Properties of the zero-phonon lines in the optical spectra of molecular crystals

A theoretical interpretation is made of the temperature dependences of the relative integrated intensity, width, and shift of the zero-phonon lines in the luminescence spectra of 1,12-benzperylene and perylene in normal alkane matrices. Temperature properties of the zero-phonon lines in spectra of some other impurity n-alkane crystals are analyzed as well. It is shown that the temperature properties of the intensity, width, and shift are well described by the theory of the electron–phonon interaction if one takes into account the interaction both with acoustic and local vibrations. The zero-phonon line shifts are also essentially determined by the lattice thermal expansion due to the anharmonicity of the crystal vibrations.