Ultrasonic Preparation And Physical Characterization Of New Optical-Function Nanomaterials

The nanomaterials are increasingly important in recent years,in order to achieve superior functional materials,many new methods have been invented by scientists.Among all the methods of preparing new nanomaterials,sonochemistry method shows a unique performance.It can form local high temperature and high pressure in solvent,thereby reducing the requirement of the reaction conditions.Due to the rapid reaction process,the abnormal growth of crystal grain in the material synthesis process is avoided.It reduces the surface free energy of tiny grains,and the whole process is safe and reliable.When using sonochemistry method to prepare nanocrystals,the choice of solvent is a crucial part as well as the adjustment of ultrasonic parameters.Organic solvents have been widely used in chemical reactions as a class of traditional solvents,and there are also many applications in the process of preparing nanomaterials using sonochemistry method.On the other hand,as a kind of special reaction solvents,room temperature ionic liquids have been applied to the sonochemical synthesis of nanomaterials.It can dissolve a variety of inorganic and organic materials,and it has many excellent characters,such as colorless,odorless,non-toxic,low melting point,hydrolysis resistance,zero vapor pressure,large viscosity coefficient,high cavitation threshold and high thermal stability.Combing the room temperature ionic liquids with the ultrasonic technology,we can get high cavitation intensity,which makes the room temperature ionic liquids "green"solvents in preparation of nanomaterials.When we study the characters of nanomaterials preparing by sonochemistry method,in addition to the use of the traditional X-ray diffraction(XRD),transmission electron microscopy(TEM),fluorescence spectroscopy(PL)and infrared spectra(IR),photoacoustic spectroscopy(PAS)has also been applied to our study as a new technology to research material absorption spectrum.In this paper,the optical properties of all samples are studied in detail.There are seven parts in this thesis as follows:In the first chapter,we briefly summary the discovery,definition,classification,properties and some common preparation methods of nanomaterials.According to the fundamental theories of sonochemistry method,the detail advantages of sonochemistry are introduced.The primary analysis methods for nanomaterials are briefly introduced.Among all the methods,the background,basic principle,development,application of PAS technology is mainly reviewed.What's more,the primary coverage and meaning of this thesis are interpreted.In the second chapter,we introduce the research process of ZnO nanomaterials,and ZnO nanocrystals are prepared in a room temperature ionic liquid and in triethylene glycol via ultrasonic irradiation respectively.The feature size and characteristics of luminescence of the two different samples are analyzed,and the advantages of room temperature ionic liquids in the preparation of nanomaterials are revealed.At the same time,ZnO doped with rare earth elements(Y3+?Tb3+?Er3+)are prepared in room temperature ionic liquid,and the luminescence properties of these samples are studied.In the third chapter,Cadmiun-doped zinc oxide nanocrystals in the quantum confinement region have been firstly synthesized by a fast and facile sonochemical method.The alloyed structure of the nanocrystals is confirmed by X-ray diffraction,transmission electron microscopy,and infrared analysis.With the increase of cadmium to zinc molar ratio,the band gap of the samples shows a strange change.The variations of band gaps of the samples can be interpreted by the crystallite size and the composition.Moreover,a plausible formation mechanism has been proposed for the current sonochemical preparation.Finally,the mechanism of the reaction is explained.In the fourth chapter,the research process of TiO2 nanomaterials are introduced and Pr3+ doped TiO2 nanocrystals are prepared by an ultrasonic sol-gel method.The structural variations of the samples during the phase transitions are studied by using the Pr3+ ion as a photoacoustic spectral probe.The results show that the sonochemistry method plays an important role in the formation of nanomaterials.The stabilization effect of the doped Pr3+ ions on the anatase phase of the samples is also discussed.In the fifth chapter,we introduce the photoluminescence of rare earth complexes.Lanthanide?-diketonate complexes Ln(btfa)3·2H2O are incorporated into silica gels by a sol-gel method.Photoacoustic spectra as well as luminescence of these complex-doped silica samples are measured and studied.Moreover,the relaxation process model is proposed based on the two results.It indicates that as a new spectral technique,the photoacoustic spectra has a broad application prospect in the study of light excitation relaxation of opaque,high reflected or high scattering samples.In the sixth chapter,the mechanism of cavitation in solution is analyzed,and ultrasound cavitation effects are simulated in a room temperature ionic liquid using modified R-P formulation by Flynn.The influence of the parameters such as the amplitude of the ultrasonic pressure(Pa),the driving frequency of the ultrasonic(f)and the initial radius of the bubble(R0)on the cavitation reaction are analyzed.Moreover,the physical parameters of room temperature ionic liquids under different ambient temperature(T0)were studied,especially the influence of viscosity coefficient on cavitation reaction.In the seventh chapter,full thesis summary and work outlook.