UpconversionEmissionen

Upconversionemissionen, also known as upconversion luminescence or anti-Stokes luminescence, describes the process where a material absorbs low-energy photons and then emits higher-energy photons. This is in contrast to typical fluorescence or phosphorescence where emitted photons have lower or equal energy to absorbed photons. The phenomenon relies on the presence of specific activator ions within a host material, often rare-earth ions like erbium, ytterbium, or thulium. These ions possess a unique energy level structure that allows for sequential absorption of multiple low-energy photons. Through mechanisms such as energy transfer upconversion (ETU) or excited-state absorption (ESA), the absorbed energy is accumulated, eventually leading to an electronic transition to a higher energy state. When the ion relaxes back to a lower energy state, it emits a photon with a larger energy, and therefore a shorter wavelength, than the absorbed photons. Commonly, infrared light is absorbed and visible light is emitted. Upconversionemissionen have found applications in various fields, including bioimaging, security inks, solar cells, and optical temperature sensing, due to their ability to convert invisible or low-energy light into detectable higher-energy light.