Impact of the thermal properties of the environment on the hot-band absorption-assisted single-photon upconversion

Single-photon hot-band absorption-assisted anti-Stokes photoluminescence (ASPL) is a non-equilibrium process which causes a local cooling effect and which therefore is accompanied by a reverse heat flux from the warmer environment. Here, we demonstrate that the thermal properties of the medium, i.e., its thermal conductivity and specific heat capacity, play a significant role in driving the ASPL of an emitter placed in it. Exploiting seven different solvents and the near-infrared tricarbocyanine dye as a single-photon upconverter, we show an obvious correlation of activation energy and the quantum yield (QY) of ASPL with the solvent thermal conductivity and specific heat capacity, respectively. A linear fit of the above correlations leads to the predictions that the maximum QY of ASPL should be observed in a vacuum where it should reach a value of similar to 10% for the exploited dye, which is close to the QY of its Stokes emission and that the high thermal conductivity of the solvent assists in a stepwise population of the hot band, which thus facilitates the hot-band absorption-assisted ASPL. These findings lead to the conclusion that the selection of a solvent with appropriate thermal properties may help one to control the efficiency of the one-photon energy upconversion.