Page 135 - Synthesis of Functional Nanoparticles Using an Atmospheric Pressure Microplasma Process - LiangLiang Lin

Rare Earth Doped Yttrium Oxide Nanophosphors Synthesis and Engineering- Controllable Photoluminescence Properties
Ln(NO3)3·6H2O were used as the starting raw materials. Electrolyte solution was prepared by mixing Y(NO3)3·6H2O and Ln(NO3)3·6H2O according to the formula (Y1-xLnx)2O3 or (Y1- x-yLn1xLn2y)2O3 and dissolving in deionized water. The plasma electrodeposition of lanthanide hydroxides was carried out in the microplasma reactor (Figure 7.1). For all experiments, an argon flow of 50 sccm gas flow rate was coupled to the capillary as the plasma gas. 10 ml (0.05 mol/L) electrolyte solution was placed in the micro reactor for the plasma treatment, with a typical processing time of 3 hours for each operation. After the plasma treatment, lanthanide-doped hydroxide sediments were formed in the electrolyte solution, which were then heat-treated at various temperatures (600-1200 °C) at a heating rate of 10 °C/min and maintained for 3 hours to obtain the oxides derivation. Then the products were scraped from the crucible for further characterization.
7.2.2 In-situ Characterization of the Microplasma
The plasma-liquid interaction was firstly characterized by electrical measurements. Experimental values of the plasma current, voltage and power were automatically logged using a LabVIEW based program. The plasma-liquid interaction was also in-situ monitored by an optical emission spectrometer (HR2000+ES, Ocean Optics, Inc.) with spectral resolution of 0.88 nm. The spectrum was recorded in the wavelength range from 200 nm to 1000 nm. The emitted light was collected by an optical fiber fixed at 20 mm from the microplasma. Moreover, in order to estimate the gas temperature, a higher resolution spectrometer (HR2000+, Ocean Optics, Inc.) with spectral resolution of 0.21 nm and wavelength range of 200-420 nm was also applied. As suggested by P. Bruggeman, 0.5 sccm N2 was added in the discharge for determining the gas temperature of plasmas in contact with liquids using the N2 SPS system by Specair fitting.7 It should be noted that, this is an emission-averaged value derived from the light gathered over entire microplasma volume, since microplasma filament has a nonuniform nature with strong radial gradients in temperature.
7.2.3 Ex-situ Characterization of the Lanthanide Doped Yttria Nanophosphors
Complementary analytical methods have been applied to characterize the obtained lanthanide doped nanophosphors. TEM analysis was carried out on a FEI Tecnai 20 (Sphera) microscopy operated with a 200 kV LaB6 filament for further investigation of the microstructures. TEM samples were prepared by dispersing a small quantity of the products into ethanol and sonicating for 30 min. Then one drop of the solution was casted on a carbon-coated Cu TEM grid (Quantifoil Micro Tools, GmbH). To get a better idea on nanoparticle size and distribution, size distribution histograms were constructed by randomly measuring 300 particles from TEM images. Thermogravimetric analysis was carried out on a Mettler-Toledo TGA/DSC 1 instrument. Approximately 10 mg sample was placed in a crucible and heated to 750 °C at a rate of 10 °C/min in a flow mixture of O2/He. EDX characterization was performed on a Quanta 3D FEG (FEI) operated at 10 kV, with a silicon drift element detector (Sapphire DPP-2) to examine the chemical composition. The surface chemical composition and binding information were furtherly assessed by an X-ray photoelectron spectroscopy (Thermo Scientific Kα), with spectra obtained using an aluminum anode (Al Kα=1486.6 eV) operating at 72W and a spot size of 400μm. The crystalline structure was characterized by
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