Size and Concentration Effects on the Photoluminescence of La2O2S:Eu3+ Nanocrystals

The effects of size and europium concentration on photoluminescence properties of La2O2S: Eu3+ nanocrystals (similar to 20 nm) and the corresponding bulk were studied. The results indicate that in nanocrystals, the absorption edge largely shifted to blue in comparison to the bulk, which was mainly attributed to the variation of phonon-excitation relaxation. Two excitation bands were observed, located at similar to 250 and similar to 330 nm, respectively, corresponding to the charge transfer (CT) transitions of Eu-O and Eu-S. Relative to the CT transition of Eu-O, that of Eu-S increased greatly with europium concentration. The dependence of photoluminescence intensity on concentration showed that in the nanocrystals and the bulk, Eu3+ ions had two different quenching mechanisms, respectively, the exchange interaction and electric dipole-dipole interaction.