PEGylated upconverting luminescent hollow nanospheres for drug delivery and in vivo imaging.

Upconversion luminescent hollow Y2 O3 :Yb(3+) /Er( 3+) nanospheres can be synthesized by an etching-free process, which hold promising potential for applications such as drug delivery, angiography, and high-contrast cellular as well as tissue imaging, with no damage from radiation or toxicity.