Photoluminescence (PL) is the most common characterization technique for materials used for photovoltaic and light-emitting applications. Incident photons are absorbed by a sample that will then release photons at energies characteristic of the material under study after selection rules dictated by quantum mechanics. The lifetime of the excited electrons will depend on the material quality and time-resolved PL allows the study of radiative and non-radiative recombination. Gap energy, quantum confinement, crystal purity are typical information extracted by PL.