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Gallium(II) selenide
Encyclopedia
Gallium selenide (Ga
Se
) is a chemical compound
. It has a hexagonal layer structure, similar to that of GaS
. It is a photoconductor, a second harmonic generation
crystal in nonlinear optics
, and has been used as a far-infrared conversion material at 14-31 THz and above.
s Gallium selenide crystals show great promise as a nonlinear optical material and photoconductor. Non-linear optical materials are used in the frequency conversion
of laser light. Frequency conversion involves the shifting of the wavelength of a monochromatic source of light, usually laser light, to a higher or lower wavelength of light that cannot be produced from a conventional laser source.
Several methods of frequency conversion using non-linear optical materials exist. Second harmonic generation
leads to doubling of the frequency of infrared carbon dioxide laser
s. In optical parametric generation, the wavelength of light is doubled. Near-infrared solid-state laser
s are usually used in optical parametric generations.
One original problem with using gallium selenide in optics is that it is easily broken along cleavage lines and thus it can be hard to cut for practical application. It has been found, however, that doping the crystals with indium
greatly enhances their structural strength and makes their application much more practical. There remain, however, difficulties with crystal growth that must be worked out before gallium selenide crystals may become more widely used in optics.
s is carried out by the reaction of GaMe3
with trioctyl phosphine selenium (TOPSe) in a high temperature solution of trioctyl phosphine (TOP) and trioctyl phosphine oxide (TOPO).
A solution of 15 g TOPO and 5 mL TOP is heated to 150 °C overnight under nitrogen, removing any water that may be present in the original TOP solution. This initial TOP solution is vacuum distilled at 0.75 torr, taking the fraction from 204 °C to 235 °C. A TOPSe solution (12.5 mL TOP with 1.579 g TOPSe) is then added and the TOPO/TOP/TOPSe reaction mixture is heated to 278 °C. GaMe3 (0.8 mL) dissolved in 7.5 mL distilled TOP is then injected. After injection, the temperature drops to 254 °C before stabilizing in the range of 266-268 °C after 10 minutes. GaSe nanoparticles then begin to form, and may be detected by a shoulder in the optical absorption spectrum in the 400-450 nm range. After this shoulder is observed, the reaction mixture is left to cool to room temperature to prevent further reaction. After synthesis and cooling, the reaction vessel is opened and extraction of the GaSe nanoparticle solution is accomplished by addition of methanol
. The distribution of nanoparticles between the polar (methanol) and non-polar (TOP) phases depends on experimental conditions. If the mixture is very dry, nanoparticles partition into the methanol phase. If the nanoparticles are exposed to air or water, however, the particles become uncharged and become partitioned into the non-polar TOP phase.
Gallium
Gallium is a chemical element that has the symbol Ga and atomic number 31. Elemental gallium does not occur in nature, but as the gallium salt in trace amounts in bauxite and zinc ores. A soft silvery metallic poor metal, elemental gallium is a brittle solid at low temperatures. As it liquefies...
Se
Selenium
Selenium is a chemical element with atomic number 34, chemical symbol Se, and an atomic mass of 78.96. It is a nonmetal, whose properties are intermediate between those of adjacent chalcogen elements sulfur and tellurium...
) is a chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
. It has a hexagonal layer structure, similar to that of GaS
Gallium(II) sulfide
Gallium sulfide, GaS, is a chemical compound of gallium and sulfur. The normal form of gallium sulfide as made from the elements has a hexagonal layer structure containing Ga24+ units which have a Ga-Ga distance of 248pm. This layer structure is similar to GaTe, GaSe and InSe...
. It is a photoconductor, a second harmonic generation
Second harmonic generation
An optical frequency multiplier is a nonlinear optical device, in which photons interacting with a nonlinear material are effectively "combined" to form new photons with greater energy, and thus higher frequency...
crystal in nonlinear optics
Nonlinear optics
Nonlinear optics is the branch of optics that describes the behavior of light in nonlinear media, that is, media in which the dielectric polarization P responds nonlinearly to the electric field E of the light...
, and has been used as a far-infrared conversion material at 14-31 THz and above.
