Currently the main research focus is on lanthanide nanothermometry applications. Traditional temperature sensors (contact thermometers) have many intrinsic constraints and they are not suitable for temperature measurements of e.g. fast-moving objects, or with resolution at the micron scale. This has stimulated scientists to work on the development of new thermometers that can operate in an accurate way, and overcome the limitations of traditional thermometers. Recent developments in technologies have generated the need for reliable temperature sensors in e.g. nanoelectronics, nanophotonics, chemical (micro) reactors or thermal barrier coatings. Also for diagnostic purposes, temperature measurements play a crucial role in biomedicine, as conditions such as inflammation and diseases such as cancer are accompanied by hyperlocal temperature changes in the affected tissues.