Study On Fabrication And Properties Of DAST Micro/Nanometer Optical Materials

Organic nonlinear material of 4-N,N-dimethylamino-4'-N'-methyl-stilbazolium tosylate?DAST?has excellent nonlinear optical?NLO?properties and fast response speed,holding great potentional applications in frequency conversion,optical parametric oscillation,electro-optical modulation,integrated photon devices,terahertz?THz?,etc.The mechanical,electrical,thermal and optical properties of micro-or nano-meter scale materials are significantly different from those of bulk materials.Although the precipitation method or the substrate supported rapid evaporative crystallization?Substrate Support Rapid Evaporation Crystallization,SSREC?method can be used in preparing DAST,it is still difficult to prepare DAST and its derivatives in micro-or nano-meter scale materials quickly and controllably.Therefore,some new methods for the fabrication of DAST micro or nano materials,including the precipitation template method,solvent dispersion method,solvent method,and etc.,have been explored and developed in this thesis.Consequently,many kinds of micro and nano materials of DAST,such as micro waveguides,nanowires,dendrites,and hexagonal nano sheets,have been successfully prepared.The important results of this work include:?1?Organic DAST was synthesized and purified by using Dean stark equipment.Based on this,DAST optical waveguides with the lengths of 0.6mm-5mm and widths of 0.1mm-0.5mm were prepared after appropriate amount of ammonia water,ammonia acetate and ammonia oleate were added into the DAST methanol solution.Results revealed that the as-prepared DAST waveguides exhibit strong fluorescence properties.In addition,the phenomenon of exciton polariton propagation in DAST waveguide was experimentally detected.These results are helpful for expanding the applications of DAST.?2?In this work,large-scale DAST dendrite arrays were also grown directly by evaporation in sealed environment.The characterizations of XRD,UV and IR indicated that the resultant DAST dendrites are monocrystalline.Through the analysis of the nucleation limited aggregation model?NLA model?,the nucleation phenomenon can not be ignored in the case of high driving force.Combined with the preferred orientation of grain growth,symmetrical or asymmetric dendrites and fractal structures were yielded.?3?DAST nanowires with the diameters of hundreds of microns were prepared by solvent dispersion method without any additives.The propagation of exciton polaritons in the DAST nanowires was observed by fluorescence microscopy.At the same time,we also measured and theoretically investigated the directionality of the SHG signal of DAST nanowires.Particularly,DAST nanowires can be bent by hydrophilic treatment on the silicon substrate.Considering the structure and external environment of DAST,it is believed that the growth of DAST nanowires is controlled by the integration of the Coulomb force,large dipole moment,and surface tension.?4?By controlling the solubility of DAST powder in aqueous solution,DAST·H₂O hexagonal nano tablets were successfully prepared.According to the chemical structures of water and DAST,the reason for the formation of DAST·H₂O hexagonal nano sheet was explained by hydrogen bond.The results of XRD and FTIR revealed that the as-prepared DAST·H₂O nano tablets contain a lot of water,thus degrading the second harmonic generation?Second Harmonic Generation,SHG?activity.In addition,the effects of annealing on the DAST·H₂O hexagonal nano tablets were also investigated.