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About Thulium

Thulium Bohr

Thulium was discovered by Swedish chemist Per Teodor Cleve in 1879 when he was looking for impurities in samples of rare earth oxides. He isolated two new oxides, which eventually led to the identification and naming of the elements holmium and thulium. Thulium is named after Thule, Scandinavia.

Despite being very rare and expensive, thulium has several commercial uses. Notably, it is used as a dopant for garnets used as laser gain media, and such lasers are used in medical laser applications such as laser surgery as well as in industrial and military applications. The radioactive isotope thulium-170 can be produced in nuclear reactors and is found in portable x-ray devices used for medical diagnostics and manufacturing quality-control applications. Additionally, this isotope can be used for radiotherapy cancer treatment.

Other specialized roles for thulium exist or are under development. Notably, thulium may be used in high-temperature superconductors, magnetic ceramic materials, personal radiation dosimeters, and phosphors for use in anti-counterfeiting features of modern currency notes.

Thulium is a rare earth element and can theoretically be found in any rare earth containing mineral, but as a heavy rare earth element (HREE) it is more common in HREE-enriched minerals such as xenotime and euxenite. Additionally, thulium is present in ion adsorption clays, which are a major source of HREEs due to their relative ease of processing, despite the low percentage quantities of rare earths they contain. In any source of rare earths, thulium will make up an extremely small percentage of the total rare earth content, as it is one of the rarest of the rare earth elements.

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Elemental Thulium Picture Thulium emits blue light upon excitation, a property that is exploited in flat panel display screens. Thulium also has useful applications in low-levelradiation detection and other luminescence applications, such as halide discharge lamps. Flat panel screens depend critically on bright blue High Purity (99.999%) Thulium Oxide (Tm2O3) Powderemitters. Thulium is available as metal and compounds with purities from 99% to 99.999% (ACS grade to ultra-high purity). Elemental or metallic forms include pellets, rod, wire and granules for evaporation source material purposes. High Purity (99.999%) Thulium (Tm) Sputtering TargetThulium oxide is available in powder and dense pellet form for such uses as optical coating and thin film applications. Oxides tend to be insoluble. Terbium fluorides is another insoluble form for uses in which oxygen is undesirable such as metallurgy, chemical and physical vapor deposition and in some optical coatings. Thulium is also available in soluble forms including chlorides, nitrates and acetates. These compounds can be manufactured as solutions at specified stoichiometries.


Thulium Properties

Thulium (Tm) atomic and molecular weight, atomic number and elemental symbolThulium is a Block F, Group 3, Period 6 element. Thulium Bohr ModelThe number of electrons in each of Thulium's shells is 2, 8, 18, 31, 8, 2 and its electronic configuration is [Xe]4f136s2. In its elemental form, CAS 7440-30-4, thulium has a silvery-white appearance. The thulium atom has a radius of 172.4.pm and its Van der Waals radius is unknown. Thulium is representative of the other lanthanides (rare earths) similar in chemistry to Yttrium. Thulium, first discovered by Theodore Cleve in 1879, is found in small quantities in minerals such as monazite. Thulium is named after "Thule", which is the ancient name of Scandinavia.

