Preparation, Characterization And Functionalization Of Rare Earth Luminescent And Up-converting Nanoparticles

Rare-earth doped luminescent materials have been widely used in phosphors, display monitors, X-ray imaging, scintillators, lasers and amplifies for fiber-optic communications due to their advantages of high absorptive capacity, high conversion efficiency and broader emission range covering from ultraviolet to infrared range. Up-converting luminescence is a unique phenomena observed in rare-earth luminescent materials. When excited with infrared light, rare earth up-converting luminescent nanocrystals can produce visible light with a narrow band width (long life time), stable light emission (less susceptible to environmental impact) and low background. Thus, rare earth up-converting luminescent nanocrystals are believed to have wider applications in biological fluorescent labeling and imaging.At present, applications of rare earth up converting luminescent nanocrystals in fields of biological fluorescent labeling and imaging are limited because of several factors. Firstly, there are less methods by which one can synthesize high quality rare earth luminescent nanocrystals with well controlled size, morphology and unique luminescent properties. Secondly, the water solubility and biocompatibility of rare earth nanocrystals synthesized via conventional methods are relatively poor. Thirdly, there are few effective methods for the surface modification and functionalization of rare earth luminescent nanocrystals, making them difficult to bioconjugate with biomolecules.Based on the above research background, we try to develop a new method for synthesis of rare earth fluorescent and up-converting luminescent nanocrystals. The methods for the surface modification and functionalization of rare earth luminescent nanocrystals were also developed by the process of inorganic coating and surface oxidation.The main results of the present works were summarized as follows: 1. The microemulsion-hydrothermal synthesis method was developed to synthesize rare earth YVO₄, Y_0.78Yb_0.20Er_0.02VO₄ and Y_0.78Yb_0.20Tm_0.02VO₄ nanocrystals. Their size, size distribution, morphology, microstructure and phase structure as well as up-converting luminescent properties were systematically investigated by means of X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and fluorescence spectroscopy techniques. The results indicated that the YVO₄, Y_0.78Yb_0.20Er_0.02VO₄ and Y_0.78Yb_0.20Tm_0.02VO₄ nanocrystals prepared by microemulsion-hydrothermal method showed well dispersed tetragonal structures with weaker aggregation and smaller sizes comparing to those obtained by solid diffusion or sol-gel methods. Moreover,Y_0.78Yb_0.20Er_0.02VO₄ and Y_0.78Yb_0.20Tm_0.02VO₄ prepared by microemulsion-hydrothermal method displayed unique up-conversion luminescence.2. Rare earth NaY_0.95Eu_0.05F₄ and NaY_0.78Yb_0.20Er_0.02F nanocrystals were prepared by thermally decomposing of rare earth trifluoroacetic acid complexes in high boiling point solvents. Surface coating and modification of the NaY_0.95Eu_0.05F₄ and NaY_0.78Yb_0.20Er_0.02F nanocrystals were performed by using a unique water/CTAB/hexanol microemulsion system as coating media. By controlling the amount of organic silane-coated precursors [TEOS (TEOS), 3-aminoethyl trimethoxysilane (APS)], the composition of microemulsion and the concentration of rare earth nanocrystals, the controlled surface modification and functionalization of the NaY_0.95Eu_0.05F₄ and NaY_0.78Yb_0.20Er_0.02F nanocrystals were achieved. Moreover, the surface modification and functionalization had no obvious effects on the structures and fluorescent and up-conversion luminescent properties of NaY_0.95Eu_0.05F₄ and NaY_0.78Yb_0.20Er_0.02F₄ nanocrystals. The obtained NaY_0.95Eu_0.05F₄ and NaY_0.78Yb_0.20Er_0.02F nanocrystals with well coated surfaces show great promising to be used as fluorescent probes in applications of biological fluorescent labeling and imaging.