Theory of Photoluminescence by Metallic Structures

Light emission by metals at room temperature is quenched by fast relaxation processes. Nevertheless, Mooradian reported in 1969 the observation of photoluminescence by metals pumped by a laser. While this phenomenon is currently at the heart of many promising applications, it is still poorly understood. In this work, we report a theory which reproduces quantitatively previously published experimental data of photoluminescence by metallic nanoparticles. We first provide a general formula that relates the emitted power for a frequency, direction and polarization state to a sum over all transitions involving matrix elements, electronic distribution of all bands and Green's tensors. We then consider the case of intraband recombination and derive a closed-form expression of the emitted power depending only on macroscopic quantities. This formula, which is a generalization of Kirchhoff's law, answers many of the open questions related to intraband photoluminescence.