Fluorescence spectrometry light source

When a transparent medium was irradiated with an intense source of monochromatic light, and llie scattered radiation was examined spectroscopically, not only is light of the exciting frequency, v, observed (Rayleigh scattering), blit also some weaker bands of shifted frequency are detected. Moreover, while most of the shifted bands are of lower frequency, v - Aii, there are some at higher frequency, v + Aiq, By analogy to fluorescence spectrometry (see below), the former are called Stokes bands and the latter a iti-Stakes bands. The Stokes and anti-Stokes... 

Atomic Fluorescence Spectrometry. A spectroscopic technique related to some of the types mentioned above is atomic fluorescence spectrometry (AFS). Like atomic absorption spectrometry (AAS), AFS requires a light source separate from that of the heated flame cell. This can be provided, as in AAS, by individual (or multielement lamps), or by a continuum source such as xenon arc or by suitable lasers or combination of lasers and dyes. The laser is still pretty much in its infancy but it is likely that future development will cause the laser, and consequently the many spectroscopic instruments to which it can be adapted to, to become increasingly popular. Complete freedom of wavelength selection still remains a problem. Unlike AAS the light source in AFS is not in direct line with the optical path, and therefore, the radiation emitted is a result of excitation by the lamp or laser source. 

The fluorescence intensity is directly proportional to the intensity of the light source. Therefore intense sources are preferred. Excitation wavelengths are in the UV and visible regions of the spectmm, so some of the same sources used in UV /VIS absorption spectrometry are used for fluorescence. The optical materials will of course be the same—quartz for the UV, glass for the visible region. 

Atomic fluorescence spectrometry (AES) is an analytical method used to determine the concentration of elements in samples. The sample is converted to gaseous atoms, and the element of interest is excited to a higher electronic energy level by a light source. Following excitation, the atoms are deactivated by the emission of a photon. The measured fluorescence is this emission process. Instrumentation for AES... 

AFS is a method of elemental analysis that involves the use of a light source to excite gaseous atoms radiatively to a higher energy level, followed by a deactivation process that involves emission of a photon. This emission process provides the measured fluorescence signal. AFS can be distinguished from the related atomic spectrometric techniques of atomic absorption spectrometry (AAS) and atomic emission spectrometry (AES) because it involves both radiative excitation and deexcitation. 

Conventional optical absorption spectrometry has detection limits of between 0.01 and 1 mM for the actinides. Highly sensitive spectroscopic methods have been developed, based on powerful laser light sources. Time resolved laser fluorescence spectroscopy (TRLFS), based on the combined measurement of relaxation time and fluorescence wavelength, is capable of speciating Cm(III) down to 10 mol/L but is restricted to fluorescent species like U(VI) and Cm(III). Spectroscopic methods based on the detection of nonradiative relaxation are the laser-induced photoacoustic spectroscopy (LPAS) and the laser-induced thermal leasing spectroscopy (LTLS). Like conventional absorption spectroscopic methods, these newly developed methods are capable of characterizing oxidation and complexation states of actinide ions but with higher sensitivity. 

The utility of laser diodes for spectroscopic applications has been demonstrated in molecular absorption spectrometry, molecular fluorescence spectrometry, atomic absorption spectrometry, and as light sources for detectors in various chromatographic methods. Recent advances in laser diode technology fueled by consumer demand for high-speed, high-capacity DVD players have resulted in the availability of blue laser diodes with output powers up to 50 mW at 473 nm. These light sources are appearing routinely in commercial spectrometric systems. 

Like all atomic spectroscopic techniques, emission and fluorescence spectrometry require the production of free atoms (or ions) in the gaseous phase for detection. These two techniques require the population of a particular excited electronic state and determine concentration by monitoring the radiative relaxation process, i.e. by detection of the photon produced. In general, the intensity of the light emitted should be proportional to the gas-phase atom density and, ultimately, to the concentration of the analyte atoms in the sample being introduced to the atomization source. Likewise, it follows that increasing the excited-state population will enhance the sensitivity of the method. 

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