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Triplet Exciton Diffusion and Quenching in Matrix-Free Solid Photon Upconversion Films

Title data

Raišys, Steponas ; Adomėnienė, Ona ; Adomėnas, Povilas ; Rudnick, Alexander ; Köhler, Anna ; Kazlauskas, Karolis:
Triplet Exciton Diffusion and Quenching in Matrix-Free Solid Photon Upconversion Films.
In: The Journal of Physical Chemistry C. (February 2021) .
ISSN 1932-7455
DOI: https://doi.org/10.1021/acs.jpcc.0c11048

Abstract in another language

Efficient triplet exciton hopping (diffusion) in amorphous solid films is essential for triplet–triplet annihilation (TTA) and TTA-mediated photon upconversion (UC) at low excitation power densities. However, enhanced triplet diffusion, particularly in high-emitter-content UC films, also facilitates their trapping and quenching at nonradiative decay sites, thus deteriorating UC efficiency. In this work, triplet exciton diffusion and quenching are studied in matrix-free solid UC films based on two novel bisfluorene-anthracene (BFA) emitters, i.e., one with methyl substitution (BFA-Me) and the other with a phenyl substitution (BFA-Ph), and a standard platinum octaethylporphyrin (PtOEP) sensitizer. By analyzing temperature-dependent TTA-UC dynamics and accounting for various singlet exciton-related processes, we are able to discern triplet exciton quenching occurring explicitly in the emitter and show that it is one of the dominating mechanisms impeding the UC performance of BFA/PtOEP films, particularly at elevated temperatures. Regardless of the lower density of quenchers present in the BFA-Ph film, twice as large triplet diffusivity estimated in this film (D = (2.13 ± 0.64) × 10–9 cm2·s–1) at room temperature as compared to that in the BFA-Me film caused more rapid triplet quenching. This resulted in the shifting of the optimal UC performance of BFA-Ph to lower temperatures (T = 160 K) with respect to that of BFA-Me (T = 220 K). To obtain a high UC quantum yield, which for these materials can be estimated to reach >5% at room temperature and above, the excessive diffusion to the remaining quenching sites needs to be suppressed, e.g., by increasing the intermolecular distance through side groups.

Further data

Item Type: Article in a journal
Refereed: Yes
Institutions of the University: Faculties > Faculty of Mathematics, Physics und Computer Science > Department of Physics
Faculties > Faculty of Mathematics, Physics und Computer Science > Department of Physics > Chair Experimental Physics II - Optoelectronics of Soft Matter
Faculties > Faculty of Mathematics, Physics und Computer Science > Department of Physics > Chair Experimental Physics II - Optoelectronics of Soft Matter > Chair Experimental Physics II - Optoelectronics of Soft Matter - Univ.-Prof. Dr. Anna Köhler
Result of work at the UBT: Yes
DDC Subjects: 500 Science > 530 Physics
Date Deposited: 22 Feb 2021 08:03
Last Modified: 22 Feb 2021 08:03
URI: https://eref.uni-bayreuth.de/id/eprint/63240