Cadmium sulfide properties

Heterogeneous Photocatalysis. Heterogeneous photocatalysis is a technology based on the irradiation of a semiconductor (SC) photocatalyst, for example, titanium dioxide [13463-67-7] Ti02, zinc oxide [1314-13-2] ZnO, or cadmium sulfide [1306-23-6] CdS. Semiconductor materials have electrical conductivity properties between those of metals and insulators, and have narrow energy gaps (band gap) between the filled valence band and the conduction band (see Electronic materials Semiconductors). 

The intermetallic compounds with Group 16 (VIA) elements including CdS, CdSe, and CdTe have interesting semiconductor properties for photoconductors, photovoltaic cells, and ir windows. Cadmium sulfide is widely used as a phosphor in television tubes. 

Xi D, Zhang H, Furst S, Chen B, Pei Q (2008) Electrochemical synthesis and photovoltaic property of cadmium sulfide-polybithiophene interdigitated nanohybrid thin films. J Phys ChemC 112 19765-69... 

Let us add here that the fabrication of polycrystalline semiconductive films with enhanced photoresponse and increased resistance to electrochemical corrosion has been attempted by introducing semiconductor particles of colloidal dimensions to bulk deposited films, following the well-developed practice of producing composite metal and alloy deposits with improved thermal, mechanical, or anti-corrosion properties. Eor instance, it has been reported that colloidal cadmium sulfide [105] or mercuric sulfide [106] inclusions significanfly improve photoactivity and corrosion resistance of electrodeposited cadmium selenide. 

Popescu, V. Pica, E. M. Pop, I. Grecu, R. 1999. Optical properties of cadmium sulfide thin films, chemically deposited from baths containing surfactants. Thin... 

Cadmium sulfate hydrate, 4 515 physical properties of, 4 509t Cadmium sulfate monohydrate, 4 515 physical properties of, 4 509t Cadmium sulfide, 4 503, 515-516, 518, 521 colloidal precipitation color, 7 343t color and bad gap, 7 335t physical properties of, 4 509t piezochromic material, 6 607 Cadmium sulfide photodetectors, 19 137 Cadmium sulfide photoconductor, fabrication and performance of, 19 155-156... 

The main sulfide phosphors are the group II-V ones based on high purity zinc and cadmium sulfides activated by dopants, primarily using copper and silver but also manganese, gold and rare earths. The nature and concentration of the activator, the composition of the flux and the firing conditions, normally in furnaces at 800-1500 °C, influence the luminescent properties. 

Cadmium sulfide suspensions are characterized by an absorption spectrum in the visible range. In the case of small particles, a quantum size effect (28-37) is observed due to the perturbation of the electronic structure of the semiconductor with the change in the particle size. For the CdS semiconductor, as the diameter of the particles approaches the excitonic diameter, its electronic properties start to change (28,33,34). This gives a widening of the forbidden band and therefore a blue shift in the absorption threshold as the size decreases. This phenomenon occurs as the cristallite size is comparable or below the excitonic diameter of 50-60 A (34). In a first approximation, a simple electron hole in a box model can quantify this blue shift with the size variation (28,34,37). Thus the absorption threshold is directly related to the average size of the particles in solution. 

In certain solids such as titanium dioxide or cadmium sulfide, the energy of the band gap corresponds to that of light (visible, ultraviolet, or infrared), with the result that the solid, when illuminated, may become electrically conducting or acquire potent chemical redox characteristics because of the promotion of electrons to the conduction band (which is normally unoccupied). These properties have obvious practical significance and are considered at length in Chapter 19. 

Production. The raw material for the production of cadmium yellow pigments is high-purity cadmium metal (99.99 %), cadmium oxide, or cadmium carbonate. If the metal is used it is first dissolved in mineral acid. A zinc salt is then added to the solution the amount added depends on the desired shade. The zinc salt is followed by addition of sodium sulfide solution. An extremely finely divided cadmium sulfide or cadmium zinc sulfide precipitate is formed, which does not possess any pigment properties. This intermediate product can also be obtained by mixing the cadmium or cadmium-zinc salt solution with sodium carbonate solution. An alkaline cadmium carbonate or cadmium zinc carbonate precipitate is formed which reacts in suspension with added sodium sulfide solution. 

