Sno < Sub > 2 < / Sub > And Sns < Sub > 2 < / Sub >, Ito Glow Micro-nano Structure Design, Synthesis And Performance Research

In this thesis, we report three sorts of metal oxide miro&nano structures such asdepressive SnO₂nanowires clusters, porous SnO₂mirospheres, hexagonal SnS₂nanoplates, and polyhedral ITO particles. The synthesis, characterization, andluminescence properties of these structures were carefully investigated. The SnO₂andITO structures were synthesized via a methods of directly thermal evaporation ofmetal oxide, while the hexagonal SnS₂nanoplates were obtained by a solvothermalmethod using a mixture of ethylene glycol （EG） and distilled water as solvent. Themorphologies of all the as-prepared products were characterized by a field emissionscanning electron microscope （FESEM, JEOL-JSM-6700F） equipped with an energydispersive spectrometer （EDS, Link ISIS, Oxford）. The crystal phases of products wereidentified by x-ray diffraction （XRD, D/MAX2500VL/PC） with CuKα （λ=1.54）radiation, transmission electron microscopy （TEM, HITACHI H-800） and highresolution electron microscopy （HRTEM, JEOL JSM-2010）. X-ray photoelectronspectroscopy （XPS） and Raman spectra are obtained from Laser Confocal RamanMicroscope （LABRAM-RH, JY. co., France） and XPS spectrometer （ESCALAB250,Thermo-VG Scientific）, respectively. Photoluminescence （PL） spectrum of the SnO₂and SnS₂products were obtained on a fluorescence spectrophotometer （HITACHIF-4500） using a Xe lamp with an excitation wavelength of325nm at room temperature,while the PL spectrum of ITO samples were measured on a steady-statespectrofluorometer （FLUOROLOG-3-TAU） at room temperature using a He–Cd laseras the excitation source. Cathodoluminescence （CL） spectroscopy of ITO samples wereperformed at room temperature by means of a Gatan MonoCL system attached to ascanning electron microscope. The electron spin resonance （ESR） spectra of ITOsamples were recorded on an Electron Spin Resonance Spectrometer （JES-FA200） at amodulation frequency of100kHz with modulation amplitude of0.1mT and a sweepwidth of30mT. The main results are summarized as follows:1. Study on the annealing-dependent photoluminescence properties of SnO₂nanowires clusters. In chapter three, SnO₂cluster-system structures were synthesizedvia a two step temperature-rising thermal evaporation method with short oxidation time.Field emission scanning electron microscopy, X-ray diffraction and transmissionelectron microscopy were used to characterize the morphological and structural feature of the product with nanowire cluster and nanoparticle cluster. The photoluminescencespectra exhibit that, as annealing time longing in air, the intensity of the newly foundstrong ultra-violet emission decreases while the green emission enhances. Ramanspectrum and X-ray photoelectron spectroscopy investigations reveal that the relativelydecreasing intensity was dominated by the increasing oxygen vacancy. Furthercalculation based on the SnO₂crystal lattices with H2O molecules at different steps inevaporation process was performed with Chem3D software. It confirms that, instead ofthe influence of H2O molecules from air, the decreasing intensity is the result of thecombined action of the formation of oxygen vacancy and the energetic oxygencompensation in annealing treatment. According to the different annealing time in air,we can synthesize different intensities of green emission of the optical target which willbe applied on luminescence devices.2. Porous SnO₂microspheres: The effect of surrounding atmospheres on the PL property.In chapter four, one step thermal evaporation method was utilized to synthesize porousSnO₂microspheres. A set of experiments of different storage periods in water and ethanolsurrounding atmospheres were carried out. The PL results pointed out that the intensities of PLpeak exhibited a more sensitivity of stored samples in water surrounding atmospheres than theircounterpart in ethanol surrounding atmospheres. The comparison of PL property and theanalysis of XPS results indicated that since there are three kinds of oxidation states on thesurface of stored samples in water surrounding atmospheres, the interaction of the three statesand the effect of ultraviolet excitation light in the PL measurement can change the oxidevacancy on the surface of spheres. The sensitivity of PL spectrum was lower than that fromsample stored in surrounding atmospheres of ethanol which is easy to evaporate. The surfaceabsorption balance-controlled oxide vacancy content leads to the more sensitive PL property.The annealing test in Ar gas in700℃was also performed on sample. The comparison of thePL spectra to that from the water atmosphere-stored sample leads to the surface disorder as adeceasing function of surface oxygen content, which means that tuning the surface disorder isthe key to the changes of PL intensities.3. Hexagonal SnS₂nanoplates: synthesis, groth mechanism, and luminescenceproperty.In chapter five, hexagonal SnS₂particles were synthesized via a solvothermal methodusing a mixture of ethylene glycol （EG） and distilled water as solvent. Comprehensive synthesisparameters were considered to obtain the products including the solution formulation, the initialcharge ratio, the holding temperature, the keeping time of the holding temperature, and theproportion of atoms Sn:S. According to the calibrated SAED, a model of mono hexagonal SnS₂ molecule was established with Chem3D software. Based on the model, the interactions betweenEG and the hexagonal SnS₂molecule and between hexagonal SnS₂molecules were studied. Theresults indicated that The EG has an effect of on the growth of hexagonal SnS₂nanoplates in[001]. The hexagonal SnS₂nanoplates exhibited a red emission at761nm, which is attributed tothe sulfur vacancy based on the analysis of XPS and Raman spectra. A large band gap of3.52eV of the hexagonal SnS₂nanoplates was calculated by the light absorption measurement invisible region. The large band gap meets the acquirement of dye-sensitized solar cells （DSSC）.An experiment of dye N719absorption on the surface of hexagonal SnS₂nanoplates was alsocarried out. The results indicated that the hexagonal SnS₂nanoplates have, somehow, anabsorbency of N719. Therefore, the hexagonal SnS₂nanoplates synthesized via solvothermalmethod can be applied in the photoanode material in DSSCs.4. Polyhedral ITO particles: Synthesis, characterization and origins of luminous emissionin wide visible range.In chapter six, a bi-precursors thermal co-evaporation was developed tosynthesized polyhedral ITO particles. Structural characterization results demonstrated that thetetrakaidecahedronal ITO particles had additional six {001} crystal surfaces compared with theoctahedronal ones. A more enhanced intensity of normalized PL emission at432nm was foundin octahedronal ITO particles than in the tetrakaidecahedronal ones. According to the ESRinvestigation, it was attributed to the more oxygen vacany in octahedronal ITO, which alsoleads to the uniform light area in CL spectrum, however, dark area was discovered intetrakaidecahedronal ITO particles. The luminous properties of both samples were characterizedby photoluminescence （PL） and cathodoluminescence （CL） spectroscopy. A broad visibleluminous emission around570nm was observed. Studies revealed that the emission consistedof three peaks of511nm,564nm, and622nm which were attributed to radioactiverecombination centers such as single ionized oxygen vacancy, indium interstitial, and antisiteoxygen, respectively.