关键词: radiative cooling, optical properties of La$_{2}$O$_{3}$ and HfO$_{2}$, first-principles calculations, Monte Carlo simulations

Abstract: Radiative cooling materials have gained prominence as a zero-energy solution for mitigating global warming. However, a comprehensive understanding of the atomic-scale optical properties and macroscopic optical performance of radiative cooling materials remains elusive, limiting insight into the underlying physics of their optical response and cooling efficacy. La$_{2}$O$_{3}$ and HfO$_{2}$, which represent rare earth and third/fourth subgroup inorganic oxides, respectively, show promise for radiative cooling applications. In this study, we used multiscale simulations to investigate the optical properties of La$_{2}$O$_{3}$ and HfO$_{2}$ across a broad spectrum. First-principles calculations revealed their dielectric functions and intrinsic refractive indices, and the results indicated that the slightly smaller bandgap of La$_{2}$O$_{3}$ compared to HfO$_{2}$ induces a higher refractive index in the solar band. Additionally, three-phonon scattering was found to provide more accurate infrared optical properties than two-phonon scattering, which enhanced the emissivity in the sky window. Monte Carlo simulations were also used to determine the macroscopic optical properties of La$_{2}$O$_{3}$ and HfO$_{2}$ coatings. Based on the simulated results, we identified that the particle size and particle volume fraction play a dominant role in the optical properties. Our findings underscore the potential of La$_{2}$O$_{3}$ and HfO$_{2}$ nanocomposites for environment-friendly cooling and offer a new approach for high-throughput screening of optical materials through multiscale simulations.

Key words: radiative cooling, optical properties of La$_{2}$O$_{3}$ and HfO$_{2}$, first-principles calculations, Monte Carlo simulations