Heavy rare earth elements (‘HREE’), which are less common and more valuable, include europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu) and commonly Yttrium (Y)
Europium is used as a phosphor in all TVs and computer screens to create red and blue light, and when combined with green Terbium phosphors, trichromatic fluorescent lighting is created. Europium isotopes are the best known neutron absorbers and therefore the element is ideal for control rods in nuclear reactors. The element is also used in fluorescent light bulbs, alloys, as an agent in fluorescent glass, and to dope plastic and glass to make lasers.
When added to iron, chromium, or related alloys, gadolinium greatly improves the workability and raises resistance to high temperature oxidization. It is also utilized in microwave applications, CDs, computer memory devices, MRI image enhancing, neutron radiography, and for making phosphors in TV tubes. One final use of Gadolinium comes in nuclear reactors as an emergency shut-down mechanism.
Terbium is used in colour TV tubes and fluorescent lamps as a green phosphor. In combination with Europium blue and red phosphors, the three create trichromatic fluorescent lighting, which is much brighter than conventional fluorescent lighting. Another green application for Terbium can be found in combination with neodymium for production of the world’s most heat resistant super magnets. The element is also used in alloys, crystal stabilizers in fuel cells that operate at high temperatures, specialty lasers, and to dope calcium fluoride, sodium borate and strontium molybdate materials. Terbium is a component of Terfenol-D, a material that is used in transducers, high-precision liquid fuel injectors and in a new form of audio equipment that has the potential to revolutionize the speaker industry.
Dysprosium’s thermal neutron absorption cross-section and high melting point enables it to be used in nuclear control applications. The element can be added to Neodymium-iron-boron magnets to raise the strength and corrosion resistance of applications like drive motors for hybrid electric vehicles. Like Terbium, Dysprosium is a component of Terfenol-D; a very promising material for future technology applications. It is also used in CDs, chemical reaction testing, laser materials, and dosimeters.
Holmium has one of the highest known magnetic moments. The element is imperative in the creation of the strongest, artificially generated magnetic fields. Holmium is also used in nuclear control rods, solid-state lasers in eye-safe medical and dental microwave equipment, and as a yellow and red glass, and cubic zirconia colourant.
Erbium is used in neutron-absorbing control rods, creating lasers for cutting and welding, and as a doping agent for optical fibers. As an alloy additive, Erbium lowers the hardness and improves the workability of numerous metals. In oxide form, the element is used as a pink colourant in glass and porcelain enamel glazes, and it is often used in photographic filters.
Thulium is the 2nd rarest of REEs, only next to Promethium, which does not occur naturally in the earth’s crust. Because of its scarcity and high price, there are few widely-used Thulium applications. Its current uses are mainly scientific experimentation, and in portable x-ray devices use for areas where electric power is not available.
Ytterbium is used some in solar cells, optical glasses, crystals, and ceramics. It can be utilized as a doping material for high power solid-state lasers and as an alloy that helps to strengthen stainless steel. Like Thulium, Ytterbium is employed in portable x-ray machines where electricity is not available.
Lutetium is mainly used as a catalyst in refining petroleum, hydrogenation and polymerization processes, and in organic LEDs. Lutetium is currently being investigated as an agent for possible cancer treatments. It is also used in x-ray phosphors and computer memory devices.
Yttrium is most widely used in phosphors for white and grey colours in LEDs, and in tri-chromatic fluorescent lighting. For its physical and chemical properties, Yttrium is regularly alloyed with chromium, molybdenum, zirconium, titanium, aluminum and magnesium. Yttrium is used as a deoxidizer for vanadium and other nonferrous metals, and as a catalyst in the polymerization of ethylene. It has medical applications in cancer treatment, arthritis and joint inflammation, in artificial joints, prosthetic devices, and needles. The element can also be found in optical and camera lenses, cubic zirconia jewelry, super conductor materials, high performance spark plugs, yttrium-stabilized zirconia, solid electrolytes, exhaust systems, catalytic converters, turbocharger components, and piston rings.