Structure and optical properties of Cu2O nanocrystals in a sodium-borate glass

A multi-technique approach was applied to characterize the crystalline structure, morphology, and optical properties of spherical Cu2O nanocrystals embedded in 72B2O3-28Na2O glass. Cu-doped sodium borate glass plates were obtained using the melt-quenching method, followed by isothermal annealing in the 420-500 degrees C range. This procedure allowed us to obtain several glass samples in which nearly spherical Cu2O nanocrystals with different average radii and dispersion radii were embedded. The morphology and crystalline structure of the nanocrystals were characterized by TEM, SAED, XRD, and SAXS techniques, and UV-Vis and PL techniques were used for optical characterization. UV-Vis absorbance allowed us to determine the band gap energies of the samples. The experimental values of the band gap energies as a function of the radius of the Cu2O nanocrystals agree with those predicted by a theoretical model that accounts for size-dependent quantum confinement effects in spherical semiconducting nanocrystals. The nanocomposite exhibited photoluminescence, which could be assigned to Cu and O vacancies in the crystalline lattice of the Cu2O nanocrystals.