Research On Asymmetric Microcavity For Fluorescence Enhancement And Directional Emission

With the development of micro-nano photonics technology,researchers are more and more inclined to use micro-nano optoelectronic structures to control the luminescence properties of fluorescent substances,in order to enhance the interaction between light and substances.Fluorescence detection can be performed by utilizing the characteristic of enhanced fluorescence by micro-nanostructures.Among them,the fluorescence ratio probe in the fluorescence detection method can provide a background signal that is not disturbed by the environment,so that the naked eye can better distinguish the color of fluorescence,so it is widely used in the detection of biological small molecules and ions.More accurate detection of the biological information of the target to be measured is accomplished by inducing changes in the fluorescence intensity of the fluorescent probe at two or more wavelengths by the target to be measured.Techniques that enhance fluorescence emission can improve fluorescence detection sensitivity,thereby reducing measurement time.Quantum dots have the advantages of high fluorescence intensity and good fluorescence stability,which can be used as an ideal fluorescent probe.However,the low fluorescence ratio value is still an open problem.The inability to produce more pronounced color changes and achieve higher contrast detection greatly limits the application of fluorescence ratiometric sensing.Meanwhile,fluorescence emission is the basis for a wide range of applications in light-emitting devices,analytical chemistry,spectroscopy,sensing,and imaging,which is widely used in gene sequencing,neuronal mapping,early diagnosis,and other fields.However,the omnidirectional radiation characteristics of fluorescent emitters lead to low signal acquisition efficiency.Therefore,a feasible method to control its emission directivity is urgently needed.In this paper,aiming at fluorescence ratio probes and fluorescence directional emission to achieve high fluorescence ratio value and in-plane directional fluorescence emission,two micro-nano structures that can enhance fluorescence are proposed,which break the symmetry of the cavity structure.We systematically study the effect of structure on the fluorescence emission of quantum dots.The main contents are as follows:The first research work proposes a regular hexagonal microcavity structure that can be used as a microfluidic channel to transport biological solutions.We systematically study the effects of the polarization direction of quantum dots,the position of small regular hexagon,the position of quantum dots,and structural parameters on the fluorescence enhancement of the structure by the finite difference time domain method.The results show that,when the polarization direction of the quantum dot light source is z polarization,the center of the small regular hexagon is at(0,-0.8),the position of the quantum dot light source is at(0.9,-1.8),and d1=3μm,d2=2μm,the regular six the edge-shaped microcavity structure is well optimized,and a good directional fluorescence emission effect is achieved.When the regular hexagonal microcavity structure is used as a microfluidic channel to transport biological solutions,the guidance and collection of different biological solutions can be realized in the straight microchannel with a regular hexagonal cross-sectional shape.The second research work proposes an asymmetric hexagonal microcavity structure that can improve the sensitivity of ratiometric fluorescence sensing in the near-infrared second region.Due to the combined action of the whispering gallery mode and the FP cavity mode in the microcavity,the interaction between light and matter is enhanced,and a high fluorescence emission ratio of up to 19.31 is achieved;at the same time,in the FP cavity mode,the structure realizes a high fluorescence emission ratio along the long side of the structure.The directional emission of this structure is less than 30 degrees along the y direction.On the one hand,the asymmetric hexagonal microcavity structure can detect the presence of biological solutions,on the other hand,it can be used as microfluidic channels to transport biological solutions.