Erbium

The erbium is a chemical element of the periodic table whose symbol is Er and its atomic number is 68. Erbium is a somewhat rare silver-colored element that belongs to the lanthanides and appears associated with other lanthanides in the gadolinite mineral from Ytterby (Sweden).

Principal uses of Erbium include its pink colored Er³⁺ ions, which have fluorescent optical properties particularly useful in certain laser applications. Erbium-doped glasses or crystals can be used as optical amplification media, where Er³⁺ ions are optically pumped at around 980 or 1480 nm and then irradiate light at 1530 nm in stimulated emission. This process results in an unusually mechanically simple laser optical amplifier for signals transmitted over fiber optics. The 1550 nm wavelength is especially important for optical communications because standard single-mode optical fibers have minimal loss at this particular wavelength.

In addition to fiber optic amplifying lasers, a wide variety of medical applications (ie dermatology, dentistry) rely on the 2940 nm emission of the erbium ion (see Er:YAG laser) when illuminated at another wavelength, which is highly absorbed in the water of the tissues, so its effect is very superficial. Such superficial deposition of tissue from laser energy is useful in laser surgery, and for the efficient production of steam that ablates enamel by common types of dental lasers.

Features

Fragments of metal raft.

Erbium is a trivalent, malleable element, relatively stable in air, and does not oxidize as quickly as other rare earth metals. Its salts are pink and the element causes a characteristic absorption spectrum in the visible, ultraviolet, and near-infrared spectrum. Its oxide is erbia. Erbium properties are greatly influenced by the amount and type of impurities present. Erbium has no known biological role, although some believe it is capable of stimulating metabolism. Erbium-doped crystals or glasses can be used in optical amplification, in which erbium ions are optically pumped around the 980 nm or 1480 nm wavelengths and irradiate light at 1550 nm wavelengths. This process can be used to create lasers and optical amplifiers. The 1550 nm wavelength is especially important for optical communications because standard optical fibers have minimal losses at this wavelength.

Physical properties

Erbium chloride(III) in the sunlight, showing some rose fluorescence of Er⁺³ from natural ultraviolet light.

A trivalent element, the metallic pure erbium is malleable, soft but stable in air, and does not oxidize as quickly as other rare-earth metals. Its salts are pink in color, and the element has a characteristic absorption spectrum with sharp bands in visible, ultraviolet, and near-infrared light. Otherwise, it looks a lot like the other rare earths. Its sesquioxide is called erbia. The properties of erbium are dictated to some extent by the type and amount of impurities present. Erbium has no known biological role, but it is believed that it may stimulate metabolism.

Erbium is ferromagnetic below 19 K, antiferromagnetic between 19 and 80 K, and paramagnetic above 80 K.

Erbium can form atomic groups in the form of an Er₃N helix, where the distance between the erbium atoms is 0.35 nm. Those clusters can be isolated by encapsulating them in fullerene molecules, as confirmed by transmission electron microscopy.

Chemical Properties

Erbium metal retains its luster in dry air, however develops a patina in moist air and burns to form erbium(III) oxide:

4 Er + 3 O₂ → 2 Er₂O₃

Erbium is quite electropositive and reacts slowly with cold water and fairly quickly with hot water to form erbium hydroxide:

2 Er (s) + 6 H₂O (l) → 2 Er(OH)₃ (aq) + 3 H₂ (g)

Erbium metal reacts with all halogens:

2 Er (s) + 3 F₂ (g) → 2 ErF₃ (s)

2 Er (s) + 3 Cl₂ (g) → 2 ErCl₃ (s) [violet]

2 Er (s) + 3 Br₂ (g) → 2 ErBr₃ (s) [violet]

2 Er (s) + 3 I₂ (g) → 2 ErI₃ (s) [violet]

Erbium dissolves in dilute sulfuric acid, forming solutions containing hydrated Er(III) ions, which exist in hydrated complexes [Er(OH₂)₉] ³⁺ reddish pink:

2 Er (s) + 3 H₂SO₄ (aq) → 2 Er³⁺ (aq) + 3 SO2−
4 (aq) + 3 H₂ (g)

Applications

The applications of erbium are varied; It is commonly used as a photographic filter and due to its resistance it is useful as a metallurgical additive. Other uses of erbium are:

• It is used in nuclear technology as a neutron damper.
• Used as a dopant in fiber optic amplifiers.

