Energy structure and fluorescence of Eu2+ in ZnS : Eu nanoparticles

Eu2+-doped ZnS nanoparticles with an average size of around 3 nm were prepa red, and an emission band around 530 nm was observed. By heating in air at 150 degrees C, this emission decreased, while the typical sharp line emissi on of Eu3+ increased. This suggests that the emission around 530 nm is from intraion transition of Eu2+: In bulk ZnS:Eu2+, no intraion transition of E u2+ was observed because the excited states of Eu2+ are degenerate with the continuum of the ZnS conduction band. We show that the band gap in ZnS:Eu2 + nanoparticles opens up due to quantum confinement, such that the conducti on band of ZnS is higher than the first excited state of Eu2+, thus enablin g the intraion transition of Eu2+ to occur.