Temperature-Dependent Evolution of Photoluminescence – Rate, Coherence, Entropy, and Chemical Potential

Photoluminescence (PL) is a fundamental light-matter interaction where absorbed photons are re-emitted, playing a major role in optoelectronics, energy harvesting, and spectroscopy. This talk explores the temperature-dependent evolution of PL, exploiting the tools of optics and thermodynamics. A key focus is on the evolution with temperature of the entropy per photon and chemical potential, as the emission shifts from being pump-induced to thermally dominated. Interestingly, we identify a temperature range where a quasi-conserved rate and entropy are associated with previously reported blue-shift of the spectrum, followed by a rapid transition to thermal behavior. The chemical potential, initially near the photon energy limit (h), decreases with increasing temperature and approaches zero as thermal equilibrium is reached. This is in contrast to the smooth reduction of coherence length with temperature. Additionally, we discuss the photon statistics evolution of a single-frequency PL with temperature and relate it to the chemical potential. These findings provide a deeper understanding of photoluminescence, potentially impacting device design and performance.