The High Pressure Effects in Optical Spectra of Impurity Crystals

It is customary to assume that the optical spectra of glasses have some distinctive features which are caused by two-level systems (TLS) in the host. In the last few years the new data appeared which indicated that TLS can be found in the crystals as well. Among the evidences are the spectral jumps observation in the single molecule spectrum of p-terphenyl doped with pentacene molecular crystal [1], the revealing of the anomalous quasylinear thermal dependency of zero-phonon line halfwidth in the spectra of perylene in n-octane matrices [2,3] etc.