The use of red light or near-infrared radiation as a luminescent probe for in vivo bio imaging is crucial in order to restrict the strong absorption of short-wavelength light below 600 nm in tissue. It is demonstrated that the emission color of Yb/Ho codoped NaYF4 nanoparticles can be tuned from green to red by incorporating Ce3+ ions. However, compared with that of the NaYF4:Yb/Ho nanoparticles, the photoluminescence intensity of the Ce3+-tridoped NaYF4:Yb/Ho nanoparticles is drastically reduced. In this work, Ce3+-incorporated core/shell NaYF4:Yb3+50%@NaYF4:Ho3+0.5% nanoparticles are prepared. A strong red emission and a high-intensity ratio between the red emission and green emission are obtained in these upconversion nanoparticles. The emission intensity increases by a factor higher than 120 when compared with that of the NaYF4:Yb/Ho/Ce nanoparticles. This result indicates that the Ce3+ incorporation into the

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