Oxygen vacancies and band gap modulation in rare earth phosphates synergistically enhance radiative heat dissipation

Abstract

Rare-earth compounds have been emerging as promising materials for infrared radiative cooling in electronic devices, owing to their exceptional thermal stability, tunable optical properties, and unique phonon-mediated thermal emission within the atmospheric transparency window. This study investigates the infrared (IR) emission behavior of various rare-earth (REPO₄) phosphates, focusing on the influence of rare earth ion species, structural characteristics, and temperature effects on their spectral properties. Three distinct morphologies of REPO₄ (RE = Y, Ce, Sm) nanopowders were successfully synthesized via a precipitation method using citric acid as metal ion complexing agent. It is discovered that spherical YPO₄ particles enhance lateral IR scattering and promote IR absorption. Additionally, the IR emissivities of all three samples are significantly influenced by oxygen vacancies and the band gap. Oxygen vacancies increase the free carrier concentration, which enhances IR emissivity, while a reduction in the band gap lowers the energy barrier for electron transitions, facilitating IR absorption. The synergistic effects of these factors yield a remarkable broadband IR emissivity of up to 0.966 for YPO₄. The composite film created by embedding REPO₄ into PDMS achieved a cooling effect of up to 8.1 °C at an input power of 8 W (power density of 5000 W/m²), demonstrating its effectiveness for cooling electronic devices. These findings indicate the great potential of rare-earth phosphates in advancing sustainable radiative cooling technologies for next-generation electronics.