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Open Access Nano Express

Vibration-assisted upconversion of molecular luminescence induced by scanning tunneling microscopy

Kuniyuki Miwa, Mamoru Sakaue and Hideaki Kasai*

Author Affiliations

Department of Applied Physics, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan

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Nanoscale Research Letters 2013, 8:204  doi:10.1186/1556-276X-8-204

Published: 1 May 2013

Abstract

We investigate the effects of coupling between a molecular exciton, which consists of an electron and a hole in a molecule, and a surface plasmon (exciton-plasmon coupling) on the electron transitions of the molecule using nonequilibrium Green’s function method. Due to the exciton-plasmon coupling, excitation channels of the molecule arise in the energy range lower than the electronic excitation energy of the molecule. It is found that the electron transitions via these excitation channels give rise to the molecular luminescence and the vibrational excitations at the bias voltage lower than the electronic excitation energy of the molecule. Our results also indicate that the vibrational excitations assist the emission of photons, whose energy exceeds the product of the elementary charge and the bias voltage, (upconverted luminescence).

Keywords:
Upconversion; Molecular luminescence; Scanning tunneling microscope; Surface plasmon; Molecular vibration; Exciton-plasmon coupling; Nonequilibrium Green’s function method