Bismuth germanium oxide or bismuth germanate is an inorganic chemical compound of bismuth, germanium and oxygen. Most commonly the term refers to the compound with chemical formula Bi 4 Ge 3 O 12 (BGO), with the cubic evlitine crystal structure, used as a scintillator. (The term may also refer to a different compound with formula Bi12GeO20, an electro-optical material with sillenite structure, and Bi 2 Ge 3 O 9.)
Bi4Ge3O12 has a cubic crystal structure (a = 1.0513 nm, z = 4, Pearson symbol cI76, space group I43d No. 220) and a density of 7.12 g/cm3. [1] When irradiated by X-rays or gamma rays it emits photons of wavelengths between 375 and 650 nm, with peak at 480 nm it produces about 8500 photons per megaelectronvolt of the high energy radiation absorbed. It has good radiation hardness (parameters remaining stable up to 5.104 Gy), high scintillation efficiency, good energy resolution between 5 and 20 MeV, is mechanically strong, and is not hygroscopic. Its melting point is 1050 °C. It is the most common oxide-based scintillator. [2]
Bismuth germanium oxide is used in detectors in particle physics, aerospace physics, nuclear medicine, geology exploration, and other industries. Bismuth germanate arrays are used for gamma pulse spectroscopy. BGO crystals are also used in positron emission tomography detectors.
Commercially available crystals are grown by the Czochralski process and usually supplied in the form of cuboids or cylinders. Large crystals can be obtained. Crystal production is typically done around 1100 °C, i.e. around 50 °C above its melting point. [3]
Bi12GeO20 has a cubic crystal structure (a = 1.01454 nm, z = 2, Pearson symbol cI66, space group I23 No. 197) and a density of 9.22 g/cm3. [4] This bismuth germanate has high electro-optic coefficients (3.3 pm/V for Bi12GeO20), [5] making it useful in nonlinear optics for building Pockels cells, and can also be used for photorefractive devices for ultraviolet range.
The Bi12GeO20 crystals are piezoelectric, show strong electro-optical and acousto-optical effects, and find limited use in the field of crystal oscillators and surface acoustic wave devices. [6] Single crystal rods and fibers can be grown by floating zone process from a rod of mixture of bismuth oxide and germanium oxide. [7] The crystals are transparent and brown colored. [8]
The crystals of BGO and similar compounds BSO (Bi12SiO20, bismuth silicon oxide, sillenite) and BTO (Bi12TiO20), are photorefractive and photoconductive. BGO and BSO crystals are efficient photoconductors with low dark conductivity. They can be used in electro-optical applications, like optical PROM, PRIZ spatial light modulators, realtime hologram recording, correlators, and systems for adaptive correction of ultrashort laser pulses, and in fiber optic sensors for electric and magnetic fields. Waveguide structures allow uniform illumination over wide spectral range. Thin film sillenite structures, which can be deposited e.g. by sputtering, have wide range of potential applications. BSO crystals are used in optically addressed spatial light modulators and in liquid crystal light valves. [9] The optical activity of BTO is much smaller than of BGO and BSO. [10] Unlike somewhat similar performing perovskites, sillenites aren't ferroelectric.
The materials can find use in phased-array optics.
When sputtering, the target has to be kept below 450 °C as otherwise the bismuth vapor pressure would get the composition out of stoichiometry, but above 400 °C to form the piezoelectric γ phase. [11]
Germanium is a chemical element with the symbol Ge and atomic number 32. It is lustrous, hard-brittle, grayish-white and similar in appearance to silicon. It is a metalloid in the carbon group that is chemically similar to its group neighbors silicon and tin. Like silicon, germanium naturally reacts and forms complexes with oxygen in nature.
Optics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light. Because light is an electromagnetic wave, other forms of electromagnetic radiation such as X-rays, microwaves, and radio waves exhibit similar properties.
A scintillator is a material that exhibits scintillation, the property of luminescence, when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate. Sometimes, the excited state is metastable, so the relaxation back down from the excited state to lower states is delayed. The process then corresponds to one of two phenomena: delayed fluorescence or phosphorescence. The correspondence depends on the type of transition and hence the wavelength of the emitted optical photon.
Caesium iodide or cesium iodide is the ionic compound of caesium and iodine. It is often used as the input phosphor of an X-ray image intensifier tube found in fluoroscopy equipment. Caesium iodide photocathodes are highly efficient at extreme ultraviolet wavelengths.
Zinc selenide (ZnSe) is a light-yellow, solid compound comprising zinc (Zn) and selenium (Se). It is an intrinsic semiconductor with a band gap of about 2.70 eV at 25 °C (77 °F). ZnSe rarely occurs in nature, and is found in the mineral that was named after Hans Stille called "stilleite".
Bismuth(III) oxide is perhaps the most industrially important compound of bismuth. It is also a common starting point for bismuth chemistry. It is found naturally as the mineral bismite (monoclinic) and sphaerobismoite, but it is usually obtained as a by-product of the smelting of copper and lead ores. Dibismuth trioxide is commonly used to produce the "Dragon's eggs" effect in fireworks, as a replacement of red lead.
Lanthanum(III) oxide, also known as lanthana, chemical formula La2O3, is an inorganic compound containing the rare earth element lanthanum and oxygen. It is used in some ferroelectric materials, as a component of optical materials, and is a feedstock for certain catalysts, among other uses.
Barium titanate (BTO) is an inorganic compound with chemical formula BaTiO3. Barium titanate appears white as a powder and is transparent when prepared as large crystals. It is a ferroelectric, pyroelectric, and piezoelectric ceramic material that exhibits the photorefractive effect. It is used in capacitors, electromechanical transducers and nonlinear optics.
