Enhancing the fluorescence emission by flexible metal-dielectric-metal structures
doi: 10.37188/CO.2021-0084
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摘要: 增强荧光发射可以提高荧光检测灵敏度、提高LED的亮度，在提高发光器件性能方面具有重要意义。由于金属结构在增强局域场、增强荧光发射方面具有很好效果，而柔性电介质材料具有灵活的可弯曲性特性，本文提出一种由金属-电介质-金属（MDM）组成的柔性结构以增强荧光发射。利用时域有限差分方法系统研究了该结构对量子点定向发射增强的影响。理论计算表明柔性MDM结构局部起伏和弧度对荧光增强起促进作用，且可以使位于结构中心位置量子点的量子效率增强约7倍。此外，还可以改变电介质的折射率和厚度从而实现目标波长的可调谐性。实验结果表明该柔性MDM结构对荧光增强有一定的促进作用，这一发现对未来的显示技术和柔性发光器件都有很大的价值，对高效柔性器件的开发应用具有一定的指导意义。Abstract: The technology of enhancing fluorescence emission can increase the sensitivity of fluorescence detection and the brightness of Light Emitting Diodes (LEDs), and is of great significance in improving the performance of light-emitting devices. Since the metal structure has a good effect in enhancing the local field and fluorescence emission, and the flexible dielectric material has flexible bendability characteristics, on the basis of above, we propose a flexible structure composed of Metal-Dielectric-Metal (MDM) to enhance the fluorescence emission. The influence of the structure on the directional emission enhancement of quantum dots is systematically studied by using the finite difference time domain method. Theoretical calculations show that the local undulations and arcs of the flexible MDM structure can promote fluorescence enhancement and increase the quantum efficiency of the quantum dots located at the center of the structure by about 7 times. They can alao change the refractive index and thickness of the dielectric to achieve the tunability of the target wavelength. At the same time, the experimental results shows that the flexible MDM structure does have a positive effect on the fluorescence enhancement. This discovery is valuable for future display technologies and flexible light-emitting devices. It is of certain guiding significance for the development and application of high-efficiency flexible devices.
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Key words:
- fluorescence enhancement /
- flexible structure /
- directional emission /
- tunable wavelength
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图 1 银和PVA组成的MDM结构模型示意图，其中橙色区域代表银膜，其厚度为d1；蓝色区域代表电介质PVA，其厚度为d2，上层银膜内半径为R，结构所对应圆心角为θ
Figure 1. Schematic diagram of the MDM structure model composed of silver and PVA, in which: the orange area represents the silver film with a thickness of d1; the blue area represents the dielectric PVA with a thickness of d2, the inner radius of the upper silver film is R, and the central angle corresponding to the structure is θ
图 2 （a）不同偏振态下量子点的功率曲线；（b−d）不同偏振态的量子点在波长515 nm处的电场分布图
Figure 2. (a) Power curves of quantum dots in different polarization states; (b−d) electric field profiles of quantum dots in different polarization states at 515 nm wavelength
图 3 在MDM不同圆心角下量子点的功率曲线及珀塞尔因子
Figure 3. Power curves and Purcell factors of quantum dots for the MDM structures with different center angles
图 4 MDM半径不同时，量子点的功率曲线及珀塞尔因子
Figure 4. Power curves and Purcell factors of quantum dots for the MDM structures with different radii
图 5 MDM电介质层厚度及折射率不同时量子点发光功率曲线
Figure 5. Luminous power curves of quantum dots for the MDM structures with different dielectric layer thicknesses and refractive indexes
图 6 MDM不同上下层银膜厚度时量子点发光功率曲线和珀塞尔因子
Figure 6. Luminous power curves and Purcell factors of quantum dots for the MDM structures with different upper and lower silver film thicknesses
图 7 490 nm波长下，金属-电介质-金属结构、金属-电介质结构、金属结构中量子点发光的电场分布图、功率曲线和珀塞尔因子
Figure 7. The electric field distribution diagrams, power curves and Purcell factors for quantum dots in metal-dielectric-metal structure, metal-dielectric structure and metal structure at 490 nm wavelength
图 8 位于MDM结构和柔性PVA基底中不同位置的（a）两相干光源和（b）两非相干光源的远场荧光功率曲线
Figure 8. Far-field fluorescence power curves of (a) two coherent dipole sources and (b) two incoherent dipole sources located at different positions in the MDM structure and flexible PVA substrate
图 10 MDM结构。（a）平面；（b）弯曲（俯视图）
Figure 10. MDM structures. (a) planar; (b) curved (top view)
图 11 光学显微镜下MDM结构的（a）明场图像；（b）375nm激光照射下的暗场发光图像
Figure 11. (a) Bright field image of MDM structure under optical microscope; (b) dark field luminescence image under 375nm laser irradiation
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