Spontaneous Light Emission from Molecular Junctions
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Abstract: The study of light emission  from a molecular junction is recently gaining research interest. This has direct relevance to develop novel optoelectronic devices  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, 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).