Triplet energy transfer (TET) from quantum dots (QDs) to molecular acceptors has received intense research interest because of its promising application as triplet sensitizers in photon up-conversion. Compared to QD band edge excitons, the role and mechanism of trap state mediated TET in QD-acceptor complexes have not been well understood despite the prevalence of trap states in many QDs. Herein, TET from trap states in CdSe QDs to adsorbed 9-anthracene carboxylic acid (ACA) is studied with steady state photoluminescence, transient absorption spectroscopy, and time-resolved photoluminescence. We show that both band edge and trap excitons undergo direct Dexter energy transfer to form the triplet excited state of ACA. The rate of TET decreases from (0.340 ± 0.002) ns−1 to (0.124 ± 0.004) ns−1 for trap excitons with decreasing energy from 2.25 eV to 1.57 eV, while the TET rate from band edge excitons is 13–37 times faster than trapped excitons. Despite slightly higher TET quantum efficiency from band edge excitons (∼100%) than trapped excitons (∼95%), the overall TET process from CdSe to ACA is dominated by trapped excitons because of their larger relative populations. This result demonstrates the important role of trap state mediated TET in nanocrystal sensitized triplet generation.
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21 August 2020
Research Article|
August 18 2020
Trap state mediated triplet energy transfer from CdSe quantum dots to molecular acceptors
Special Collection:
Up- and Down-Conversion in Molecules and Materials
Tao Jin
;
Tao Jin
Department of Chemistry, Emory University
, 1515 Dickey Dr., Atlanta, Georgia 30322, USA
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Tianquan Lian
Tianquan Lian
a)
Department of Chemistry, Emory University
, 1515 Dickey Dr., Atlanta, Georgia 30322, USA
a)Author to whom correspondence should be addressed: [email protected]
Search for other works by this author on:
a)Author to whom correspondence should be addressed: [email protected]
Note: This paper is part of the JCP Special Topic on Up- and Down-Conversion in Molecules and Materials.
J. Chem. Phys. 153, 074703 (2020)
Article history
Received:
July 16 2020
Accepted:
August 04 2020
Citation
Tao Jin, Tianquan Lian; Trap state mediated triplet energy transfer from CdSe quantum dots to molecular acceptors. J. Chem. Phys. 21 August 2020; 153 (7): 074703. https://doi.org/10.1063/5.0022061
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