Uses
It is said to have potential for optical applications but the exploitation of this potential has been limited by the ability to readily grow single crystalSingle crystal
A single crystal or monocrystalline solid is a material in which the crystal lattice of the entire sample is continuous and unbroken to the edges of the sample, with no grain boundaries...
s Gallium selenide crystals show great promise as a nonlinear optical material and photoconductor. Non-linear optical materials are used in the frequency conversion
Frequency conversion
Frequency conversion may refer to different processes affecting frequency of physical phenomena:* A frequency changer is an electronic device that converts alternating current of one frequency to alternating current of another frequency....
of laser light. Frequency conversion involves the shifting of the wavelength of a monochromatic source of light, usually laser light, to a higher or lower wavelength of light that cannot be produced from a conventional laser source.
Several methods of frequency conversion using non-linear optical materials exist. Second harmonic generation
Second harmonic generation
An optical frequency multiplier is a nonlinear optical device, in which photons interacting with a nonlinear material are effectively "combined" to form new photons with greater energy, and thus higher frequency...
leads to doubling of the frequency of infrared carbon dioxide laser
Carbon dioxide laser
The carbon dioxide laser was one of the earliest gas lasers to be developed , and is still one of the most useful. Carbon dioxide lasers are the highest-power continuous wave lasers that are currently available...
s. In optical parametric generation, the wavelength of light is doubled. Near-infrared solid-state laser
Solid-state laser
A solid-state laser is a laser that uses a gain medium that is a solid, rather than a liquid such as in dye lasers or a gas as in gas lasers. Semiconductor-based lasers are also in the solid state, but are generally considered as a separate class from solid-state lasers .-Solid-state...
s are usually used in optical parametric generations.
One original problem with using gallium selenide in optics is that it is easily broken along cleavage lines and thus it can be hard to cut for practical application. It has been found, however, that doping the crystals with indium
Indium
Indium is a chemical element with the symbol In and atomic number 49. This rare, very soft, malleable and easily fusible post-transition metal is chemically similar to gallium and thallium, and shows the intermediate properties between these two...
greatly enhances their structural strength and makes their application much more practical. There remain, however, difficulties with crystal growth that must be worked out before gallium selenide crystals may become more widely used in optics.
Synthesis
Synthesis of GaSe nanoparticleNanoparticle
In nanotechnology, a particle is defined as a small object that behaves as a whole unit in terms of its transport and properties. Particles are further classified according to size : in terms of diameter, coarse particles cover a range between 10,000 and 2,500 nanometers. Fine particles are sized...
s is carried out by the reaction of GaMe3
Trimethylgallium
Trimethylgallium, Ga3, often abbreviated to TMG or TMGa, is the preferred metalorganic source of gallium for metalorganic vapour phase epitaxy of gallium-containing compound semiconductors, such as GaAs, GaN, GaP, GaSb, InGaAs, InGaN, AlGaInP, InGaP and AlInGaNP.-Properties:TMG is a clear,...
with trioctyl phosphine selenium (TOPSe) in a high temperature solution of trioctyl phosphine (TOP) and trioctyl phosphine oxide (TOPO).
- GaMe3 + P[(CH2)7CH3]3Se → GaSe
A solution of 15 g TOPO and 5 mL TOP is heated to 150 °C overnight under nitrogen, removing any water that may be present in the original TOP solution. This initial TOP solution is vacuum distilled at 0.75 torr, taking the fraction from 204 °C to 235 °C. A TOPSe solution (12.5 mL TOP with 1.579 g TOPSe) is then added and the TOPO/TOP/TOPSe reaction mixture is heated to 278 °C. GaMe3 (0.8 mL) dissolved in 7.5 mL distilled TOP is then injected. After injection, the temperature drops to 254 °C before stabilizing in the range of 266-268 °C after 10 minutes. GaSe nanoparticles then begin to form, and may be detected by a shoulder in the optical absorption spectrum in the 400-450 nm range. After this shoulder is observed, the reaction mixture is left to cool to room temperature to prevent further reaction. After synthesis and cooling, the reaction vessel is opened and extraction of the GaSe nanoparticle solution is accomplished by addition of methanol
Methanol
Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...
. The distribution of nanoparticles between the polar (methanol) and non-polar (TOP) phases depends on experimental conditions. If the mixture is very dry, nanoparticles partition into the methanol phase. If the nanoparticles are exposed to air or water, however, the particles become uncharged and become partitioned into the non-polar TOP phase.
External links
- Gallium Selenide Nanoparticles Used In Solar Energy Conversion (ScienceDaily).