Are rare earths part of a bright future for lighting and displays?
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High purity of rare-earth metals is important for many advanced applications, but separating rare earths from the oxides they form is a costly procedure and definitely not an easy one.
Are rare earths part of a bright future for lighting and displays? By Eva Karatairi Feature Editor Henning Höppe
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re we running out of europium? This is the kind of question that generates blank looks. The slightest hint, however, that smartphones cannot be upgraded would generate an uproar. Europium belongs to the lanthanides group, which are part of the 17 rare-earth elements. Many of them face high risk for shortage in the near future, something that raises concerns over the future of high-tech applications. Screens in smartphones and laptops need rare earths for the expression of red, blue, and green colors. Rare earths are also found in phone circuits. Neodymium is necessary for the permanent magnets in speakers—the same category of powerful magnets found in electric motors and wind turbines. If rare earths are in short supply, is there a possibility that we keep in our pockets the latest version of a mobile phone? A look at the abundance of rare earths in the Earth’s crust could reassure one’s fears, as it would reveal that they are not actually so rare, at least in terms of occurrence in the outermost solid layer of our planet. Even thulium, the least abundant among them, is more plentiful than gold and silver. It is rare, however, to find them in exploitable concentrations. Not only are the identified resources restricted, but onethird of the global reserves are in China, a country that also controls around 90% of the world’s rare-earth oxides production. Furthermore, demand is expected to increase steadily in the years to come, partly because of the foreseen advances in green technologies. These facts combined together reveal the reasons behind the serious concerns over their availability. High purity of rare-earth metals is important for many advanced applications, but separating rare earths from the oxides they form—in the minerals they are found in—is a costly procedure and not an easy one. The reason that makes their extraction, purification, and recycling processes so difficult is the same one that gives rise to their unique spectroscopic and magnetic properties. All 15 lanthanide elements have the same electron arrangement in their outer shell (6s 2 , 5d 1 ) and thus a very similar chemical character. Apart from these outer 6s and 5d shells, two more filled orbitals (5p and 5s) shield the 4f subshell of their atoms, except for La3+ and Lu3+. The way electrons occupy this 4f orbital and the number of unpaired electrons in it differentiates one element from the other. Furthermore, transitions of electrons between the f orbitals and d and f
orbitals (f-f and d-f transitions, respectively) result in the luminescent character of rare earths. With major applications in the display and lighting industry, phosphors have proven to be a perfect field for rare earths to unfold their extraordinary op
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