Optical Absorption in Nano-Structures: Classical and Quantum Models

Abstract

In the last decade, nano-structured materials have gained a significant interest for applications in solar cells and other optical and opto-electronic devices. Due to carrier confinement, the absorption characteristics in these structures are quite different from the absorption in bulk materials and thin films. Optical absorption coefficients of a silicon nano-wire are obtained based on a semiclassical model where the photon-electron interaction is described by the interaction of an electromagnetic wave with the electrons in the valence band of a semiconductor. The absorption characteristics showed enhanced optical absorption but no resonant peaks. In our modified model, we have identified optically active inter band transitions by performing electronic structure calculations on unit cells of nano-dimensions. The absorption spectrum obtained here shows explicit excitonic processes. This absorption is tunable from the visible region to near UV portion of the solar spectrum. In our previous work on thin films (100 nm) of ITO, we have used classical Drude model to describe free electron absorption. Using the imaginary part of the calculated complex dielectric function, we have plotted the absorption coefficient versus wavelength of the photon and compared with the experimental data showing good agreement between theory and experiment.

The Effect of Quantum Confinement on Optical Properties of CdSe Quantum Dots at Room Temperature

“…Since the size of 1.4 nm taking only the ultraviolet range (This size has a large energy gap which is compatible with the special high-energy ultraviolet transmittance), while the size of 10 nm includes the ultraviolet, visible, and infrared range (This size possess a narrow energy gap, which is compatible with most transitions compatible with ultraviolet, visible and infrared spectrum) [28]. Also, it is seen the response of the quantum sizes to wavelengths begins at 1.4 nm, while the sizes are smaller could not be absorbed this range of wavelengths because the energy gap for them is so large [29]. For this reason, the quantum dots size of 1.4 nm can absorb the wavelength of 300 nm that it has an energy gap of about 3.571 eV.…”

“…Therefore it will allow more energy to be absorbed when the optical gap is smaller. Now, it can explain the mechanism that causes the absorption coefficient to decrease according to the following relationship 𝐸𝐸 = ℎ.𝑐𝑐 λ [29], where the ability of the incident light energy to excite the electrons from the top of the valence band to the bottom of the conduction band is reduced because it does not have an energy equal to or greater than the energy gap of the quantum size of its excitation [30] The absorption coefficient gradually decreases as the quantum dot size decreases from 10 nm to 1.4 nm [29,31]]. This leads to believe that CdSe quantum dots can be present in tuning colours according to size.…”

Application of Nanomaterials in Environmental Improvement

“…For a cluster of 18 atoms, the band gap energy is taken as (1.82) eV with radius 1 nm. The absorption coefficient for nanostructure is given as [26]:…”

Scattering by nanoantenna in complex medium.

“…La dinámica de nanopartículas en fluidos o en arreglos de varias nanoantenas [11]. Los materiales nanoestructurados han ganado un interés significativo para aplicaciones en células solares en la industria energética y otros dispositivos ópticos y optoelectrónicos que son comprendidos desde modelos clásicos hasta los cuánticos en procesos de dispersión que se puede generar desde las longitudes de onda de la región visible hasta el UV cercano del espectro, que puede tener como fuente la energía solar [12].…”