Cadmium sulfide photoconductivity

Cadmium Sulfide Photoconductor. CdS photoconductive films are prepared by both evaporation of bulk CdS and settHng of fine CdS powder from aqueous or organic suspension foUowed by sintering (60,61). The evaporated CdS is deposited to a thickness from 100 to 600 nm on ceramic substates. The evaporated films are polycrystaUine and are heated to 250°C in oxygen at low pressure to increase photosensitivity. Copper or silver may be diffused into the films to lower the resistivity and reduce contact rectification and noise. The copper acceptor energy level is within 0.1 eV of the valence band edge. Sulfide vacancies produce donor levels and cadmium vacancies produce deep acceptor levels. 

Othei photoconductive pigments (qv) which found commercial appHcation are cadmium sulfide [1306-23-6] CdS, or the alloy with Se, CdS Se ... 

Photoconductive drums of copying machines coated with selenium arsenate or cadmium sulfide... 

In many semiconductors the majority of the photoelectrons are produced by excitation from the valence band, the process thus simultaneously producing holes. Surface traps may act as recombination centers for electron-hole recombination and a change in the number or energy of these surface traps, or a change in the height of the surface barrier, may change the rate of recombination. For example Bube (9,10) has concluded that it is through this effect that the adorption of water vapor influences the photoconductivity of cadmium sulfide. 

When hydrogen sulfide is passed into cadmium salt solutions, cadmium sulfide is formed as a yellow precipitate with a zinc blende structure (cubic, (i-form). The P-form can be converted into the a-form (e.g., by heating). a-Cadmium sulfide shows photoconductivity due to defects in the crystal lattice (usage in photovoltaic cells) [3.106]. The solubility in water at 25°C is 1.46 x 10 10 mol/L [3.107], Cadmium sulfide forms the basis for all cadmium pigments. 

Colloids of semiconductors are also quite interesting for the transmembrane PET, as they possess both the properties of photosensitizers and electron conductors. Fendler and co-workers [246-250] have shown that it is possible to fix the cadmium sulfide colloid particles onto the membranes of surfactant vesicles and have investigated the photochemical and photocatalytic reactions of the fixed CdS in the presence of various electron donors and acceptors. Note, that there is no vectorial transmembrane PET in these systems. The vesicle serves only as the carrier of CdS particles which are selectively fixed either on the inner or on the outer vesicle surface and are partly embedded into the membrane. However, the size of the CdS particle is 20-50 A, i.e. this particle can perhaps span across the notable part of the membrane wall. Therefore it seems attractive to use the photoconductivity of CdS for the transmembrane PET. Recently Tricot and Manassen [86] have reported the observation of PET across CdS-containing membranes (see System 32 of Table 1), but the mechanism of this process has not been elucidated. Note, that metal sulfide semiconductor photosensitizers can be deposited also onto planar BLMs [251],... 

The three basic types are photoconductive, photovoltaic, and photo-emissive, and all are sensitive to both heat and light. The resistance of a photoconductive cell is lowered when it is illuminated and, over a small range, its response is linear. Cells containing lead sulfide, which is sensitive at wavelengths greater than 700 nm, and cadmium sulfide or selenide, with a sharp response maximum at 710 nm, have been used but may not give a stable response and are largely restricted to specialized applications in other fields. Silicon photodiodes and transistors are sensitive from 340 to 1200 nm with a peak at 900 nm. 

Li QG, Penner RM (2005) Photoconductive cadmium sulfide hemicylindiical shell nanowire ensembles. Nano Lett 5 1720-1725... 

A subsequent paper described the photoconductive characteristics of an inorganic-organic hybrid composite, in which PVK serves as a polymeric charge-transporting matrix, and in which QDs composed of surface-passivated cadmium sulfide serve as... 

Li, Q.G. Penner, R.M. (2005). Photoconductive Cadmium Sulfide Hemicylindrical Shell Nanowire Ensembles. Nano Letters, Vol. 5, No. 9, (September 2005), pp. 1720-1725, ISSN 1530-6984... 

This phenomenon is used in photographic light meters. A photoinduced ciurent is measured, and its magnitude is a direct function of the intensity of the incident hght radiation, or the rate at which the photons of light strike the photoconductive material. Visible light radiation must induce electronic transitions in the photoconductive material cadmium sulfide is commonly used in light meters. 

Since the Institute was among the few research establishments in Berlin to survive relatively undamaged the physical destruction and social unrest that accompanied the end of the war and the fall of the Third Reich, alheit thoroughly looted, it became a refuge for scientists who lacked other institutional ties and needed to retool professionally. This included, in addition to Havemann and Kallmann, Rudolph Frerichs, who worked in the AEG research laboratory until the end of the war on the use of cadmium sulfide crystals in photo-detectors for military purposes. During his sojourn at the Institute, Frerichs continued his research into photoconductivity and the synthesis of photoconductive crystals. In 1947, he departed for the U.S.A. and resumed his academic career at Northwestern University in Evanston, Illinois. The electrochemist Friedrich Todt and chemists Willy Lautsch and Richard Asmus were similarly orphaned and led research groups at the Institute that focused upon topics such as issues in corrosion research, pharmaceuticals and the production of scientific chemicals, respectively. 

The cadmium chalcogenide semiconductors (qv) have found numerous appHcations ranging from rectifiers to photoconductive detectors in smoke alarms. Many Cd compounds, eg, sulfide, tungstate, selenide, teUuride, and oxide, are used as phosphors in luminescent screens and scintiUation counters. Glass colored with cadmium sulfoselenides is used as a color filter in spectroscopy and has recently attracted attention as a third-order, nonlinear optical switching material (see Nonlinear optical materials). DiaLkylcadmium compounds are polymerization catalysts for production of poly(vinyl chloride) (PVC), poly(vinyl acetate) (PVA), and poly(methyl methacrylate) (PMMA). Mixed with TiCl, they catalyze the polymerization of ethylene and propylene. 

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