Applications involving photoluminescence (PL) measurements in NIR have been rapidly growing in recent years. The demand comes mainly from several areas in materials science, such as fiber optics telecommunication, solar energy conversion, lasing media, LED and OLED technologies and development of upconversion nanoparticles for biomedical analyses and bioimaging. Most of these applications involve rare earth ions (lanthanides), many of which emit in NIR. Often these ions are used with ligand photosensitizers which improve their light absorption properties as lanthanide ions themselves are very weak absorbers. They are used as dopants in lasing media and glasses and are made into nanoparticles of varying size and shape in order to control their optical properties. The PL lifetime is the key parameter in assessing the optical efficiency of devices involving lanthanides as well as in quality control during their manufacturing.