Emission of photons in the form of incoherent thermal radiation is the process that governs many energy conversion schemes and contributes to the energy efficiency of appliances and buildings. Conventional approaches to enhance or suppress thermal emission as well as shape the thermal emission spectrum has been based on searching for appropriate material candidates: natural, idealized and composite (e.g. photonic crystals and metamaterials). In this work, we explore an approach to the radiative heat extraction based on the manipulation of emission via the proper choice of morphology of active thermal emitters and/or passive thermal extractors having one or more dimensions on the scale at or below the thermal emission peak wavelength.
At the core of this approach is the engineering of the local density of confined photon states in two- and three-dimensional potential traps, which include wells, wires, and dots. By building upon the parallels with the engineering of the electronic density of states in quantum wells, wires and dots, we aim to develop a fundamental understanding to the tailoring of far-field thermal emission/absorption by the morphology-dependent local density of states in low-dimensional structures. We will present several examples of micro- and nano-object designs with tailored thermal emission/absorption spectra for applications including selective solar absorption, thermophotovoltaic energy conversion, radiative cooling and thermal up-conversion of photon energy.