Light-induced temporal broadening of optical lines of individual molecules in polymers and glasses

The spectral diffusion theory developed for explaining the logarithmic temporal broadening of the optical line of an individual impurity center and based on spontaneous tunnel transitions in a polymer or glass is supplemented by taking into account the tunnel transitions occurring in the center itself upon the absorption of a photon. This light-induced additional tunneling leads to a sharp temporal broadening of the optical line from an individual impurity molecule occurring against the background of a slower logarithmic line broadening. It is shown that the inclusion of light-induced tunneling can explain the difference in the temporal line broadening of three individual Terylene molecules introduced in polyethylene, which was measured in experiments by the group headed by M. Orrit [A. M. Boiron et al., Chem. Phys. 247, 119 (1999)].