Lanthanides

The lanthanides (or lanthanoids) are 15 metallic elements with atomic numbers 57 (lanthanum) through 71 (lutetium). They occupy the f‑block of the periodic table and are chemically very similar: they all readily form +3 cations, and their 4f electron shell is progressively filled across the series. These silvery, reactive metals exhibit the so‑called lanthanide contraction: atomic and ionic radii decrease steadily from La to Lu, leading to subtle shifts in their properties. Lanthanides are often found together in minerals (e.g. monazite, bastnäsite) and were historically called “rare earths” not because they are scarce in the crust, but because they occur dispersed and are hard to separate.

Lanthanides have unique magnetic, optical, and electronic behaviors that make them technologically vital. For example, neodymium and samarium yield very strong permanent magnets; cerium compounds act as catalysts and glass additives; europium and terbium phosphors produce red and green light in displays; and several lanthanides (Nd, Er, Ho, etc.) are used in lasers and fiber‐optic amplifiers. Together, these features make lanthanides critical in high-tech applications from smartphones and electric vehicles to medical imaging and green energy technology.

Key properties and uses of the lanthanides include:

• Silvery, soft metals that tarnish readily in air (except the heavier ones which are more corrosion-resistant). They have high densities and high melting points.

• Trivalent chemistry: nearly all lanthanides prefer the +3 oxidation state, leading to similar chemical behavior across the series. (Notably, Ce can also be +4, and Eu/Yb commonly show +2.)

• Lanthanide contraction: the steady decrease in ionic radius from La to Lu affects their coordination chemistry and causes neighboring elements in later periods to have unexpectedly similar sizes.

• Abundance: Individually, lanthanides are more common than precious metals, but natural ores contain complex mixtures of many lanthanides. Extraction involves elaborate chemical separations.

• Technological importance: Lanthanides are used in powerful magnets, catalysts, phosphors, lasers, batteries, and nuclear materials. Their unfilled f‑electrons give rise to sharp emission lines (useful in lasers and lighting) and strong paramagnetism (used in MRI contrast agents and magnetocaloric applications).

Lanthanide Elements (La–Lu)

Lanthanum (La, 57)

Main article: Periodic table/Lanthanides/Lanthanum

As the first lanthanide, lanthanum is a relatively reactive metal (it tarnishes in air and burns easily). It has no huge single use but is important in several high-tech areas. Lanthanum(III) oxide is added to glass for camera and telescope lenses, where it increases the refractive index and clarity of the glass. This yields lenses with less distortion (chromatic aberration), allowing for high-quality photography and optics. Lanthanum is also a component of mischmetal (a mix of rare earth metals) used in lighter flints. Perhaps most impactfully, lanthanum is used in nickel-metal hydride (NiMH) rechargeable batteries, like those in some hybrid cars. The battery’s negative electrode alloy contains lanthanum; in fact, a typical hybrid car battery may contain a few kilograms of lanthanum. Interestingly, lanthanum compounds can even help clean pool water – lanthanum chloride is used to precipitate phosphates and keep algae at bay in swimming pools. Alloys of lanthanum with nickel form hydrogen-absorbing materials useful for hydrogen storage. Overall, though it flies under the radar, lanthanum’s role in optics and batteries makes it quietly significant.

Cerium (Ce, 58)

Main article: Periodic table/Lanthanides/Cerium

Cerium is the most abundant of the lanthanides. It has a notable dual oxidation state chemistry (common states +3 and +4). Cerium oxide (CeO₂) is a major application: it is used in the catalytic converters of car exhaust systems, where it helps oxidize CO and hydrocarbons and also stores oxygen to aid other catalyst components. CeO₂ is also a superb glass-polishing agent – a fine cerium oxide powder is used to polish telescope mirrors, camera lenses, and eyewear during manufacture. If you’ve ever used a common lighter or seen old flint spark strikers, you’ve encountered cerium: mischmetal, a blend of rare earths (typically ~50% cerium), is used to make the “flint” in cigarette lighters, which sparks when scratched. Cerium’s pyrophoric nature (it readily gives sparks) makes it ideal for that application. Additionally, cerium compounds produce a blue coloration in some glass and ceramics. In the lab, cerium(IV) sulfate is a strong oxidizing agent (Ceric ammonium nitrate is used in analytical chemistry). With its multiple uses from cars to everyday gadgets, cerium is one of the workhorse rare earths.

