Selective absorption of solar energy in ultrafine chromium particles

Ultrafine chromium particles prepared by evaporation in argon + air are found to be highly absorbing over the solar spectrum and highly transparent in the infrared. Such spectral selectivity is the distinctive feature of a coating in an efficient photothermal converter for solar energy. Optical transmittance through coatings with mass density ≲0.5 g/m2 agrees well with calculations based on the Maxwell-Garnett theory, whereas coatings with larger mass density exhibit a transmittance too low to be directly reconciled with this theory.