  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. Cu nanoparticles in size range of 2-65 nm have been grown depending
on annealing conditions. Annealing in air results in copper oxide nanoparticles
(Cu2O) growth as well. Transmission electron microscopy (TEM) and optical
spectroscopy of the copper nanoparticles in silica matrix have been performed.
The copper nanoparticles of two types are grown: spherical mature particles and
elliptical seed particles. 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 half-width of the surface plasmon peak decreases appreciably
at the lowering of temperature from 293 K to 77 and 4.2K 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, probably, by the coupling of the excited incoming and outgoing
emitted photons with surface plasmon.