Praseodymium (Pr, 59)

Main article: Periodic table/Lanthanides/Praseodymium

Praseodymium is a soft, silvery metal named from the Greek prasios didymos, “green twin,” referring to green salts it forms and its discovery alongside “twin” neodymium. One of praseodymium’s claims to fame is its role in specialty glass: along with neodymium, it is a component of didymium glass, which is used in the goggles of glassblowers and welders. This glass filters out the intense yellow light from sodium in flames, protecting eyes and allowing one to see the workpiece. Praseodymium compounds also color glass and ceramics yellow. In alloy form, praseodymium is used with magnesium to create high-strength metals for aircraft engines. Magnetically, praseodymium is often added to neodymium-iron-boron magnets (the strongest magnets) in small amounts to improve certain properties. Some electric car motors use Nd-Fe-B magnets that include praseodymium and dysprosium to maintain performance at temperature. Praseodymium’s bright ions are also used in certain types of lasers and in fiber optic amplifiers (though erbium is more common for communications wavelengths). While not as famous as Nd or Eu, praseodymium quietly supports these technologies.

Neodymium (Nd, 60)

Main article: Periodic table/Lanthanides/Neodymium

Neodymium is arguably the superstar of the lanthanides in terms of visibility in tech. It’s best known for neodymium magnets – actually an alloy Nd₂Fe₁₄B – which are the strongest permanent magnets available. These magnets are found everywhere: in earbuds and headphones, computer hard drives, electric vehicle motors, wind turbine generators, and small toy magnets[1]. The strength of Nd-based magnets has enabled the miniaturization of many electronic devices (tiny yet powerful speaker drivers in smartphones, for example). Neodymium also lends a beautiful reddish-purple tint to glass; Nd-doped glass (“didymium” glass, containing Nd and Pr) is used in protective eyewear and was historically used to make a famous glass called “Heliolite” or “Alexandrite” glass that changes color under different lighting. In lasers, the Nd:YAG laser (neodymium-doped yttrium aluminum garnet) is extremely important – emitting infrared light, it’s used in everything from laser cutting machines to medical surgery and laser rangefinders. We can thank neodymium for enabling a lot of modern high-tech magnetism and photonics.

Promethium (Pm, 61)

Main article: Periodic table/Lanthanides/Promethium

Promethium is special among the lanthanides for being radioactive – all its isotopes are unstable (the longest-lived has a half-life of about 17.7 years). It’s also extremely rare in nature (trace amounts are continuously produced in uranium ores via fission, but at any moment there’s very little on Earth). Discovered in the 1940s, it was named after Prometheus, who stole fire from the gods – an apt name for an element “created” by human ingenuity (it was first identified in nuclear reactor products). Promethium’s scarcity means few uses, but one isotope, promethium-147, has been used in specialized atomic batteries (beta emission from Pm-147 can generate electricity in a thermoelectric device). Such promethium batteries have powered things like remote sensing equipment and were even considered for pacemakers (though other isotopes like plutonium-238 ended up more commonly used in such nuclear batteries). Pm-147’s beta rays have also been used in thin glow-in-the-dark paint (though promethium-based luminous paint has also fallen out of favor) and in compact thickness gauges for manufacturing (measuring material thickness by beta backscatter). Due to its radioactivity, promethium isn’t something encountered in daily life – it’s largely of interest in nuclear science.

Samarium (Sm, 62)

Main article: Periodic table/Lanthanides/Samarium

Samarium is another silvery metal with significant magnetic applications. It is most famous for samarium–cobalt magnets, which were the first generation of rare-earth magnets deployed (before neodymium magnets were developed). Sm–Co magnets are extremely powerful and, importantly, can withstand higher temperatures without losing magnetism, compared to Nd magnets[2]. They are used in applications like high-performance electric motors, turbocharger rotors, and even guitar pickups. Another major use of samarium is as a neutron absorber in nuclear reactors: samarium-149, produced in reactors, is a strong neutron absorber and helps control the reactor (in fact, the accumulation of Sm-149 can limit reactor re-start until it decays – a phenomenon known as the samarium nuclear poison). Samarium oxide is used in specialty infrared absorbing glass and optical filters. Samarium has also made a medical impact: the radioactive isotope samarium-153 is used in a drug (samarium lexidronam) to alleviate pain in bone cancer metastases, as it concentrates in bone and emits beta radiation to ease pain. Alloys of samarium (like Sm–Co) are also used in some aerospace and military technologies. While not as ubiquitous as neodymium, samarium’s contributions, especially in early magnet technology and niche medical/nuclear roles, are quite important.

