In optical spectroscopy, photoluminescence involves first the excitation of a molecule by the absorption of ultraviolet or visible radiation and then the detection and analysis of the emitted photons (emission) from the electronically excited molecule. Depending on the spin multiplicities of the excited and ground states, fluorescence or phosphorescence phenomenon is observed. Fluorescence corresponds to the relaxation of the molecule from the singlet excited state to the singlet ground state with emission of photon. There are many kinds of fluorescence spectrometers (spectrofluorimeters) available depending on the use and applications of the fluorescence property. The following types of measurements are generally performed with a spectrofluorimeter: i) recording of emission spectra and ii) excitation spectra. From these measurements, one can obtain the fluorescence quantum yield, chemical composition of the examined specimens, and qualitative and quantitative analytical information.