Upconversion nanoparticles have been demonstrating great potentials in deep-tissue imaging with less or without photon-damage because they can convert the excitation light in the near-infrared wavelength region (700 nm < λex< 1200 nm) to the emission light in the visible region (400 nm < λem< 700 nm). This study presents a facile method for the synthesis of amine functionalized hydrophilic NaGdF4: Yb3+, Er3+ upconverting nanostructures. The prepared nanoparticles were subjected to various characterizations including transmission electron microscopy (TEM) and high-resolution TEM, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD). The fluorescence and magnetic properties of the produced upconversion nanoparticles were further investigated by a fluorometer and a vibrating sample magnetometer (VSM) analysis. It is found that the ratio of the emission intensity of the synthesized upconverting nanoparticles in aqueous at 540 nm to their emission intensity at 660 nm (I540/I660) is about 8.3 times of the ratio (I540/I660) of the upconverting nanoparticle in the format of powder. The difference between the samples in aqueous media and in the format of powder may be caused by the water molecules absorbed onto the surface ligands of the nanoparticles, which is likely to decrease upconversion fluorescence by nonradiative decay. This method provided a facile synthesis route to the preparation of amine functionalized hydrophilic NaGdF4: Yb3+, Er3+ upconverting nanoparticle.
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