Dopant

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "Dopant" – news · newspapers · books · scholar · JSTOR (December 2008) (Learn how and when to remove this template message)

A dopant (also called a doping agent) is a small amount of a substance added to a material to alter its physical properties, such as

properties. The amount of dopant is typically very low compared to the material being doped.

When doped into crystalline substances, the dopant's atoms get incorporated into the crystal lattice of the substance. The crystalline materials are frequently either crystals of a semiconductor such as silicon and germanium for use in solid-state electronics, or transparent crystals for use in the production of various laser types; however, in some cases of the latter, noncrystalline substances such as glass can also be doped with impurities.

In solid-state electronics using the proper types and amounts of dopants in semiconductors is what produces the

.

Transparent crystals

Lasing media

The procedure of doping tiny amounts of the metals chromium (Cr), neodymium (Nd), erbium (Er), thulium (Tm), ytterbium (Yb), and a few others, into transparent crystals, ceramics, or glasses is used to produce the active medium for solid-state lasers. It is in the electrons of the dopant atoms that a population inversion can be produced, and this population inversion is essential for the stimulated emission of photons in the operation of all lasers.

In the case of the natural ruby, what has occurred is that a tiny amount of chromium dopant has been naturally distributed through a crystal of aluminium oxide (corundum). This chromium both gives a ruby its red color, and also enables a ruby to undergo a population inversion and act as a laser. The aluminium and oxygen atoms in the transparent crystal of aluminium oxide served simply to support the chromium atoms in a good spatial distribution, and otherwise, they do not have anything to do with the laser action.

In other cases, such as in the

series of elements, such as neodymium. Then, these dopant atoms actually carry out the lasing process in the crystal. The rest of the atoms in the crystal consist of yttrium, aluminium, and oxygen atoms, but just as above, these other three elements function to simply support the neodymium atoms. In addition, the rare-earth element erbium can readily be used as the dopant rather than neodymium, giving a different wavelength of its output.

In many

. The optical dopants are characterized with lifetime of excitation and the effective absorption and emission cross-sections, which are main parameters of an active dopant. Usually, the concentration of optical dopant is of order of few percent or even lower. At large density of excitation, the cooperative quenching (cross-relaxation) reduces the efficiency of the laser action.

Examples

The medical field has some use for

Phosphors and scintillators

In context of phosphors and scintillators, dopants are better known as activators, and are used to enhance the luminescence process.^[2]

Semiconductors

The addition of a dopant to a

, and solid sources footnote.

Others

The color of some gemstones is caused by dopants. For example, ruby and sapphire are both aluminium oxide, the former getting its red color from chromium atoms, and the latter doped with any of several elements, giving a variety of colors.

See also

• List of semiconductor materials

References