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Coatings composed of mixed nanoparticles in Silica and Titania sol matrices were prepared by sol–gel spray coating method. The coatings were characterized using scanning electron microscopy (SEM), FT-IR spectroscopy and Infrared thermal imaging. The thermal Infrared Emissivity of the coatings was determined using IR-1 spectrometer. The coating solutions were applied onto sand blasted aluminum substrates. Results indicated that mixed nanoparticles can be well dispersed in sol to give coatings with good heat emission properties. High emissivity of 0.915–0.941 was achieved, and the coatings showed cooling efficiency of 7.3–14%. The coatings can be prepared in an easy and controlled way using sol–gel method and are a potential in radiative cooling applications.

This work aims to investigate the influence of Ca${}^{2+}$ doping on the infrared emission properties of DyTa₃O₉ ceramics. DyTa₃O₉ is considered a promising high-temperature thermal protection material due to its low thermal conductivity and good high-temperature stability. However, there is currently no research on the infrared radiation performance of such materials. We synthesized DyTa₃O₉ ceramics with different Ca${}^{2+}$ doping concentrations using the solid-phase reaction method and systematically investigated the effect of doping concentration on the infrared emissivity of DyTa₃O₉ ceramics. When Ca${}^{2+}$ is doped into the DyTa₃O₉ lattice, the original Dy elements are replaced by Ca, resulting in an increase in lattice constants and enhanced lattice distortion. The doping of Ca${}^{2+}$ introduces impurity energy levels, making it possible for some low-energy electron transitions, achieving an enhancement in infrared absorption and emission capabilities. When the Ca${}^{2+}$ doping concentration reaches 7.5% mol, the average infrared emissivity in the 3–5$\mu$m and 8–12$\mu$m ranges are 0.85 and 0.92, respectively, representing a 19.7% and 21% increase compared to DyTa₃O₉. This novel high-infrared-emissivity ceramic holds great potential for applications in high-temperature energy conservation and aerospace thermal protection.

PtO_x films were deposited by direct current (DC) reactive magnetron sputtering in Ar/O₂ mixture atmosphere at substrate temperatures ranging from 200^∘C to 400^∘C. The influence of substrate temperature on the structure, morphology, composition, electrical resistivity and infrared emissivity of PtO_x films was studied. The X-ray photoelectron spectroscopy (XPS) and grazing incidence X-ray diffraction (GIXRD) results revealed that the as-deposited amorphous PtO_x films were mainly composed of PtO and PtO₂ phases. It was found that with the increase in the substrate temperature, the proportion of PtO phase in the films increased, while the electrical resistivity and infrared emissivity of the films decreased with the increasing substrate temperature.

In this work, Ni-doped ZnO/Al composites were prepared by a facile chemical co-precipitation method. The morphology and structure of the as-prepared composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), respectively. It was found that the flake-like Al powders were successfully coated by Ni-doped ZnO nanoparticles with slight aggregation and Ni${}^{2+}$ was successfully doped into the crystal lattice of ZnO. Moreover, the effects of ZnO concentration and doped Ni concentration on the infrared emissivity of ZnO/Al composites at the waveband range of 8–14$\mu$m were studied. The results showed that the ZnO/Al composites exhibited the lowest infrared emissivity of 0.34 with 50wt.% ZnO concentration. Meanwhile, the electromagnetic parameters and microwave absorbing properties of Ni-doped ZnO/Al composites in the frequency range of 2–18GHz were explored. Significantly, 12mol.% Ni-doped ZnO/Al composites presented the lowest infrared emissivity of 0.37 and the maximum reflection loss reached $-$32.5dB at 13.6GHz with a thickness of 4.5mm. The excellent microwave absorbing properties could be attributed to the good impedance match, crystal lattice defects and interfacial polarization. It was believed that the Ni-doped ZnO/Al composites could be used as potential infrared-microwave compatible stealth materials.