Enhanced Fluorescence Of Quantum Dots Based On Nanoparticle-on-mirror (NPoM) System

Several technologies in the field of modern micro-nano optics,such as quantum communication and optical sensing,have put forward higher requirements on compact and high-performance optical source.Quantum dots exhibit great potential in constructing nanosource due to its high stability,narrow-band and tunable emission.Utilizing surface plasmon resonance residing on metallic sturctures to enhance photoluminescence of quantum dots attracts widespread interest to increase brightness and rate of optical source.Among various design,the nanoparticle-on-mirror（NPo M）system taking advantage of simple preparation process and large enhancement have been widely investigated.However,precise assembly of quantum dots and metallic structure still remains challenge.In this paper,we proposed to fabricate the NPo M structure based on one-step spin-coating method using composite Au-quantum dot emitter.This method reduces randomness in the assembly process and realize controllable preparation of the NPo M structure.The main contents are as follows:（1）Au@SiO₂@QD composite nano-emitters are prepared by assembling Au nanoparticles and quantum dot emitters.The advantages of this preparation method are as fellows:1)Improve the probability of quantum dots placed in the metal nanogap structure,so that the luminophore and the cavity structure are spatially coupled;2)The method of coating the silica spacer layer ensures about 3～5 nm isolation between the quantum dots and the metal structure to prevent quenching;3)The experimental process is controllable step by step,and high structural consistency is obtained.In the preparation process,the method of surface modification overcomes the difficulty of connecting Au@Si O₂ nanoparticles and quantum dots.The characterization results show that the final prepared composite nanoluminophore with a particle size of about 70 nm,a spacer layer thickness of about 3～5 nm,and a stable connection between gold nanoparticles and quantum dots.（2）Single-particle imaging experiments were used to characterize the fluorescence radiation intensity of quantum dots in different structures.The experimental results show that the"composite nanoluminophore-silver thin film"structure has the most significant enhancement effect.Compared with a single quantum dot,the single particle fluorescence intensity of the mirror nanoparticle structure device based on the silver film is enhanced by147 to 164 times,and the fluorescence intensity of the mirror nanoparticle structure device based on the gold film is enhanced by 41 to 58 times.Numerical simulation calculations show that the"composite nano-luminophore-silver thin film"structure has a more obvious enhancement effect on the local field than the"composite nano-luminophore-gold thin film"structure.This research provides a new idea for quantum dot fluorescence enhancement technology,which has wide range of applications in the field of micro-nano optics.