6 The 2 nd Asian Symposium on Electromagnetics and Photonics Engineering August 28-30, 2013, Tabriz, Iran ASEPE 2013- Plasmonics I, OWdA2 Near-Field Intensifying in Multi-shell Nanoparticles (Si/Au/SiO 2 ) Mohsen Mazloum 1 , Amir Maghoul *2 , Ahmad SalmanOgli 3 Photonics and Nanocrystal Research Laboratory, University of Tabriz, Tabriz, IRAN 1 Mazloum@tabrizu.ac.ir; 2 amaghoul@tabrizu.ac.ir * ; 3 a.salmanogli@tabrizu.ac.ir Abstract-In this article, the near-field optical properties of multi-shell nanoparticle (Si/Au/SiO 2 ) are investigated. Recently, the use of organic fluorophores because of their low cost and biocompatibility were commonly established. But, the most of their in the near infrared region have a relatively low quantum yield and susceptible to photobleaching that are dramatically influence on biological application. For solving this problem, in this article, the use of a novel nanoparticle to enhance the quantum efficiency of existing fluorescent molecules are suggested.It has been known that the surface plasmon resonance of nanoparticle in nearby of its can alter the any organic fluorophores optical properties such as absorption and emission. Therefore, due to the unique plasmonic properties of the nanoparticles and their tunability in the near infrared region they can absorb resonant light; effectively convert light to heat and highly amplification of near-field efficiency.Hence, the near-field optical properties of Si/Au/SiO 2 core/shell nanoparticle as a very important factor is perused and simulated. Furthermore, for reaching to a better nanostructure, it is obligatory to manipulate the Au and SiO 2 shell thickness.It is notable that plasmon-plasmon interactions of raised modes by nanoparticle’s core and shell havean essential role to manipulate of nanoparticle’s near-field features. Keywords-near-infrared (NIR); nanoparticle (NPs); surface plasmon resonance (SPR) I. INTRODUCTION In this section, because of near-field augmentation importance, the short review of its application in biological is reported. In biological application[1-6] the use of organic fluorophores, which emit in the near-infrared (NIR), has rapidly developed in the past few decades due to their low cost and biocompatibility when used in small doses. However, most organic fluorophores in the NIR have a relatively low quantum yield, they are susceptible to photo bleaching and their excitation-emission profiles are often prone to changes in local chemical environment. There are several approaches to improving the properties of NIR organic fluorophores: (1) complex organic synthesis techniques to synthesize physiologically safe fluorescent molecules; (2) use nanostructures or nanoparticle (NPs) to enhance the quantum efficiency of existing fluorescent molecules which have already been approved. Well, NPs and quantum dots exhibit unique [7-10], remarkably vivid optical properties due to excitation of their surface plasmons by incident light. Plasmon excitation results in significantly enhanced local fields at the NPs surfaces. Obviously, surface plasmon resonance (SPR) as an important optical property has been commonly used in diverse applications such as deep tissue imaging. It is known that the plasmon resonance is due to the collective excitation of the electrons in the materials at the specific frequency determined by the material properties and geometry of the nanostructure [11-17]. This is very useful in designing of NPs for application of biosensing, deep tissue imaging, and thermal therapy. Because of the geometry and composition dependent plasmon resonance of the multi-layered nanostructure, allows one to access frequencies in the electromagnetic spectrum from the visible to the NIR. It was shown that the nature of the NPs’ plasmon resonance (based on quantum mechanical theoretical investigations) have shown by a strong interaction, or hybridation, between plasmon associated with the sphere and surface of the shell, which is responsible for the plasmon tunability of the nanoshells. In addition, a splitting of the plasmon resonance into two modes has been predicted for NPs with a metal shell around a dielectric core and this phenomenon is related to the difference in polarization between the NP’s outer and inner surfaces. Therefore, the NPs multi-layer plasmon resonance reveals several distinctive modes with the symmetric and anti-symmetric polarization. The symmetric mode is found in the visible to infrared and anti-symmetric mode is found in the ultraviolet region of the spectrum and moreover, the latter case cannot easily be resolved due to interband transition in the metal shells. It has been known that the emissive properties and lifetime of fluorophores are modified in the presence of metals or noncomplex. Plasmon resonance when coupled to molecular fluorescence provides one of the most effective routes for enhancing the photo stability and increasing the quantum yield of fluorophores. The NPs/fluorophores interaction results from (i) the modification of the electromagnetic field and (ii) the photonic mode density in the vicinity of the fluorophores. However, an increase in the fluorescence intensity results primarily from a combination of (i) increased absorption by the molecule due to interaction with the enhanced near-field, (ii) increased radiative decay rate of the molecule without significant changes in the non-radiative decay rates, and (iii) increased coupling efficiency of the fluorescent emission to the far-field [18-22].In this article, the near-field enhancement is essentially investigated. The alteration of NPs parameters influences on near-field enhancing is probed. In all simulation plasmon modes hybridization or plasmon-plasmon interaction as the essential parameters is perused. Step-by-step of this article are presented as follow: (I) the interaction of light with NPs; (II) applying of boundary conditions and then Maxwell’s equations solving; (III) the calculation of electrical and magnetic fields as incident, internal, and scattered forms and finally, the NPs’ near-field scattering efficiency are simulated.