NaI crystals in which the coexistence of STP and CP has been established previously.</jats:p>