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Proceedings Paper

Singlet-based photon upconversion in multichromophore organic thin films (Presentation Recording)
Author(s): Daniel H. Weingarten; Michael LaCount; Garry Rumbles; Jao van de Lagemaat; Mark T. Lusk; Sean E. Shaheen
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Paper Abstract

Solid-state energy upconversion has many potential applications, from nonlinear photonics and biophotonics to expanding the spectrum available for solar energy harvest. In organic molecular systems, upconversion is frequently done in solution to mitigate aggregation-induced photoluminescence quenching or to facilitate the diffusion of triplet donors in Triplet-Triplet Annihilation (TTA) systems. Here we demonstrate an organic thin film upconversion system utilizing two-photon absorption (TPA) properties to improve upconversion efficiency. In blend films of Stilbene-420 and Rhodamine 6G we observe a tenfold increase in up-converted fluorescence compared to the fluorescence yield of TPA in pristine stilbene films. While TPA normally has quadratic dependence on excitation intensity, these blend films exhibit sub-quadratic intensity dependence, indicating a combination of linear and quadratic upconversion processes and dramatically improving upconversion efficiency at lower excitation intensities. This improvement in intensity dependence allows for relatively efficient upconversion upon excitation by a nanosecond laser pulse, in contrast to the more expensive femtosecond lasers generally required for excitation in TPA microscopy and similar systems. Time-resolved photoluminescence decay measurements reveal that all excited states involved in this upconversion process are singlets, which indicates the potential for reduced energy losses when compared to TTA upconversion systems and their inherent intersystem-crossing energy losses. We observe emission from both the Rhodamine 6G donor molecules and Stilbene-420 acceptor molecules, indicating the presence of prompt fluorescence from the donor as well as upconversion to the acceptor, and FRET losses from acceptor back to donor. By fitting to a kinetic model we extract rates for these competing processes.

Paper Details

Date Published: 5 October 2015
PDF: 1 pages
Proc. SPIE 9562, Next Generation Technologies for Solar Energy Conversion VI, 95620C (5 October 2015); doi: 10.1117/12.2188991
Show Author Affiliations
Daniel H. Weingarten, Univ. of Colorado at Boulder (United States)
Michael LaCount, Colorado School of Mines (United States)
Garry Rumbles, National Renewable Energy Lab. (United States)
Jao van de Lagemaat, National Renewable Energy Lab. (United States)
Mark T. Lusk, Colorado School of Mines (United States)
Sean E. Shaheen, Univ. of Colorado at Boulder (United States)

Published in SPIE Proceedings Vol. 9562:
Next Generation Technologies for Solar Energy Conversion VI
Oleg V. Sulima; Gavin Conibeer, Editor(s)

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