Difference in Luminescence Properties between Sm Doped ZnS and Eu Doped ZnS

A sharp luminescence peak from Sm doped ZnS at 650 nm which can be assigned as 4 G 5/2 - 6 H 9/2 transition of Sm 3+ ion was observed; however, no luminescence peak related to Eu 3+ , which can have luminescence in the similar spectral region, was observed from Eu doped ZnS. A defect level situated at about 0.36 eV above the valence band was detected only in Sm doped ZnS by infrared absorption spectroscopy. The cause of the difference in the luminescence properties between Sm doped ZnS and Eu doped ZnS was reasonably explained by the model of defect related energy transfer associated with the 0.36 eV level.