TRIPLET-STATES AND TRIPLET EXCITONS IN CHEMICALLY MIXED-CRYSTALS OF ACRIDINE WITH ANTHRACENE

Spectral and temporal characteristics and their temperature dependence for the long-lived (phosphorescence and delayed fluorescence) emissio n of chemically mixed crystals of acridine IT (host) with anthracene ( guest) were studied under conditions of various spectral resolutions a nd different modes of excitation. The energy of 0-0 transitions of exc iton band and of trap states have been determined and tile nature and energy scheme of the triplet states of crystals have been established. The complex arrangement of host molecules into two different pairs in the crystal structure of acridine II is revealed in the energetic ''d oublet'' structure of the trap states for both, the shallow and the de ep traps (of acridine and of anthracene origin, respectively). Migrati on of triplet excitation energy in these chemically mixed crystals is controlled predominantly by the triplet-triplet annihilation of excito ns (either heterogeneous or homogeneous) almost in the whole temperatu re range. The formation of triplet excimers of acridine was definitely ruled out.