Metal–organic frameworks (MOFs) are a novel category of hybrid porous multifunctional materials with excellent qualitative features. These properties can be fine-tuned via the judicial choice of organic ligands and metal ions and by changing the synthetic reaction conditions. Among the various excellent applications exhibited by MOFs, the photoluminescence behaviour is very appealing and originates from their metal ions, linker, or entrapped guest molecules in their cavity. Thus, due to the tuneable luminescent properties of MOFs, they can act as sensors, enabling the selective and sensitive detection of a diverse range of analytes. In general, the sensing of analytes by MOFs can be accomplished either through a fluorescence “turn-on” (fluorescence intensity increases) or “turn-off” (fluorescence intensity decreases) process. Between them, the former is more important and significant in terms of real-time applications. This is because the “turn-on” emission occurs with the signal lighting (increases the fluorescence intensity) against a dark background. Therefore, this review summarizes the recent advances in MOFs as “turn-on” sensors for the recognition of a wide range of analytes (hazardous compounds, volatile organic molecules, cations, biomolecule, anions, etc.) and their sensing mechanism.

Metal–organic frameworks (MOFs ) are excellent candidates for use in chemistry, material sciences and engineering thanks to their interesting qualitative features and potential applications. Quite interestingly, the luminescence of MOFs can be engineered by regulation of the ligand design, metal ion selection and encapsulation of guest molecules within the MOF cavity. Temperature is a very crucial physical parameter and the market share of temperature sensors is rapidly expanding with technology and medicinal advancement. Among the wide variety of available temperature sensors, recently MOFs have emerged as potential temperature sensors with the capacity to precisely measure the temperature. Lanthanide-based thermometry has advantages because of its ratiometric response ability, high quantum yield and photostability, and therefore lanthanide-based MOFs were initially focused on to construct MOF thermometers. As science and technology have gradually changed, it has been observed that with the inclusion of dye, quantum dots, etc. within the MOF cavity, it is possible to develop MOF-based thermometry. This review consolidates the recent advances of MOF-based ratiometric thermometers and their mechanism of energy transfer for determining the temperature (thermal sensitivity and temperature uncertainty). In addition, some fundamental points are also discussed, such as concepts for guiding the design of MOF ratiometric thermometers, thermometric performance and tuning the properties of MOF thermometers.