Registration Number
0223U005493,
0123U102728
, R & D reports
Title
Persistent luminescence - a new paradigm for innovative applications of organic semiconductor systems
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Head
Kadashchuk Andrii K., Кандидат фізико-математичних наук
Registration Date
22-12-2023
Organization
Institute of Physics of National Academy of Sciences of Ukraine
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Comprehensive research was carried out using the methods: thermally stimulated luminescence, light-induced ESR and LDMR, conventional and time-resolved luminescence spectroscopy, photocurrent measurements for amorphous films of model carbazole-based and heavy-atom-free material mCBP-CN which has a high efficiency of intersystem crossing (ISC), and also for host-guest composite with DMAC-TRZ admixture. It was found that: highly efficient intrinsic charge-carrier generation is observed already upon photoexcitation to the lowest singlet state, and the generation yield practically does not depend on the photon energy, despite the large exciton binding energy; the photocurrent reveals a super-linear dependence on the cw-photoexcitation intensity even below 1 mW/cm2, and its temperature dependence exhibits a prominent maximum near 160 K and significant signal roll off at higher temperatures, that correlates remarkably with that of delayed fluorescence (DF) which is induced by triplet-triplet exciton annihilation (TTA), and DF has also a signal maximum about 120 K. Thus, the photoconductivity is determined mainly by the TTA-induced production of geminate pairs of charges and only little by their subsequent dissociation. Moreover, the field-assisted dissociation probability of photogenerated charge pairs becomes almost temperature-independent at temperatures below 100 K. So, the mechanism of intrinsic photogeneration of charge carriers via TTA, which promotes the incoherent up-conversion of the electronic excitation energy of molecule enabling thereby the autoionization of a high-energy excited state, is proposed, and this mechanism is determined merely by the properties of the mCBP-CN matrix and remains unchanged for the composite with DMAC-TRZ. The high efficiency of TTA is due to the high probability of ISC, the high energy level of the triplet state, the long lifetime of triplet excitations, and the energy disorder for triplet localized states in mCBP-CN films.
Product Description
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Vakhnin Olexandr Yurievych
Kadashchuk Andriy K
Fishchuk Ivan I.
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2023-12-23
