Controlled agglomeration of Tb-doped Y2O3 nanocrystals studied by x-ray absorption fine structure, x-ray excited luminescence, and photoluminescence

Abstract

Local environment surrounding Y atoms in ${\mathrm{Y}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}\mathrm{:Tb}$ nanocrystals under various heat treatment conditions has been investigated by using the extended x-ray absorption fine structure (EXAFS) technique. X-ray excited luminescence (XEL) with the incident x-ray energy near Y K edge and Tb L edges has also been measured to investigate the mechanisms of x-ray-to-visible down conversion in these doped nanoparticles. The observed changes in EXAFS, XEL, and photoluminescent data can be explained on the basis of increased average size of the nanoparticles as confirmed by transmission electron microscopy studies. Our results thus demonstrate that the doped nanoparticles can agglomerate to a controllable degree by varying the heat treatment temperature. At higher temperatures, the local environment surrounding Y atoms in the nanoparticles is found to become similar to that in bulk ${\mathrm{Y}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}$ while the XEL output still shows the characteristics of nanocrystals. These results indicate that appropriate heat treatment can afford an effective means to control the intensity and signal-to-background ratio of green luminescence output of these doped nanocrystal phosphors, potentially useful for some device applications.