Trivalent Yb/Ho/Ce tri-doped core/shell NaYF 4 nanoparticles for tunable upconversion luminescence from green to red

Three types of β-NaYF4 nanoparticles, uncoated core (NaYF4:Yb/Ho/Ce), single-layer coated [email protected] (NaYF4:Yb/Ho/ [email protected]4:Yb) and double-layer coated [email protected]@shell (NaYF4:Yb/[email protected]4:[email protected]4:Yb) with Ce3+ doped in core, first and second shell, respectively, were synthesized through solvothermal method to investigate the cross-relaxation between Ho3+ and Ce3+ for the tunable upconversion luminescence. By doping Ce3+ into different layers with different doping concentrations, a systematical investigation on the tunable upconversion luminescence from green to red was conducted. The results showed that a remarkable color tuning could be achieved from green to red when increasing the doping concentration of Ce3+ in the same layer of Ho3+. And if Ce3+ and Ho3+ were separated in different layers, the color tuning would be depressed significantly due to the reduced cross-relaxation between Ho3+ and Ce3+. Moreover, the UC emission intensity of [email protected] and [email protected]@shell was enhanced significantly compared with that of unmodified core nanoparticles.