Optical absorption by nanoparticles of Cu ₂ O

Cuprous oxide (Cu 2 O) particles coated with polyacrylamide having diameters in the range from 4.8 to 8.6 nm were prepared by a chemical method. The optical absorption of these particles was found to be characterized by excitons with corresponding energies varying from 2.6 to 2.25 eV in the particle size range mentioned above. A second optical-absorption maximum signifying surface states within the band gap is exhibited by the specimens with relevant energies varying from 2.6 to 1.77 eV in this particle size range.