Luminescence intensity of Ag⁺ doped Y₂O₃:Eu nanocrystals

Eu³⁺ doped Y₂O₃ nanocrystalline and bulk powders with small content of Ag⁺ were prepared by chemical self-combustion. An interesting phenomenon was observed: with an increase in Ag⁺ content the luminescent intensity of the nanosized crystal is enhanced at first and then maintains a stable level; however for the bulk powder there is no obvious change in the luminescent intensity when the Ag⁺ content is varied. The morphology and crystal structure were characterized by transmission electron microscopy (TEM) and X-ray Diffraction (XRD), respectively. Emission spectra were measured for nano- and bulk samples. The fluorescence decay curves for all the samples, including nanosized and bulk ones, either with or without Ag⁺, were measured. It is found that the lifetime for the nanosized sample with Ag⁺ is longer than that without Ag⁺, and the lifetime for the bulk sample has no change. From these experimental results we come to the conclusion that the Ag⁺ ion may link with a surface O^2-, which has a free bond, then the surface unsaturated dangling bonds can be eliminated. The elimination of surface dangling bonds may cause the increase of luminescence efficiency of Eu⁺ doped nanosized Y₂O₃.