ABSTRACTMetal nanoclusters (NCs) of lithium, zinc, silver and gold embedded in MgO were created by means of ion implantation of Li, Zn, Ag and Au ions into single crystals of MgO(100) and subsequent thermal annealing. Nanoclusters of the compound semiconductor CdSe were obtained by implantation of both Cd and Se ions. Solid noble gas clusters were formed by Kr ion implantation. Optical and structural properties of the NCs were investigated using optical absorption spectroscopy (OAS), high-resolution X-ray diffraction (XRD) and cross-sectional transmission electron microscopy (XTEM). The mean nanocluster size is estimated from the broadening of the Mie plasmon optical absorption bands using the Doyle formula. These results are compared with the NC size as obtained from XRD (using the Scherrer formula) and from direct XTEM observations. The three methods are found to be in reasonable agreement with a mean size of 4.0 and 10 nm found for the Au and Ag clusters, respectively. Using TEM observations, the relative interface energies of MgO//Au and MgO//Ag interfaces are also determined. In the case of MgO//Au, they are found not to be in agreement with theoretical predictions in the literature. CdSe nanoclusters were found to adopt different crystal structures dependent on the size. Small ones (<5 nm) appear to have a rock salt structure, larger ones the sphalerite structure. The solid krypton NC's are under high pressure. The pressure of individual Krypton bubbles was determined from the moiré fringes