Page 136 - Synthesis of Functional Nanoparticles Using an Atmospheric Pressure Microplasma Process - LiangLiang Lin
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Chapter 7
X-ray diffraction (XRD) using a Rigaku Powder Diffractometer (Cu-Kα1 radiation, λ=1.54056 Å). The scans were recorded in a 2q step of 0.02 and a dwell time of 20s. Raman measurements were performed using a LabRAM HR Evolution Confocal Raman microscope (Horiba Jobin-Yvon) equipped with an 1800 lines/mm grating. The excitation wavelength was 632.8 nm, and spectra were measured in the 0-2000 cm-1 range. The photoluminescence measurements were performed at room temperature on a luminescence spectrometer (Perkin Elmer, Model LS-50B) using certain wavelength as the excitation source.
7.3 Results and Discussions
Figure 7.1(a) shows representative images of the reactor, plasma-liquid interaction process and the plasma-treated electrolyte solution to illustrate this concept. Optical emission spectrum (OES) is record to identify the intermediate radicals (Figure 7.1(b), detailed radiative transition information: Supplementary Material Table S1). The most prominent spectral feature is the argon atomic transitions between highly excited electronic states (4p→4s) in the wavelength region of 690-1000 nm. The emission band of OH radicals, with a strong peak starting at 305 nm and falling off towards 325 nm (the 3064 Å system), is also clearly observed. Less intensive emission lines of atomic hydrogen (486nm, 657 nm) and atomic oxygen (777 nm) species are also detected, indicating the presence of high energy electrons and the dissociation of water molecules under the plasma treatment.8 Furthermore, by fitting the experimental spectrum with the simulated one using the N2 SPS system, the gas temperature during plasma-liquid interactions is estimated to be ~2000 K, suggesting the non-equilibrium characteristic of the plasma.9 In this plasma configuration, the above electrode is negatively-biased. Electrons are driven and accelerated towards the solution surface to collide with water molecules. Hydroxyl radicals can be released from water under electron impacts to form precipitant ions. Meanwhile, since Y3+ and Eu3+ are homogenously mixed at the molecular level, luminescent ions can be uniformly embedded into the host matrix. Based on the OES result, Figure 7.1(c) gives an overview of possible reaction pathways of the plasma-induced lanthanide doping process.
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