(739e) Structure and Low Temperature Spectral Emissivity of Erbium Doped Metal Oxide Nanofibers for Application as Selective Emitters in Thermophotovoltaic Devices

A series of novel, thermally excited selective emitter material (e.g., Er₂Ti₂O₇) for thermophotovoltaic (TPV) energy conversion is described in this work. The photovoltaic material's properties are very sensitive to the crystal structure and crystal field environment. The X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier transformation IR (FTIR) have been applied to investigate the crystal structure and optical properties of the selective emitter materials. It has been shown that different crystal structures were formed by controlling the annealing conditions. Both the crystal structure and host materials will affect emission properties of selective emitter materials. Lattice parameter, grain size and particle size distribution profiles have been investigated. Gaussian multipeak fitting module has been applied to analyze center peak bandwidth of Er³⁺ emission bands at 1.53μm. The experimental measurements show that power densities can be obtained up to 125 W/mole of Er, in the wavelength range between 1.3 and 1.7 μm, at temperature of 500^oC. Excitation mechanisms of thermal induced Er³⁺ emission in polycrystalline metal oxide matrices have been proposed. Optimize surrounding environment of Er³⁺ ion will inhibit the non-radiative de-excitation of Er³⁺ and enhance energy transfer efficiency from matrices to 4f electrons of Er³⁺ ion. The emissive power spectrums of selective emitter materials are matched very efficiently to the response of GaSb and InGaAs photovoltaic cell in TPV devices.