Optical Property Of Medium And High Refractive Index Dielectric Composite Nanostructures

In the field of nanophotonics,the optical property of medium and high refractive index dielectric nanostructures and metal nanoparticles has important research value.Under the excitation of femtosecond（fs）pulsed laser,surface plasmon polaritons（SPPs）will be generated on the surface of metal nanoparticles.Affected by the electric field of incident light,the SPPs collectively oscillate to form surface plasmon resonance（SPR）or localized surface plasmon resonance（LSPR）.However,the metal nanoparticles excited by fs pulsed laser have ohms loss,which is not conducive to the integration of metal nanoparticles and nanophotonic device.The medium and high refractive index dielectric materials are used to prepare nanoparticles for the development of nanoscale light sources because of their low ohmic loss.According to Mie theory,medium and high refractive index dielectric nanoparticles can support Mie resonance,including magnetic dipole resonance（MDR）,electric dipole resonance（EDR）,magnetic quadrupole resonance（MQR）,electric quadrupole resonance（EQR）and other higher-order resonance modes.The strong laser-matter interaction can be generated when the MDR of medium and high refractive index nanostructure is excited by fs pulsed laser,and the auger effect is enhanced by a large number of carriers induced by strong laser-matter interaction.The Auger effect continuously excites the carriers from a low energy state to a high energy state,increasing the probability of radiation transition.This paper focuses on the optical properties of medium and high refractive index dielectric nanostructures,providing new schemes for the preparation of nanoscale light source.To this end,the following studies are carried out.1.The laser-matter interaction can be realized in a heterogeneous nanostructure composed of Silicon（Si）nanospheres and Tungsten sulfide（WS₂）nanoshell.The resonance coupling between EDR and exciton resonance（EXR）occurs in the Si@WS₂ core-Ωshell nanostructure when it is excited by fs pulsed laser at the near-infrared（NIR）wavelength of 770 nm-800 nm.The EDR-EXR resonance coupling achieves the modulation of the resonant mode of Si@WS₂core-Ωshell nanostructure,demonstrating the influence of WS₂ nanoshell on the optical properties of Si nanostructure.2.Three kinds of Si@Pd core-Ωshell nanocavities are constructed by vaporizing Palladium（Pd）nanofilm onto the surface of Si nanospheres on glass,Si and Au substrates.The plasmon resonance induces the generation of hot electrons in metal nanocavity.With assistance of Mie-SPR resonance and Mie-LSPR resonance,the hot electrons are injected into Si nanospheres to modify the nonlinear optical properties of Si nanospheres.Therefore,the Mie-Plasmon resonance regulates the resonant modes of Si@Pd core-Ωshell nanocavity,demonstrating the influence of Pd nanoshell on the optical properties of Si nanosphere.3.Titanium dioxide（TiO₂）is a preferred photocatalytic material due to its excellent photostability,non-toxicity and low cost.Therefore,Ti O₂ hybrid nanospheres are established as a new nanoscale light source in this paper.First of all,Ti O₂ nanospheres are medium refractive index nanospheres that support Mie resonances,such as MDR,EDR,etc.However,Ti O₂ is a wide indirect band gap（3.2 e V）semiconductor,and the Ti O₂ nanospheres cannot be excited to emit luminescence by NIR fs pulsed laser.Through previous studies,it is found that the optical response of dielectric nanospheres can be adjusted by the injection of hot electrons.Therefore,the effects of different metals（Ti,Pd,Au）as a nanoscale plasmon sources on the optical properties of Ti O₂ hybrid nanospheres are studied,and shows the application prospect of Ti O₂ hybrid nanospheres as an integrated nanoscale white light source.