Spontaneous Light Emission from Molecular Junctions

Abstract

Abstract: The study of light emission [1] from a molecular junction is recently gaining research interest. This has direct relevance to develop novel optoelectronic devices [2] and to understand light-matter interaction in the non-equilibrium systems at a fundamental level. In this work, I have studied the theory for spontaneous light emission (SLE) from a molecular junction. I have computed the signal based on doublesided ladder diagrams which are standard for traditional(equilibrium) spectroscopy. For understanding the SLE process, it is important to understand the electron-transport in molecular junction. So I have given a brief explanation for the same in my thesis. I have addressed in my thesis, some recent current-induced SLE experiments where “upconversion” is observed and discussed the proposed mechanism for the same. From our perturbative calculations[3], the signal is shown to have two leading order contributions, identified as Current Induced Fluorescence(CIF) and Electroluminescence(EL). This allows us to identify a general mechanism that explains the origin of the “upconversion” signal, which has been observed in a variety of molecular junction experiments. We have also found the existence of a bias dependent peak similar to what was observed in several experiments[4,5]. Along with this perturbative calculation, I have studied the SLE process with Quantum Master Equation (QME)[6].