Stimulated luminescence in rare-earth-doped MgS

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Abstract
Optically stimulated luminescence and thermally stimulated luminescence in MgS:Ce,Sm and MgS:Eu,Sm have been investigated. It appears that samarium in the form of Sm3+ ion acts as a thermally stable electron trap in MgS:Ce,Sm and MgS:Eu,Sm. A Sm3+ ion becomes a Sm2+ ion capturing an electron when these materials are exposed to UV radiation at room temperature, while the free hole is captured by a Ce3+ (or Eu2+). On optically stimulating an UV treated sample, the trapped electrons are released from Sm2+ ions and are recaptured by Ce4+ (or Eu3+) ions leading to the luminescence which is characteristic of Ce3+ (or Eu2+) emission. However, thermal stimulation of these UV treated samples results in luminescence which is characteristic of Sm3+ emissions, indicating that the thermoluminescence results from the release of holes from Ce4+ (or Eu3+) and Sm3+ acts as a luminescence center.