On the transition from photoluminescence to thermal emission and its implication on solar energy conversion

TL;DR

This paper explores the transition from photoluminescence to thermal emission at high temperatures, revealing how endothermic PL can be harnessed for efficient solar energy conversion with a theoretical efficiency limit of 70%.

Contribution

It provides the first experimental study of high-temperature endothermic PL and proposes thermally enhanced PL (TEPL) as a novel approach for solar energy conversion.

Findings

PL photon rate remains conserved with temperature increase

A sharp transition from PL to thermal emission occurs at high temperatures

Endothermic-PL produces significantly more energetic photons than thermal emission

Abstract

Photoluminescence (PL) is a fundamental light-matter interaction, which conventionally involves the absorption of energetic photon, thermalization and the emission of a red-shifted photon. Conversely, in optical-refrigeration the absorption of low energy photon is followed by endothermic-PL of energetic photon. Both aspects were mainly studied where thermal population is far weaker than photonic excitation, obscuring the generalization of PL and thermal emissions. Here we experimentally study endothermic-PL at high temperatures. In accordance with theory, we show how PL photon rate is conserved with temperature increase, while each photon is blue shifted. Further rise in temperature leads to an abrupt transition to thermal emission where the photon rate increases sharply. We also show how endothermic-PL generates orders of magnitude more energetic photons than thermal emission at similar temperatures. Relying on these observations, we propose and theoretically study thermally enhanced PL (TEPL) for highly efficient solar-energy conversion, with thermodynamic efficiency limit of 70%.