Lutetium

Lutetium — Material Page

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Lutetium (Lu, atomic number 71) is the last and heaviest of the lanthanides — a dense (9.841 g/cm³), silvery-white HCP metal with the highest melting point (1,663 °C), highest Young's modulus (69 GPa), and greatest hardness of any lanthanide, reflecting the full contraction of the 4f shell (4f¹⁴) and the dominance of 5d bonding in its metallic state. Lu has two natural isotopes: ¹⁷⁵Lu (97.41%, stable, I = 7/2, NMR-active) and ¹⁷⁶Lu (2.59%, radioactive, β⁻, t½ = 3.76 × 10¹⁰ yr). The ¹⁷⁶Lu→¹⁷⁶Hf decay is the basis of the Lu-Hf geochronometer, one of the principal chronometers for dating garnet-bearing metamorphic and igneous rocks. Lu is the rarest of the non-radioactive lanthanides (~0.5 ppm crustal abundance) and is extracted primarily from xenotime (YPO₄) and ion-adsorption clay deposits as a minor fraction of total REE production.

The dominant and most rapidly growing application of Lu is in nuclear medicine: ¹⁷⁷Lu (t½ = 6.647 days, β⁻ 0.498 MeV max + 208 keV γ), produced by neutron irradiation of ¹⁷⁶Lu or ¹⁷⁶Yb targets, is the active radionuclide in two FDA-approved targeted radiotherapy drugs — ¹⁷⁷Lu-DOTATATE (Lutathera, AAA/Novartis, 2018) for somatostatin receptor-positive gastroenteropancreatic neuroendocrine tumors (GEP-NETs), and ¹⁷⁷Lu-PSMA-617 (Pluvicto, AAA/Novartis, 2022) for metastatic castration-resistant prostate cancer (mCRPC). ¹⁷⁷Lu's β⁻ delivers localized tissue dose (~1–2 mm mean tissue range) while the 208 keV γ enables simultaneous SPECT/CT imaging for dosimetry and response monitoring — combining therapy and imaging in a single radiopharmaceutical (theranostic). The commercial success of Lutathera and Pluvicto has driven a major expansion in ¹⁷⁷Lu production infrastructure globally, making Lu supply a strategically important REE issue.

Lu₂SiO₅:Ce (LSO) and Lu₂(1-x)Y₂xSiO₅:Ce (LYSO) are the dominant scintillator crystals in commercial PET scanners — their high density (7.4 g/cm³), fast Ce³⁺ decay time (~40 ns), high light yield (~32 photons/keV), and good energy resolution make them the preferred detector material for time-of-flight PET (TOF-PET), where LYSO's 200–250 ps coincidence time resolution enables significant image quality improvements over older BGO-based systems. Lu is also used as a sintering aid in Si₃N₄ and SiAlON ceramics (Lu₂O₃ additions suppress grain boundary phases), as a catalyst for alkylation and polymerization reactions, and in Lu-aluminum garnet (LuAG:Ce, LuAG:Pr) scintillator crystals for high-energy physics calorimeters.

