Abstract
The temperature dependences of photoluminescence (PL) decay rates and the PL spectrum of a thermally activated delayed-fluorescence emitter, 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN), are investigated. It is found that not only the lowest singlet () and triplet () excited states but also an additional triplet excited state () lying between and play an important role in the exciton decay process, particularly around 100 K. At around this temperature, some of the triplet excitons are thermally activated into but not up to , and they then decay into the ground state () with phosphorescence emission. Therefore, two kinds of phosphorescence, originating from and , are observed. The temperature dependence of the PL decay rates of 4CzIPN can be explained by a four-level model consisting of , , , and , and its energy gaps between and and between and are determined to be and , respectively.
1 More- Received 23 August 2016
DOI:https://doi.org/10.1103/PhysRevApplied.7.034002
© 2017 American Physical Society