Near-Infrared Sensors Based On SPR Enhanced Upconversion Fluorescence

Infrared light can interact with matter to result in photothermal effect and photoelectric effect,which show great potential in medical theranostics,sensing,industrial automatic control,environmental monitoring,optical communications,military night vision,and,aerospace and weapon detection.Especially,the 980 nm near-infrared light located in biological tissue optical window,have been often utilized in the field including biological imaging,photodynamic therapy and laser surgery,and also in industrial production,display imaging.In this paper,a photoconductive composite films composed with NaYF4:Yb3+,Er3+upconversion fluorescence nanocrystals and polymer semiconductor poly(3-hexylthiophene-2,5-diyl)(P3HT)were utilized to perform the detection of 980 nm NIR light.The emission of NaYF4:Yb3+,Er3+nanoparticles excited by 980 nm NIR light,could be absorbed by the P3HT to produce hole-electron pairs,and resulted in current with the external bias.This current were finally enhanced by the plasmonic Au nanoparticles,and could indicate the existence and power of 980 nm NIR light.The organic photoconductive material combining up-converted fluorescent nanocrystals with P3HT is highly efficient,inexpensive,portable,low-toxic,and easy fabrication,and is expected to become an ideal photon collection,photon storage,and phototransistor material in the future.The main content and results of this article are as follows:(1)Pure ? phase NaYF4:Yb3+,Er3+ upconversion nanocrystals were prepared by thermal decomposition.In this paper,by adjusting the type and concentration of surface ligands,spherical nanoparticles with sizes of 17 nm and 44 nm and 77 nm were controllably prepared.The effect of 980 nm NIR excitation power on the luminescence of three different sizes of NaYF4:Yb3+,Er3+ nanoparticles were discussed.Under the excitation of 980 nm continuous NIR laser,the nanocrystals had strong green fluorescence at 528 nm and 542 nm,which were due to the transitions of 2H11/2 ?4I15/2 and 4S3/2?4I15/2 of Er3+.The red fluorescence at the center wavelength of 657 nm comes from the transition of 4F9/2?4I15/2 of Er3+.Under the excitation of 980nm NIR with the same excitation power of 5W/cm2,the green fluorescence intensity of NaYF4:Yb3+ and Er3+ nanoparticles with size of 44nm was 14 times higher than that of 17nm nanoparticles,and the size of nanoparticle with 77nm was higher.The fluorescence is 67 times that of the 17 nm size.Further studies show that with the increase of the power density of the excitation light,the proportions of the green and red light of the three upconverted nanoparticles appear to increase first and then decrease.(2)Au nanoparticle about 9 nm in size was successfully prepared with oleylamine as a reducing agent and a capping ligand,and based on this,the upconversion fluorescence was enhanced by localized surface plasmon of precious metal.According to NaYF4:Yb3+,Er3+ and Au molar ratio 0.005:1,0.01:1,0.05:1,Na nanoparticles were loaded on the surface of NaYF4:Yb3+,Er3+ particles,and NaYF4:Er3+,Yb3+ on Au nanoparticles were loaded.The upconversion fluorescence of nanocrystals was enhanced by 67%.(3)Fabricating the intercalation electrode on the silicon substrate with oxide layer,and then spin-coating the Au-loaded NaYF4:Er3+,Yb3+ nanoparticles with P3HT onto the substrate.Under the excitation of 980 nm near-infrared light with a power density of 1 W/cm2,the device obtained a current increase of 6.7 times.