Upconversion of infrared light by graphitic micro-particles due to photo-induced structural modification

Recent reports of upconversion and white light emission from graphitic particles warrant an explanation of the physics behind the process. We offer a model, wherein the upconversion is facilitated by photo-induced electronic structure modification allowing for multi-photon processes. As per the prediction of the model, we experimentally show that graphite upconverts infrared light centered around 1.31 μm to broadband white light centered around 0.85 μm. Our results suggest that upconversion from shortwave infrared (∼3 μm) to visible region may be possible. Our experiments show that the population dynamics of the electronic states involved in this upconversion process occur in the timescale of milliseconds.