Exciton Luminescence Band Associated with Emission of an Acoustical Phonon in Anthracene Crystals

Abstract

A broad luminescence band appears just below the zero-phonon luminescence band of the exciton. It is found from an analysis of the reabsorption effect on the luminescence spectrum that the secondary distribution model of the polaritons is not applicable to this band. The spectral shape changes with varying the temperature between 1.8 and 4.2 K. The broad band is assigned to the sideband associated with emission of an acoustical phonon. The luminescence spectrum of the acoustical phonon sideband is calculated with taking account of the polariton effect. The calculated spectrum coincides with the experimental curve. The energy width of the spatial dispersion of the exciton is estimated to be 5±1 cm⁻¹ for wave vector K perpendicular to the (001)-plane. The zero-phonon luminescence band is found to be influenced considerably by the reabsorption effect.