Pure cadmium selenide [1306-24-7], CdSe, is brownish black and has no pigment properties. Like cadmium sulfide, it is dimorphous and occurs in hexagonal and cubic modifications. Cadmium selenide is insoluble in dilute acid. It readily liberates hydrogen selenide in concentrated hydrochloric acid. It dissolves completely in fuming nitric acid, the Se2 - ions being converted to SeO2 ions. Cadmium selenide is an n-type semiconductor. 

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],... 

Substitution of the lattice cadmium ions in a CdS colloidal particle by the ions of another metal is often accompanied by the formation of the so-called coated particles CdS/MexSy. Such particles are readily produced via the substitution of cadmium ions by other ions if only their sulfide are less soluble compared to the cadmium sulfide. Our studies on the luminescence properties of such particles and regularities of their luminescence... 

The mercuric compounds, in which mercury is bipositive, differ somewhat in their properties from the corresponding compounds of zinc and cadmium. The differences are due in part to the very strong tendency of the mercuric ion, Hg + +, to form covalent bonds. Thus the covalent nvstal mercuric sulfide, HgS, is far less soluble than cadmium sulfide or zinc sulfide (Chap. 22). 

Photochemistry of Titanium Dioxide Colloids. Another semiconductor colloid used in our studies is titanium dioxide which has a band gap of 3.2 eV. As in the case of cadmium sulfide, excitation of aqueous suspensions of this particle leads to electron-hole pair separation which can be intercepted with suitable redox reagents. In the absence of externally added solutes, the photogenerated electron-hole pair recombines to give the starting material and the light energy is dissipated to the medium as heat. Two types of TiOj samples are used in this study. TiOj prepared at high temperature (80°C) which behaves very similarly to commercial samples, and TlOj prepared at low temperature (35°C) which has a particle size of 300 100 A radius and shows different properties. 

It is too ideal for one Cd4S4 nanocluster to occupy one sodalite cage. In the treatment of zeolite with H2S many mesoporous defects will be produced, and these mesoporous defects may accommodate larger cadmium sulfide clusters. Therefore, in the microporous crystal with a particular structure, there may exist many different cadmium sulfide particles with various sizes. However, the content of these cadmium sulfide clusters located defects is usually limited, and, as a result, they have little effect on the electronic spectral properties of the composite. Detailed composition and structural analysis indicates that the nanoclusters contain not only Cd and S, but also O. In fact, these clusters can be written as Cd4(S,0)4. 

Chang, S.Y., Liu, L., and Asher, S.A., Preparation and properties of tailored morphology, monodisperse colloidal silica-cadmium sulfide nanocomposites, J. Am. Chem. Soc., 116, 6739, 1994. 

Matijevic, E. and Wilhehny. D.M., Preparation and properties of monodispersed spherical colloidal particles of cadmium sulfide. J. Colloid Intetf. Sci., 86, 476, 1982. 

PHOTOLUMINESCENT PROPERTIES OP CADMIUM SULFIDE CONTACTED WITH GASEOUS LEWIS ACIDS AND BASES... 

Photoluminescent Properties of Cadmium Sulfide Contacted with Gaseous Lewis Acids and Bases (G. J. Meyer, E. R. M. Luebker, G. C. Lisensky, and A. B. Ellis)... 

A soft, silvery metal, cadmium has chemical properties that are similar to those of zinc. However, compared to zinc, cadmium is very rare. Cadmium sulfide ores are one source of this metal. It is also present in zinc ores, but in such small amounts that it is usually only produced as a by-product of zinc refining. Cadmiums discovery is even linked with zinc. In 1817, the German chemist Friedrich Strohmeyer (1776-1835) discovered cadmium when he was studying the compound zinc oxide. 

From this discussion, it should be obvious that the two most important properties of cathode-ray phosphors are the response to electron-beaun excitation (brightness) and the decay time. We require a long-decay phosphor for radar applications and a short-decay phosphor for television usage. Nearly all the cathode-ray phosphors are based on the zinc and cadmium sulfides because they exhibit the highest efficiency to cathode-ray excitation. ZnS forms a series of solid solutions with CdS whose emission band can be shifted from the blue (ZnS Ag) to the red phosphor. 

Table 9 Physical properties of cadmium sulfide, selenide and telluride...

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