Lutetium tantalate is a chemical compound of

lutetium Lutetium is a chemical element with the symbol Lu and atomic number 71. It is a silvery white metal, which resists corrosion in dry air, but not in moist air. Lutetium is the last element in the lanthanide series, and it is traditionally counted am ...

tantalum Tantalum is a chemical element with the symbol Ta and atomic number 73. Previously known as ''tantalium'', it is named after Tantalus, a villain in Greek mythology. Tantalum is a very hard, ductile, lustrous, blue-gray transition metal that ...

and

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...

with the formula LuTaO₄. With a

density Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematical ...

of 9.81 g/cm³, this salt is the densest known white stable material. (Although

thorium dioxide Thorium dioxide (ThO2), also called thorium(IV) oxide, is a crystalline solid, often white or yellow in colour. Also known as thoria, it is produced mainly as a by-product of lanthanide and uranium production. Thorianite is the name of the minera ...

ThO₂ is also white and has a higher density of 10 g/cm³, it is radioactively unstable; while not radioactive enough to make it unstable as a material, even its low rate of decay is still too much for certain uses such as phosphors for detecting ionising radiation.) The white color and high density of LuTaO₄ make it ideal for phosphor applications, though the high cost of lutetium is a hindrance.

Properties

Under

standard conditions Standard temperature and pressure (STP) are standard sets of conditions for experimental measurements to be established to allow comparisons to be made between different sets of data. The most used standards are those of the International Union ...

, LuTaO₄ has a

monoclinic In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic s ...

(labeled as M'; Pearson symbol mP12,

Space group In mathematics, physics and chemistry, a space group is the symmetry group of an object in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of an object that leave it uncha ...

= P2/a, No 13) fergusonite-type crystal structure. This can be changed to an I2/a (M) structure by annealing at 1,600 °C. Both structures are stable under standard conditions. In the M' structure, the lutetium atom is 8-fold coordinated with oxygen and forms a distorted

antiprism In geometry, an antiprism or is a polyhedron composed of two parallel direct copies (not mirror images) of an polygon, connected by an alternating band of triangles. They are represented by the Conway notation . Antiprisms are a subclass o ...

with a C₂ site symmetry. The structure of lutetium tantalate is identical to that of yttrium tantalate (YTaO₄) and gadolinium tantalate (GdTaO₄). Lutetium tantalate itself is weakly

fluorescent Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, ...

. Bright emission is achieved by incorporating small amounts (about 1%) of various

rare-earth The rare-earth elements (REE), also called the rare-earth metals or (in context) rare-earth oxides or sometimes the lanthanides (yttrium and scandium are usually included as rare earths), are a set of 17 nearly-indistinguishable lustrous silve ...

dopants during the crystal growth process, for example, with europium (sharp red line at 610 nm),

samarium Samarium is a chemical element with symbol Sm and atomic number 62. It is a moderately hard silvery metal that slowly oxidizes in air. Being a typical member of the lanthanide series, samarium usually has the oxidation state +3. Compounds of samar ...

(red: 610 nm),

terbium Terbium is a chemical element with the symbol Tb and atomic number 65. It is a silvery-white, rare earth metal that is malleable, and ductile. The ninth member of the lanthanide series, terbium is a fairly electropositive metal that reacts with w ...

(green-yellow: 495 and 545 nm lines),

praseodymium Praseodymium is a chemical element with the symbol Pr and the atomic number 59. It is the third member of the lanthanide series and is considered to be one of the rare-earth metals. It is a soft, silvery, malleable and ductile metal, valued for i ...

(red: 615 nm),

thulium Thulium is a chemical element with the symbol Tm and atomic number 69. It is the thirteenth and third-last element in the lanthanide series. Like the other lanthanides, the most common oxidation state is +3, seen in its oxide, halides and other c ...

(blue: 455 nm),

dysprosium Dysprosium is the chemical element with the symbol Dy and atomic number 66. It is a rare-earth element in the lanthanide series with a metallic silver luster. Dysprosium is never found in nature as a free element, though, like other lanthanides, ...

(orange: 580 nm) or niobium (blue: 400 nm, broad peak). The emission is best excited by

electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no ...

X-rays An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nbs ...

ultraviolet light Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...

at 220 nm. The high density of LuTaO₄ favors X-ray excitation, which has relatively more efficient, stronger absorption in LuTaO₄, compared to other materials. LuTaO₄ also exhibits

thermoluminescence Thermoluminescence is a form of luminescence that is exhibited by certain crystalline materials, such as some minerals, when previously absorbed energy from electromagnetic radiation or other ionizing radiation is re-emitted as light upon he ...

— it glows in the dark when heated after illumination.

Preparation

To prepare a sample of lutetium tantalate, powders of lutetium and tantalum oxides (Lu₂O₃ and Ta₂O₅) are mixed and annealed at a temperature above 1,200 °C for several hours. To prepare a phosphor, a small fraction of appropriate material, such as an oxide of another rare-earth metal, is added to the mixture before annealing. After cooling, the product is leached with water, washed, filtered and dried, resulting in a white powder consisting of micrometre-sized particles of LuTaO₄.

References

{{Lutetium compounds Lutetium compounds Tantalates Phosphors and scintillators