Photoluminescence properties of Mn2+-doped II–VI semiconductor nanocrystals

Our recent photoluminescence studies on ZnS:Mn2+- and CdS:Mn2+-nanocrystals dispersed in polyvinyl alcohol polymer films are reviewed. Both nanocrystal samples show Mn2+ 3d intrashell luminescence with high quantum efficiencies of about 20% at room temperature under the interband excitation. Noticeable characteristics of our nanocrystal samples are that the luminescence involving some trap state is much weaker than the Mn2+ luminescence, unlike other reports, and that thermal quenching of the Mn2+ luminescence is remarkably weak, compared with the corresponding bulky crystal powder. These two characteristics lead to the above high quantum efficiencies of the Mn2+ luminescence at room temperature. In addition, we examine the dominant excitation mechanism of Mn2+ in the nanocrystals under the interband excitation and the validity of the sp–d mixing model proposed previously to explain the high luminescence quantum efficiency.