Singh Mahi R, Persaud Patrick D, Yastrebov Sergey
Department of Physics and Astronomy, The University of Western Ontario, London N6A 3K7, Canada. F Ioffe Physical-Technical Institute Laboratory of Electrical and Optical Phenomena in Semiconductors, St Petersburg 194021, Russia.
Nanotechnology. 2020 Apr 9;31(26):265203. doi: 10.1088/1361-6528/ab81c9. Epub 2020 Mar 20.
A theory of the two-photon florescence for a metallic nanoshell in the presence of quantum emitters has been developed. The metallic nanoshell is made of a metallic nanosphere as a core and a dielectric material as a shell. An ensemble of quantum emitters is deposited on the surface of the dielectric shell. A probe field is applied to study the two-photon process in the metallic nanoshell. Surface plasmon polaritons are created at the interface between the core and shell due to coupling between probe photons and surface plasmons present at the surface of the metallic nanosphere. The intensity of the surface plasmon polariton field is huge when the probe photon energy is in resonance with the polariton resonance energy. Induced electric dipoles are created in each quantum emitter due to the surface plasmon polariton field and the probe field. Dipoles in quantum emitters interact with each other via the dipole-dipole interaction. The dipole-dipole interaction is calculated using the many-body theory and mean field approximation. It is found that the dipole-dipole interaction has new term which is induced by the surface plasmon polariton field. An analytical expression of the two-photon florescence is derived in the presence the dipole-dipole interaction. Our theory predicts that the intensity of the two-photon florescence is enhanced in the presence of quantum emitters relative to the florescence of the metallic nanoshell in isolation. Physics behind the enhancement is the presence of the dipole-dipole interaction between the ensemble of quantum emitters. It is also found that as the concentration of quantum emitters increases, the dipole-dipole field also increases. This in turn, increases the two-photon florescence as function of the concentration. Finally, we have compared our theory with experiments of a metallic nanoshell which is made for Au nanosphere core and the SiO shell. The metallic nanoshell is surrounded by various concentrations of Cadmium-Selenium quantum dots as quantum emitters. A good agreement between theory and experiment is found.
已建立一种关于存在量子发射体时金属纳米壳层的双光子荧光理论。该金属纳米壳层由作为核心的金属纳米球和作为壳层的介电材料构成。一组量子发射体沉积在介电壳层的表面。施加探测场以研究金属纳米壳层中的双光子过程。由于探测光子与金属纳米球表面存在的表面等离子体之间的耦合，在核心与壳层的界面处产生表面等离子体激元。当探测光子能量与等离子体激元共振能量共振时，表面等离子体激元场的强度极大。由于表面等离子体激元场和探测场，在每个量子发射体中产生感应电偶极子。量子发射体中的偶极子通过偶极 - 偶极相互作用相互作用。使用多体理论和平均场近似计算偶极 - 偶极相互作用。发现偶极 - 偶极相互作用有由表面等离子体激元场诱导的新项。在存在偶极 - 偶极相互作用的情况下推导了双光子荧光的解析表达式。我们的理论预测，相对于孤立的金属纳米壳层的荧光，在存在量子发射体时双光子荧光的强度会增强。增强背后的物理原理是量子发射体集合之间存在偶极 - 偶极相互作用。还发现随着量子发射体浓度的增加，偶极 - 偶极场也增加。这反过来又使双光子荧光作为浓度的函数而增加。最后，我们将我们的理论与以金纳米球核心和二氧化硅壳制成的金属纳米壳层的实验进行了比较。该金属纳米壳层被各种浓度的镉 - 硒量子点作为量子发射体包围。理论与实验之间发现了良好的一致性。
