Erbium is a chemical element; it has symbol Er and atomic number 68. A silvery-white solid metal when artificially isolated, natural erbium is always found in chemical combination with other elements. It is a lanthanide, a rare-earth element, originally found in the gadolinite mine in Ytterby, Sweden, which is the source of the element's name.
Erbium's principal uses involve its pink-colored Er3+ ions, which have optical fluorescent 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 and then radiate light at in stimulated emission. This process results in an unusually mechanically simple laser optical amplifier for signals transmitted by fiber optics. The wavelength is especially important for optical communications because standard single mode optical fibers have minimal loss at this particular wavelength.
In addition to optical fiber amplifier-lasers, a large variety of medical applications (e.g. dermatology, dentistry) rely on the erbium ion's emission (see ) when lit at another wavelength, which is highly absorbed in water in tissues, making its effect very superficial. Such shallow tissue deposition of laser energy is helpful in laser surgery, and for the efficient production of steam which produces enamel ablation by common types of dental laser.
Characteristics
Physical properties
A trivalent element, pure erbium
metal is malleable (or easily shaped), soft yet stable in air, and does not
oxidation as quickly as some other rare-earth metals. Its salts are rose-colored, and the element has characteristic sharp absorption spectra bands in
visible light,
ultraviolet, and near
infrared.
Otherwise it looks much like the other rare earths. Its
sesquioxide is called
erbia. Erbium's properties are to a degree dictated by the kind and amount of impurities present. Erbium does not play any known biological role, but is thought to be able to stimulate
metabolism.
Erbium is Ferromagnetism below 19 K, antiferromagnetic between 19 and 80 K and Paramagnetism above 80 K.
Erbium can form propeller-shaped atomic clusters Er3N, where the distance between the erbium atoms is 0.35 nm. Those clusters can be isolated by encapsulating them into fullerene molecules, as confirmed by transmission electron microscopy.
Like most rare-earth elements, erbium is usually found in the +3 oxidation state. However, it is possible for erbium to also be found in the 0, +1 and +2
Chemical properties
Erbium metal retains its luster in dry air, however will tarnish slowly in moist air and burns readily to form erbium(III) oxide:
- 4 Er + 3 O2 → 2 Er2O3
Erbium is quite electropositive and reacts slowly with cold water and quite 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 the halogens:
- 2 Er (s) + 3 F2 (g) → 2 ErF3 (s) pink
- 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 readily in dilute sulfuric acid to form solutions containing hydrated Er(III) ions, which exist as rose red Er(OH2)93+ hydration complexes:
- 2 Er (s) + 3 H2SO4 (aq) → 2 Er3+ (aq) + 3 (aq) + 3 H2 (g)
Isotopes
Naturally occurring erbium is composed of 6 stable
, Er, Er, Er, Er, Er, and Er, with Er being the most abundant (33.503% natural abundance). 32
have been characterized, with the most stable being Er with a
half-life of , Er with a half-life of , Er with a half-life of , Er with a half-life of , and Er with a half-life of . All of the remaining
radioactive isotopes have half-lives that are less than , and the majority of these have half-lives that are less than 4 minutes. This element also has 26
, with the most stable being Er with a half-life of .
The isotopes of erbium range in Er to Er. The primary decay mode before the most abundant stable isotope, Er, is electron capture, and the primary mode after is beta decay. The primary before Er are element 67 (holmium) isotopes, and the primary products after are element 69 (thulium) isotopes.
Er has been identified as useful for use in Auger therapy, as it decays via electron capture and emits no Gamma ray. It can also be used as a radioactive tracer to label Antibody and Peptide, though it cannot be detected by any kind of imaging for the study of its biological distribution. The isotope can be produced via the bombardment of Er with Thulium or Er with Holmium, the latter of which is more convenient due to Ho being a stable primordial isotope, though it requires an initial supply of Er.
Compounds
Oxides
Erbium(III) oxide (also known as erbia) is the only known oxide of erbium, first isolated by Carl Gustaf Mosander in 1843, and first obtained in pure form in 1905 by
Georges Urbain and Charles James.
It has a cubic structure resembling the
bixbyite motif. The Er
3+ centers are octahedral.
The formation of erbium oxide is accomplished by burning erbium metal,
erbium oxalate or other
oxyacid salts of erbium.
Erbium oxide is insoluble in water and slightly soluble in heated mineral acids. The pink-colored compound is used as a
phosphor activator and to produce
infrared-absorbing glass.
Halides
Erbium(III) fluoride is a pinkish powder
that can be produced by reacting erbium(III) nitrate and ammonium fluoride.
It can be used to make infrared light-transmitting materials
and up-converting luminescent materials,
and is an intermediate in the production of erbium metal prior to its reduction with calcium.
Erbium(III) chloride is a violet compounds that can be formed by first heating erbium(III) oxide and ammonium chloride to produce the
ammonium salt of the pentachloride (NH
42ErCl
5) then heating it in a vacuum at 350-400 °C.
[
] It forms crystals of the type, with
monoclinic crystals and the
point group C2/m.
Erbium(III) chloride hexahydrate also forms monoclinic crystals with the point group of
P2/
n (
P2/
c) -
C42h. In this compound, erbium is octa-coordinated to form ions with the isolated completing the structure.
Erbium(III) bromide is a violet solid. It is used, like other metal bromide compounds, in water treatment, chemical analysis and for certain crystal growth applications.
Organoerbium compounds
Organoerbium compounds are very similar to those of the other lanthanides, as they all share an inability to undergo
pi backbonding. They are thus mostly restricted to the mostly ionic cyclopentadienides (isostructural with those of lanthanum) and the σ-bonded simple alkyls and aryls, some of which may be polymeric.
