In this work we review the fundamental properties of several spherical and cylindrical, passive and active, coated nano-particles (CNPs) with emphasis on their potential for nanoantenna and nano-amplifier synthesis. For the spherical geometries, the nano-particles are excited by an electric Hertzian dipole, which represents, e.g., a stimulated atom or molecule. The cylindrical nano-particles are excited by a magnetic line source. In the active cases, gain is added to the core region of the particle. For simplicity, it is modelled by a canonical, frequency independent gain model. We demonstrate that specific CNPs can be designed to be resonant and well-matched to their respective excitation sources. With active cores, these designs can lead to extremely large total radiated powers. For both configurations, insights into the effects of the nano-particle material composition, source location and orientation will be given on the basis of studying their near-field and power flow density distributions, their total radiated powers, and their directivity properties.