Multicolor tuning towards single red-emission band of upconversion nanoparticles for tunable optical component and optical/x-ray imaging agents via Ce3+ doping

A simple strategy of Ce3+ doping is proposed to realize multicolor tuning and predominant red emission in BaLnF(5): Yb3+/Ho3+ (Ln(3+) = Gd3+, Y3+, Yb3+) systems. A tunable upconversion (UC) multicolor output from green/yellow to red can be readily achieved in a fixed Yb3+/Ho3+ composition by doping Ce3+, providing an effective route for multicolor tuning widely used for various optical components. Moreover, compared with Ce3+-free UC nanoparticles (UCNPs), a remarkable enhancement of the red-to-green (R/G) ratio is observed by doping 30% Ce3+, arising from the two largely promoted cross-relaxation (CR) processes between Ce3+ and Ho3+. UCNPs with pure red emission are selected as in vivo UC bioimaging agents, demonstrating the merits of deep penetration depth, the absence of autofluorescence and high contrast in small animal bioimaging. Moreover, such fluorescence imaging nanoprobes can also be used as contrast agents for three-dimensional (3D) x-ray bioimaging by taking advantage of the high K-edge values and x-ray absorption coefficients of Ba2+, Gd3+, and Ce3+ in our designed nanoprobes. Thus, the simultaneous realization of multicolor output, highly enhanced R/G ratio, and predominant red emission makes the Ce3+-doped UCNPs very useful for widespread applications in optical components and bioimaging.