Abstract

Electron spectra of molecular crystals are quite sensitive to the structural changes of a lattice. It allowed to establish by spectrum that at cooling of tetracene crystals lower than 160K it was observed that phase transition of the first kind occurs [1-2]. It is assumed that at the phase transition, a weak tricli­nic lattice transits into a monoclinic one. Increased concentration of structural defects is observed in tetracene crystals subjected to the phase transition. These defects in tetracene lattice are the places of localization of singlet and triplet excitons and they make an essential influence on the energy transfer and luminescence spectra. We carried out investigations of luminescence by spectroscopy method with the time resolution that allowed at low tempered spectra to observe bands responsible for luminescence of free excitons and excitons localized on defects [3]. It has been determined that values of free excitons lifetime in tetracene crystals at 4,2K lies in the range from 1 to 2,5 nanoseconds.

© 1984 Optical Society of America