Europium (Eu, 63)

Main article: Periodic table/Lanthanides/Europium

Europium is a soft metal named after the continent of Europe. It is unique among lanthanides in that it’s extremely good at absorbing neutrons (Eu-151 and Eu-153 have high capture cross-sections) and also among the most reactive lanthanides (it oxidizes easily, often stored under oil). Europium’s big claim to fame is in phosphors: Europium-doped compounds produce bright red and blue phosphorescence. In fact, the red phosphor in old CRT television screens (and in LED or fluorescent lighting) is typically europium-doped yttrium oxide (Y₂O₃:Eu³⁺). Without europium, the development of color TV in the 1960s (needing a strong red emitter) would have been delayed. Europium is also used in anti-counterfeiting security inks – for example, euro banknotes famously contain europium-based fluorescent markers that glow red under UV light. In nuclear applications, europium oxide is sometimes used in control rods (since Eu can absorb neutrons well). Europium alloys can be used in some types of lasers and quantum research. Because of its strong luminescent properties, europium shows up in any technology that needs reliable red or blue emission. Not bad for an element many haven’t heard of!

Gadolinium (Gd, 64)

Main article: Periodic table/Lanthanides/Gadolinium

Gadolinium is a silvery metal with two notable traits: it is strongly paramagnetic (with seven unpaired electrons, Gd³⁺ ions have a high magnetic moment), and it has an enormous ability to absorb neutrons (even more than europium in some cases). Gadolinium’s magnetic properties make it extremely useful in medicine – gadolinium compounds (chelated for safety) are widely used as MRI contrast agents. When injected, Gd-based contrast enhances the MRI images by affecting the local magnetic field, improving visualization of blood vessels and tissues. About one-third of MRI scans employ a gadolinium contrast agent, highlighting its importance in diagnostics. In nuclear reactors, gadolinium is often used as a burnable poison in fuel or in control rods, due to its voracious neutron appetite (Gd can help regulate reactivity and then safely burn out). Gadolinium compounds also find use in phosphors for TV screens and X-ray intensifying screens (e.g. Gd₂O₂S:Tb is a green phosphor in radiography). In materials science, gadolinium garnets (like GGG – gadolinium gallium garnet) are used as substrates for microwave components and magnetic bubble memory films. Gadolinium’s ability to become strongly magnetic at low temperatures has made it a subject of research in magnetic refrigeration (it exhibits a strong magnetocaloric effect near room temperature). Although few people encounter gadolinium directly, anyone who’s had an MRI likely benefited from it.

Terbium (Tb, 65)

Main article: Periodic table/Lanthanides/Terbium

Terbium is another lanthanide that plays a supporting role in modern tech. It is perhaps best known for providing green light in electronic displays and lighting. Terbium-doped phosphor (such as terbium-doped phosphates or silicates) gives a brilliant green used in fluorescent lamps and CRT displays, complementing europium’s red and blue to yield full color. Terbium is also a critical additive in high-performance magnets and magnetostrictive materials. A small percentage of terbium (and dysprosium) is added to neodymium magnet alloys to allow them to function at higher temperatures – for example, in wind turbine generators or electric vehicle motors that run hot. Terbium helps the magnets “stay strong above 180 °C” by improving their coercivity (resistance to demagnetization). Another fascinating terbium application is in Terfenol-D, an alloy of terbium, iron, and dysprosium that changes shape rapidly in magnetic fields (magnetostrictive). Terfenol-D is used in advanced sonar systems, actuators, and speakers (it can convert electromagnetic energy to precise mechanical vibrations). In solid-state technology, terbium is used in some semiconductor devices and as a dopant in fiber optic amplifiers (though praseodymium and erbium are more common there). Though hidden behind the scenes, terbium’s contributions to color displays and green tech are significant.

