利用Ag@SiO_2纳米粒子等离子体共振增强发光二极管辐射功率的数值研究

金属纳米粒子利用其局域表面等离子体共振效应(LSPR),可以增强附近荧光分子的自发辐射速率,因而在光学传感、光电器件等领域中具有潜在的应用价值.金属纳米粒子的LSPR与其自身的材料、形状、尺寸以及周围环境介质密切相关,这影响着纳米粒子在具体器件中的应用.本文利用三维时域有限差分法,研究了相同体积的球形、椭球形、立方形与三棱柱形银纳米粒子对薄膜发光二极管辐射功率的影响;计算了不同形状银纳米粒子对偶极子光源辐射功率和薄膜器件光出射强度的增强,并结合LSPR效应讨论了辐射功率变化的物理机理.研究结果表明:银纳米粒子自身形状尖锐程度的增加有利于提高LSPR的共振强度;同时纳米粒子的形状影响了LSPR共振电场与薄膜器件中偶极子辐射电场之间的耦合作用,其中立方形纳米粒子因为能实现最强的耦合作用而对器件的辐射功率增强最大.在此基础上进一步讨论了不同薄膜材料对LSPR共振及光源辐射功率的影响,发现较高的材料折射率有利于增强金属纳米粒子的LSPR与器件的耦合作用,从而改善发光二极管性能.

Numerical research of emission properties of localized surface plasmon resonance enhanced light-emitting diodes based on Ag@SiO2 nanoparticles

Metal nanoparticles have potential applications in the fields of optical sensing and optoelectronic devices, due to the localized surface plasmon resonance (LSPR) which enhances the spontaneous emission rate of nearby fluorescent molecules. The LSPR of metal nanoparticles is closely related to its material, shape, size and ambient medium, which affects the applications of nanoparticles in specific devices. In this paper, the LSPR effect of silver nanoparticles (SNPs) with different shapes of sphere, ellipsoid, cube, and triangular-prism, is investigated by using a three-dimensional finite difference time domain. The absorption and scattering spectra of the individual SNPs are first calculated. The resonance peaks are red shifted and enhanced with sharpness increasing from the nano-sphere to the nano-triangular-prism because the surface charges accumulate in the sharp corners. Then the effects of SNPs on the radiation power of the dipole source and light extraction efficiency of the light-emitting diodes (LEDs) are studied. The dipole radiation power decreases near the resonance wavelength due to the absorptions of SNPs, while increases after the resonance wavelength because of the coupling between the SNP LSPR and the dipole radiation. The calculated electric field distribution shows that the LSPR electric field of the SNPs concentrate near the surface of the dielectric film because of the interaction between the SNPs and the film. The concentrated electric field helps to improve the coupling between the LSPR and the dipole, which enhances the dipole radiation power in the LED. In the several kinds of SNPs, nano-cube SNP shows the most significant improvement on the dipole radiation power because of the strongest interaction with the dielectric film. In addition, the scattering effect of the SNP reduces the internal total reflection of light and improves the light extraction efficiency of the LED. Nano-ellipsoid SNP significantly enhances the light extraction because of its strongest scattering intensity. Further, the influence of the refractive index of the dielectric film on the dipole radiation power is studied. It is found that a higher refractive index of dielectric film helps to enhance the interaction between the SNPs and the film and improves the dipole radiation power. The optimized value of refractive index is acquired through detailed calculation.