Unconventional Thermal Emission from Photonic Crystals

Photonic crystals are periodic arrays of low‐loss materials with different dielectric constants. In optimally designed three‐dimensional (3D) photonic crystals with a periodicity about half a wavelength, one can realize a complete photonic band gap, in which the density of states (DOS) of the radiation field vanishes. Thermal emission is one of the phenomena in which the density of states of the radiation field plays an important role. The thermal emission spectrum of a perfect blackbody is determined by the Bose‐Einstein distribution function and the density of states of free space. This chapter discusses the unconventional thermal emission from photonic crystals. Photonic crystals are categorized by their dimensionality as 3D, two‐dimensional (2D), and one‐dimensional (1D) crystals. It introduces the topic of thermal emission control by using 2D semiconductor photonic crystals and discusses thermal emission from multilayer dielectric films.