RARE-EARTH GARNET SELECTIVE EMITTER

Thin film (Ho)-yttrium aluminum garnet (YAG) and Er-YAG emitters with a platinum substrate exhibit high spectral emittance in the emission band (epsilon(lambda) almost-equal-to 0.75, I-4(15/2)-I-4(13/2), for Er-YAG and epsilon(lambda) almost-equal-to 0.65, I-5(7)-I-5(8) for Ho-YAG) at 1500 K. In addition, low out-of-band spectral emittance, epsilon(lambda)<0.2, suggest these materials would be excellent candidates for high efficiency selective emitters in thermophotovoltaic (TPV) systems operating at moderate temperatures (1200-1500 K). Spectral emittance measurements of the thin films were made (1.2<lambda<3.0 mum) and compared to the theoretical emittances calculated using measured values of the spectral extinction coefficient.