General Properties

Property	Value	Notes
Atomic Number	71	4f¹⁴5d¹6s²; +3 is the only stable oxidation state. The completely filled 4f shell (4f¹⁴) makes Lu³⁺ (4f¹⁴) diamagnetic — Lu has no 4f magnetic contribution, giving it the simplest electronic structure of any lanthanide and making it useful as a non-magnetic reference in studies of 4f magnetism. ¹⁷⁵Lu (I = 7/2) is NMR-active.
Atomic Mass	174.967 u	Two natural isotopes: ¹⁷⁵Lu (97.41%, stable) and ¹⁷⁶Lu (2.59%, β⁻, t½ = 3.76 × 10¹⁰ yr, producing ¹⁷⁶Hf). The ¹⁷⁶Lu/¹⁷⁵Lu → ¹⁷⁶Hf/¹⁷⁷Hf Lu-Hf isotopic system is a key geochronometer for garnet-bearing rocks; garnet strongly fractionates Lu from Hf, giving large spread in ¹⁷⁶Lu/¹⁷⁷Hf ratios across coexisting minerals useful for isochron age determinations.
Density (20 °C)	9.841 g/cm³	Highest density of any lanthanide — direct consequence of the full lanthanide contraction. Relevant to LSO/LYSO scintillator crystal density calculations (host crystal density determines X-ray/γ stopping power in PET detectors) and to Lu₂O₃ ceramic sintering aid volume fraction calculations.
Melting Point	1,663 °C (1,936 K)	Highest melting point of any lanthanide. Requires vacuum arc or electron-beam melting for high-purity Lu metal production; Lu is produced by metallothermic reduction of LuF₃ with Ca. The high melting point also applies to Lu₂O₃ (mp ~2,490 °C), making it a candidate refractory oxide for high-temperature structural ceramics.
Boiling Point	3,402 °C	High boiling point consistent with Lu's strong metallic bonding. Relevant to Lu evaporation source preparation for MBE deposition of Lu-doped oxide films and to LuAG and LSO crystal growth from Lu₂O₃-containing oxide melts by Czochralski pulling.
Thermal Conductivity	16.4 W/m·K	Moderate-low conductivity for a heavy lanthanide. Relevant to thermal management of Lu-based scintillator crystal arrays in PET detectors operating under continuous γ irradiation and to Lu₂O₃ sintering aid thermal conductivity contributions in Si₃N₄ ceramics.
Electrical Resistivity	91 nΩ·m (20 °C)	Moderate resistivity typical of heavy lanthanides. Lu does not show anomalous magnetic resistivity contributions (it is diamagnetic), giving a smooth, nearly linear resistivity-temperature relationship — useful as a non-magnetic reference in comparative resistivity studies of lanthanide metals.
Crystal Structure	HCP (α-Lu), a = 3.505 Å, c = 5.551 Å	HCP structure; the smallest lattice parameters of any lanthanide, reflecting complete lanthanide contraction. Lu is the end-member of the lanthanide series and has the smallest ionic radius (0.861 Å in 6-coordination for Lu³⁺), closest to the transition metals, which accounts for its relatively high hardness and melting point compared to earlier lanthanides.

Mechanical Properties

Property	Value	Notes
Tensile Strength	~275 MPa	The highest tensile strength of any lanthanide, consistent with Lu's complete 4f shell and strong 5d metallic bonding. Lu can be machined and rolled into foil under inert atmosphere, and is used in sputtering target and scintillator precursor form.
Young's Modulus	69 GPa	Highest Young's modulus of any lanthanide — reflects the strong metallic bonding of Lu with its fully contracted 4f shell. Used in thermal stress modeling of LuAG and LYSO scintillator crystals under thermal cycling in detector arrays.
Hardness	~80–95 HB (annealed)	Hardest of the lanthanide metals — significantly harder than lighter lanthanides such as La (~35 HB) or Ce (~25 HB). Lu can still be machined under inert atmosphere but requires more robust tooling than lighter lanthanides.
Elongation at Break	~15%	Moderate ductility for a heavy lanthanide. Lu can be rolled into foil and drawn into wire under Ar; high-purity Lu foil is used for ¹⁷⁷Lu production targets (¹⁷⁶Lu enriched foil for high specific-activity ¹⁷⁷Lu production) and for sputtering targets in Lu-doped oxide film research.
Poisson's Ratio	0.26	Typical for an HCP lanthanide. Used in elastic modeling of Lu₂O₃ sintering aid contributions to Si₃N₄ ceramic mechanical properties and in LuAG crystal thermal stress calculations.

Chemical Properties

Property	Value / Behavior	Notes
Oxidation States	+3 only (Lu³⁺: LuCl₃, Lu₂O₃, Lu(NO₃)₃); diamagnetic (4f¹⁴)	Lu³⁺ has the smallest ionic radius of any lanthanide (0.861 Å, 6-coordinate), giving it the highest charge density and strongest Lewis acidity among the trivalent lanthanides — relevant to its use as a Lewis acid catalyst for Diels-Alder reactions and polymerization. Lu³⁺ DOTA chelate (Lu-DOTA) is a key building block for ¹⁷⁷Lu radiopharmaceuticals: Lu-DOTA-TATE (Lutathera) and Lu-DOTA-PSMA-617 (Pluvicto).
Corrosion Resistance	Moderate; forms stable Lu₂O₃ surface layer in dry air; reacts slowly with water; dissolves in dilute acids	More air-stable than the light lanthanides (La, Ce, Pr) due to the protective adherence of the Lu₂O₃ surface layer. Lu metal should still be stored under inert atmosphere for prolonged periods; fine powder is potentially flammable.
Surface Oxide	Lu₂O₃ (cubic C-type, white) forms in air	Lu₂O₃ (mp ~2,490 °C) is a refractory oxide used as a sintering aid in Si₃N₄ and SiAlON ceramics, as a high-κ gate dielectric candidate (κ ~ 10–12), and as the primary precursor for LSO/LYSO scintillator crystal growth and for ¹⁷⁷Lu radiopharmaceutical synthesis (Lu₂O₃ dissolved in HCl to give LuCl₃ for radiolabeling).

