Different nanostructures, including nanowires, particles, tubes, rods etc. have been intensively studied primarily due to unique properties caused by lowered dimensionality and quantum effects, as well as important applications in nanotechnology. Such nanostructures, embedded in different matrices, can be understood as artificial solids with their properties defined by properties of nanostructural unit, similarly as by atomic configuration of materials. Control of structure and size of the basic nano-units allows us to design properties of materials built by these units (nanomaterials), due to the quantum confinement effect. This effect is mostly felt by delocalized electrons for which, in a macroscopic material, the approximation of infinite periodic potential is valid. That means that in the environment filled by e.g. 1023 atoms, an electron doesn't „see“ the edge of the material but it can move freely in any direction. On the other hand, if an isolated unit of the material is reduced to microscopic size, the electron's environment is drastically reduced and it „notices“ the lack of atoms outside the edge of the nano-object. This means that the approximation of infinite periodic potential is no longer valid and with it most of literature values for material properties. Since the electron is now confined at a microscopic scale, it is no longer delocalized. Recent research has shown a possibility of producing an especially interesting nanostructured material made of spatially ordered 3D networks of Ge nanowires in Al2O3 (alumina) matrix. Although semiconductor and metal networks have already been produced by different techniques, the process of production, possibilities of structure variations as well as its optical and electrical properties required additional research. The first part of this dissertation contains results of novel research carried out to deepen the understanding of these materials. An additional interesting option is the possibility of adding metal during the growth of the nanowires that changes the material properties. More precisely, the possibility of doping the nanowires with aluminium has been explored. The original cause for preparing these materials was protecting the pure Ge from oxidation by the oxygen from the matrix, but also a relevant increase in the order quality of the networks was observed. This is due to the reaction of aluminium with oxygen from the atmosphere. Third type of researched materials is made of nanoparticles with germanium core and metal shell. The thickness of the shell and the type of metal were varied, and interesting consequentialities of structural to optical properties were noticed. Firstly, just a few atomic layers of metal protects the germanium from oxidation. Secondly, the addition of metal in general enhances optical absorption by an order of magnitude. Thirdly, the type of metal in the shell as well as its thickness drastically influence the shape of the curve depicting absorption dependence on incident wavelength, in two ways. Germanium absorption peak at around 4 eV can change it's position due to quantum confinement and change it's intensity due to enhanced electric field in the core caused by localized plasmons in the shell. On the other hand, infrared absorption can be greatly enhanced for shells large enough because they start to overlap and allow delocalized plasmon states. Application in photovoltaic devices requires desirable optical properties, primarily high absorption, and it is shown in this thesis that the researched samples are a significant improvement compared to simpler, already studied, materials with basic germanium nanoparticles. Also, we need to understand the conduction mechanisms which have also been investigated. Finally, because of potential application of researched materials in photovoltaic, quantum efficiency was also measured.