Swift heavy ion irradiation is one of the most versatile techniques to alter and monitor the properties of materials in general and at nanoscale in particular. The materials modification can be controlled by a suitable choice of ion beam parameters such as ion species, fluence and incident energy. It is also possible to choose these ion beam parameters in such a way that ion beam irradiation can cause annealing of defects or creation of defects at a particular depth. Here, we present a review of our work on swift heavy ion induced modifications of III-V semiconductor heterostructures and multi-quantum wells in addition to synthesis of Ge nanocrystals using atom beam co-sputtering, RF magnetron sputtering followed by RTA, swift heavy ion irradiation, respectively. We also present the growth of GeO2 nanocrystals by microwave annealing. These samples were studied by using XRD, Raman, PL, RBS and TEM. The observed results and their explanation using possible mechanisms are discussed in detail.