Dysprosium (Dy, 66)

Main article: Periodic table/Lanthanides/Dysprosium

Dysprosium is named from the Greek dysprositos, “hard to get at,” reflecting the difficulty in separating it from other rare earths. True to its name, pure dysprosium was hard-won, and it continues to be relatively scarce. Dysprosium has become crucial for its role in high-temperature permanent magnets. In NdFeB magnets used in motors and generators, adding a few percent dysprosium dramatically raises the magnet’s Curie point (temperature at which it loses magnetism) and its coercivity. This means a Nd magnet with Dy can operate in a hot car engine or wind turbine without demagnetizing. Many hybrid/electric car motors and wind turbines depend on dysprosium-enhanced magnets. Dysprosium is also used with terbium in Terfenol-D magnetostrictive alloy. Additionally, dysprosium oxide–nickel cement is used in neutron-absorbing control rods in nuclear reactors (Dy soaks up neutrons well). A quirky property: dysprosium iodide is used in high-intensity lighting (like halide lamps for film projectors or stadium lights) to produce a bright white light. Because of rising demand in clean energy tech, dysprosium has been deemed a critical element. It may be “hard to get,” but its magnetic superpowers make it worth the effort.

Holmium (Ho, 67)

Main article: Periodic table/Lanthanides/Holmium

Holmium often hides in the shadow of its neighbors, but it has some superlative properties. Holmium has the highest magnetic moment of any naturally occurring element – in other words, holmium atoms are like very strong little magnets (with 10.6 Bohr magnetons). In practice, pure holmium metal is used in the poles of the strongest static magnets as a magnetic flux concentrator[3]. For example, in certain laboratory magnets or medical MRI machines, pieces of holmium alloy help shape and focus magnetic fields. Holmium also finds use in nuclear reactors as a burnable poison (similar to dysprosium and gadolinium) because it absorbs neutrons. In lasers, holmium-doped YAG lasers emit a wavelength (2.1 microns) useful in medicine for cutting bone or ablating tissues with minimal depth penetration (e.g. in eye and kidney surgeries). Despite its very high magnetic strength in ion form, holmium is not ferromagnetic at room temperature – interestingly it only becomes ferromagnetic at low temperatures (~20 K). Holmium oxide has a notable feature too: it’s used as a optical calibration standard because of its sharp absorption peaks, and holmium oxide glass filters are used to calibrate spectrophotometers. All told, holmium might not be well-known, but it plays niche yet important roles where magnetism and precision light matter.

Erbium (Er, 68)

Main article: Periodic table/Lanthanides/Erbium

If you enjoy the benefits of the fiber-optic internet, you have erbium to thank. Erbium-doped fiber amplifiers (EDFAs) are the technology that allows long-haul fiber optic cables (carrying internet and phone data) to work. Tiny concentrations of erbium in glass fibers, when pumped with a laser, can amplify a 1550 nm signal (the standard telecom wavelength) along the cable. This discovery in the 1980s revolutionized telecommunications, enabling signals to be boosted optically without converting to electrical signals over distances. Thus, erbium literally helps carry data across oceans. Erbium also produces a pink hue in glass and glazes; it’s used to color some decorative glass and cubic zirconia gemstones. In medicine, Er:YAG lasers (erbium-doped yttrium aluminum garnet) emit 2940 nm infrared light, which is strongly absorbed by water. These lasers are used for precise laser skin resurfacing (e.g. treating acne scars or wrinkles) and in dentistry to painlessly ablate cavities in teeth (the water in tissue absorbs the laser, causing very controlled evaporation of material). Erbium oxide is sometimes added to ceramics to add resilience. Erbium isn’t used in large volumes, but its impact on communications and medical lasers is outsized.

Thulium (Tm, 69)

Main article: Periodic table/Lanthanides/Thulium

Thulium is one of the least abundant lanthanides and is quite expensive, so its uses are accordingly limited. One standout application is as a portable X-ray source: thulium-170, a radioactive isotope, emits X-rays and has been used in small irradiation devices for medical imaging or industrial inspection where electricity or large X-ray tubes aren’t available. These thulium-powered devices can function as compact X-ray machines (for example, for field clinics or for checking welds in remote pipelines). Thulium is also used in some lasers: Tm:YAG lasers emit around 2 microns and are useful in surgery (somewhat similar to holmium lasers) and in pumping mid-infrared laser systems. There’s research into thulium-doped fiber lasers as well, for eye-safe LIDAR and telecommunications beyond the erbium band. In general, due to cost, no bulk industrial use has emerged for thulium – it remains a laboratory curiosity and a specialty source of radiation and laser light. Fun fact: natural thulium is almost entirely one isotope (Tm-169), and when bombarded in a reactor it forms Tm-170 for those X-ray sources.

