Ytterbium is a chemical element with
symbol Yb and atomic number 70. It is
the fourteenth and penultimate element
in the lanthanide series, which is the
basis of the relative stability of its
+2 oxidation state. However, like the
other lanthanides, its most common
oxidation state is +3, seen in its
oxide, halides and other compounds. In
aqueous solution, like compounds of
other late lanthanides, soluble
ytterbium compounds form complexes with
nine water molecules. Because of its
closed-shell electron configuration, its
density and melting and boiling points
differ from those of the other
lanthanides.
In 1878, the Swiss chemist Jean Charles
Galissard de Marignac separated in the
rare earth "erbia" another independent
component, which he called "ytterbia",
for Ytterby, the village in Sweden near
where he found the new component of
erbium. He suspected that ytterbia was a
compound of a new element that he called
"ytterbium". In 1907, the new earth
"lutecia" was separated from ytterbia,
from which the element "lutecium" was
extracted by Georges Urbain, Carl Auer
von Welsbach, and Charles James. After
some discussion, Marignac's name
"ytterbium" was retained. A relatively
pure sample of the metal was obtained
only in 1953. At present, ytterbium is
mainly used as a dopant of stainless
steel or active laser media, and less
often as a gamma ray source.
Natural ytterbium is a mixture of seven
stable isotopes, which altogether are
present at concentrations of 3 parts per
million. This element is mined in China,
the United States, Brazil, and India in
form of the minerals monazite, euxenite,
and xenotime. The ytterbium
concentration is low, because the
element is found among many other rare
earth elements; moreover, it is among
the least abundant ones. Once extracted
and prepared, ytterbium is somewhat
hazardous as an eye and skin irritant.
The metal is a fire and explosion
hazard.
Characteristics 
= Physical properties =
Ytterbium is a soft, malleable and
ductile chemical element that displays a
bright silvery luster when in its pure
form. It is a rare earth element, and it
is readily attacked and dissolved by the
strong mineral acids. It reacts slowly
with cold water and it oxidizes slowly
in air.
Ytterbium has three allotropes labeled
by the Greek letters alpha, beta and
gamma; their transformation temperatures
are −13 °C and 795 °C, although the
exact transformation temperature depends
on the pressure and stress. The beta
allotrope exists at room temperature,
and it has a face-centered cubic crystal
structure. The high-temperature gamma
allotrope has a body-centered cubic
crystalline structure. The alpha
allotrope has a hexagonal crystalline
structure and is stable at low
temperatures. Normally, the beta
allotrope has a metallic electrical
conductivity, but it becomes a
semiconductor when exposed to a pressure
of about 16,000 atmospheres. Its
electrical resistivity increases ten
times upon compression to 39,000
atmospheres, but then drops to about 10%
of its room-temperature resistivity at
about 40,000 atm.
In contrast with the other rare-earth
metals, which usually have
antiferromagnetic and/or ferromagnetic
properties at low temperatures,
ytterbium is paramagnetic at
temperatures above 1.0 kelvin. However,
the alpha allotrope is diamagnetic. With
a melting point of 824 °C and a boiling
point of 1196 °C, ytterbium has the
smallest liquid range of all the metals.
Contrary to most other lanthanides,
which have a close-packed hexagonal
lattice, ytterbium crystallizes in the
face-centered cubic structure. As a
result, its density is significantly
lower than, e.g., those of the
neighboring elements thulium and
lutetium. The melting and boiling points
of ytterbium are also significantly
lower than those of thulium and
lutetium. These properties stem from the
closed-shell electron configuration of
ytterbium, which causes only the two 6s
electrons to be available for metallic
bonding.
= Chemical properties =
Ytterbium metal tarnishes slowly in air.
Finely dispersed ytterbium readily
oxidizes in air and under oxygen.
Mixtures of powdered ytterbium with
polytetrafluoroethylene or
hexachloroethane burn with a luminous
emerald-green flame. Ytterbium reacts
with hydrogen to form various
non-stoichiometric hydrides. Ytterbium
dissolves slowly in water, but quickly
in acids, liberating hydrogen gas.
Ytterbium is quite electropositive, and
it reacts slowly with cold water and
quite quickly with hot water to form
ytterbium(III) hydroxide:
2 Yb + 6 H2O → 2 Yb(OH)3 + 3 H2
Ytterbium reacts with all the halogens:
2 Yb + 3 F2 → 2 YbF3 [white]
2 Yb + 3 Cl2 → 2 YbCl3 [white]
2 Yb + 3 Br2 → 2 YbBr3 [white]
2 Yb + 3 I2 → 2 YbI3 [white]
The ytterbium(III) ion absorbs light in
the near infrared range of wavelengths,
but not in visible light, so the mineral
ytterbia, Yb2O3, is white in color and
the salts of ytterbium are also
colorless. Ytterbium dissolves readily
in dilute sulfuric acid to form
solutions that contain the colorless
Yb(III) ions, which exist as nonahydrate
complexes:
2 Yb + 3 H2SO4 → 2 [Yb(H2O)9]3+ + 3 SO2−
4 + 3 H2
= Yb(II) vs. Yb(III) =
Although usually trivalent, ytterbium
readily forms divalent compounds. This
behavior is unusual to most lanthanides,
which almost exclusively form compounds
with an oxidation state of +3. The +2
state has a valence electron
configuration of 4f14 because the fully
filled f-shell gives more stability. The
yellow-green ytterbium(II) ion is a very
strong reducing agent and decomposes
water, releasing hydrogen gas, and thus
only the colorless ytterbium(III) ion
occurs in aqueous solution. Samarium and
thulium also behave this way in the +2
state, but europium(II) is stable in
aqueous solution. Ytterbium metal
behaves similarly to europium metal and
the alkaline earth metals, dissolving in
ammonia to form blue electride salts.