Symbol: Tm
Atomic Number: 69
Atomic Weight: 168.93
Element Category: Lanthanide
Group, Period, Block: n/a, 6, f
Color: silvery-gray
Other Names: Tulio
Melting Point: 1545°C, 2813°F, 1818.15 K
Boiling Point: 1950°C, 3542°F, 2223.15 K
Density: 9321 kg/m3
Liquid Density @ Melting Point: 8.56 g·cm3
Density @ 20°C: 9.33 g/cm3
Density of Solid: 9321 kg·m3
Specific Heat: 0.0382 Cal/g/K @ 25 °C
Superconductivity Temperature: N/A
Triple Point: N/A
Critical Point: N/A
Heat of Fusion (kJ·mol-1): 18.4
Heat of Vaporization (kJ·mol-1): 247
Heat of Atomization (kJ·mol-1): 233.43
Thermal Conductivity: 0.169 W/cm/K @ 298.2 K
Thermal Expansion: (r.t.) (poly) 13.3 µm/(m·K)
Electrical Resistivity: 79.0 µΩ-cm @ 25°C
Tensile Strength: 60 MPa
Molar Heat Capacity: 27.03 J·mol-1·K-1
Young's Modulus: 74.0 GPa
Shear Modulus: 30.5 GPa
Bulk Modulus: 44.5 GPa
Poisson Ratio: 0.213
Mohs Hardness: N/A
Vickers Hardness: 520 MPa
Brinell Hardness: 471 MPa
Speed of Sound: N/A
Pauling Electronegativity: 1.25
Sanderson Electronegativity: N/A
Allred Rochow Electronegativity: 1.11
Mulliken-Jaffe Electronegativity: N/A
Allen Electronegativity: N/A
Pauling Electropositivity: 2.75
Reflectivity (%): N/A
Refractive Index: N/A
Electrons: 69
Protons: 69
Neutrons: 100
Electron Configuration: [Xe]4f136s2
Atomic Radius: 176 pm
Atomic Radius,
non-bonded (Å):
2.27
Covalent Radius: 190±10 pm
Covalent Radius (Å): 1.77
Van der Waals Radius: 227 pm
Oxidation States: 2, 3, 4 (basic oxide)
Phase: Solid
Crystal Structure: hexagonal close-packed
Magnetic Ordering: paramagnetic
Electron Affinity (kJ·mol-1) 99.248
1st Ionization Energy: 59.70 kJ·mol-1
2nd Ionization Energy: 1162.66 kJ·mol-1
3rd Ionization Energy: 2284.79 kJ·mol-1
CAS Number: 7440-30-4
EC Number: 231-140-2
MDL Number: MFCD00011281
Beilstein Number: N/A
SMILES Identifier: [Tm]
InChI Identifier: InChI=1S/Tm
InChI Key: FRNOGLGSGLTDKL-UHFFFAOYSA-N
PubChem CID: 23961
ChemSpider ID: 22400
Earth - Total: 35 ppb
Mercury - Total: 27 ppb
Venus - Total: 37 ppb
Earth - Seawater (Oceans), ppb by weight: 0.0002
Earth - Seawater (Oceans), ppb by atoms: 0.000007
Earth -  Crust (Crustal Rocks), ppb by weight: 450
Earth -  Crust (Crustal Rocks), ppb by atoms: 50
Sun - Total, ppb by weight: 0.2
Sun - Total, ppb by atoms: 0.001
Stream, ppb by weight: 0.009
Stream, ppb by atoms: 0.0001
Meterorite (Carbonaceous), ppb by weight: 30
Meterorite (Carbonaceous), ppb by atoms: 3
Typical Human Body, ppb by weight: N/A
Typical Human Body, ppb by atom: N/A
Universe, ppb by weight: 0.1
Universe, ppb by atom: 0.001
Discovered By: Per Teodor Cleve
Discovery Date: 1879
First Isolation: Per Teodor Cleve (1879)

Health, Safety & Transportation Information for Thulium

Thulium is not toxic in its elemental form, however. safety data for Thulium and its compounds can vary widely depending on the form. For potential hazard information, toxicity, and road, sea and air transportation limitations, such as DOT Hazard Class, DOT Number, EU Number, NFPA Health rating and RTECS Class, please see the specific material or compound referenced in the Products tab. The below information applies to elemental (metallic) Thulium.


Safety Data
Material Safety Data Sheet MSDS
Signal Word Danger
Hazard Statements H228-H319-H335
Hazard Codes F,Xi
Risk Codes 15-17-36/37
Safety Precautions 26-36-43
RTECS Number N/A
Transport Information UN 3089 4.1/PG 2
WGK Germany 3
Globally Harmonized System of
Classification and Labelling (GHS)
Exclamation Mark-Acute Toxicity Flame-Flammables

Thulium Isotopes

Naturally occurring thulium (Tm) has 1 stable isotope, 169Tm.

