Lopushanska B. Optical properties of semiconductor nanocrystals of Ag(Cu)–In–S system

The thesis is devoted to the fabrication of colloidal semiconductor nanocrystals of the (Ag,Cu)–(In,Ga)–S family of various size and chemical composition, determination of their average size and crystalline structure and investigation of their optical characteristics. Ag–In–S, Cu–In–S, Ag–Ga–S, and Ag–(In,Ga)–S colloidal nanocrystals were synthesised from aqueous solutions at mild conditions with various precursor concentration ratios, their size-selective fractioning was performed. From optical absorption and X-ray diffraction data the average size of nanocrystals in the fractions is determined (from 1.7 to 3.4 nm with the accuracy of 0.5—0.6 nm). Optical characteristics of the Ag–In–S colloidal nanocrystal solutions are shown to remain stable after long-time (half a year) ageing at room temperature. Features in the Raman spectra of the Ag–In–S nanocrystals are related to phonon confinement and scattering by surface phonons. Based on the optical absorption and resonant Raman spectroscopy data it is shown that adding zinc at the second stage of the colloidal synthesis to the Ag–In–S nanocrystals results in gradient-like doping of the nanocrystals with Zn content decreasing from the surface to the nanocrystal centre.