= Isotopes =
Natural ytterbium is composed of seven
stable isotopes: 168Yb, 170Yb, 171Yb,
172Yb, 173Yb, 174Yb, and 176Yb, with
174Yb being the most abundant isotope,
at 31.8% of the natural abundance). 27
radioisotopes have been observed, with
the most stable ones being 169Yb with a
half-life of 32.0 days, 175Yb with a
half-life of 4.18 days, and 166Yb with a
half-life of 56.7 hours. All of its
remaining radioactive isotopes have
half-lives that are less than two hours
and most of these have half-lives are
less than 20 minutes. Ytterbium also has
12 meta states, with the most stable
being 169mYb.
The isotopes of ytterbium range in
atomic weight from 147.9674 atomic mass
unit for 148Yb to 180.9562 u for 181Yb.
The primary decay mode of ytterbium
isotopes lighter than the most abundant
stable isotope, 174Yb, is electron
capture, and the primary decay mode for
those heavier than 174Yb is beta decay.
The primary decay products of ytterbium
isotopes lighter than 174Yb are thulium
isotopes, and the primary decay products
of ytterbium isotopes with heavier than
174Yb are lutetium isotopes.
Occurrence 
Ytterbium is found with other rare earth
elements in several rare minerals. It is
most often recovered commercially from
monazite sand. The element is also found
in euxenite and xenotime. The main
mining areas are China, the United
States, Brazil, India, Sri Lanka, and
Australia; and reserves of ytterbium are
estimated as one million tonnes.
Ytterbium is normally difficult to
separate from other rare earths, but
ion-exchange and solvent extraction
techniques developed in the mid- to late
20th century have simplified separation.
Known compounds of ytterbium are rare
and have not yet been well
characterized. The abundance of
ytterbium in the Earth's crust is about
3 mg/kg.
As an even-numbered lanthanide, in
accordance with the Oddo-Harkins rule,
ytterbium is significantly more abundant
than its immediate neighbors, thulium
and lutetium, which occur in the same
concentrate at levels of about 0.5%
each. The world production of ytterbium
is only about 50 tonnes per year,
reflecting the fact that ytterbium has
few commercial applications. Microscopic
traces of ytterbium are used as a dopant
in the Yb:YAG laser, a solid-state laser
in which ytterbium is the element that
undergoes stimulated emission of
electromagnetic radiation.
Production 
It is somewhat difficult to separate
ytterbium from other lanthanides due to
its similar properties. As a result, the
process is somewhat long. First,
minerals such as monazite or xenotime
are dissolved into various acids, such
as sulfuric acid. Ytterbium can then be
separated from other lanthanides by ion
exchange, as can other lanthanides. The
solution is then applied to a resin,
which different lanthanides bond to in
different matters. This is then
dissolved using complexing agents, and
due to the different types of bonding
exhibited by the different lanthanides,
it is possible to isolate the compounds.
Ytterbium is separated from other rare
earths either by ion exchange or by
reduction with sodium amalgam. In the
latter method, a buffered acidic
solution of trivalent rare earths is
treated with molten sodium-mercury
alloy, which reduces and dissolves Yb3+.
The alloy is treated with hydrochloric
acid. The metal is extracted from the
solution as oxalate and converted to
oxide by heating. The oxide is reduced
to metal by heating with lanthanum,
aluminium, cerium or zirconium in high
vacuum. The metal is purified by
sublimation and collected over a
condensed plate.
Compounds 
The chemical behavior of ytterbium is
similar to that of the rest of the
lanthanides. Most ytterbium compounds
are found in the +3 oxidation state and
its salts in this oxidation state are
nearly colorless. Like europium,
samarium, and thulium, the trihalides of
ytterbium can be reduced to the
dihalides by hydrogen, zinc dust, or by
the addition of metallic ytterbium. The
+2 oxidation state only occurs in solid
compounds and reacts in some ways
similarly to the alkaline earth metal
compounds; for example, ytterbium(II)
oxide shows the same structure as
calcium oxide.
= Halides =
Ytterbium forms both dihalides and
trihalides with the halogens fluorine,
chlorine, bromine, and iodine. The
dihalides are susceptible to oxidation
to the trihalides at room temperature
and disproportionate to the trihalides
and metallic ytterbium at high
temperature:
3 YbX2 → 2 YbX3 + Yb
Some ytterbium halides are used as
reagents in organic synthesis. For
example, ytterbium(III) chloride is a
Lewis acid and can be used as a catalyst
in the Aldol and Diels–Alder reactions.
