Surface excitons optical response

III. Surface-Exciton Photodynamics and Intrinsic Relaxation Mechanisms A. The Optical Response of the Surface Exciton... 

The optical response of a monomolecular layer consists of scattered waves at the frequency of the incident wave. Since the surface model is a perfect infinite layer, the scattered waves are reflected and transmitted plane waves. In the case of a 3D crystal, we have defined (Section I.B.2) a dielectric permittivity tensor providing a complete description of the optical response of the 3D crystal. This approach, which embodies the concept of propagation of dressed photons in the 3D matter space, cannot be applied in the 2D matter system, since the photons continue propagating in the 3D space. Therefore, the problem of the 2D exciton must be tackled directly from the general theory of the matter-radiation interaction presented in Section I. 

In these conditions, the transition from the absorbing excitonic state to the emissive excitonic state will involve at least one phonon, if we discard the optical response of the surface investigated in Section III.A. It is convenient to separate the probability P(ha l hoj2) of the secondary emission into a... 

Silicon nanoparticles (Si NPs) with sizes in the order of bulk exciton Bohr radius [1, 2] present interesting optical properties for fluorescent labeling in biological imaging applications with their potential nontoxicity [3-6], However, the origin of their photoluminescence has been subjected to intense debate for almost two decades. This debate has been focused on whether quantumatomic-scale defects at the surface of the nanocrystals are responsible for the light emission [7]. 

Quantum confinement is defined as the space where the motions of electrons and holes in a semiconductor are restricted in one or more dimensions. This quantum confinement occurs when the size of semiconductor crystallites is smaller than the bulk exciton Bohr radius. Quantum wells, quantum wires, and quantum dots are confined in one, two, and three dimensions, respectively [1, 2]. The confinement can be created due to electrostatic potentials, the presence of an interface between different semiconductor materials, and the presence of a semiconductor surface. A valence band and a conduction band are separated by an energy range known as the band gap ( g). These amounts of energy will be absorbed in order to promote an electron from the valence band to the conduction band and emitted when the electron relaxes directly fi om the conduction band back to the valence band. By changing the size of the semiconductor nanoparticles, the energy width of the band gap can be altered and the optical and electrical responses of these particles are changed (Fig. 1). 

Nanoparticles are commensurable in size with boron s radius of excitons in semiconductors. This governs their optical, luminescence and redox properties. Since the intrinsic size of nanoparticles is commensurable with that of a molecule, this ensures specifics of the kinetics of chemical processes on their surface." Current investigations are concentrated on the study of boundary regions between nanoparticles and the polymer because these interfaces are responsible for the behavior of adsorption and catalysis. 

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