Identifier	Value
Symbol	Lu
Atomic Number	71
CAS Number	7439-94-3
UN Number	UN3089 (powder)
EINECS Number	231-103-0

Isotope	Type	Notes
¹⁷⁵Lu	Stable	97.41% natural abundance; I = 7/2, NMR-active. ¹⁷⁵Lu NMR (I = 7/2; large quadrupole moment; chemical shift range ~3,000 ppm) is used to characterize Lu³⁺ coordination in DOTA-based radiopharmaceutical chelate complexes (Lutathera, Pluvicto), Lu-doped scintillator glass, and Lu₂O₃ ceramic grain boundary phases. Thermal neutron σ = 21 barn; ¹⁷⁵Lu(n,γ)¹⁷⁶Lu contributes a small amount to ¹⁷⁶Lu activation in irradiated Lu targets used for ¹⁷⁷Lu production.
¹⁷⁶Lu	Radioactive	2.59% natural abundance; I = 7; t½ = 3.76 × 10¹⁰ yr; β⁻ decay to ¹⁷⁶Hf (E_max = 596 keV) + 307 keV γ. The ¹⁷⁶Lu/¹⁷⁵Lu → ¹⁷⁶Hf/¹⁷⁷Hf Lu-Hf isotopic system is widely used in geochronology: garnet, zircon, and pyroxene strongly partition Lu relative to Hf, enabling isochron dating of garnet-bearing metamorphic rocks (eclogites, granulites), mantle peridotites, and chondritic meteorites. ¹⁷⁶Lu is also the direct precursor for no-carrier-added (nca) ¹⁷⁷Lu production via ¹⁷⁶Lu(n,γ)¹⁷⁷Lu (σ = 2,065 barn) in high-flux research reactors — enriched ¹⁷⁶Lu targets (97–99.7% ¹⁷⁶Lu) are irradiated to produce high specific-activity ¹⁷⁷Lu for Lutathera and Pluvicto radiopharmaceutical manufacturing. Additionally, ¹⁷⁶Yb(n,γ)¹⁷⁷Yb → ¹⁷⁷Lu (β⁻) provides an alternative production route giving chemically separable, ultra-high specific-activity ¹⁷⁷Lu for next-generation radiopharmaceutical applications.
¹⁷⁷Lu	Radioactive (produced)	Not naturally occurring; t½ = 6.647 days; β⁻ (E_max = 498 keV, mean tissue range ~0.7 mm) + 208 keV γ (11% abundance, suitable for SPECT imaging). Produced by neutron irradiation of ¹⁷⁶Lu or ¹⁷⁶Yb targets. Active radionuclide in two FDA-approved targeted radiotherapy drugs: ¹⁷⁷Lu-DOTATATE (Lutathera) for GEP-NETs and ¹⁷⁷Lu-PSMA-617 (Pluvicto) for mCRPC. The 208 keV γ allows simultaneous SPECT/CT dosimetry imaging alongside β⁻ tumor dose delivery — the defining feature of Lu-177 theranostic radiopharmaceuticals. Global ¹⁷⁷Lu production is expanding rapidly at reactor sites in Europe, North America, and Asia to meet growing clinical demand.

