Excitation/emission photons

Excitation emission Photon Electron Ion Neutral particle... 

The experimental data concerning fluorescence dependence on exciting emission photons beam density are depicted in figure 3. P is the fluorescent intensivity in arbitrary units. 

Figure 3. Dependence of excited AIBN fluorescence intensivity in arbitrary units on exciting emission photons beam density (in GW/cm2).

As we have seen, the electron is the easiest probe to make surface sensitive. For that reason, a number of hybrid teclmiques have been designed that combine the virtues of electrons and of other probes. In particular, electrons and photons (x-rays) have been used together in teclmiques like PD [10] and SEXAFS (or EXAFS, which is the high-energy limit of XAES) [2, Hj. Both of these rely on diffraction by electrons, which have been excited by photons. In the case of PD, the electrons themselves are detected after emission out of the surface, limiting the depth of sampling to that given by the electron mean free path. 

Palladium clusters deposited on amorphous carbon have been studied by XPS and UPS [28] and both techniques show broadening of the d-band peak as cluster size increases. The d-threshold shifts towards Ep as cluster size increases. In UPS studies the d-emission of the single atom has its peak at 3.0 eV below Ep, whereas the d-threshold is 2eV below Ep. Palladium clusters evaporated onto Si02 have been studied by UPS [38]. At large coverages of the Pd metal evaporated (> 10 atoms/cm ), a high emission intensity at Ep excited with photons of 21.2 eV (He(I)) or 40.8 eV (He(II)) as excitation source, is observed. This feature is characteristic in the spectra from bulk Pd samples. At the lowest metal coverage (3 x 10 atoms/cm ),... 

Two-photon emission is a process in which electronic transition between quantum levels occurs through the simultaneous emission of two photons. [27] presents more details about two-photon emission. Since metal clusters emit in the near-infrared region, they can be made useful for two-photon imaging with infrared excitation. Two-photon emission of Au25 clusters is observed at 830 nm by exciting at... 

Luminescence is a well-established class of analytical spectroscopic techniques where a species emits light after excitation. Emission is an elecnonic nansition from an excited state as opposed to the ground state as is the case in most other spectroscopies. Photoluminescence, or light-induced fluorescence (LIE), is the most common route to induce emission where sufficient incident photons of a particular energy excite the target species via absorption. Although less common, nomadiative excitation can also occur via a chemical reaction termed chemiluminescence. Unless otherwise stated, the terms luminescence and fluorescence within this review infers excitation by light induction. 

Wavelength filters to isolate emission photons from excitation photons... 

AFS involves the emission of photons from an atomic vapour that has been excited by photon absorption. For low absorbance signals (and thus for low... 

X-ray fluorescence can be induced by other means of excitation besides photons, such as by bombarding the sample with fast electrons, protons or o-radiation. Although in the latter case it cannot properly be called fluorescence because excitation is not induced by photons, the X-ray emission produced yields an identical spectrum. 

The OH T,) —> OH(2 ] j) resonant emission was observed from the photo-dissociation process at Kr (123.6 mn) and Xe (147 nm) radiations [40], Most ofthe released energy is transferred into OH rotation during excitation. Two photon... 

Source nuclide Half-life Excitation mode Photon emission and energies Abundance Element X-rays excited usefully... 

Fluorescence lifetimes were measured by time-correlated single photon counting using a mode-locked, synchronously pumped, cavity-dumped pyridine I dye laser (343 nm) or Rhodamine 6G dye laser (290 nm). Emissive photons were collected at 90° with respect to the excitation beam and passed through a monochromator to a Hamamatsu Model R2809U microchannel plate. Data analysis was made after deconvolution (18) of the instrument response function (FWHM 80 ps). 

The central component of the system is a glass capillary which serves as a reaction chamber for hybridization and as an optical waveguide for the transport of both the excitation and emission photons. The interior surface of the capillary, which is chemically modified to support probe sequence molecules, forms a reusable transducer for repeated detection of target sequences. After hybridization... 

Depending on the excitation method used, luminescence techniques are divided into photoluminescence excited by photons, cathodoluminescence generated under the action of cathode rays, X-ray luminescence excited by X-rays, candoluminescence generated under the action of heat, and sonoluminescence excited by ultrasound. Emission generated under the action of a stream of ions from alkali metals in vaccum is called ionoluminescence radiation which atoms emit on optical excitation in plasma is known as atomic fluorescence chemiluminescence is the emission of radiation generated by the energy of chemical reactions, it does not require an external excitation source. The excitation source needed in each particular case is chosen on the basis of this classification. 

In selecting fluorescent compounds, their efficiency in conversion of excitation photons to emission photons is important. The quantum yield of a fluorophore is a measure of the efficiency of conversion from excitation photon to emission photon. The ratio of the number of photons emitted (emission photons) to the number of... 

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