Controlled synthesis, bioimaging and toxicity assessments in strong red emitting Mn2+ doped NaYF4:Yb3+/Ho3+ nanophosphors

Rare earth, Yb3+/Ho3+ doped NaYF4 nanophosphors showed augmentation of visible green and red light emission by the introduction of Mn2+ as a co-dopant. Nanophosphors were characterized for their morphology and upconversion (UC) fluorescence, as a function of co-dopant concentration. The effect of Mn2+ doping has been investigated to explore the UC mechanism of the phosphors. With the introduction of Mn2+, the intensity of all the emission bands was increased, in particular the red band, which was most significant at 40 mol% doping. A possible mechanism for the enhancement of the red emission has been proposed. The prepared UC nanoparticles were functionalized with polyethylene glycol-polyethylene imine co-polymer to make them water dispersible and successfully applied for cancer cell imaging.