Scientific & Research Applications

Use Case	Form Typically Used	Description
¹⁷⁷Lu Radiopharmaceutical Research	¹⁷⁶Lu-enriched Lu₂O₃ or LuCl₃ targets (97–99.7% ¹⁷⁶Lu); no-carrier-added ¹⁷⁷LuCl₃ post-irradiation	¹⁷⁷Lu-labeled peptide and small-molecule conjugates are the most actively researched targeted radiotherapy platform in nuclear medicine. Beyond the approved Lutathera and Pluvicto drugs, research is active in ¹⁷⁷Lu-labeled antibodies (radioimmunotherapy), ¹⁷⁷Lu-labeled bone-targeting bisphosphonates, and ¹⁷⁷Lu-labeled nanoparticles for combination therapy/imaging. The 6.6-day half-life, soft β⁻, and imageable γ make ¹⁷⁷Lu near-ideal for peptide receptor radionuclide therapy (PRRT).
LSO / LYSO Scintillator Research	Lu₂SiO₅:Ce (LSO) and Lu₂(1-x)Y₂xSiO₅:Ce (LYSO) single crystals (0.1–0.5 mol% Ce); grown from Lu₂O₃ + SiO₂ + Y₂O₃ melts by Czochralski	LSO and LYSO are the benchmark scintillators for time-of-flight PET (TOF-PET) — LYSO's ~200–250 ps coincidence time resolution (vs. ~500 ps for BGO) directly improves image signal-to-noise ratio. Research addresses LYSO crystal growth optimization for large arrays, new co-dopants (Sm, Ca) to improve timing resolution below 200 ps, and LYSO-SiPM detector modules for next-generation total-body PET systems.
Lu-Hf Geochronology	Lu and Hf isotope ratio measurement by MC-ICP-MS; garnet mineral separation from rock samples	The ¹⁷⁶Lu→¹⁷⁶Hf decay system (t½ = 3.76 × 10¹⁰ yr) is widely applied to date garnet growth in metamorphic and igneous rocks — garnet's strong Lu/Hf fractionation gives well-defined isochrons for eclogite, granulite, and kimberlite dating. Combined Lu-Hf and Sm-Nd garnet ages constrain the timing of high-pressure metamorphism in collisional orogens and provide pressure-temperature-time paths for tectonic reconstructions.
LuAG Scintillator & Laser Crystal Research	Lu₃Al₅O₁₂:Ce (LuAG:Ce) and Lu₃Al₅O₁₂:Pr (LuAG:Pr) single crystals grown by Czochralski or micro-pulling-down	LuAG:Ce (~520 nm emission, ~55 ns decay) and LuAG:Pr (~310 nm, <20 ns decay) are fast scintillators for high-energy physics (calorimetry at CERN), industrial CT, and synchrotron X-ray imaging. LuAG:Ce transparent ceramic alternatives to single crystals are actively researched for cost reduction. LuAG is also an efficient laser host for Ho³⁺ and Tm³⁺ mid-IR laser operation.
Lewis Acid Catalysis Research	Lu(OTf)₃ (lutetium triflate), Lu(III) β-diketonates, LuCl₃ in aqueous and organic media	Lu³⁺'s small ionic radius and high charge density make it the strongest Lewis acid among the trivalent lanthanide triflates. Lu(OTf)₃ catalyzes Diels-Alder reactions, Mukaiyama aldol additions, allylation reactions, and ring-opening polymerization of lactide/caprolactone in water — an advantage for green chemistry since lanthanide triflates are water-stable Lewis acids unlike many conventional Lewis acid catalysts.

