Metal halide perovskite (MHP) semiconductors, such as methylammonium lead iodide (MAPbI3), have recently received tremendous attention in materials science, as these have yielded high efficiency solar cells, X-ray detectors and LEDs. However, one of the most fundamental material properties of MHPs still remains debated: whether their bandgap is direct or slightly indirect. The nature of the bandgap determines both the light absorption properties and the lifetime of light-generated charge carriers. Both of these properties are important for e.g. the efficiency of a solar cell or the suitability of MHPs to be used as photocatalysts. For this research we aim to reveal the nature of the bandgap and investigate whether this can be manipulated. To do so, we will study the absorption of light and the recombination of charge carriers as a function of temperature and pressure using different optical spectroscopy techniques. Furthermore, we will make a link between the bandgap and the photocatalytic activity of MHPs. Finally, we will study lead-free perovskites, like silver-bismuth double perovskites, as these are less toxic, which is of importance considering its potential application in photocatalysis.