Individual semiconductor nanostructures and single impurities are offering interesting options to achieve and explore the ultimate limits in device miniaturization. Therefore we study the formation and electro-optic properties of individual semiconductor nano objects such as quantum dots, quantum rings and single impurities. To this end scanning probe techniques and atom probe tomography are used to determine the true 3D structure of various semiconductor nanostructures. By this we aim to understand and control their formation during growth and to link their structure to the electro-optic properties that we determine for instance by confocal microscopy. Scanning probe microscopy is furthermore used to explore and manipulate single (magnetic) impurities in a semiconductor material. This work has allowed for a deep understanding of quantum mechanical aspects that determine the properties of a whole range of impurities and defects in semiconductors.