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Synthesis and Physical Properties of Micron and Nanoscale Inorganic Materials

Author: WangZhiJun
Tutor: YaoLianZeng;LiXiaoGuang
School: University of Science and Technology of China
Course: Materials Physics and Chemistry
Keywords: University of Science and Technology of China Nanobelts Doctoral Dissertation Porous alumina template Nano-materials Dendritic Hexagonal phase Nanostructures Emission spectra Reaction conditions
CLC: TB321
Type: PhD thesis
Year: 2007
Downloads: 362
Quote: 1
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Abstract


In this dissertation, hydrothermal and template technique for the synthesis of micron- and nano-scale inorganic materials were enriched and developed. Several inorganic materials have been fabricated via various and logical routes. The control of the morphology and size of the products and the growth mechanism and fluorescence spectrum have also been investigated. The main contents can be summarized as following:1. The cubic NaYF4 nano-spheres and the hexagonal NaYF4 micro-prisms have been prepared separately via a complex-assisted hydrothermal route by controlling the reaction conditions. The dependence of the crystal morphology on the reaction conditions, such as the molar ratios of the initial reactants, the time, and the temperature, is investigated in detail. We have synthesized NaEuF4 crystals with spindle-like and rod structures by controlling the solution reaction conditions, such as the molar ratio of F-/Eu3+, pH value of the mother liquors and the reaction time. Strong orange and red light emission is observed from room - temperature emission spectrum of as-prepared NaEuF4 crystals.2. Trivalent lanthanide ions (Ln3+) doped NaYF4 microstructures have been synthesized using a hydrothermal method. Varying the dopants （Eu, Sm, Pr, Yb and Er） leads to different optical properties. The efficient green and red up-conversion （UC） luminescence of 2 mol% Er3+ and 20 mol%Yb3+ codoped NaYF4 is detected under a 980-nm IR excitation. There are three emission bands located at 520-527, 538-548, and 655 ran corresponding to an electron transfer from the excited states 2H11/2, 4S3/2, and 4F9/2 to the ground state 4I15/2, respectively. In Eu3+ doped NaYF4, the bright orange and red emissions near 590 nm and 615 nm are noticeable due to 5D0—7F1 transition and 5D0—7F2 transitions, respectively. The characterize emissions of Sm3+ are observed in the yellow to red region, which correspond to a group of typical 4G5/2—6HJ （J=5/2, 7/2, 9/2, 11/2） transitions in Sm3+ doped NaYF4 microstructures. In Pr3+ doped NaYF4, there are two strong emission bands located at 483, and 602-608nm corresponding to an electron transfer of 3P0—3H4 and 1D2—3H4、3P0—3H6, respectively.3. Silver dendritic hierarchical structures have been synthesized using a simple surfactant-free method by carrying out the silver mirror reaction on the surface of a porous anodic aluminium oxide （AAO） template. The length of the stem is several tens of micrometers; the length of the each leaf ranges from 0.5 to 4μm with a width of about 100～300 nm. Single crystalline silver nanobelts with a thickness of around 5-10 nm and a width of about 60-80 nm are obtained when the silver dendritic nanostructures are ultrasonically treated. The ultrasonic treatment facilitates the pyramid-like leaf-tip silver nanoparticles to separate from the stem of dendritic hierarchical structures and revealed the Ag nanobelts. The synthetic strategy presented here is simple and environmentally friendly, and may provide a promising method to prepare dendritic hierarchical structures and nanobelts.4. The CdS nanobelts with high quality and even morphology have been fabricated via a rapid evaporation route on Si substrate without any catalyst. XRD, SEM and HRTEM investigations reveal that the as-prepared samples are single-crystals of CdS nanobelts with a hexagonal wurtzite structure growing along the [001] direction. The VS model is proposed for the growth mechanism of CdS nanobelts.

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