We present here our analysis of thin film materials crucial for the development of thermophotovoltaic (TPV) selective emitters and thermal barrier coatings (TBCs), emphasizing their high refractive index, excellent thermal stability, and transparency to infrared radiation. Utilizing spectroscopic ellipsometer measurements across the wavelength range of 210 to 2500 nm and temperatures ranging from room temperature to 1000°C, we examine the impact of temperature variations on the electronic band structures of these materials. Our study begins with the characterization of magnesium oxide and strontium titanate substrates, followed by the analysis of individual composite layers consisting of cerium oxide and barium zirconate deposited onto these substrates. Subsequently, we extend our analysis to multi-layer samples comprising combinations of these materials, aiming to project their potential performance in TPV and TBC applications.