Industrial & Commercial Applications

Sector	Form / Grade Used	Description
¹⁷⁷Lu Radiopharmaceuticals (Lutathera & Pluvicto)	¹⁷⁷LuCl₃ solution (no-carrier-added, produced from ¹⁷⁶Lu-enriched Lu₂O₃ targets); 99.9%+ Lu₂O₃ precursor	Lutathera (¹⁷⁷Lu-DOTATATE) received FDA approval in 2018 for somatostatin receptor-positive GEP-NETs, demonstrating 79% reduction in risk of disease progression or death vs. octreotide in the NETTER-1 trial. Pluvicto (¹⁷⁷Lu-PSMA-617) received FDA approval in 2022 for mCRPC, demonstrating 38% reduction in risk of death vs. standard of care in the VISION trial. Combined global market for Lu-177 radiopharmaceuticals exceeded $1B/year by 2024 and is growing rapidly.
PET Scanner Scintillators (LYSO/LSO)	LYSO crystal arrays (Lu₂(1-x)Y₂xSiO₅:Ce, x ≈ 0.1–0.3); 99.9%+ Lu₂O₃ precursor	LYSO is the dominant detector crystal in modern clinical PET scanners (Siemens Biograph, GE Discovery MI, United Imaging). TOF-PET systems using LYSO achieve ~200–250 ps timing resolution, improving effective sensitivity by ~4–10× compared to non-TOF BGO systems of equivalent size. Each full-ring PET scanner contains ~1–3 kg of Lu in LYSO crystal arrays; total-body PET systems (uExplorer, PennPET Explorer) use up to ~10 kg Lu per scanner.
Si₃N₄ Ceramic Sintering Aid	Lu₂O₃ powder (0.5–5 wt% addition to Si₃N₄ pressing powder; 99%+ purity)	Lu₂O₃ as a sintering aid in Si₃N₄ ceramics promotes densification while forming a more refractory grain boundary glassy phase than Y₂O₃, improving high-temperature creep resistance above 1,200 °C. Lu-Si₃N₄ ceramics maintain strength and oxidation resistance at temperatures where Y-Si₃N₄ softens, relevant to gas turbine and cutting tool applications.
Optical & High-Temperature Ceramics	Lu₂O₃ transparent ceramics (hot-pressed or SPS-sintered; 99.9%+ Lu₂O₃); LuAG:Ce ceramic scintillators	Transparent Lu₂O₃ ceramics (cubic structure, no birefringence) are studied for high-power laser windows and scintillator applications requiring the high density and refractive index of Lu₂O₃ in a scalable ceramic form. LuAG:Ce transparent ceramics are pursued as cost-effective alternatives to single-crystal LuAG for industrial X-ray CT and security screening detector arrays.

Purity	Applications	Notes
99% (2N)	Used in optical applications, industrial catalysts, and basic research.	Standard grade suitable for general scientific and industrial use.
99.9% (3N)	Preferred in nuclear medicine, laser crystal growth, and scintillator development.	High-purity grade for advanced technology and precision research.

Synonym / Alternative Name	Context
Lu	Chemical symbol; from Lutetia (Latin for Paris), named independently by Georges Urbain and Carl Auer von Welsbach in 1907. Used in ¹⁷⁷Lu radiopharmaceutical product documentation (Lutathera, Pluvicto), LYSO scintillator crystal specifications, and ICP-MS REE analysis databases (¹⁷⁵Lu as primary analytical isotope).
Lu metal	Commercial designation for elemental Lu in ingot, rod, foil, or powder form. Used in ¹⁷⁶Lu-enriched target procurement specifications for ¹⁷⁷Lu production, sputtering target datasheets, and LuAG crystal growth precursor documentation.
Lu element	Scientific designation distinguishing elemental Lu from Lu compounds. Used in condensed matter physics literature on Lu as a non-magnetic lanthanide reference, in Lu-Hf geochronology papers specifying Lu isotope systematics, and in scintillator physics publications on LYSO crystal properties.
Lutetium metal	Full commercial designation used in REACH/RoHS documentation, ASTM REE metal standards, and procurement specifications for Lu additions to Si₃N₄ ceramics, scintillator crystal growth, and ¹⁷⁷Lu radiopharmaceutical target material production.
Lutetium element	Used in academic databases (WebElements, NIST), educational resources, and nuclear medicine texts specifying ¹⁷⁶Lu neutron activation cross-section (2,065 barn) for ¹⁷⁷Lu production and ¹⁷⁷Lu physical decay properties for PRRT dosimetry.
Lutetium rare earth metal	Trade and regulatory designation classifying Lu among the heavy rare-earth elements (HREEs) on critical materials lists. Lu supply security is increasingly scrutinized given growing ¹⁷⁷Lu radiopharmaceutical demand and the limited number of facilities producing enriched ¹⁷⁶Lu targets at scale.
Lutetium rare earth element	Geochemical and mineralogical designation used in REE deposit assessments (xenotime as primary Lu source), Lu-Hf isotope geochemistry publications, and IUPAC nomenclature for Lu-bearing mineral phases. Lu is the end-member of the lanthanide series and has the smallest ionic radius, used as a reference point in lanthanide contraction discussions.
Element 71	Periodic table designation used in XRF/ICP-MS software, nuclear data libraries (ENDF/B-VIII for ¹⁷⁶Lu β⁻ decay data and ¹⁷⁶Lu(n,γ) cross-section), and reactor physics codes tracking ¹⁷⁶Lu activation during ¹⁷⁷Lu production irradiations.

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