Spontaneous Light Emission from Molecular Junctions: Theoretical Analysis of Upconversion Signal

Yadalam, Hari Kumar and Mitra, Souvik and Harbola, Upendra (2019) Spontaneous Light Emission from Molecular Junctions: Theoretical Analysis of Upconversion Signal. In: JOURNAL OF PHYSICAL CHEMISTRY A, 123 (49, SI). pp. 10594-10598.

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Abstract

Spontaneous light emission from a current-carrying molecular junction is analyzed. There are two leading processes, fluorescence and electroluminescence, as defined using Liouville space diagrams within the perturbative method, that contribute to the light emission from junctions. This allows us to identify a general mechanism that explains the origin of the so-called upconversion electroluminescence (UCEL) signal, which has been observed in a variety of molecular junctions Umera et al. Chem. Phys. Lett. 2007, 448, 232; Dong et al. Nat. Photonics 2010, 4, 50]. Here, we show that a double-peak signal, one at energy less than the applied bias and the other at higher energy (UCEL), is generated due to overlap between two processes: one is electron transfer to create the required excited state, and the other is radiative relaxation of the excited state. The lifetimes induced by the lead interactions play a crucial role in determining the required overlap between these processes. Our analysis shows that, unlike the higher-energy signal, the low-erenergy peak is sensitive to the applied bias and does not correspond to any optical resonance in the junction. The signal at higher energy is enhanced as the temperature is increased. We demonstrate our findings using nonperturbative analytic results for a model system.

Item Type:	Journal Article
Publication:	JOURNAL OF PHYSICAL CHEMISTRY A
Publisher:	AMER CHEMICAL SOC
Additional Information:	Copyright of this article belongs to AMER CHEMICAL SOC, 1155 16TH ST, NW, WASHINGTON, DC 20036 USA
Keywords:	FLUORESCENCE
Department/Centre:	Division of Chemical Sciences > Inorganic & Physical Chemistry
Date Deposited:	06 Jan 2020 11:34
Last Modified:	06 Jan 2020 11:34
URI:	http://eprints.iisc.ac.in/id/eprint/64289

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