Ytterbium(II) iodide may be used, like
samarium(II) iodide, as a reducing agent
for coupling reactions. Ytterbium(III)
fluoride is used as an inert and
non-toxic tooth filling as it
continuously releases fluoride ions,
which are good for dental health, and is
also a good X-ray contrast agent.
= Oxides =
Ytterbium reacts with oxygen to form
ytterbium(III) oxide, which crystallizes
in the "rare-earth C-type sesquioxide"
structure which is related to the
fluorite structure with one quarter of
the anions removed, leading to ytterbium
atoms in two different six coordinate
environments. Ytterbium(III) oxide can
be reduced to ytterbium(II) oxide with
elemental ytterbium, which crystallizes
in the same structure as sodium
chloride.
History 
Ytterbium was discovered by the Swiss
chemist Jean Charles Galissard de
Marignac in the year 1878. While
examining samples of gadolinite,
Marignac found a new component in the
earth then known as erbia, and he named
it ytterbia, for Ytterby, the Swedish
village near where he found the new
component of erbium. Marignac suspected
that ytterbia was a compound of a new
element that he called "ytterbium".
In 1907, the French chemist Georges
Urbain separated Marignac's ytterbia
into two components: neoytterbia and
lutecia. Neoytterbia would later become
known as the element ytterbium, and
lutecia would later be known as the
element lutetium. The Austrian chemist
Carl Auer von Welsbach independently
isolated these elements from ytterbia at
about the same time, but he called them
aldebaranium and cassiopeium; the
American chemist Charles James also
independently isolated these elements at
about the same time. Urbain and Welsbach
accused each other of publishing results
based on the other party. The Commission
on Atomic Mass, consisting of Frank
Wigglesworth Clarke, Wilhelm Ostwald,
and Georges Urbain, which was then
responsible for the attribution of new
element names, settled the dispute in
1909 by granting priority to Urbain and
adopting his names as official ones,
based on the fact that the separation of
lutetium from Marignac's ytterbium was
first described by Urbain; after
Urbain's names were recognized,
neoytterbium was reverted to ytterbium.
The chemical and physical properties of
ytterbium could not be determined with
any precision until 1953, when the first
nearly pure ytterbium metal was produced
by using ion-exchange processes. The
price of ytterbium was relatively stable
between 1953 and 1998 at about
US$1,000/kg.
Applications 
= Source of gamma rays =
The 169Yb isotope, which is created
along with the short-lived 175Yb isotope
by neutron activation during the
irradiation of ytterbium in nuclear
reactors, has been used as a radiation
source in portable X-ray machines. Like
X-rays, the gamma rays emitted by the
source pass through soft tissues of the
body, but are blocked by bones and other
dense materials. Thus, small 169Yb
samples act like tiny X-ray machines
useful for radiography of small objects.
Experiments show that radiographs taken
with a 169Yb source are roughly
equivalent to those taken with X-rays
having energies between 250 and 350 keV.
169Yb is also used in nuclear medicine.
= World's most stable atomic clock =
Ytterbium clocks hold the record for
stability with ticks stable to within
less than two parts in 1 quintillion.
The clocks developed at the National
Institute of Standards and Technology
rely on about 10,000 rare-earth atoms
cooled to 10 microkelvin and trapped in
an optical lattice—a series of
pancake-shaped wells made of laser
light. Another laser that "ticks" 518
trillion times per second provokes a
transition between two energy levels in
the atoms. The large number of atoms is
key to the clocks' high stability.
= Doping of stainless steel =
Ytterbium can also be used as a dopant
to help improve the grain refinement,
strength, and other mechanical
properties of stainless steel. Some
ytterbium alloys have rarely been used
in dentistry.
= Ytterbium as dopant of active media =
The ytterbium +3 ion is used as a doping
material in active laser media,
specifically in solid state lasers and
double clad fiber lasers. Ytterbium
lasers are highly efficient, have long
lifetimes and can generate short pulses;
ytterbium can also easily be
incorporated into the material used to
make the laser. Ytterbium lasers
commonly radiate in the 1.06–1.12 µm
band being optically pumped at
wavelength 900 nm–1 µm, dependently on
the host and application. The small
quantum defect makes ytterbium a
prospective dopant for efficient lasers
and power scaling.
The kinetic of excitations in
ytterbium-doped materials is simple and
can be described within the concept of
effective cross-sections; for most
ytterbium-doped laser materials, the
McCumber relation holds, although the
application to the ytterbium-doped
composite materials was under
discussion.
Usually, low concentrations of ytterbium
are used. At high concentrations, the
ytterbium-doped materials show
photodarkening or even a switch to
broadband emission instead of efficient
laser action. This effect may be related
with not only overheating, but also with
conditions of charge compensation at
high concentrations of ytterbium ions.
Much progress has been made in the power
scaling Lasers and Amplifiers produced
with ytterbium doped optical fibers.
Power levels have increased from the 1
kW regimes due to the advancements in
components as well as the Yb doped
fibers themselves. Fabrication of Low
NA, Large Mode Area fibers enable
achievement of near perfect beam
qualities (M2
