Photo external

A role is also played by the temperature and frequency dependence of the photocurrent, the variable surface sensitivity at various parts of the cathode and the vector effect of polarized radiation [40]. All the detectors discussed below are electronic components whose electrical properties vary on irradiation. The effects depend on external (photocells, photomultipliers) or internal photo effects (photoelements, photodiodes). 

Photocells and photomultipliers (secondary electron multipliers, SEM) are mainly employed in photometry. These are detectors with an external photo-effect . 

Phosphorus-containing pesticides la 254 Phosphorus insecticides lb 83 Phosphorus pesticides lb 32 Photochemical activation lb 13 Photochemical reactions lb 15,17 Photodiodes la 24,29 Photo effect, external la 24 -, internal la 24, 29 Photo element la 24,29 Photography, exposure times la 137 -, instmmentation la 137 Photomultiplier la 25ff -, disadvantages la 27 -, energy distribution la 26 -, head on la 27 -, maximum sensitivity la 28 -, side on la 27 -, spectral sensitivity la 28 -, window material la 28 Photocells la 25 Phloxime lb 116... 

These devices have special function, namely to irradiate the liquid phase with light to induce a photoreaction or photoinduced reaction. Hence the characteristic feature is a transparent section within the reactor, often in the visible or commonly in the UV spectral region. The devices may have integrated photo energy sources or on-line analysis units. Otherwise, this is performed by external instruments. 

It should be noted immediately that not all the frequencies absorbed by a semiconductor are photocatalytically active, but only those that are also photoelectrically active, i.e., that cause an internal photoelectric effect in the semiconductor. Note further that the sign and magnitude of the photo-catalytic effect depend on the past history of the specimen exposed to illumination i.e., they depend on the external influences to which the specimen in question was subjected in the course of the whole of its life, and also on the conditions of the experiment (temperature, intensity of illumination, etc.). For example, by introducing into the semiconductor an impurity of any concentration or by adsorbing foreign gases on its surface it is possible to render its catalytic activity more or less sensitive to illumination. 

Figure 12. Schematic lay-out of compact optical sensor chip without need of external optical apparatus with identical microresonators as sensors LED broad band source, for example Light Emitting Diode, MR-F microresonator used as optical filter, MR-S microresonator used as optical sensor, PD Photo Diode.

The photopolymerization of mixtures of maleimides and vinyl ethers is shown to be an efficient, rapid process in the absence of external photo initiators. Polymerization proceeds both in the presence and absence of oxygen. Films produced by the photopolymerization of maleimide/vinyl ether systems exhibit little absorbance at wavelengths greater than 300 nm. The thermal stability of these films are also excellent. 

Figure 5.20 Sol-gel silica entrapped cells such as those of Saccharomyces cerevisiae shown here are highly stabilized and freely accessible to external nutrients acting as potent bioreactors. (Photo courtesy of Giovanni Carturan.)...

The electronic microscopy method on the EM-125 (fig. 1) for definition of ZnCFO particles size and characteristic of its surface was applied. Known zinc oxide was chosen as the object of comparison. The electronic photos of powders testify, that new composite and zinc oxide have external similarity under the form of particles, wide range on dispersiveness (0,4-6,0 microns for zinc oxide, fig. la 0,3-6,0 microns for ZnCFO, fig. lb) also contain as crystal as amorphous phases in their structure. 

Magnetic field effects have been used to study the photo-Eries rearrangement of 4-methoxyphenyl acetate [49] and 1-naphthyl acetate [50], These effects can be subdivided into internal and external. 

In this case the quantity n indicates how many times the number of reactive particles adsorbed per unit surface increases under illumination (other external conditions remaining the same). Evidently, the rate of the heterogeneous reaction in which these particles participate will be a function of fi and thus will be sensitive to illumination. If An = Ap = 0 (photo-electrically inactive absorption of light), then according to (41) m = 1, and illumination has no effect on the reaction rate. 

In fact, in 1972, Fujishima and Honda (10) demonstrated that O2 evolution on n-type Ti02 occurs as a photocurrent, proportional to the light intensity (Figure 1) of wavelengths less than 415 nm, i.e. for photon energies equal to or greater than the band gap of Ti02 3.0 eV. In this work and that of Ohnishi et al. (11) a platinum black metal cathode was connected in an external circuit to an indium contact on the back side of the photo-anode (see... 

Electrons, generated near the semiconductor-electrolyte interface are unable to stay in this region because of the electric field there which drives them into the bulk of the TiOz crystal, out through the metallic contact, the external circuit (where the photo-current may be measured) and into the catalytically active metal. At the interface of this metal with the electrolyte solution, reaction occurs ... 

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