UPSC Prelims 2025Question 81Science & Technology

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?

Options

(a)Both Statement I and Statement II are correct and Statement II explains Statement I
(b)Both Statement I and Statement II are correct but Statement II does not explain Statement I
(c)Statement I is correct but Statement II is not correct
(d)Statement I is not correct but Statement II is correct

Correct answer: a

Decision rule

In Statement I/II pairs, II explains I only if it names the property that makes I's application possible; a merely related truth does not.

(a) Both Statement I and Statement II are correct and Statement II explains Statement I

Statement I:
Some rare earth elements (REEs) such as yttrium, europium, terbium, and cerium are indeed used in the manufacture of flat television screens and computer monitors. They play a critical role in the display technology by enhancing color quality and brightness.
Statement II:
Many rare earth elements have phosphorescent properties, meaning they can absorb energy and then emit light over time. This phosphorescence is essential for producing vivid colors on flat-panel displays like LED, LCD, and plasma screens.
Relation:
The phosphorescent properties (Statement II) explain why rare earth elements are used in display manufacturing (Statement I), as their ability to emit light after excitation helps in creating clear, bright, and colorful screens.

(b) Both Statement I and Statement II are correct but Statement II does not explain Statement I – Incorrect: Phosphorescent properties directly explain the use of REEs in display screens.
(c) Statement I is correct but Statement II is not correct – Incorrect: Phosphorescence is a well-known property of many rare earth elements.
(d) Statement I is not correct but Statement II is correct – Incorrect: REEs are indeed used in manufacturing flat screens.

Rare Earth Element	Use in Displays	Phosphorescent Property
Europium (Eu)	Red phosphor in CRT, LED, LCD displays	Strong red phosphorescence
Terbium (Tb)	Green phosphor in display screens	Green phosphorescence
Yttrium (Y)	Host material for phosphors in screens	Enhances brightness and color fidelity
Cerium (Ce)	Used in fluorescent materials	Contributes to brightness and luminescence

Concept	Explanation
Phosphorescence	The process where a material emits light after absorbing energy; crucial in display tech.
Rare Earth Elements	Group of 17 elements used in electronics, magnets, batteries, and display technology.
Flat Screen Displays	Includes LCD, LED, OLED, and plasma screens where phosphors emit colored light.

With the rise of advanced display technologies (OLED, quantum dots), rare earth elements remain critical components in the electronics industry.
The strategic importance of rare earth elements is increasing globally due to their role in electronics, renewable energy, and defense technologies.

Concept / Term	Explanation / Relevance
Rare Earth Elements (REEs)	A group of 17 elements including the 15 lanthanides plus scandium and yttrium; critical in high-tech applications.
Phosphorescence	The emission of light by a substance that has absorbed energy; rare earth elements exhibit this property, crucial for color displays.
Europium (Eu)	Used as a red phosphor in CRTs, LEDs, and LCDs; emits red light due to phosphorescence.
Terbium (Tb)	Used as a green phosphor in display screens; contributes to green luminescence.
Yttrium (Y)	Acts as a host material for phosphors; enhances brightness and color fidelity in displays.
Cerium (Ce)	Used in fluorescent materials and phosphors; enhances brightness and luminescence.
Flat Screen Displays	Includes LCD, LED, OLED, and plasma screens that rely on phosphorescent materials for color output.
Phosphors	Substances that emit light when exposed to radiation or electrical energy; used in display screens.
Display Technologies	Technologies such as CRT, LCD, LED, OLED that utilize phosphorescent rare earth elements for color generation.
Strategic Importance of REEs	Critical for electronics, renewable energy, defense, and communication technologies worldwide.