UPSC Prelims 2025 Q81: Rare Earth Elements in Display Screens
Consider the following statements:
Statement I: Some rare earth elements are used in the manufacture of flat television screens and computer monitors.
Statement II: Some rare earth elements have phosphorescent properties.
Which one of the following is correct in respect of the above statements?
- Both Statement I and Statement II are correct and Statement II explains Statement I
- Both Statement I and Statement II are correct but Statement II does not explain Statement I
- Statement I is correct but Statement II is not correct
- Statement I is not correct but Statement II is correct
Answer: (a) Both Statement I and Statement II are correct and Statement II explains Statement I
Statement-wise explanation
- Statement-I: correct — Rare earth elements are used to make phosphors, the materials that give off coloured light in display screens. The US Geological Survey (USGS) notes that yttrium, europium and terbium phosphors are the red, green and blue phosphors used in many televisions and panels. It also says that colour cathode-ray tubes and liquid-crystal displays used in computer monitors and televisions use europium as the red phosphor, and that no substitute is known. So some rare earths are indeed used in flat TV screens and computer monitors.
- Statement-II: correct — Many rare earth ions, such as trivalent europium (red), divalent europium (blue) and trivalent terbium (green), absorb energy and give it out again as light. This property is called luminescence; phosphorescence, a slow afterglow, is one kind of it. Europium-doped strontium aluminate, used in glow-in-the-dark paints, is a standard example of true phosphorescence. Statement-II explains Statement-I: rare earths are used in screens because they glow in sharp, pure colours when energised.
How to eliminate
Statement-I can be checked from general knowledge. Rare earths come up again and again as inputs for 'electronics, screens, magnets, batteries', so it is very likely true. Statement-II gives the reason why a metal would be needed in a screen: the screen has to emit light, and 'phosphor' is the word for a material that does this. Once both statements are accepted, ask the linking question: does the property in Statement-II account for the use in Statement-I? Here it does directly. Glowing in colour is exactly the job a display needs done, so the causal link holds. The fact to remember: europium (red), terbium (green) and yttrium (host material) are the classic rare earth phosphors in TVs, monitors and fluorescent lamps. One trap is that the precise physics term is 'luminescence' or 'fluorescence', not strictly 'phosphorescence'. UPSC used the looser word, and the official key treats it as correct.
Know more
Rare earth elements (REEs) are 17 metals: the 15 lanthanides (lanthanum to lutetium) plus scandium and yttrium. They are not actually rare in the Earth's crust. They are hard to find in concentrated deposits and hard to separate from each other, because their chemistry is so similar.
Why they glow. Many rare earth ions have electrons in a shielded inner shell (the 4f orbitals). When these ions are excited by electrons, UV light or a blue LED, they release the energy as light of a very narrow, fixed colour. That makes them ideal phosphors. Fluorescence stops almost as soon as the energy source is switched off. Phosphorescence keeps glowing afterwards. Both are forms of luminescence.
| Element | Main use linked to light or electronics |
|---|---|
| Europium | Red (Eu³⁺) and blue (Eu²⁺) phosphors; anti-counterfeit marks on euro notes |
| Terbium | Green phosphor; also used in magnets |
| Yttrium | Host lattice for red phosphors; LED phosphor (YAG) |
| Cerium | Glass polishing; activator in YAG:Ce white LEDs |
| Neodymium, Praseodymium, Dysprosium | Permanent magnets for EV motors, wind turbines, speakers |
| Lanthanum | Camera lenses; hybrid-car batteries |
Beyond screens. By value, most rare earth demand today comes from permanent magnets (Nd, Pr, Dy, Tb). These magnets power electric vehicles, wind turbines and defence systems.
India's angle. India's main source of rare earths is monazite, a phosphate mineral found in beach sands along the coasts of Kerala, Tamil Nadu, Odisha and Andhra Pradesh. Monazite also contains thorium, so it is handled by IREL (India) Ltd under the Department of Atomic Energy. China refines most of the world's rare earths. This is why REEs sit at the centre of India's critical-minerals policy.
NCERT Concepts to Revise
- Rare earth elements: Both statements are about rare earth elements, so you need to know which 17 metals the group includes, such as europium, terbium and yttrium.
- Monazite: Monazite is India's main rare earth ore, the source of the elements used in display phosphors.