Photons generation

Efficiency. Efficiency of a device can be reported in terms of an internal quantum efficiency (photons generated/electrons injected). The external quantum efficiency often reported is lower, since this counts only those photons that escape the device. Typically only a fraction of photons escape, due to refraction and waveguiding of light at the glass interface (65). The external efficiency can be increased through the use of shaped substrates (60). 

Fig. 8. The photodiode detector (a) band model where the photon generates electron—hole pairs that are separated by the built-in potential setting up a photocurrent (b) physical model for a planar diode. The passivation is typically Si02 for Si diodes, an In oxide for InSb diodes, and CdTe for HgCdTe...

For a simplified case, one can obtain the rate of CL emission, =ft GI /e, where /is a function containing correction parameters of the CL detection system and that takes into account the fact that not all photons generated in the material are emitted due to optical absorption and internal reflection losses q is the radiative recombination efficiency (or internal quantum efficiency) /(, is the electron-beam current and is the electronic charge. This equation indicates that the rate of CL emission is proportional to q, and from the definition of the latter we conclude that in the observed CL intensity one cannot distii pish between radiative and nonradiative processes in a quantitative manner. One should also note that q depends on various factors, such as temperature, the presence of defects, and the... 

Figure 1-3. In Ihis improved bilaycr device structure lor a polymer LED an extra ECHB layer has been inserted between the PPV and the cathode metal. The EC11B material enhances the How of electrons but resists oxidation. Electrons and holes then accumulate near the PPV/EC1113 layer interface. Charge recombination and photon generation occurs in the PPV layer and away from the cathode.

A noise power equivalent to one photon generates an interference signal which has an amplitude equals to twice the rms photon noise of the source. But as only the in-phase components of the source generates an interference with the local oscillator, the result is that the spectral Noise Equivalent Power of the heterodyne receiver is hv. 

Several spectroscopic, microscopic and diffraction techniques are used to investigate catalysts. As Fig. 4.2 illustrates, such techniques are based on some type of excitation (in-going arrows in Fig. 4.2) to which the catalyst responds (symbolized by the outgoing arrows). For example, irradiating a catalyst with X-ray photons generates photoelectrons, which are employed in X-ray photoelectron spectroscopy (XPS) -one of the most useful characterization tools. One can also heat a spent catalyst and look at what temperatures reaction intermediates and products desorb from the surface (temperature-programmed desorption, TPD). 

A pin-diode has three layers p-doted layer, i intrinsic interaction layer, n-doted layer. The outer layers provide the electrical field. In the inner layer photons generate electron-hole-pairs which result in a current, although the diode is operated in reverse-biasing mode. 

Fig. 7.3. Typical raw data showing the low flux image obtained from detection of individual X-ray photons by a CCD detector. The image shows a 512 x 512 pixel region of the CCD. Each X-ray photon generates a charge that is proportional to its energy...

Conversely, a quantum yield

greater than unity cannot be achieved during a straightforward photochemical reaction, since the second law of photochemistry clearly says that one photon is consumed per species excited. In fact, values of > 1 indicate that a secondary reaction(s) has occurred. A value of > 2 implies that the product of the photochemical reaction is consumed by another molecule of reactant, e.g. during a chain reaction, with one photon generating a simple molecule of, say, excited chlorine, which cleaves in the excited state to generate two radicals. Each radical then reacts in propagation reactions until the reaction mixture is exhausted of reactant. 

The surface-state model. The absorption of a photon generates an exciton within a quantum-confined silicon crystallite but its radiative recombination occurs at localized electtonic states on the surface of the crystallites [Ko5] or in defects in the oxide coverage of the crystallites [Pr5]. 

ECL (electrochemiluminescence) Meso Scale Discovery Binding of ruthenium-labeled moiety to partner on specialized microplate surface produces amplified photon generation... 

Santori, C., Fattal, D., Vuckovic, J., Solomon, G.S., and Yamamoto Y., 2004, Single-photon generation with InAs quantum dots. New J. Physics 6 89-105. 

Ip( i) is the photocurrent density at wavelength X. IPCE becomes 100% when all photons generate electron-hole pairs. However, in practical situations IPCE is always less than 100% due to the losses corresponding to the reflection of incident photons, their imperfect absorption by the semiconductor and recombination of charge carriers within the semiconductor, etc. 

Zhou W, Kuebler SM, Braun KL, Yu T, Ober JKC, Ober CK, Perry JW, Marder SR (2002) An efficient two-photon-generated photoacid applied to positive-tone 3D microfabrication. Science 296 1106-1109... 

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