fluorescencj

Fluorescence is a form of luminescence in which a substance absorbs light or other electromagnetic radiation at one wavelength and then almost immediately emits light at a longer wavelength. The emission typically occurs within nanoseconds of excitation. Fluorescent materials, or fluorophores, include organic dyes, fluorescent proteins, and certain inorganic compounds such as quantum dots or crystal lattices.

Mechanism and properties: When a fluorophore absorbs a photon, an electron is promoted from the ground singlet state to an excited singlet state. The molecule quickly relaxes to the lowest excited singlet state, and then returns to the ground state by emitting a photon. The emitted light has lower energy and thus a longer wavelength than the absorbed light, a difference known as the Stokes shift. The efficiency of fluorescence is described by the quantum yield, which depends on how often excited molecules decay radiatively versus via nonradiative pathways. Fluorescence can be influenced by environmental factors such as pH, temperature, and solvent polarity.

Differences from related phenomena: Fluorescence is distinct from phosphorescence, which involves triplet excited states and can produce light for longer times after excitation. In fluorescence, emission ceases almost immediately when the excitation source is removed.

Applications: Fluorescence is widely used in science and industry for imaging and sensing. In biology, it enables fluorescence microscopy, confocal imaging, and flow cytometry, with fluorescent proteins like GFP and synthetic dyes serving as probes. Fluorescence spectroscopy and imaging are also employed in chemistry, medicine, environmental monitoring, and diagnostics. Detection typically involves exciting samples with a light source and measuring the emitted light with detectors such as cameras, photomultiplier tubes, or spectrometers.