[Greenwood and Earnshaw, pp. 1248–9]
History
Erbium (for
Ytterby, a village in
Sweden) was discovered by Carl Gustaf Mosander in 1843.
[ Note: The first part of this article, which does NOT concern erbium, is a translation of: C. G. Mosander (1842) "Något om Cer och Lanthan" Some, Förhandlingar vid de Skandinaviske naturforskarnes tredje möte (Stockholm) Transactions, vol. 3, pp. 387–398.] Mosander was working with a sample of what was thought to be the single metal oxide
yttria, derived from the mineral
gadolinite. He discovered that the sample contained at least two metal oxides in addition to pure yttria, which he named "
erbia" and "
terbia" after the village of Ytterby where the gadolinite had been found. Mosander was not certain of the purity of the oxides and later tests confirmed his uncertainty. Not only did the "yttria" contain yttrium, erbium, and terbium; in the ensuing years, chemists, geologists and spectroscopists discovered five additional elements:
ytterbium,
scandium,
thulium,
holmium, and
gadolinium.
Erbia and terbia, however, were confused at this time. Marc Delafontaine, a Swiss spectroscopist, mistakenly switched the names of the two elements in his work separating the oxides erbia and terbia. After 1860, terbia was renamed erbia and after 1877 what had been known as erbia was renamed terbia.
Occurrence
The concentration of erbium in the Earth crust is about 2.8 mg/kg and in seawater 0.9 ng/L.
(Concentration of less abundant elements may vary with location by several orders of magnitude
[Abundance of elements in the earth’s crust and in the sea, CRC Handbook of Chemistry and Physics, 97th edition (2016–2017), p. 14-17] making the relative abundance unreliable). Like other rare earths, this element is never found as a free element in nature but is found in
monazite and bastnäsite ores.
It has historically been very difficult and expensive to separate rare earths from each other in their ores but
ion-exchange chromatography methods
[Early paper on the use of displacement ion-exchange chromatography to separate rare earths: ] developed in the late 20th century have greatly reduced the cost of production of all rare-earth metals and their chemical compounds.
The principal commercial sources of erbium are from the minerals xenotime and euxenite, and most recently, the ion adsorption clays of southern China. Consequently, China has now become the principal global supplier of this element.[Asad, F. M. M. (2010). Optical Properties of Dye Sensitized Zinc Oxide Thin Film Deposited by Sol-gel Method (Doctoral dissertation, Universiti Teknologi Malaysia).] In the high-yttrium versions of these ore concentrates, yttrium is about two-thirds of the total by weight, and erbia is about 4–5%. When the concentrate is dissolved in acid, the erbia liberates enough erbium ion to impart a distinct and characteristic pink color to the solution. This color behavior is similar to what Mosander and the other early workers in the lanthanides saw in their extracts from the gadolinite minerals of Ytterby.
Production
Crushed minerals are attacked by hydrochloric or
sulfuric acid that transforms insoluble rare-earth oxides into soluble chlorides or sulfates. The acidic filtrates are partially neutralized with caustic soda (sodium hydroxide) to pH 3–4.
Thorium precipitates out of solution as hydroxide and is removed. After that the solution is treated with
ammonium oxalate to convert rare earths into their insoluble
. The oxalates are converted to oxides by annealing. The oxides are dissolved in
nitric acid that excludes one of the main components,
cerium, whose oxide is insoluble in HNO
3. The solution is treated with magnesium nitrate to produce a crystallized mixture of
of rare-earth metals. The salts are separated by
ion exchange. In this process, rare-earth ions are sorbed onto suitable ion-exchange resin by exchange with hydrogen, ammonium or cupric ions present in the resin. The rare earth ions are then selectively washed out by suitable complexing agent.
Erbium metal is obtained from its oxide or salts by heating with
calcium at under argon atmosphere.
Applications
Lasers and optics
A large variety of medical applications (i.e., dermatology, dentistry) utilize erbium ion's emission (see ), which is highly absorbed in water (absorption coefficient about ). Such shallow tissue deposition of laser energy is necessary for laser surgery, and the efficient production of steam for laser enamel ablation in dentistry.
Common applications of erbium lasers in dentistry include ceramic cosmetic dentistry and removal of brackets in orthodontic braces; such laser applications have been noted as more time-efficient than performing the same procedures with rotary dental instruments.
Erbium-doped optical fibers are the active element in erbium-doped fiber amplifiers (EDFAs), which are widely used in optical communications.
Other applications
When added to
vanadium as an
alloy, erbium lowers hardness and improves workability.
An erbium-
nickel alloy Er
3Ni has an unusually high specific heat capacity at liquid-helium temperatures and is used in
cryocoolers; a mixture of 65% Er
3cobalt and 35% Er
0.9Ytterbium0.1Ni by volume improves the specific heat capacity even more.
Erbium oxide has a pink color, and is sometimes used as a colorant for glass, cubic zirconia and porcelain. The glass is then often used in sunglasses and jewellery,[Stwertka, Albert. A Guide to the Elements, Oxford University Press, 1996, p. 162. ] or where infrared absorption is needed.
Erbium is used in Nuclear power technology in neutron-absorbing .
Biological role and precautions
Erbium does not have a biological role, but erbium salts can stimulate
metabolism. Humans consume 1 milligram of erbium a year on average. The highest concentration of erbium in humans is in the
, but there is also erbium in the human
kidneys and
liver.
Erbium is slightly toxic if ingested, but erbium compounds are generally not toxic.
Metallic erbium in dust form presents a fire and explosion hazard.
Further reading
-
Guide to the Elements – Revised Edition, Albert Stwertka (Oxford University Press; 1998), .
External links
