news
What Is Fluorescence?
What Is Fluorescence?
Fluorescence is the emission of light by a substance that has absorbed electromagnetic radiation.fluorescence brightening agent cbs-351 It is one of two types of luminescence (the other being phosphorescence).fluorescence brightening agent cbs-351 Many common minerals, such as fluorspar, and biological organisms exhibit this property.fluorescence brightening agent cbs-351 Some fluorescent dyes and stains are used in scientific applications, such as examining tissue under a microscope. Other uses include the production of fluorescent lamps and LEDs, cosmic-ray detection, and in forensics, where fingerprinting and other identifying characteristics are detected by using fluorescent reagents.
The chemical properties of a fluorophore depend on its electronic state, which is a function of the distribution of negative electrons and the geometry of the molecular orbitals.fluorescence brightening agent cbs-351 This distribution and geometry determine the color of a fluorophore, and they can be observed at atomic resolution in a fluorescent microscope.fluorescence brightening agent cbs-351
In the laboratory, the process of fluorescence is studied using ultraviolet and visible radiation that are absorbed by molecules and excitably shifted into higher energy states.fluorescence brightening agent cbs-351 fluorescence brightening agent cbs-351 When the molecules return to their ground states, they emit photons with lower energy and longer wavelengths than the absorbed radiation.fluorescence brightening agent cbs-351 The emission spectrum of a fluorescent molecule displays a set of peak intensities that are unique to the particular molecule and its environment.fluorescence brightening agent cbs-351 This spectral signature is distinct from other spectroscopy techniques, such as absorption and Raman spectroscopy.
Excited molecules may emit photons by radiative decay, a non-radiative process in which the excited state loses energy to its surroundings, or they can emit photons via a recombination process.fluorescence brightening agent cbs-351 The latter involves the recombination of an electron from the low energy excited state with a hole from the ground state.fluorescence brightening agent cbs-351 This recombination emits a photon with a lower energy, and it has a shorter lifetime than radiative decay.fluorescence brightening agent cbs-351
The lifetime of a fluorescent compound depends on the concentration of the substrate.fluorescence brightening agent cbs-351 At low concentrations, the fluorescent compound may only be visible for a few nanoseconds.fluorescence brightening agent cbs-351 At higher concentrations, the lifetime may extend to tens of nanoseconds.fluorescence brightening agent cbs-351 When the concentration of a fluorescent compound is known, it is possible to calculate the lifetime by plotting the time between emission and spontaneous decay. This time can be compared with other decay times, such as those measured by radiometric methods, to determine the rate at which the compound is decomposing.
It is important to understand that fluorescence measurements are subject to a number of interferences.fluorescence brightening agent cbs-351 Rayleigh scattering from the sample itself, 2nd order scattering from solvents and Raman scattering all distort the fluorescence signal.fluorescence brightening agent cbs-351 These interferences are removed by the use of monochromators, a light chopper and dual excitation filters, or by the use of a host computer controlling the illumination system.
0users like this.
