Preparation And Characteristic Absorption Properties Of KTN@Cu/Ag Core-shell Nanoparticles

Researchers have been drawn to the localized surface plasmon resonance（LSPR）phenomenon in recent years due to its widespread application in electrochemistry,optical detection,biosensing,surface enhanced Raman scattering and other fields.In the extinction spectrum,this phenomenon has a distinct characteristic peak.Many factors will influence the excitation position of the characteristic peak,such as changing the particle morphology,the surrounding dielectric environment or the design of core-shell structure to form a complex structure.In the LSPR excitation materials,Au and Ag are always the focus objects.Due to the high price and high preparation cost of precious metals such as Au and Ag,Cu has garnered a lot of attention in recent years because of its large reserves on the planet,inexpensive preparation cost,and excellent optical qualities.The preparation process of KTN(KTa_x-1Nb_xO₃)dielectric material is simple,and the morphology of its nanoparticles can be controlled.Therefore,in order to broaden the regulation range of LSPR characteristic peaks of single metal and reduce the cost of materials,the influence of Cu/Ag metal layer with different thickness coated on KTN nanoparticles with different morphologies on LSPR extinction spectrum was investigated,and the drift direction of LSPR peak was predicted.The formation mechanism of each characteristic peak was discussed by combining FDTD simulation with experiment.The coupling effect between the materials is used to expand the regulation range of LSPR peak.Firstly,the finite-difference time-domain（FDTD）simulation is used to establish the model and simulate the LSPR performance of Cu@Ag core-shell and inverse core-shell nanospheres arrays.The results show that increasing the shell thickness of the core-shell nanospheres makes the LSPR peak redshift,and the redshift amplitude is larger than that of the same size of the elemental nanospheres.This shows that the core-shell nanospheres have a wider LSPR characteristic peak regulation range than the elemental nanospheres.Secondly,the LSPR properties of KTN@Ag nanoparticles with different morphologies were investigated by simulation and experiment.The effects of different Ag loading rates on the characteristic peaks were investigated,and the excitation mechanism of each characteristic peak was analyzed.The results showed that the LSPR peaks of KTN@Ag NRs（nanorods）and NPs（nanoplates）particles had a wide range of regulation,which were 762-592 nm and 742-585 nm,respectively.According to the simulation results,the larger Ag shell thickness will enhance the shielding effect,resulting in a weakening of the LSPR peak blue shift trend,eventually leading to the cessation of blue shift and then red shift as particle size increases.The characteristic peaks of KTN@Ag nanoparticles were broadened in the experiment due to the uneven distribution and particle size of KTN nanoparticles,but the drift trend of LSPR characteristic peaks was consistent with the simulation results.Thirdly,the LSPR performance of KTN@Cu nanoparticles was investigated by simulation and experiment.The simulation results show that the LSPR characteristic peak of KTN@Cu NCs（nanocubes）particles red-shifts from 360 nm to 380 nm and the LSPR characteristic peak of KTN@Cu NRs particles red-shifts from 250 nm to320 nm when the loading rate of Cu increases from 9.1 wt.%to 16.7 wt.%.The increase of shell thickness will make the LSPR characteristic peak of KTN@Cu NPs particles blue shift significantly.The characteristic peak blue shifts from 871 nm to720 nm as the shell thickness increases from 10 nm to 30 nm.Meanwhile,the flaky nanoparticles can effectively eliminate the large resonance damping of Cu in the short wavelength direction.In the experiment,when the loading rate of Cu increased from9.1 wt.%to 16.7 wt.%,the LSPR characteristic peak of KTN@Cu NCs red shifted from 348 nm to 401 nm,and the LSPR characteristic peak of KTN@Cu NRs red shifted from 337 nm to 545 nm.Due to the broadening of the characteristic peaks,the characteristic peaks with insignificant intensity cannot be distinguished due to multi-peak overlap.Finally,the LSPR characteristics of KTN@Cu/Ag multilayer core-shell nanoparticles were investigated.In the simulation,it was found that KTN@Ag@Cu NCs and NRs nanoparticles exhibited clearer LSPR characteristic peaks than KTN@Cu@Ag NCs and NRs nanoparticles when adjusting different Cu/Ag ratios.At the same time,the three-layer composite NPs particles are not affected by the metal of the middle shell,so the LSPR characteristic peaks can be regulated in both directions.In the experiment,the characteristic peaks of KTN@Cu@Ag NCs and NRs particles were red-shifted from 413 nm to 453 nm and 500 nm to 725 nm,respectively,when the Cu/Ag mass ratio was reduced from 0.185/0.05 to 0.155/0.15 due to the broadening and superposition of each peak.Compared with the double-layer core-shell nanoparticles,this multilayer composite structure shows a more flexible spectral regulation range,and significantly reduces the preparation cost while expanding the regulation range of LSPR peak.It can be considered that the material has broad potential in many applications.