Nuclide Isotopic Mass Half-Life Mode of Decay Nuclear Spin Magnetic Moment Binding Energy (MeV) Natural Abundance
(% by atom)
145Tm 144.97007(43)# 3.1(3) µs Unknown (11/2-) N/A 1121.94 -
146Tm 145.96643(43)# 240(30) ms p to 145Er (6-) N/A 1139.33 -
147Tm 146.96096(32)# 0.58(3) s ß+ to 147Er; p to 146Er 11/2- N/A 1147.41 -
148Tm 147.95784(43)# 0.7(2) s ß+ to 148Er (10+) N/A 1164.81 -
149Tm 148.95272(32)# 0.9(2) s ß+ to 149Er; ß+ + p to 148Ho (11/2-) N/A 1172.89 -
150Tm 149.94996(21)# 3# s ß+ to 150Er (1+) N/A 1190.28 -
151Tm 150.945483(22) 4.17(10) s ß+ to 151Er (11/2-) N/A 1198.36 -
152Tm 151.94442(8) 8.0(10) s ß+ to 152Er (2#)- N/A 1206.44 -
153Tm 152.942012(20) 1.48(1) s a to 149Ho; ß+ to 153Er (11/2-) N/A 1214.52 -
154Tm 153.941568(15) 8.1(3) s ß+ to 154Er; a to 150Ho (2-) N/A 1222.6 -
155Tm 154.939199(14) 21.6(2) s ß+ to 155Er; a to 151Ho (11/2-) N/A 1239.99 -
156Tm 155.938980(17) 83.8(18) s ß+ to 156Er; a to 152Ho 2- N/A 1248.07 -
157Tm 156.93697(3) 3.63(9) min ß+ to 157Er 1/2+ N/A 1256.15 -
158Tm 157.936980(27) 3.98(6) min ß+ to 158Er 2- N/A 1264.23 -
159Tm 158.93498(3) 9.13(16) min ß+ to 159Er 5/2+ N/A 1272.31 -
160Tm 159.93526(4) 9.4(3) min ß+ to 160Er 1- N/A 1280.39 -
161Tm 160.93355(3) 30.2(8) min ß+ to 161Er 7/2+ N/A 1288.46 -
162Tm 161.933995(28) 21.70(19) min ß+ to 162Er 1- N/A 1296.54 -
163Tm 162.932651(6) 1.810(5) h ß+ to 163Er 1/2+ N/A 1304.62 -
164Tm 163.93356(3) 2.0(1) min ß+ to 164Er 1+ N/A 1312.7 -
165Tm 164.932435(4) 30.06(3) h EC to 165Er 1/2+ 0.139 1320.78 -
166Tm 165.933554(13) 7.70(3) h EC to 166Er 2+ 0.092 1328.86 -
167Tm 166.9328516(29) 9.25(2) d EC to 167Er 1/2+ -0.197 1336.94 -
168Tm 167.934173(3) 93.1(2) d EC to 168Er; ß- to 168Yb 3+ 0.23 1345.01 -
169Tm 168.9342133(27) Observationally Stable - 1/2+ -0.2316 1353.09 100
170Tm 169.9358014(27) 128.6(3) d EC to 170Er; ß- to 170Yb 1- 0.2476 1361.17 -
171Tm 170.9364294(28) 1.92(1) y ß- to 171Yb 1/2+ -0.2303 1369.25 -
172Tm 171.938400(6) 63.6(2) h ß- to 172Yb 2- N/A 1377.33 -
173Tm 172.939604(5) 8.24(8) h ß- to 173Yb (1/2+) N/A 1385.41 -
174Tm 173.94217(5) 5.4(1) min ß- to 174Yb (4)- N/A 1384.17 -
175Tm 174.94384(5) 15.2(5) min ß- to 175Yb (1/2+) N/A 1392.25 -
176Tm 175.94699(11) 1.85(3) min ß- to 176Yb (4+) N/A 1400.33 -
177Tm 176.94904(32)# 90(6) s ß- to 177Yb (7/2-) N/A 1408.41 -
178Tm 177.95264(43)# 30# s ß- to 178Yb N/A N/A 1407.17 -
179Tm 178.95534(54)# 20# s ß- to 179Yb 1/2+# N/A 1415.25 -
Thulium Elemental Symbol

Recent Research & Development for Thulium

  • Multi-kW peak power acousto-optically tunable thulium-doped fiber laser system. Gutty F, Grisard A, Joly A, Larat C, Papillon-Ruggeri D, Lallier E. Opt Express. 2015 Mar 9
  • All-fiber multiwavelength thulium-doped laser assisted by four-wave mixing in highly germania-doped fiber. Huang T, Li X, Shum PP, Wang QJ, Shao X, Wang L, Li H, Wu Z, Dong X. Opt Express. 2015 Jan 12
  • Reversible C-C coupling in phenanthroline complexes of divalent samarium and thulium. Nocton G, Ricard L. Chem Commun (Camb). 2015 Feb 28
  • Elemental Bioimaging of Thulium in Mouse Tissues by Laser Ablation-ICPMS as a Complementary Method to Heteronuclear Proton Magnetic Resonance Imaging for Cell Tracking Experiments. Reifschneider O, Wentker KS, Strobel K, Schmidt R, Masthoff M, Sperling M, Faber C, Karst U. Anal Chem. 2015 Apr 21
  • Stretched-pulse and solitonic operation of an all-fiber thulium/holmium-doped fiber laser. Kadel R, Washburn BR. Appl Opt. 2015 Feb 1
  • Efficacy and Safety of 120-W Thulium:Yttrium-Aluminum-Garnet Vapoenucleation of Prostates Compared with Holmium Laser Enucleation of Prostates for Benign Prostatic Hyperplasia. Hong K, Liu YQ, Lu J, Xiao CL, Huang Y, Ma LL. Chin Med J (Engl). 2015 5th Apr
  • Pulse-shaping mechanisms in passively mode-locked thulium-doped fiber lasers. Li H, Liu J, Cheng Z, Xu J, Tan F, Wang P. Opt Express. 2015 Mar 9
  • Collateral damage to the ureter and Nitinol stone baskets during thulium fiber laser lithotripsy. Wilson CR, Hardy LA, Irby PB, Fried NM. Lasers Surg Med. 2015 Apr 14.
  • A prospective, randomized comparison of a 1940 nm and a 2013 nm thulium: yttrium-aluminum-garnet laser device for Thulium VapoEnucleation of the prostate (ThuVEP): First results. Tiburtius C, Gross AJ, Netsch C. Indian J Urol. 2015 Jan-Mar: Indian J Urol
  • All-fiber multiwavelength thulium-doped laser assisted by four-wave mixing in highly germania-doped fiber. Huang T, Li X, Shum PP, Wang QJ, Shao X, Wang L, Li H, Wu Z, Dong X. Opt Express. 2015 Jan 12: Opt Express