| Metal nanoparticle is composed of metal clusters with nanoscale size.It possesses the characteristics of localized electromagnetic enhancement,large specific surface area,and high specific surface energy,which is ascribed to the unique physical mechanisms of quatum confinement,surface effect and small size effect compared with bulk material.The combination of optoelectronical characteristics for several metal nanoparticles can push the applications to the fields of solar cell,photoelectric detection,and surface signal enhancement.The unique optoelectronical properties of combined metal nanoparticle with the interaction of light field have been concerned by the researchers.The linear and nonlinear optical properties of combined Au-Ag metal nanoparticles are investigated using theoretical simulation and experimental measurement.The localized surface plasmon resonance(LSPR)characteristics of combined Au-Ag metal nanoparticles is analyzed by use of the finite difference time domain(FDTD)method;The nonlinear absorption properties of combined Au-Ag metal nanoparticles are studied by Z-scan technique;The nonlinear and transient absorption dynamics of combined Au-Ag metal nanoparticles are studied by pump probe technique.The linear optical properties of Au@Ag nanopheres are analyzed by FDTD method.Under the shell thickness of Ag are unchanged,the absoption peak of LSPR has a red shift with the increasing of the radius for Au nucleus,which is ascribed to the change of oscillation period for free electron due to the response enhancement of phase delay.When the radius for Au nucleus is 26.5 nm,the thickness of Ag shell increases from 4nm to 11 nm,the absorption peak of LSPR has a blue shift and intensiy enhancement,which is changed from 655.8 nm to 511.9 nm with the intensity increasing from 0.44 to0.49.In addition,the period and dielectric environment for the linear optical property of Au@Ag nanopheres are analyzed.The change of LSPR absorption peak with the gold nucleus radius,Ag shell thickness,the period and dielectric environment are summarized,which provide the practical guidance for the application to signal enhancement in optical sensing.The linear optical properties of Au-Ag nanoshuttle are analyzed by FDTD method.When the diameter of nanoshuttle is controlled at 16 nm,with the increasing of nanoshuttle length from 64.0 nm to 72.0 nm,LSPR longitudinal absorption peak has a red shift from 758.5 nm to 793.7 nm,which ascribed to the weakness of the coupling for nanoshuttle at horizontal direction.Under the conditions of length holds 60 nm,with the increasing of the nanoshuttle diameter from 16 nm to 20 nm,LSPR longitudinal absorption peak has a blue shift from 738.9 nm to 676.2 nm.In addition,the linear optical properties of Au-Ag nanoshuttle are analyzed based on these variables of the length,width,period,cone height,and dielectric environment,which provide the theoretical guidance for the application to the optical sensing and wide band filtering.The nonliear optical property of Au@Ag nanophere is investigated by wavelength and pump energy-dependent open-aperture Z-scan experiment.When the pump wavelength is changed from 450 to 600 nm,obvious saturated absorption can be observed under the laser pulse excitation with the energy of 260?J.When we continue to increase the pump energy to 760?J,the conversion from saturated absorption(SA)to reverse saturated absorption(RSA)can be founded,which is attributed to the absorption change from ground-state bleaching to free-electron absorption.When the pulse energy is fixed at 760?J,the nonlinear absorption coefficient of Au@Ag nanophere is the largest under the excitation of laser with the wavelength corresponding to the resonant absorption peak,which is 1.3×10-11m/W.The nonliear optical property of Au-Ag nanoshuttle is investigated by open-aperture Z-scan experiment.Incident pulse energy is related to nonliear absorption property of Au-Ag nanoshuttle.The phenomenon of the conversion from SA to RSA can be observed with the increasing of pulse energy.Under the 500 nm nanosecond laser excitation at the pump energy of 760?J,the nonlinear coefficients is 1.6×10-11m/W.The ultrafast dynamics of Au-Ag nanoshuttle is measured using white-light pump-probe technique at the wavelength range from 450 to 750 nm.The obvious signal of transient absorption density at 475-680 nm can be observed with two totally different specieses.The ground-state bleaching signal appears at 450-530 nm with the lifetime of several picoseconds.Simultaneously,the excited-state absorption coexists at the several tens of picoseconds at 530-680 nm.It is found that excited-state dynamics is composed of a fast and slow species and produces the observation of biexponential decay kinetics,which separately ascribed to the picosecond timescale electron-electron and lattice-lattice interaction with hundreds of picoseconds after the photoninduced excitation. |
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