Influence of annealing conditions on size and optical properties of copper nanoparticles embedded in silica matrix

Copper nanoparticles have been grown in silica matrix by annealing of the sol–gel prepared porous matrix impregnated with the copper nitrate. The annealing has been performed in air, successively in air and hydrogen, and in hydrogen. An annealing in air results in copper oxide nanoparticles (Cu2O) growth as well. Transmission electron microscopy proves the formation of the spherical copper nanoparticles in size range of 2–65 nm depending on annealing conditions. Optical spectroscopy of the copper nanoparticles has been performed. The surface plasmon peak has been observed clearly in absorption spectra of Cu nanoparticles. Surface plasmon peak in absorption spectra of Cu nanoparticles demonstrates slight blue shift with decrease of the particle size. The bandwidth of the surface plasmon peak decreases appreciably at the lowering of temperature from 293 K to 77 and 4.2 K that is due to strong electron–phonon interaction. The low-frequency Raman scattering data are in agreement with electron microscopy and absorption data. Photoluminescence from the copper nanoparticles has been observed. Efficiency of the luminescence increases appreciably at the decrease of particle size. The observed increase is explained by the coupling of the excited incoming and outgoing emitted photons with surface plasmon.