• When the vanadium is added as a alloy element, the erb lowers the hardness and improves machining.
• Erbium oxide has a pink color and is sometimes used as a coloring for glass and porcelain enamels. That same glass is often used in sunglasses and cheap jewelry.
• The silicon optic fibers doped with erb are the active element in the fiber amplifiers doped with erb (EDFA), which are widely used in optical communications. The same fibers can be used to create laser fibers. The fiber doped together with erb and iterbium is used in high-power laser fibers, which are gradually replacing the CO laser fibers₂ in welding and cutting applications.

History

Erbium (from Ytterby, a Swedish town) was discovered by Carl Gustaf Mosander in 1843. Mosander separated "yttria" of the mineral gadolinite into three fractions that he named yttria, erbia, and terbia. He named the new element after the town of Ytterby, where large concentrations of yttria and erbium were found. Erbia and terbia, however, were confused at that time. After 1860 terbia was renamed erbia and in 1877 what was known as erbia was renamed terbia. Quite pure erbium oxide (Er₂O₃) was isolated independently by Georges Urbain and Charles James in 1905. It was not until 1934 that sufficiently pure erbium was obtained until when it was possible to reduce the anhydrous chloride with potassium vapor.

Abundance and obtaining

Monazita sand.

The concentration of erbium in the earth's crust is about 2.8 mg/kg and in seawater 0.9 ng/L. This concentration is enough for erbium to rank 45th in abundance of elements in the earth's crust.

Like other rare earths, this element is never found as a free element in nature, but is found bound in monazite sand minerals. Historically it has been very difficult and expensive to separate rare earths from each other in their minerals, but ion exchange chromatography methods developed at the turn of the century XX have greatly reduced the cost of production of all rare earth metals and their chemical compounds.

Like other rare earths, erbium is never found as a free element in nature, but it is found in minerals such as monazite. Historically it has always been difficult and expensive to separate rare earths from one another from their ores but ion exchange based production techniques developed at the turn of the century XX has significantly lowered the cost of all rare earths and their chemical compounds. The main commercial sources of erbium are the minerals xenothyme and euxenite and recently ion adsorption clays from South China. In yttrium-rich samples of this type of ore, yttrium represents about 2/3 of the total mass; and erbia (erbium oxide) represents between 4 and 5%. This amount of erbium is sufficient to confer a characteristic pink color to the solution when the erbium-rich sample is dissolved in an acid medium. This color behavior is remarkably similar to what Mosander and other rare earth scientists might have seen in their gadolinite samples from Ytterby.

Isotopes

Erbium occurs in nature as a mixture of 6 stable isotopes: ¹⁶²Er, ¹⁶⁴Er, ¹⁶⁶Er, ¹⁶⁷ Er, ¹⁶⁸Er, and ¹⁷⁰Er; being ¹⁶⁶Er the most abundant (33.503% abundance). Twenty-nine radioisotopes have been characterized, the most stable being ¹⁶⁹Er with a half-life of 9.4 days, ¹⁷²Er with a half-life of 49.3 hours, ¹⁶⁰Er with one of 28.58 hours, the ¹⁶⁵Er with one of 10.36 hours and the ¹⁷¹Er with one of 7.516 hours. The remaining radioactive isotopes have half-lives of less than 3.5 hours and most of them have half-lives of less than 4 minutes. Erbium also has 13 metastates, the most stable being ^167mEr (t_½ 2.269 seconds).

The atomic mass of erbium isotopes varies between 142.9663 u (¹⁴³Er) and 176.9541 u (¹⁷⁷Er). The main mode of decay for isotopes before the most abundant stable isotope, ¹⁶⁶Er, is electron capture and the main mode for isotopes after it is beta decay. The primary decay products before ¹⁶⁶Er are isotopes of element 67 (holmium) and the primary decay products after are isotopes of element 69 (thulium).

Precautions

Like the other lanthanides, erbium compounds have low or moderate toxicity, although their toxicity has not been investigated in detail. Powdered erbium metal poses a fire and explosion hazard.