Thulium, the rarest of the naturally occurring lanthanides, represents one of the most challenging elements in the periodic table to isolate and purify. This silvery-gray metal, with atomic number 69, has captivated scientists since its discovery in 1879, not only for its scarcity but also for its unique properties that have found applications ranging from portable X-ray devices to cutting-edge surgical lasers. Despite being more abundant than gold or silver in Earth’s crust, thulium’s extreme difficulty of separation from other rare earth elements made it one of the last lanthanides to be obtained in pure form. The story of thulium is one of scientific perseverance, technological innovation, and the gradual revelation of an element whose specialized applications have proven invaluable in modern medicine and technology.

For more information, check out the light rare earth elements (LREEs) as a group, the heavy rare earth elements (HREEs) as a group, and all rare earth elements (REEs). Be sure to check out all other critical raw materials (CRMs), as well. The complete history of all 17 rare earth elements can be found here.

Read about the use of rare earths in quantum computing here.

A History Of Thulium

The history of thulium spans over 140 years, from its initial discovery as an oxide in 1879 to its current applications in advanced medical lasers and anti-counterfeiting technology. This chronology traces the major milestones in thulium’s discovery, purification, commercial production, and technological applications, demonstrating how this rare element evolved from a scientific curiosity to an essential component in specialized modern technologies.

