Abstract: In semiconductors with weak spin-orbit coupling, spin-selection rules allow electron spins and nuclear spins to influence electrical and optical material properties. Such spin-dependent processes enable a number of applications ranging from readout of spin quantum computers and spin-electronic devices to semiconductor spin spectroscopy. The latter is of great importance for understanding the role that spins play for efficiencies of solar cells, light emitting diodes and other electronic devices. In this talk I will discuss our recent progress on the development of a spin-selection rule based coherent spin spectroscopy and I will summarize our research-activities and -results using this technique. I will then discuss in detail an experiment demonstrating the control of the electric current in organic light emitting diodes by spin-beat oscillations of Coulomb-coupled charge carriers pairs. The beat oscillations are due to a difference of the local magnetic hyperfine fields caused by a bath of hydrogen nuclear spins in the vicinity of the charge carrier pairs. The observation of this effect provides insights into how nuclear spins in organic semiconductors influence conductivity and electroluminescence.