Rare-earth oxide materials emit thermal radiation in a narrow spectral region, and can be used for a variety of different high-temperature applications, such as the generation of electricity by thermophotovoltaic conversion of thermal radiation. However, because a detailed understanding of the mechanism of selective emission from rare-earth atoms has so far been missing, attempts to engineer selective emitters have relied mainly on empirical approaches. In this work, we present a new quantum thermodynamic model to describe the mechanisms of thermal pumping and radiative de-excitation in rare-earth oxide materials. By evaluating the effects of the local crystal-field symmetry around a rare-earth ion, this model clearly explains how and why only some of the room-temperature absorption peaks give rise to highly efficient emission bands at high temperature (1,000-1,500 degrees C). High-temperature emissivity measurements along with photoluminescence and cathodoluminescence results confirm the predictions of the theory.

We present a brief survey of the most significant contributions to the study and the development of selective emitters for high-temperature applications. After a brief introduction and some necessary notes on definitions and experimental methods, this review presents the many different solutions proposed so far from the point of view of both the optimization of the functional properties of selective emitters and the fulfilment of the severe thermostructural requirements imposed by most high-temperature applications such as thermophotovoltaics.

No abstract

No abstract