Size dependence of Eu2+ fluorescence in ZnS:Eu2+ nanoparticles

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Abstract
The emission bands of the 4.2, 3.2 and 2.6 nm sized ZnS:Eu 2+ nanoparticles are peaking at 670, 580 and 520 nm, respectively. The emission of the 4.2 nm sized nanoparticles originates from the recombination of the Eu 2+ -bound exciton, while the emission of the 3.2 and 2.6 nm sized nanoparticles is from the Eu 2+ intra-ion transition of 4f 6 5d 1 (t 2g )–4f 7 . Possible mechanisms for the size dependence of the 4f 6 5d 1 (t 2g )–4f 7 transition of Eu 2+ in ZnS:Eu 2+ nanoparticles were investigated, and it was concluded that the decreases in the electron–phonon coupling and in crystal field strength upon a decrease in size are the two major factors responsible for the shift.