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

Abstract Three types of β-NaYF 4 nanoparticles, uncoated core (NaYF 4 :Yb/Ho/Ce), single-layer coated core@shell (NaYF 4 :Yb/Ho/ Ce@NaYF 4 :Yb) and double-layer coated core@shell@shell (NaYF 4 :Yb/Ho@NaYF 4 :Yb@NaYF 4 :Yb) with Ce 3+ doped in core, first and second shell, respectively, were synthesized through solvothermal method to investigate the cross-relaxation between Ho 3+ and Ce 3+ for the tunable upconversion luminescence. By doping Ce 3+ 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 Ce 3+ in the same layer of Ho 3+ . And if Ce 3+ and Ho 3+ were separated in different layers, the color tuning would be depressed significantly due to the reduced cross-relaxation between Ho 3+ and Ce 3+ . Moreover, the UC emission intensity of core@shell and core@shell@shell was enhanced significantly compared with that of unmodified core nanoparticles.