As a result, a maximum temperature drop of 40 and 15 K has been demonstrated when the nanoribbons are pumped with a 514 or 532 nm laser. Nanoribbons of CdS show a net cooling due annihilation of phonons, during anti-Stokes luminescence at ~510 nm.Thin films of CdS can be piezoelectric and have been used as transducers which can operate at frequencies in the GHz region.However interest in compound semiconductors for TFTs largely waned after the emergence of amorphous silicon technology in the late 1970s. CdS was also one of the first semiconductor materials to be used for thin-film transistors (TFTs). In thin-film form, CdS can be combined with other layers for use in certain types of solar cells.CdS crystals can act as a gain medium in solid state laser.both polymorphs are piezoelectric and the hexagonal is also pyroelectric.when doped with for example Cu + (" activator") and Al 3+ ("coactivator") CdS luminesces under electron beam excitation ( cathodoluminescence) and is used as phosphor.when combined with a p-type semiconductor it forms the core component of a photovoltaic ( solar) cell and a CdS/Cu 2S solar cell was one of the first efficient cells to be reported (1954).the conductivity increases when irradiated, (leading to uses as a photoresistor).Īs well as this obvious property other properties result: The proximity of its band gap to visible light wavelengths gives it a coloured appearance. Ĭadmium sulfide is a direct band gap semiconductor (gap 2.42 eV). There is also a high pressure form with the NaCl rock salt structure. In both of these forms the cadmium and sulfur atoms are four coordinate. The more stable hexagonal wurtzite structure (found in the mineral Greenockite) and the cubic zinc blende structure (found in the mineral Hawleyite). The proposed mechanism involves the electron/hole pairs created when incident light is absorbed by the cadmium sulfide followed by these reacting with water and sulfide: Production of an electron–hole pair CdS + hν → e − + h + Reaction of electronĢe − + 2H 2O → H 2 + 2OH − Reaction of holeĢh + + S 2− → S Structure and physical properties Ĭadmium sulfide has, like zinc sulfide, two crystal forms. When solutions of sulfide containing dispersed CdS particles are irradiated with light, hydrogen gas is generated: H 2S → H 2 + S ΔH f = +9.4 kcal/mol Screen printing using a slurry containing dispersed CdS Ĭadmium sulfide can be dissolved in acids.Spraying with precursor cadmium salt, sulfur compound and dopant.Other methods to produce films of CdS include In the chemical bath deposition method, thin films of CdS have been prepared using thiourea as the source of sulfide anions and an ammonium buffer solution to control pH: Cd 2+ + H 2O + (NH 2) 2CS + 2 NH 3 → CdS + (NH 2) 2CO + 2 NH 4 +Ĭadmium sulfide can be produced using metalorganic vapour phase epitaxy and MOCVD techniques by the reaction of dimethylcadmium with diethyl sulfide: Cd(CH 3) 2 + Et 2S → CdS + CH 3CH 3 + C 4H 10 Special methods are used to produce films of CdS as components in some photoresistors and solar cells. Ĭadmium sulfide is sometimes associated with sulfate reducing bacteria. When cadmium sulfide selenides are required the CdSe is co-precipitated with CdS and the cadmium sulfoselenide is created during the calcination step. Pigment production usually involves the precipitation of CdS, the washing of the solid precipitate to remove soluble cadmium salts followed by calcination (roasting) to convert it to the hexagonal form followed by milling to produce a powder. It has been asserted that chemical precipitation methods result in the cubic zincblende form. The preparative route and the subsequent treatment of the product, affects the polymorphic form that is produced (i.e., cubic vs hexagonal). This reaction has been used for gravimetric analysis and qualitative inorganic analysis. Its vivid yellow color led to its adoption as a pigment for the yellow paint "cadmium yellow" in the 18th century.Ĭadmium sulfide can be prepared by the precipitation from soluble cadmium(II) salts with sulfide ion. As a compound that is easy to isolate and purify, it is the principal source of cadmium for all commercial applications. It occurs in nature with two different crystal structures as the rare minerals greenockite and hawleyite, but is more prevalent as an impurity substituent in the similarly structured zinc ores sphalerite and wurtzite, which are the major economic sources of cadmium. Cadmium sulfide is the inorganic compound with the formula CdS.
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