NaMn₃F₁₀:Yb,Er Red Light Emission Upconversion Nanoparticle Preparation And Its Application In Cell Imaging Applications

In recent years, Lanthanide-doped upconversion nanoparticles(UCNPs) have drawn more and more attention in a variety of biomedical applications. The UCNPs can upconvert near-infrared(NIR) photons into those with higher-energy. UCNPs with single-band red emission are also favorite for biological imaging applications, since red light can penetrate much more deeply through most tissues, up to several millimeters in optimal cases compared to other visible wavelengths, and is easier to be detected compared to NIR wavelength. Mn doped Na YF4 nanoparticles exhibit very promising performance, because they can contribute to single-band red(~660 nm) emission. In addition, Nd doped shells as sensitizers are a popular technique to convert the excited wavelength from 980 nm to 808 nm, in order to avoid the laser-induced overheating effects at 980 nm wavelength(very close to the absorption peak of water). Therefore, it is the most ideal choice to synthetize UCNPs with 808 nm excitation and red single-band emission for bio-imaging applications. However, the conventional synthesis route of Mn doped UCNPs requires relatively harsh conditions, e.g., high temperature and high pressure, which are harmful for the formation of core-shell structures. In this dissertation, a novel strategy is proposed to synthesize core-shell structured Na Mn3F10:Yb,Er @ Na Mn3F10:Yb,Nd UCNPs with both 808 nm excitation and single-band red emission by using an improved solvothermal method. The detailed studies in this dissertation are as follows:(1) Mn doped Na YF4:Yb,A(A=Er, Ho, and Tm) nanoparticles are synthesized by using a facile and user-friendly solvothermal method, which could be carried out in the flask under ordinary pressure. The method is beneficial to form core-shell structures. The effect of the concentration of Mn ions on the optical properties of the nanoparticles was investigated. The intensity ratio between red emission and green emission can be enhanced by a factor of more than 300 by using Na Mn3F10: 20%Yb, 2%Er.(2) The reheating process in the present improved solvothermal method can overcome the problem that Mn doped UCNPs with core-shell structured are very difficult to be synthetized. Experimental results show that core/shell structured Na Mn3F10: 20%Yb,2%Er @ Na Mn3F10 and Na Mn3F10: 20%Yb, 2%Er @ Na Mn3F10: 20%Yb with both inert Na Mn3F10 and active Na Mn3F10: 20%Yb shell layer are helpful to enhance the red emission. The 808 nm excitation was achieved by using core/shell structured Na Mn3F10: 20%Yb, 2%Er @ Na Mn3F10: 20%Yb, 20%Nd.(3) With hydrophilic modifications, the prepared UCNPs serve as optical nanoprobes for He La cellular imaging cells. A good image quality has been obtained with excellent light stability and low autofluorescence interference by using a laser confocal scanning microscope. Finally, cellular imaging by using the UCNPs as nanopropes with both 808 nm excitation and single-band red emission(i.e., Na Mn3F10: 20%Yb, 2%Er @ Na Mn3F10: 20%Yb, 20%Nd) was successfully realized.