Fluorescence spectroscopy

Fluorescence spectroscopy is a spectroscopic technique in analytical chemistry. It uses fluorescence phenomena for the qualitative and quantitative analysis of materials.

Physical Basics

Fluorescence is the light - emission by prior absorption of a photon, if the decay of radiation is very short (ie, the lifetime of the excited state is of the order from 1 to 100 nanoseconds). According to the following equation, the intensity of fluorescent radiation is directly proportional to the intensity of the excitation radiation.

With

This formula is only valid for weak absorption, ie So that (1), the emitted photons are absorbed only to a negligible fraction of back ( 2) for the fraction of the absorbed photons is true:

The excitation takes more energy, therefore, the fluorescence spectra are shifted to the longer wavelength ( Stokes shift ). Molecules which possess suitable spaced vibrational levels, can take over the energy radiation-free and thus lead to the fluorescence quenching ( quenching) in sufficient proximity. To account for these effects can be used with a standard addition.

Unit Design

The structure is similar to a fluorimeter a photometer, however, the fluorescence is always measured with a certain emission wavelength () in the angle of 90 ° so as not to detect the excitation radiation () with. In contrast to this, the radiation intensity of the photometry emission is measured perpendicular to the direction of the excitation radiation. The fluorimeter is an emission monochromator upstream to remove remnants of the excitation light (scattered light ). As a light source is usually used high-pressure gas discharge lamps. Since the 1970s, laser beams are used increasingly.