Bi3+-Doped BaYF5:Yb,Er Upconversion Nanoparticles with Enhanced Luminescence and Application Case for X-ray Computed Tomography Imaging.

ABSTRACT

In this work, BaYF520%Yb3+/2%Er3+/x%Bi3+ (abbreviated as BaYF5Yb,Er,Bix, where x = 0-3.0) upconversion nanoparticles (UCNPs) with various doping concentrations of Bi3+ were synthesized through a simple hydrothermal method. The influence of the doping amount of Bi3+ on the microstructures and upconversion luminescence (UCL) properties of the BaYF5Yb,Er,Bix UCNPs was studied in detail. The doping concentration of Bi3+ has little influence on the microstructures of the UCNPs but significantly impacts their UCL intensities. Under excitation of a 980 nm near-IR laser, the observed UCL intensities for the BaYF5Yb,Er,Bix UCNPs display first an increasing trend and then a decreasing trend with an increase in the ratio x, giving a maximum at x = 2.5. A possible energy-transfer process and simplified energy levels of the BaYF5Yb,Er,Bix UCNPs were proposed. The potential of the BaYF5Yb,Er,Bix UCNPs as contrast agents for computerized tomography (CT) imaging was successfully demonstrated. An obvious accumulation of BaYF5Yb,Er,Bix in tumor sites was achieved because of high passive targeting by the enhanced permeability and retention effect and relatively low uptake by a reticuloendothelial system such as liver and spleen. This work paves a new route for the design of luminescence-enhanced UNCPs as promising bioimaging agents for cancer theranostics.