Ytterbium (Yb, 70)

Main article: Periodic table/Lanthanides/Ytterbium

Ytterbium is named after Ytterby, the Swedish village that also gave name to yttrium, terbium, and erbium. Ytterbium’s uses have been growing quietly. It has become important in certain optical and atomic applications. Ytterbium-doped fiber lasers are some of the most efficient high-power lasers, used in industrial cutting and welding – Yb lasers operate around 1060 nm (similar to Nd:YAG) but offer advantages in fiber format (many modern laser cutters use ytterbium fiber lasers). Ytterbium is also making headlines in next-generation timekeeping: ytterbium atomic clocks using laser-cooled Yb atoms have achieved record precision and stability, potentially to be the new standard beyond cesium clocks. In materials, adding a bit of ytterbium to stainless steel improves its grain refinement and strength. Ytterbium compounds also act as phosphors and scintillators in some X-ray detectors. One isotope, Yb-169, is used as a radiation source in portable XRF analyzers (for material identification). Ytterbium even finds use as a catalyst in organic chemistry for certain reactions (Yb triflate is a Lewis acid catalyst). It is often overshadowed by its cousin yttrium in applications, but ytterbium is carving a niche in photonics and precision measurement.

Lutetium (Lu, 71)

Main article: Periodic table/Lanthanides/Lutetium

Lutetium is the last (and hardest, densest, highest-melting) of the lanthanide series. It’s also one of the most expensive lanthanides because it’s comparatively scarce and difficult to separate. Despite this, lutetium has a few cutting-edge uses. Perhaps most prominently, lutetium oxyorthosilicate (LSO) crystals, typically doped with cerium, are used in PET scanners in hospitals. These crystals scintillate (emit light) when hit by gamma rays from positron-emission tomography, allowing detection of those rays with high resolution. Lutetium-based scintillators are prized for their speed and density (helping produce clearer PET images for oncology diagnostics). Lutetium is also used as a catalyst in certain petroleum refining processes – for example, lutetium compounds have been researched as cracking catalysts to break large hydrocarbons into gasoline. In chemistry research, lutetium’s stable +3 state and smallest size among lanthanides make it useful in catalysis and organic synthesis (like Lutetium chloride as a Lewis acid). Interestingly, the isotope Lu-176 (present in natural lutetium) is used in geochronology: the Lu-Hf radiometric dating method helps date meteorites and ancient minerals, shedding light on the age of the Earth and solar system. While there’s no everyday product labeled “contains lutetium,” this element plays roles behind the scenes in medical imaging and scientific research.

After lutetium, the f-block segment of period 6 ends. We then continue along the transition metals in the d-block and finally the p-block elements of period 6:

Summary of Lanthanide Properties and Uses

The table below lists each lanthanide with its symbol, atomic number, and one notable use or property:

Element (Atomic #)	Symbol	Notable Use or Property
Lanthanum (57)	La	Nickel–metal-hydride batteries (e.g. hybrid vehicles)
Cerium (58)	Ce	Glass polishing / catalytic converters (CeO₂ catalyst)
Praseodymium (59)	Pr	Powerful Nd–Pr permanent magnets
Neodymium (60)	Nd	Strong Nd–Fe–B permanent magnets
Promethium (61)	Pm	Radioactive atomic batteries / portable X-ray sources
Samarium (62)	Sm	Samarium–cobalt (SmCo) permanent magnets
Europium (63)	Eu	Red phosphors for TV/computer screens
Gadolinium (64)	Gd	MRI contrast agents (Gd-based chelates)
Terbium (65)	Tb	Green phosphors (fluorescent lamps, displays)
Dysprosium (66)	Dy	High-temperature Nd–Fe–B magnets (wind turbines)
Holmium (67)	Ho	Pole pieces for ultra-strong magnets; neutron absorber
Erbium (68)	Er	Fiber-optic amplifiers / 1550 nm lasers (telecom)
Thulium (69)	Tm	Portable X-ray sources (radioisotope Tm-170)
Ytterbium (70)	Yb	Doping stainless steel; solid-state lasers (Yb-doped)
Lutetium (71)	Lu	Cancer therapy radiolabel (Lu-177); catalyst in oil refining

Each lanthanide is thus associated with unique technological roles. Together they enable advances in electronics, energy, medicine, and materials science, illustrating why this “hidden” row of the periodic table is vitally important in the modern world.

Sources: Authoritative chemistry and materials science references on lanthanide properties and applications.