Many-body description of STM-induced fluorescence of charged molecules

A scanning tunneling microscope is used to study the fluorescence of a model charged molecule (quinacridone) adsorbed on a sodium chloride (NaCl)-covered metallic sample. Fluorescence from the neutral and positively charged species is reported and imaged using hyper-resolved fluorescence microscopy. A many-body excitation model is established based on a detailed analysis of voltage, current and spatial dependencies of the fluorescence and electron transport features. This model reveals that quinacridone adopts a large palette of charge states, transient or not, depending on the voltage used and the nature of the underlying substrate. This model has a universal character and explains the electronic and fluorescence properties of many other molecules adsorbed on thin insulators.