High temperature oxides for selective absorption of thermal radiation

Abstract

Most high melting temperature oxides are translucent in the visible-infrared region characteristic of the blackbody thermal radiation at high temperatures. Consequently, over this broad-band spectral region, the “thermal radiation window”, they do not absorb thermal radiation. Translucent oxides, such as the zirconates, can be extensively doped with rare-earth (RE) ions (Nd, Sm, Er, Dy, Yb) to achieve selective spectral absorption, and the doped oxides exhibit low thermal conductivity. The optical absorption bands are due to electronic transitions between electronic states associated with the rare-earth ions and are relatively insensitive to other rare-earth ions within the same compound. Therefore, mixed rare-earth compounds exhibit optical absorption characteristic of the sum of the individual ions’ absorptions. By contrast, the thermal conductivity of the RE zirconates is shown to be relatively independent of composition suggesting that their optical properties in the thermal radiation window regions can be modified without affecting their thermal conduction properties.