Although Europium is one of the light rare earth elements (USGS definition) which tend to be more abundant than the heavy rare earths, it is one of the most expensive rare earth elements and has been classed as one of the critical rare earths(2). Shortages have been predicted with a high degree of probability (3). Due to the high prices of europium and terbium, lighting and display systems constitute one of the most economically relevant rare earth applications (4).
Applications of Europium (Eu)
On the role of Europium in phosphor materials
Europium is used in phosphors, i.e. materials which can emit light when exposed to a light or electron source (3) â€“ not to be confused with the element phosphorus whose light emitting properties are down to a different phenomenon (6). In order to obtain phosphor materials, salt-like host lattices (matrices) are dotted with metal ions (e.g. Eu2+ or Eu3+), which are also referred to as activators of dopants (3). Europium can create a red or blue light depending on the oxidation state (3) citing (5). Combining Eu2+ and Eu3+ in the phosphor application can yield a white light which is used in compact fluorescent bulbs (7).
Europium is the most common rare earth to be used as an activator in phosphors, closely followed by terbium, but it should be noted that rare earths used in the phosphor matrices such as yttrium are more important in terms of absolute quantities used (4). Activators are used in low concentrations of 10-2 to 10-4 g/mol of phosphor material (8). Although Europium and other rare earths such as terbium, samarium, erbium, thulium, cerium and dysprosium are used in very small quantities, they play an important role in the respective application and there is a lack of suitable substitutes in the short term (3). Rare earths are used in most energy efficient lighting technologies, including compact fluorescent light bulbs (energy saving light bulbs), fluorescent tubes, (O) LEDs, EL foils, plasma displays and LCD displays â€“ their use helps achieve good color qualities and higher energy efficiencies (3).
On the one hand, the use of the rare earths in small concentrations and mixed material products poses a challenge to any potential recycling activities for rare earths used in phosphor materials. On the other hand, the combination of an increase in the use of phosphors containing rare earths such as europium in combination with planned export restrictions of primary rare earths from China provides an incentive for the recycling of rare earths contained in lighting systems. However, recycling processes for lighting and luminescence applications are already being developed, although in some cases, the overriding intention may have been the recovery of other valuable substances present in higher concentrations or posing an environmental risk at disposal. (To give an example, mercury is recovered from LCD displays with CCFL background illumination technology (4).) Recycling processes are being developed or have been developed for TV tubes, computer monitors, lamps/ fluorescent lamps and tubes (3). Rhodia (Solvay) is operating recycling facilities for end-of-life fluorescent lamps in two locations in France (11, 12).
Compact fluorescent light bulbs, fluorescent tubes, LED light bulbs
Fluorescent lamps (compact fluorescent light bulbs or fluorescent tubes) contain a mercury vapor which is excited by electricity and thereby produces light, which then causes the coatings to glow (9).
The coatings are made up of a phosphor material containing mix which also uses rare earths as activators. Europium is often contained in fluorescent powder, which has been shown in recycling trials for fluorescent lamps (around 0.6%) (4). It is responsible for the red part of the light spectrum.
LED lights usually contain yellow luminescent substances often based on yttrium â€“ Eu2+ Ions are added in order to achieve a warm light (4).
TV screens (notebooks, monitors): CRT, LCDs, plasma displays
Europium is used in old fashioned TV-screens (cathode ray tube TVs, CRTs). Old TV Screens contain tubes of europium phosphates. When hit by the electron beam, the Europium emits an intense beam of red light (1). Although this effect can be observed with other rare earths, the Europium is particularly suitable for this application due the intense red light emitted when it is hit by the electron beams (1). CRT type TVs are still being produced in some countries but are being replaced by other technologies such as LCD displays and plasma displays.
LCD Liquid crystal display TVs use either cold cathode tubes (CCFLs, older technology) or LEDs (more recent technology) as background illumination, both of which contain low concentrations of Europium as a luminescent substance (4). In PDP (plasma display panel) and OLED technologies (organic light emitting diodes), rare earths such as Europium are used as parts of the actual displays (4). OLEDs emit light from the image pixels themselves in a similar way to plasma screens.
Other interesting uses of Eu
Other uses of europium include bank notes (where it is added to allow for a distinction of genuine notes) (7) and glow-in-the dark toys (6). Due to its nuclear absorption capacity, Europium can also be used in control rods for nuclear reactors (10).
1) Royal Society of Chemistry: Periodic Table â€“ Videos of Europium â€“ University of Nottingham. Accessed 07th April 2014 (http://www.rsc.org/periodic-table/video/63/Europium?videoid=88YOmg_FUVo)
2) Buchert, Matthias; Ã–ko-Institute e.V. (2011): Rare Earths – a Bottleneck for future Wind Turbine Technologies? â€“ Wind Turbine supply chain and logistics, Berlin, 29th August 2011
3) SchÃ¼ler , D.; Buchert, M., Liu, R. Dittrich, S., Merz, C. D â€“ Ã–ko-Institute e.V. (2011) : Study on Rare Earths and their Recycling â€“ Final Report for the Greens/EFA Group of the European Parliament
4) Buchert, M.; Manhart, A.; Bleher, D.; Pingel, D â€“ Ã–ko-Institute e.V. (2012): Recycling critical raw materials from waste electronic equipment – Commissioned by the North Rhine-Westphalia State Agency for Nature, Environment and Consumer Protection
5) Riedel, E. (Hrsg.)(2007) : Moderne Anorganische Chemie, 3. Auflage, De Gruyter Verlag
6) Wikipedia (2014): Phosphor, http://en.wikipedia.org/wiki/Phosphor, accessed 8th April 2014
7) Stewart, D. (2014) “Europium.” Chemicool Periodic Table. Chemicool.com http://www.chemicool.com/elements/europium.html, accessed 8th April 2014
8) Holleman, A.; Wiberg, N. (2007): Lehrbuch der Anorganischen Chemie, 102nd Edition Auflage. De Gruyer Verlag
9) Wikipedia (2014): Fluorescent lamp, http://en.wikipedia.org/wiki/Fluorescent_light, accessed 8th April 2014
10) Wikipedia (2014): Europium, http://de.wikipedia.org/wiki/Europium accessed 8th April 2014
11) Binnemans, K.; Jones, P.T.; Blanpain, B.; Van Gerven, T.; Yang, Y.; Walton, A., Buchert, M. (2013): Recycling of rare earths: a critical review, Journal of Cleaner Production, 51, 1-22
12) Rollat, A.; Rhodia( Solvay)(2012): How to satisfy the Rare Earths demand- Rhodia Rare Earth Systems initiatives, http://www.seii.org/seii/documents_seii/archives/2012-09-28_A_Rollat_Terres_rares.pdf accessed 9th April 2014