Tailoring thermal radiation with a hybrid metallic–dielectric (Ag/SiO_2) filter

With experimentally matched dielectric properties for an Ag layer, it is shown that the optical characteristic of the Ag/SiO2 filter has been seriously overestimated from the simple Drude dispersion, and the expected spectrum efficiency is only a half of that for the Drude model. Importantly, increasing the number of Ag-SiO2 units hampers the spectrum efficiency, uncovering thus the breakdown of photonic bandgap effect in dominating the performance of the Ag/SiO2 filter. With a simple sandwich profile, the Ag/SiO2 filter can achieve spectrum efficiency of 37% while holding the effective above-bandgap transmission up to 60%, which is also comparable with that for the classical Si/SiO2 photonic crystal filter, providing thus a flexible strategy to develop the simple yet efficient optical filter for thermophotovoltaic applications.