Enhanced efficiency of a fluorescing nanoparticle with a silver shell

Abstract

Abstract. Spontaneous emission (SE) rate and the fluorescence efficiency of a bare fluorescing nanoparticle (NP) and the NP with a silver nanoshell are analyzed rigorously by using a classical electromagnetic approach with the consideration of the nonlocal effect of the silver nano-shell. The dependences of the SE rate and the fluorescence efficiency on the core-shell structure are carefully studied and the physical interpretations of the results are addressed. The results show that the SE rate of a bare NP is much slower than that in the infinite medium by almost an order of magnitude and consequently the fluorescence efficiency is usually low. However, by encapsulating the NP with a silver shell, highly efficient fluorescence can be achieved as a result of a large Purcell enhancement and high out-coupling efficiency (OQE) for a well-designed core-shell structure. We also show that a higher SE rate may not offer a larger fluorescence efficiency since the fluorescence efficiency not only depends on the internal quantum yield but also the OQE. IntroductionFluorescent nanomaterials have been the subject of intensive research in recent years for their vast applications ranging from biomedical therapeutics and diagnostics to information storage and optoelectronics [1][2][3]. For fluorescence based applications, fluorescence efficiency, i.e. the external quantum efficiency (EQE) of the emitter, is an important issue. Due to the existence of pronounced nonradiative decay of excitons in the nanoscale structure, low EQE is an often-observed feature. Most of the strategies so far employed aim to reduce the nonradiative decay rate [4][5][6] for improving the fluorescence efficiency. The direct and effective approach to improve EQE is to increase radiative decay rate [7] and out-coupling efficiency (OQE) since EQE is the product of internal quantum yield (i.e. internal quantum efficiency) (IQE) and OQE. The enhancement of radiative decay rate results in the Purcell enhancement of IQE [8,9]. Here, we will address this issue. The radiative decay rate, i.e. spontaneous emission (SE) rate, can be enhanced by utilizing the surface plasmon effect [10][11][12] or the microcavity effect [13]. According to the near field nature of surface plasmon, the SE rate in a dielectric nanoparticle (NP) encapsulated with a metallic shell can be greatly enhanced. However, the metallic shell introduces extra absorption loss and may result in a small OQE. Consequently, fluorescence efficiency may still be low although the SE rate is greatly enhanced. Thus a rigorous theoretical study on the SE rate and OQE of emitters in nanoscale structure is desirable for getting a better physical understanding and optimal design of the nano-structure to

A Research on Temperature Dependent Characteristics of Quality Factor of Silicon MEMS Gyroscope

“…In recent years, the characteristics of silicon micro gyroscope have greatly improved, but the temperature is one of the factors that limited the characteristics of silicon micro gyroscope. Many interesting and viable technology have been reported [7][8][9][10]. The performance of silicon micro gyroscope affected by the quality factor of silicon micro gyroscope and the temperature characteristics of quality factor of silicon micro gyroscope are theoretical analyzed.…”