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State PCS PYQPrelims 2025

BPSC – Combined Competitive Examination · Question 132

Which compound is known as a glow-in-the-dark (night glowing) pigment?

  1. Europium-doped strontium aluminate
  2. Copper sulphide-doped zinc oxide
  3. Barium sulphate-doped copper carbonate
  4. Boron oxide-doped copper sulphate
Show answer & explanation

Answer: (A) Europium-doped strontium aluminate

Explanation

Europium (and dysprosium) doped strontium aluminate glows for hours after charging with light.

  • (A) Correct

    Correct: SrAl₂O₄:Eu is the main long-afterglow phosphor.

  • (B) Incorrect

    Wrong: the older phosphor was copper-doped zinc sulphide, not this.

  • (C) Incorrect

    Wrong: not a luminous pigment.

  • (D) Incorrect

    Wrong: not a luminous pigment.