| Cadmium selenide | |
|---|---|
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| IUPAC name |
Cadmium selenide
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| Other names | Cadmium(II) selenide, Cadmoselite |
| Identifiers | |
| CAS number | 1306-24-7  |
| Properties | |
| Molecular formula | CdSe |
| Molar mass | 191.37 g/mol |
| Appearance | Greenish-brown or dark red solid powder |
| Density | 5.816 g/cm3, solid |
| Melting point |
1268 °C (1541 K) |
| Solubility in water | Insoluble |
| Band gap | 1.74 eV (direct) |
| Refractive index (nD) | 2.5 |
| Structure | |
| Crystal structure | Wurtzite |
| Space group | C6v4-P63mc |
| Coordination geometry |
Tetrahedral |
| Hazards | |
| EU Index | 048-001-00-5 |
| EU classification | Harmful (Xn) Dangerous for the environment (N) |
| R-phrases | R20/21/22, R50/53 |
| S-phrases | (S2), S60, S61 |
| Related compounds | |
| Other anions | Cadmium oxide, Cadmium sulfide, Cadmium telluride |
| Other cations | Zinc selenide, Mercury(II) selenide |
| (what is this?) (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
Cadmium selenide (CdSe) is a solid, binary compound of cadmium and selenium. Common names for this compound are cadmium(II) selenide, cadmium selenide, and cadmoselite (a very rare mineral).
Cadmium selenide is a semiconducting material, but has yet to find many applications in manufacturing. This material is transparent to infra-red (IR) light, and has seen limited use in windows for instruments utilizing IR light.
Much current research on cadmium selenide has focused on nanoparticles. Researchers are concentrating on developing controlled syntheses of CdSe nanoparticles. In addition to synthesis, scientists are working to understand the properties of cadmium selenide, as well as apply these materials in useful ways.
Contents |
Structure
Three crystalline forms of CdSe are known: wurtzite (hexagonal), sphalerite (cubic) and rock-salt (cubic). The sphalerite CdSe structure is unstable and converts to the wurtzite form upon moderate heating. The transition starts at about 130 °C, and at 700 °C it completes within a day. The rock-salt structure is only observed under high pressure.[1]
Production
The production of cadmium selenide has been carried out in two different ways. The preparation of bulk crystalline CdSe is done by the High-Pressure Vertical Bridgman method or High-Pressure Vertical Zone Melting.[2]
Cadmium selenide may also be produced in the form of nanoparticles. (see applications for explanation) Several methods for the production of CdSe nanoparticles have been developed: arrested precipitation in solution, synthesis in structured media, high temperature pyrolysis, sonochemical, and radiolytic methods are just a few.[3]
Production of cadmium selenide by arrested precipitation in solution is performed by introducing alkylcadmium and trioctylphosphine selenide (TOPSe) precursors into a heated solvent under controlled conditions.[4]
- Me2Cd + TOPSe → CdSe + (byproducts).
Synthesis in structured environments refers to the production of cadmium selenide in liquid crystal or surfactant solutions. The addition to surfactants to solutions often results in a phase change in the solution leading to a liquid crystallinity. A liquid crystal is similar to a solid crystal in that the solution has long range translational order. Examples of this ordering are layered alternating sheets of solution and surfactant, micelles, or even a hexagonal arrangement of rods.
