X-ray excited luminescence and local structures in Tb-doped Y2O3 nanocrystals

Abstract

Pronounced structure in x-ray excited luminescence (XEL) has been observed in dilute Tb-doped ${\mathrm{Y}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}$ $({\mathrm{Y}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}\mathrm{:Tb})$ nanocrystals. This effect affords a means to assess different energy transfer mechanisms in the nanocrystals and also an opportunity for novel device applications. Sharp jumps and oscillations are found in the XEL output with the incident x-ray energy around the absorption edges of Y and Tb. When compared with a bulk ${\mathrm{Y}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}\mathrm{:Tb}$ sample, these effects are attributed to some unique electronic and optical properties of doped nanocrystals related to quantum confinement of charge carriers, and the main features can be explained by a proposed model of multichannel energy transfer. Extended x-ray absorption fine structure techniques have also been employed to study the effect of size variation and chemical doping on the local structures in ${\mathrm{Y}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}$ and ${\mathrm{Y}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}\mathrm{:Tb}$ nanocrystals. The local environment surrounding Y and Tb in the nanocrystals is compared with that in the respective bulk material. The results indicate that Tb impurity atoms substitute for Y sites in bulk ${\mathrm{Y}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}},$ while doping in the nanocrystals is complicated by the large fraction of surface atoms and local disorder.