Porous lanthanide-based MOFs exhibit photoluminescence, which can be influenced by interaction with small molecules. Changes in the emission properties of the MOFs allow the optical detection of these molecules. Typical targets are solvent molecules, such as water or alcohols, gases, such as oxygen or carbondioxide, or changes in the surrounding conditions, such as pH-value or temperature.
The interaction of an optical sensor material with target molecules leads to a change in chromaticity or intensity of the sensor-luminescence. Furthermore, these sensors can be categorized as turn-off sensors. Turn-on sensors exhibit an increase in emission intensity after interaction with target molecules, while turn-off sensors show decreasing intensity. If a compound contains two independent luminescence sources it is possible to dermine the quantity of the target molecules. Those materials are called ratiometric sensors.