High temperature pyrolysis synthesis is usually carried out using an aerosol containing a mixture of volatile cadmium and selenium precursors. The precursor aerosol is then carried through a furnace with an inert gas, such as hydrogen, nitrogen, or argon. In the furnace the precursors react to form CdSe as well as several by-products.[3]
Applications
Cadmium selenide in its wurtzite crystal structure is an important II-VI semiconductor. As a semiconductor CdSe is an n-type semiconductor, which is difficult to dope p-type, however p-type doping has been achieved using nitrogen.[5] CdSe is also being developed for use in opto-electronic devices, laser diodes, nanosensing, and biomedical imaging.[6] They are also used being tested for use in high-efficiency solar cells[7][8][9]
Most of the usefulness of CdSe stems from nanoparticles, that is particles with sizes below 100 nm. CdSe particles of this size exhibit a property known as quantum confinement. Quantum confinement results when the electrons in a material are confined to a very small volume. Quantum confinement is size dependent, meaning the properties of CdSe nanoparticles are tunable based on their size.[10]
Since CdSe nanoparticles have a size dependent fluorescence spectrum, they are finding applications in optical devices such as laser diodes. Using these particles, engineers are able to manufacture laser diodes that cover a large part of the electromagnetic spectrum.[11]
Along similar lines, doctors are developing these materials for use in biomedical imaging applications. Human tissue is permeable to far infra-red light. By injecting appropriately prepared CdSe nanoparticles into injured tissue, it may be possible to image the tissue in those injured areas.[12][13]
Safety information
Cadmium is a toxic heavy metal and appropriate precautions should be taken when handling it and its compounds. Selenides are toxic in large amounts.[14].
References
- ^ Lev Isaakovich Berger (1996). Semiconductor materials. CRC Press. p. 202. ISBN 0849389127. http://books.google.com/books?id=Ty5Ymlg_Mh0C&pg=PA202.
- ^ II-VI compound crystal growth, HPVB & HPVZM basics
- ^ a b Didenko, Yt; Suslick, Ks (Sep 2005). "Chemical aerosol flow synthesis of semiconductor nanoparticles.". Journal of the American Chemical Society 127 (35): 12196–7. doi:. ISSN 0002-7863. PMID 16131177.
- ^ Murray, C. B. (1993). "Synthesis and characterization of nearly monodisperse CdE (E = sulfur, selenium, tellurium) semiconductor nanocrystallites". Journal of the American Chemical Society 115: 8706. doi:.
- ^ T Ohtsuka, J Kawamata, Z Zhu, T Yao (1994). "p-type CdSe grown by molecular beam epitaxy using a nitrogen plasma source". Applied Physics Letters 65: 466. doi:.
- ^ Ma, C; Ding, Y; Moore, D; Wang, X; Wang, Zl (Jan 2004). "Single-crystal CdSe nanosaws.". Journal of the American Chemical Society 126 (3): 708–9. doi:. ISSN 0002-7863. PMID 14733532.
- ^ Califano, Marco (2004). "Direct carrier multiplication due to inverse Auger scattering in CdSe quantum dots". Applied Physics Letters 84: 2409. doi:.
- ^ Schaller, Richard D. (2005). "Effect of electronic structure on carrier multiplication efficiency: Comparative study of PbSe and CdSe nanocrystals". Applied Physics Letters 87: 253102. doi:.
- ^ Hendry, E. (2006). "Direct Observation of Electron-to-Hole Energy Transfer in CdSe Quantum Dots". Physical Review Letters 96: 057408. doi:.
- ^ Nanotechnology Structures - Quantum Confinement
- ^ Colvin, V. L.; Schlamp, M. C.; Alivisatos, A. P. (1994). "Light-emitting diodes made from cadmium selenide nanocrystals and a semiconducting polymer". Nature 370: 354. doi:.
- ^ Chan, W. C.; Nie, S. M. (1998). "Quantum Dot Bioconjugates for Ultrasensitive Nonisotopic Detection". Science 281: 2016. doi:.
- ^ Bruchez, M.;Moronne, M.; Gin, P.; Weiss, S.; Alivisatos, A. P. (1998). Science 281: 2013.
- ^ Additional safety information available at www.msdsonline.com, search 'cadmium selenide.'
Related materials
External links
- Quantum Dots in Solar Cells Science News Week of June 3, 2006; Vol. 169, No. 22 , p. 344.
- National Pollutant Inventory - Cadmium and compounds
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