DELAYED RECOMBINATION FLUORESCENCE AND PRODUCTION OF TRIPLET CHARGE-TRANSFER AND EXCITON-STATES IN VUV-EXCITED MOLECULAR-CRYSTALS

At sufficiently high excitation energies, the molecular crystals exhib it a new, slowly decaying magnetic field sensitive fluorescent compone nt. The experimentally observed properties of this special luminescenc e component in anthracene and p-terphenyle are discussed, considering in particular the excitation spectra of the intensity for energies up to 40 eV. According to the characteristic magnetic modulation of the i ntensity, the light emission follows the recombination of long lived e lectron-hole pairs created initially in a triplet spin state via a dee p valence hole. The nature of the photodynamic processes responsible f or such recombination fluorescence precursors is suggested to be conne cted with the well, documented mechanism of photoinduced exciton fissi on in triplet pair states, which involves intermolecular charge transf er transitions within a pair of neighboring molecules. It is shown tha t the measured excitation spectra are fairly interpreted on the whole explored energy domain; at the higher excitation energies, the expecte d onset of a new relaxation channel for the deep valence holes, produc ing singlet excitons, is indeed detected.