To enable the continuous evolution of information technology, increasing data transferrates are demanded. This is accompanied by rising power consumption and requisition of larger bandwidths. The integration of photonics with electronic circuits provides a solution, which facilitates the decrease of heat dissipation and allows transmitting data in parallel with the speed of light, boosting the performance ofintegrated circuits. Such a concept is preferably realized within the highly elaborated silicon processing technology, on which the whole information technology isbased on. The most pressing issue, missing for the fully integration of photonicsto electronics, is an integrated light source. Silicon-germanium-tin (SiGeSn) alloysoffer a promising extension of this platform, since they can be monolithically grownon Si and their direct bandgap in specific configurations was proven in 2015. This thesis summarizes studies on spontaneous and stimulated emission of GeSnalloys mainly based on photoluminescence (PL) and electroluminescence (EL) spectroscopy. The effect of strain relaxation in GeSn alloys, grown on top of Ge virtual substrates, on optical properties is investigated. The temperature trend of spontaneous emission provides insight on the contribution of non-radiative defect recombination. It also illustrates the indirect-to-direct bandgap transition in Ge0.875Sn0.125alloys under strain relaxation. Heterostructure PL analysis emphasizes the importance of defect engineering, since presence of defects close to the active layer heavily deteriorates light emission. To prove the concept of electrical carrier injection, GeSn-based LEDs are fabricated. Electroluminescence spectra unveil similar temperature dependent behavior as PLfrom unprocessed layers, with comparable defect-induced limitations. The examination of Ge and SiGeSn as barrier materials in multi-quantum-wells (MQWs) provesSiGeSn as the material of choice due to a better carrier confinement. Subsequently, stimulated emission from undercut microdisk cavities is investigated. For the first time, single layer GeSn microdisk lasers are presented, offering increased mode confinement due to high refractive index contrasts compared to commonFabry-Pérot lasers. The undercut leads to an almost complete strain relaxationmodifying the band structure of the gain material. Even "just direct" GeSn alloys are proven to be suitable as gain material.To further enhance the electron population at the direct Γ-valley, which is still limitedby the moderate difference between L- and Γ-valley, in-situ n-doping of directbandgap GeSn is studied. Lasing is detected in these materials, however, showing no advantage compared to the undoped lasers. This is attributed to simultaneously increased defect recombination. The first GeSn/SiGeSn heterostructure lasers yield record low thresholds in an MQW design, enabled by carrier confinement, screening from misfit dislocations and a 2D density of states. Limitations were found, on one hand, in layer stacks with large volume-strain, hindering efficient barriers from shielding defective regions. On the other hand, directness and barrier offsets are reduced by strong quantization effects. Finally, a process flow for electrically-driven laser designs with micro ring and waveguidegeometry is introduced, underlining the applicability of group IV photonics integration into Si technology.