An analysis of the optical properties of homogeneous metal and oxide nanoparticles along with double–layer nanoparticles with a metal core and an oxide shell aimed at improving the efficiency of absorption of solar radiation

Problems related to using nanoparticles for absorption of solar radiation and photothermal nanotechnologies are now being actively studied. The efficiency of using nanoparticles as photothermal agents for solar energy is determined by their spectral optical properties. We performed computer simulation of optical properties of homogeneous metal (nickel, titanium, and molybdenum) nanoparticles and their oxides, along with nanoparticles consisting of a metal core and an oxide shell, with radii in the range from 50 to 100 nm in the spectral interval between 200 and 2500 nm. The influence of nanoparticle radius, the type of metal and its oxide on spectral coefficients of efficiency absorption $(K_{\operatorname{abs}})$ and scattering $(K_{\operatorname{sca}})$ of radiation by nanoparticles is investigated. The type of nanoparticles suitable for absorption of solar radiation was chosen based on a comparative analysis of the wavelength dependences of absorption efficiency coefficients $K_{\operatorname{abs}}$, intensity of solar radiation $I_S$, and parameter $P_1=K_{\operatorname{abs}}/K_{\operatorname{sca}}$. Spherical double–layer nanoparticles consisting of nickel or titanium core and oxide shells with a radius of 75 or 100 nm can be used in the spectral interval from 200 to 2500 nm for efficient absorption of solar radiation. These results are a substantial contribution to the investigation of optical properties of nanoparticles that can be used in systems of thermal energy.