Optical properties of nanoparticles

The physical properties of metal nanoparticles are very size-dependent. This is clear for their magnetic properties, for which the shape anisotropy term is very important. This is also true for the optical properties of nanoparticles displaying plasmon bands in the visible range (Cu, Ag, Au) and for 111-V... 

It is difficult to predict the effect of surface functionalization on the optical properties of nanoparticles in general. Surface ligands have only minor influence on the spectroscopic properties of nanoparticles, the properties of which are primarily dominated by the crystal field of the host lattice (e.g., rare-earth doped nanocrystals) or by plasmon resonance (e.g., gold nanoparticles). In the case of QDs, the fluorescence quantum yield and decay behavior respond to surface functionalization and bioconjugation, whereas the spectral position and shape of the absorption and emission are barely affected. 

An intense femtosecond laser spectroscopy-based research focusing on the fast relaxation processes of excited electrons in nanoparticles has started in the past decade. The electron dynamics and non-linear optical properties of nanoparticles in colloidal solutions [1], thin films [2] and glasses [3] have been studied in the femto- and picosecond time scales. Most work has been done with noble metal nanoparticles Au, Ag and Cu, providing information about the electron-electron and electron-phonon coupling [4] or coherent phenomenon [5], A large surface-to-volume ratio of the particle gives a possibility to investigate the surface/interface processes. 

The concept of local perturbations of the director around nanoparticles, often linked to homeotropic anchoring to the nanoparticle surface, is a concept often brought forward in discussions of thermal, optical and electro-optic properties of nanoparticle-doped nematic liquid crystals, which adds a slightly different perspective to the invisibility of smaller particles in aligned nematics. This appears to be of particular relevance for particles coated with either hydrocarbon chains or pro-mesogenic as well as mesogenic units. 

It is noted that the optical properties of nanoparticles are generally assumed to be sufficiently dispersed and that they may be treated as isolated. However, in most practical situations, particle interactions are important, and sometimes, they are dominant. 

All publications on mesoporous soHds with nanoparticles discussing optical properties can be generally divided into two large groups. The first group consists of works on different kinds of semiconductor particles (metal sulfides, selenides, oxides, etc.) where such particles are obtained in mesoporous solids and their UV-visible absorption and photoluminescence spectra are recorded. As a rule, these papers state the change of optical properties of nanoparticles compared to bulk, similar to semiconductor nanoparticles prepared in any... 

Shengli Zou received B.S. and M.S. degrees in physical chemistry from Shandong University in China and a Ph.D. degree in physical chemistry from Emory University (with Professor Joel M. Bowman) in 2003. He has been a postdoctoral fellow in Professor George C. Schatz s lab at Northwestern University since December 2002. His research interests include the optical properties of nanoparticles and nanoparticle arrays and their applications in biological sensing. He is also interested in the self-assembly of biomolecules. 

When analyzing the optical properties of nanoparticles embedded in a medium, one should take into account effects arising at the particle-matrix interface, such as the static and dynamic redistributions of charges between electronic states in the particles and the environment in view of their chemical constitution [59]. 

Nanoparticles are minute and have a number of constituent atoms or molecules which vary from the properties inherent in their bulk counterparts. However, they cannot be treated as an isolated group of atoms or molecules due to them being constituents of a high number of atoms or molecules (Figure 6.6). Therefore, nanoparticles show various chemical, optical, electronic, and magnetic properties, which are extremely dissimilar from both the bulk and the constituent atoms or molecules (Eustis and El-Sayed, 2006 Daniel and Astruc, 2004). Furthermore, the optical properties of nanoparticles depend considerably on their... 

Optical properties of nanoparticles can be elucidated by solving the electromagnetic wave equations, considering the boundary conditions near the nanoparticles. In 1908, Mie formulated vector wave equations for spherical nanoparticles and... 

Following classical EM theory, prior to nineteenth century, individually Gustav Mie and J. C. Maxwell Garnett first showed the theoretical background behind the novel optical property of nanoparticles, that is, SPR, which also depends on the dielectric constant, refractive index, and their individual shape and size. The theories that help modem science to predict the optical property of noble metals are elaborated in the following sections. 

M. Quinten, Optical Properties of Nanoparticle Systems Mie and Beyond (Wiley-VCH, Weinheim, 2011)... 

The simplest theoretical approach available for modeling the optical properties of nanoparticles is the Mie theory estimation of the extinction of a metallic sphere in the long wavelength, electrostatic dipole limit. In the following equation ... 

The optical properties of nanoparticles are known to be significantly different from their corresponding bulk materials. The size effect of these NPs causes special optical responses such as surface plasmon resonances (SPRs) in metal nanoparticles or quantum size effects in semiconductors. The possibility of confining these NPs in inorganic matrices produces new functional materials with collective and novel properties. 

A. Rastar, M E. Yazdanshenas, A. Rasihidi, S. M. Bidoki, Theoretical review of optical properties of nanoparticles, J. Engin. Fibres and Fabrics 8 (2013) 85-96. 

CdSe has been of interest to synthetically adjust size-dependent electronic and optical properties and also due to their potential applications including the photostable luminescent biological labels [3], solar cells [44] and light-emitting devices (LEDs) [45], The control of these properties, when the radius of the nanoparticles becomes comparable to the bulk Exciton Bohr radius, has been of paramount interest [16], The quantum confinement of photo-created electron-hole pair allows the tuning of optical properties of nanoparticles by controlling their size. In CdSe, the conduction or lowest unoccupied band is composed of Cd 5s orbitals, whereas, the highest occupied band is formed from Se 4p orbitals. 

In modem sensing applications, nanoparticles are immobilized on a surface so they present the maximum detection surface to the analyte. The sensing signal is the optical absorption spectmm. This configuration is well known to researchers in the surface science community as surface quantum dots or supported thin-film islands, and their optical properties have been studied for a while. Specifically, the Marton-Schlesinger method and the Bedeaux Vlieger methods have provided both quantitative calculations of the optical properties of nanoparticles on a surface. One big advantage of the latter method is the effect of the substrate is naturally built into the formalism (see Fig. 1). A limitation of these methods is that the... 

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