Lithium niobate is a synthetic salt consisting of niobium, lithium, and oxygen. Its single crystals are an important material for optical waveguides, mobile phones, piezoelectric sensors, optical modulators and various other linear and non-linear optical applications. Lithium niobate is sometimes referred to by the brand name linobate.
Zinc telluride is a binary chemical compound with the formula ZnTe. This solid is a semiconductor material with a direct band gap of 2.26 eV. It is usually a p-type semiconductor. Its crystal structure is cubic, like that for sphalerite and diamond.
Solid is one of the four fundamental states of matter along with liquid, gas, and plasma. The molecules in a solid are closely packed together and contain the least amount of kinetic energy. A solid is characterized by structural rigidity and resistance to a force applied to the surface. Unlike a liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire available volume like a gas. The atoms in a solid are bound to each other, either in a regular geometric lattice, or irregularly. Solids cannot be compressed with little pressure whereas gases can be compressed with little pressure because the molecules in a gas are loosely packed.
An optical modulator is an optical device which is used to modulate a beam of light with a perturbation device. It is a kind of transmitter to convert information to optical binary signal through optical fiber or transmission medium of optical frequency in fiber optic communication. There are several methods to manipulate this device depending on the parameter of a light beam like amplitude modulator (majority), phase modulator, polarization modulator etc. The easiest way to obtain modulation is modulation of intensity of a light by the current driving the light source. This sort of modulation is called direct modulation, as opposed to the external modulation performed by a light modulator. For this reason, light modulators are called external light modulators. According to manipulation of the properties of material modulators are divided into two groups, absorptive modulators and refractive modulators. Absorption coefficient can be manipulated by Franz-Keldysh effect, Quantum-Confined Stark Effect, excitonic absorption, or changes of free carrier concentration. Usually, if several such effects appear together, the modulator is called electro-absorptive modulator. Refractive modulators most often make use of electro-optic effect, other modulators are made with acousto-optic effect, magneto-optic effect such as Faraday and Cotton-Mouton effects. The other case of modulators is spatial light modulator (SLM) which is modified two dimensional distribution of amplitude & phase of an optical wave.
A scintillating bolometer is a scientific instrument using particle physics in the search for events with low energy deposition. These events could include dark matter, low energy solar neutrinos, double beta decay or rare radioactive decay. It works by simultaneously measuring both the light pulse and heat pulse generated by a particle interaction within its internal scintillator crystal. The device was originally proposed by L. Gonzalez-Mestres and D. Perret-Gallix
In chemistry, germanate is a compound containing an oxyanion of germanium. In the naming of inorganic compounds it is a suffix that indicates a polyatomic anion with a central germanium atom, for example potassium hexafluorogermanate, K2GeF6.
Bismuth silicon oxide is a solid inorganic compound of bismuth, silicon and oxygen. Its most common chemical formula is Bi12SiO20, though other compositions are also known. It occurs naturally as the mineral sillénite and can be produced synthetically, by heating a mixture of bismuth and silicon oxides. Centimeter-sized single crystals of Bi12SiO20 can be grown by the Czochralski process from the molten phase. They exhibit piezoelectric, electro-optic, elasto-optic, photorefractive and photoconductive properties, and therefore have potential applications in spatial light modulators, acoustic delay lines and hologram recording equipment. Bi12SiO20 can be obtained as a whitish powder with band gap of approximately 3.2 eV starting from bismuth subcarbonate and silica in presence of ethyleneglycol. 29Si solid-state NMR is used to proof that the Si(IV) cations are sharing oxygen atoms with the Bi(III) cations. The 29Si chemical shift (δ) in Bi12SiO20 is −78.1 ppm. Unlike the bismuth oxide, the presence of the acidic Si(IV) cations avoid the reactivity with CO2.
Sillénite or sillenite is a mineral with the chemical formula Bi12SiO20. It is named after the Swedish chemist Lars Gunnar Sillén, who mostly studied bismuth-oxygen compounds. It is found in Australia, Europe, China, Japan, Mexico and Mozambique, typically in association with bismutite.
Bismuth titanate or bismuth titanium oxide is a solid inorganic compound of bismuth, titanium and oxygen with the chemical formula of Bi12TiO20, Bi 4Ti3O12 or Bi2Ti2O7.
Sodium bismuth titanate or bismuth sodium titanium oxide (NBT or BNT) is a solid inorganic compound of sodium, bismuth, titanium and oxygen with the chemical formula of Na0.5Bi0.5TiO3 or Bi0.5Na0.5TiO3. This compound adopts the perovskite structure.
Germanium compounds are chemical compounds formed by the element germanium (Ge). Germanium is insoluble in dilute acids and alkalis but dissolves slowly in hot concentrated sulfuric and nitric acids and reacts violently with molten alkalis to produce germanates ([GeO
3]2−
). Germanium occurs mostly in the oxidation state +4 although many +2 compounds are known. Other oxidation states are rare: +3 is found in compounds such as Ge2Cl6, and +3 and +1 are found on the surface of oxides, or negative oxidation states in germanides, such as −4 in Mg
2Ge. Germanium cluster anions (Zintl ions) such as Ge42−, Ge94−, Ge92−, [(Ge9)2]6− have been prepared by the extraction from alloys containing alkali metals and germanium in liquid ammonia in the presence of ethylenediamine or a cryptand. The oxidation states of the element in these ions are not integers—similar to the ozonides O3−.
Bismuth compounds are compounds containing the element bismuth (Bi). Bismuth forms trivalent and pentavalent compounds, the trivalent ones being more common. Many of its chemical properties are similar to those of arsenic and antimony, although they are less toxic than derivatives of those lighter elements.