Magnetic-based Fano Resonance And Surface Plasmon Enhanced Luminescence

Nanophotonics is a new frontier to control the interaction of light with matter in nanoscale,and is one of the most intriguing field in nanotechnology and optics.The exceptional light confinement property of metallic nanoparticles,which is endowed by localized surface plasmon resonances,provides a powerful tool for light manipulating in subwavelength.Besides,the inherent multipolar electric and magnetic eigenmodes in silicon nanoparticles give us a new strategy in tailoring scattering resonance for enhanced local density of electromagnetic states and offer routes to achieve multimodal resonant modes.However,constructing an efficient building block to achieve sensitive light switching,low-loss and intense light enhancement is still a difficulty,which has great potential applications in highly sensitive,ultra-stable and great compatible devices.Here,several strategies were proposed for solving these problems and the primary researches are divided into the following sections:1.To achieve low-loss and sensitive light switching,the magnetic-based Fano resonance is a great candidate.Therefore,the heterodimers combined by a gold nanoplate and a silicon nanosphere,and combined by a silver nanocube and a silicon nanosphere were proposed,and both of them generated Fano response.In the gold-silicon heterodimer,the Fano type scattering is originated from the interference between electric quadrupolar mode from gold nanoplate and magnetic dipolar mode from silicon nanosphere.The thickness and length of gold nanoplate show little impact on Fano response,while the diameter of silicon nanosphere can tune the position of Fano response efficiently.When the diameters of the silicon nanosphere are changed from 50nm to 150 nm,the Fano resonance is redshifted with about 90 nm.However,when the thickness and the width of gold nanoplate are changed by 60 nm and 100 nm respectively,the Fano peaks both shift a little.These characters not only improve the fault tolerance in manufacturing but also provide a tool to control the Fano response.Besides,this Fano response is sensitive to particle distance.With only 1 nm gap change on the heterodimer,the Fano peak and dip were shifted about 100 nm,and an obvious change in Fano lineshape was obtained.Moreover,the silver-silicon heterodimer also shows a magnetic-based Fano resonance,and the Fano lineshape is dependent on the size of the silicon nanosphere.When the diameters of the silicon nanosphere are changed from 70 nm to 130 nm,the Fano resonance is redshifted obviously with about100 nm.In addition,the Fano response also shows high sensitivity to the coupling distance.With only 0.2 nm gap change on the heterodimer,the Fano peak is blueshifted with about 100 nm.Both heterostructures provide a magnetic-based Fano resonance and allow simultaneous controlling of the electric and magnetic responses,opening a strategy for novel devices based on magnetic-based Fano resonance.2.The electric-type“hot spot”can produce an outstanding luminescence enhancement only if the emitter is aligned to the external field.In addition,the magnetic-type“hot spot”can produce a moderate enhancement for the emitter in any orientation owing to the circulation of a displacement current.Thus,several silicon dimers were constructed to fabricate nanocavities containing electric-type and magnetic-type“hot spot”.The stronger photoluminescence intensities of R6G with nanocavities both under longitudinal and transversal excitation were observed,and the maximum enhancement factor is 2.46.Moreover,the nanocavities show primary electric mode enhancement under longitudinal excitation and dominant magnetic mode enhancement under transverse excitation.Such nanocavities enable the switch between the electric mode with stronger enhancement and the magnetic mode with higher compatibility.It is useful for making nanophotonic devices with signal amplification.3.Improving luminescence intensity and achieving directional emission expand methods for transmitting and distinguishing the information of light.Here,the different configurations by coupling a specific Yb³⁺/Er³⁺/Mn²⁺co-doped Na YF₄ with gold nanoantennae at the single-particle level,and a multi-particle system consisting of Na YF₄:20%Yb,0.5%Er@Si O₂ and gold nanorods at the solution were created.Both of them can provide dominant emission enhancement.Specially,the different nanoantennae-load Na YF₄:Yb³⁺/Er³⁺/Mn²⁺configurations can realize efficient light directionality.The emission of Na YF₄:Yb³⁺/Er³⁺/Mn²⁺is greatly enhanced with a factor of?138 after modification of gold nanoantennae,and the highly linear polarization with factors of 85%and 81%in emission and excitation polarization measurements were observed.For the experiment of the multi-particle system,the distance-dependent luminescence enhancement was investigated by controlling the silica thickness of Na YF₄:20%Yb,0.5%Er.The maximum enhancement factors up to 10.3,8.0 and 9.1were obtained at 660 nm,550 nm and 410 nm,respectively.Moreover,under the optimal ratio between Na YF₄:20%Yb,0.5%Er@Si O₂ and gold nanorods,the emission intensities in the three emission bands are showing great enhancement with factors of about 10.This configuration design under single-particle level and the method of multi-particle system construction pave the way to achieve efficient modulation of upconversion fluorescence,opening a new path to realize highly sensitive detectors with polarization control devices.