Hydro-thermal synthesis of PEGylated Mn2+ dopant controlled NaYF4: Yb/Er up-conversion nano-particles for multi-color tuning

• The crystal phase of UCNPs can be tuned by doping Mn2+.
• Mn2+ doping induced multicolor output from yellow to red can be achieved.
• The enhancement of the R/G ratio was realized via increasing Mn2+concentration.

In this paper, different Mn2+ doped NaYF4: Yb/Er nanoparticles were synthesized by a simple one-pot hydrothermal method using polyethylene glycol (PEG) as coating polymer. The as-prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and upconversion (UC) spectra. The XRD results revealed that the crystal phase of NaYF4: Yb/Er nanoparticles could be readily tuned from hexagonal to cubic phase by doping Mn2+. Under the excitation of 980 nm laser, UC luminescent colors were also changed from yellow to red by doping Mn2+. Moreover, the remarkable enhancement of red to green emission (R/G) ratio from 1.79 to 10.71 was achieved when increasing Mn2+ concentration from 0% to 30%. These UC nanoparticles with controlled crystal structure, tunable output colors, and enhanced R/G ratio may have potential applications in optical devices, color display, and especially biomedical imaging.

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