Cadmium selenide

• Cadmium ( II) selenide
• Cadmium
• Cadmoselit

White to brown solid

Fixed

5.81 g · cm -3 ( 15 ° C)

1350 ° C.

Insoluble in water

Risk

Repealed as carcinogenic

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Cadmium selenide, CdSe, is the cadmium salt of hydrogen selenide. The red solid is crystallized in a hexagonal Wurzitstruktur under high pressure is a metastable form in the sodium chloride structure is known. The compound is referred to as cadmium for their use as red pigment. Cadmium selenide is a semiconductor, more precisely, a II-VI compound semiconductor. Due to the toxicity of the compound, it is used as semiconductor material in the electronics hardly use. Cadmium selenide is transparent to infrared light, which is why it is occasionally used as a window material in IR applications.

In nature, cadmium selenide can be found very rarely occurring mineral Cadmoselit.

Nanocrystals

In research, nanoparticles of cadmium selenide are the focus of many research groups. Cadmium selenide is one of the most studied systems of nanocrystals. Cadmium selenide nanocrystals can be prepared in macroscopic quantities with very low size dispersion.

The three-dimensional spatial confinement of charge carriers leads to a discretization of the electronic energy levels, which is called quantum size effect. Such quasi- zero-dimensional solid-state structures called quantum dots. The special feature of these nanocrystals is that in these dimensions, the size of the crystal and not the physical composition determines the band gap energy of the semiconductor. Even by a small change in size from 10 to 100 Å, the energy difference changed so that the wavelength of the emitted light is shifted from blue to red by UV-induced fluorescence. The smaller the particle, the smaller the emitted wavelength. These quantum size effects occur particularly strong because these dimensions less than the size of a bound electron-hole pair ( exciton ).

However, these dimensions are in addition effects on the surface of the crystal, as already about one-third of the atoms located at the surface and thus not in a regular lattice association. When you grow other semiconductors to the surface, surface defects can be specifically manipulated. This makes it possible to increase and improve the photostability for example, the quantum yield. Through stabilizer molecules, such as TOPO, these nanocrystals can also be adapted to different ( polar and non-polar ) solvents.

In particular, the particle size of the adjustable fluorescence color can be cadmium selenide nanoparticles for a range of applications, such as a biomarker for in vitro applications or as Lichtumwandler in solar cells, look quite promising.

Applications

Cadmium is still used despite significant toxicological and environmental concerns in artists' colors. Pure cadmium has no meaning as a pigment because of its brown - black color. In practice, it is mixed with cadmium yellow. With increasing selenium content, the pigment changes color from orange to red to dark red. Fabrikatorisch it was first produced in 1910 and was the not quite as resistant cinnabar ( vermilion ), so replace mercury sulphide, which it surpasses in color purity.

Although cadmium pigments were banned from many everyday objects or forbidden their use, such as in automotive paints and plastic parts, it is in addition to the already mentioned use in artists' colors still occasionally used as a pigment, for example, as a pigment for tattoos. In June 1991, the EC Directive 91/338/EEC was adopted, which provides for a ban on cadmium stabilizers, pigments and galvanic coatings for specific applications.