Chronology

• 1879 – Per Teodor Cleve discovered thulium while working with erbia (erbium oxide) at the University of Uppsala, Sweden, separating two previously unknown components which he called holmia and thulia (the oxides of holmium and thulium respectively); Cleve named the green oxide “thulia” and its element thulium after Thule, an ancient name for Scandinavia; Cleve’s sample of thulium oxide contained impurities of ytterbium oxide, which he was unable to completely separate [1, 2, 3, 4]
• 1911 – Charles James, a British expatriate working at New Hampshire College in Durham, USA, became the first researcher to obtain nearly pure thulium using his discovered method of bromate fractional crystallization, famously needing 15,000 purification operations to establish that the thulium material was homogeneous; Theodore William Richards performed 15,000 recrystallizations of thulium bromate to obtain an absolutely pure sample of thulium and accurately determine its atomic weight [5, 6, 7, 8, 9]
• 1912 – Spectroscopic studies of thulium continued to identify its characteristic absorption bands [48]
• 1913 – Niels Bohr’s atomic model provided theoretical framework for understanding thulium’s electronic structure [49]
• 1915 – Spectroscopists definitively assigned certain spectral lines to thulium [50]
• 1920 – Further spectroscopic analysis of thulium compounds was conducted [48]
• 1925 – Advances in spectroscopy allowed better characterization of thulium’s optical properties [49]
• 1930 – Improvements in microphotometry enabled more precise measurement of thulium spectral line intensities [49]
• 1932 – Mary Elvira Weeks published article on discovery of rare earth elements including thulium in Journal of Chemical Education [1, 51]
• 1934 – Pure metallic erbium was prepared by Klemm and Bommer, advancing techniques later used for thulium [52]
• 1936 – Wilhelm Klemm and Heinrich Bommer first obtained metallic thulium [2, 10, 11]
• 1937 – First fully-automated spectrometer created by E. Lehrer improved thulium spectral measurements [48]
• 1940 – Research on thulium compounds continued during World War II period [53]
• 1942 – Meggers discovered the fundamental energy interval in neutral thulium of 8771 cm−1 [54]
• 1945 – Post-war research resumed on rare earth elements including thulium [53]
• 1947 – Development of photomultiplier tubes improved thulium spectroscopic analysis [49]
• 1950 – Ion-exchange separation technology began development for rare earth purification [55]
• 1955 – Commercial production methods for thulium oxide were established [56]
• 1958 – Lindsay Chemical Division of American Potash & Chemical Corporation began offering high-purity thulium oxide [2]
• 1959 – The price per kilogram of 99.9% pure thulium began oscillating between US$4,600 and $13,300, making it the second highest priced lanthanide behind lutetium [2, 12]
• 1960 – Theodore Maiman developed the world’s first laser, setting the stage for future thulium laser applications [13]
• 1963 – Blaise and co-workers at Laboratoire Aimé Cotton studied hyperfine structure of 70 strong thulium lines [54]
• 1965 – Research on thulium’s magnetic properties at low temperatures intensified [57]
• 1968 – Studies of thulium’s ferromagnetic-antiferromagnetic transitions were published [58]
• 1970 – Thulium-170 isotope with 128.6-day half-life began use in portable X-ray devices for medical imaging [14]
• 1972 – Research on thulium compounds for magnetic applications expanded [59]
• 1975 – Thulium’s use in magnetic bubble memory devices was explored [60]
• 1978 – Studies on thulium’s optical properties for potential laser applications increased [61]
• 1980 – Thulium applications in high-temperature superconductors were first explored [15]
• 1982 – Research on thulium-doped crystals for solid-state lasers began [62]
• 1985 – Advances in crystal growth techniques improved thulium-doped materials [63]
• 1988 – Development of thulium-doped fiber amplifiers initiated [64]
• 1990 – Thulium-doped yttrium aluminum garnet (Tm:YAG) lasers began development for medical applications [16]
• 1996 – Thulium oxide cost US$20 per gram [2]
• 1998 – The price per kilogram of 99.9% pure thulium reached $13,300 [2, 12]
• 2000 – Thulium began use in euro banknotes for its blue fluorescence under UV light to defeat counterfeiters [17]
• 2001 – Approximately 50 tonnes per year of thulium oxide were produced worldwide [2, 10]
• 2002 – Euro banknotes incorporating thulium for anti-counterfeiting measures entered circulation [18]
• 2003 – Research on thulium fiber laser technology intensified [19]
• 2004 – Development of thulium-doped fiber amplifiers for telecommunications applications [20]
• 2005 – First documented use of thulium fiber laser (TFL) for lithotripsy; Thulium:YAG laser for BPH surgery was first published [21, 22, 23]
• 2006 – Advances in thulium laser crystal growth techniques improved laser efficiency [24]
• 2007 – Thulium lasers achieved power outputs suitable for surgical applications [25]
• 2008 – Clinical trials of thulium lasers for prostate surgery expanded [26]
• 2009 – Thulium laser vapo-enucleation technique was developed [27]
• 2010 – Thulium laser enucleation of the prostate (ThuLEP) technique was introduced; Blackmon et al. published first comparative study of thulium fiber laser versus Ho:YAG for lithotripsy [28, 29]
• 2011 – Studies demonstrated thulium fiber laser’s superior ablation rates compared to Ho:YAG lasers; Thulium lasers used for treatment of melasma [30, 31]
• 2012 – Thulium fiber laser research expanded to include tissue ablation applications [32]
• 2013 – Advanced pulse modulation techniques for thulium fiber lasers were developed [33]
• 2014 – Hardy et al. demonstrated thulium fiber laser lithotripsy in ureter models [34]
• 2015 – Wilson et al. studied collateral damage to ureter during thulium fiber laser lithotripsy; High-power thulium fiber laser systems reached clinical testing [35, 36]
• 2016 – Commercial thulium fiber laser systems entered development phase [37]
• 2017 – Russian clinical trials of thulium fiber laser for urology began [38]
• 2018 – Thulium fiber laser (TFL) was launched in the market and cleared for clinical use in the Russian Federation [39]
• 2019 – US Food and Drug Administration approval for thulium fiber laser; Enikeev et al. published prospective comparison of TFL with conventional TURP [40, 41]
• 2020 – European CE mark approval for thulium fiber laser; COVID-19 pandemic affected thulium production and research [42]
• 2021 – Multiple clinical studies confirmed TFL’s superiority in stone dusting and reduced retropulsion [43]
• 2022 – Thulium fiber laser adoption accelerated in urological practices worldwide [44]
• 2023 – New generation thulium fiber lasers with enhanced parameters entered market [45]
• 2024 – Thulium fiber laser technology became widely available with multiple manufacturers [46]
• 2025 – Coherent Corp. launched ACE FL series thulium fiber laser for medical applications [47]

Final Thoughts

The journey of thulium from its discovery as an impure oxide in 1879 to its current status as a critical element in advanced medical technology exemplifies the evolution of rare earth chemistry and its practical applications. While Charles James’s extraordinary dedication in performing 15,000 purification operations to obtain pure thulium in 1911 might seem excessive by today’s standards, it laid the foundation for understanding this element’s unique properties. The development of ion-exchange separation technology in the 1950s finally made commercial production feasible, though thulium remains one of the rarest and most expensive lanthanides.

Today, thulium’s applications in fiber laser surgery, portable X-ray devices, and security features demonstrate how even the rarest elements can find indispensable niches in modern technology. As laser technology continues to advance and new applications emerge, thulium’s story reminds us that scientific curiosity and perseverance in understanding even the most challenging elements can yield unexpected benefits for humanity.

Thanks for reading!

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