| Surface plasmon is the collective oscillation of free electrons in metal nanostructures at the interface of metal and dielectrics.When the frequency of incident light approaches to the frequency of collective electron oscillation,surface plasmon resonance can be excited.A highly localized and strongly enhanced electromagnetic field will be generated by the localized surface plasmon resonance,which is important to break through the optical diffraction limit,and enhance the optical field and amplify optical signals.Plasmon resonance can be damped non-radiatively through the generation of hot carriers.The decay of hot carriers will lead to significant heating of the nanostructure itself and its immediate environment,which can effectively regulates molecular reaction and crystal transformation.Benefit from the stable properties and luminescence characteristic of trivalent rare earth ion-doped luminescent materials,our work mainly focuses on the interaction of surface plasmons with rare earth ion-doped micro-nano materials.The main research work and achievements are summarized as follows:1.A universal crystal transformation/growth method has been developed by taking advantage of the thermal effect of surface plasmons and the catalytic effect of hot electrons.The polycrystalline fluoride micro-nano particles are prepared under normal temperature conditions,and are taken as the main starting sample.The fluorescence spectra of trivalent rare earth ions are selected as a probe for local crystal structure detection.The results show that,with the help of the efficient light absorption of loaded Au nanoparticles,the conversion of polycrystalline NaYF4 to single crystal Y2O3 nanoparticles can be achieved in milliseconds under the irradiation of visible light with the power of several milliwatt.After transformation,the luminescence intensity,red-green ratio and monochromaticity of the generated nanoparticle have been significantly improved.2.The regulation rule of surface plasmon-driven crystal transformation is studied.The effects of surface plasmon resonance and non-resonance excitation,as well as inter-band absorption of Au nanoparticles on crystal transformation are explored.The efficiency of plasmon-induced crystal transformation with laser intensity and the distribution of metal particles are regulated.The crystal transformation is achieved at low-temperature,the interrelationship between laser power,ambient temperature and irradiation time are revealed.The results show that compared to the plasmon resonance relaxation process,the generated thermal effect and the energy of hot electrons are lower under 442 nm laser irradiation,which significantly reduces the crystal transformation rate;Due to the efficient photothermal conversion efficiency of surface plasmons and the localized thermal effects,nanocrystals can be transformed in a low temperature environment;the crystal transformation rate and laser power density,ambient temperature,and irradiation time are mutually restricted.The conversion rate slows down as the power of the irradiated laser,the ambient temperature,or the density of Au nanoparticles decrease.3.The mechanism of interaction between surface plasmons and rare earth doped luminescent crystals is studied.The dynamic process of crystal transformation explored.The results show that the thermal effect and hot electrons produced by the plasmon relaxation process cooperate to promote the transformation of crystal particles.Hot electrons catalyze the generation of strong oxidizing instantaneous negative ion O2-by interacting with oxygen molecules and act on nanoparticles to catalyze the oxidation reaction.At the same time,the plasmonic thermal effect promotes the optimization of the crystal structure and induces the transformation of particle from polycrystalline to single crystal.In the process of crystal transformation,the element of Na disappears first,and the crystal particle transforms into oxyfluoride and then into oxide.Due to the aggregation effect of Au nanoparticles during the transformation process,both hot electrons yield and photothermal conversion efficiency are reduced,as a result the crystal transformation rate obviously slows down.The plasmoninduced particles exhibit "memory" characteristics of the induced conditions,due to the influence of the plasmonic thermal effect on the fluorescent radiation.4.The new applications of the interaction between surface plasmons and micro-nano crystals are explored.With the thermal effect of surface plasmons,an in-situ heat treatment method for micro-nano materials is designed,which shows high spatial resolution,high speed,mild conditions,low consumption,and independent of high-temperature environment.And with the help of this technic,the controllable doping of ions in crystal particles,controllable transformation between monocrystalline,polycrystalline and amorphous nanostructures,embedded structures of noble metal nanoparticles in luminescent crystals,etc.are realized.And with the help of the embedded structure,the regulation efficiency of plasmon on the fluorescent radiation of the system is greatly improved and the up-conversion luminescence is selectively enhanced.The main innovations:1.It is proposed for the first time to use the thermal effect of surface plasmons and the catalysis of hot electrons to realize fast and controllable nanocrystal transformation,and the rare earth oxide single crystal nanoparticle is obtained at room temperature or even low temperature,which overcomes the limitations of traditional methods for growing single crystal materials.2.Through the exploration of the excitation mechanism and energy transfer channel of plasmon catalysis,as well as the regulation of temperature and atmosphere environment on the plasmon-induced crystal transformation,the mechanism of hot electrons and thermal effect in plasmon-induced crystal transformation is revealed.3.With the thermal effect of surface plasmons,the embedded structure of plasmon nanoparticles in the rare earth-doped luminescent crystal is realized,which improves the efficiency of plasmon resonance in the micro-nano crystal system.4.The "memory" property of plasmon-induced nanoparticles to the induced conditions is discovered. |
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