It is shown that the ordinary semiclassical theory of the absorption of light by exciton states is not completely satisfactory (in contrast to the case of absorption due to interband transitions). A more complete theory is developed. It is shown that excitons are approximate bosons, and, in interaction with the electromagnetic field, the exciton field plays the role of the classical polarization field. The eigenstates of the system of crystal and radiation field are mixtures of photons and excitons. The ordinary one-quantum optical lifetime of an excitation is infinite. Absorption occurs only when "three-body" processes are introduced. The theory includes "local field" effects, leading to the Lorentz local field correction when it is applicable. A Smakula equation for the oscillator strength in terms of the integrated absorption constant is derived.

a Quantum-Mechanical Theory of the Contribution of Excitons to the Complex Dielectric Constant of Crystals.

In the context of quantifying entanglement we study those functions of a multipartite state which do not increase under the set of local transformations. A mathematical characterization of these monotone magnitudes is presented. They are then related to optimal strategies of conversion of shared states. More detailed results are presented for pure states of bipartite systems. It is show that more than one measure are required simultaneously in order to quantify completely the non-local resources contained in a bipartite pure state, while examining how this fact does not hold in the so-called asymptotic limit. Finally, monotonicity under local transformations is proposed as the only natural requirement for measures of entanglement.

On the characterization of entanglement

Black silicon (BSi) represents a very active research area in renewable energy materials. The rise of BSi as a focus of study for its fundamental properties and potentially lucrative practical applications is shown by several recent results ranging from solar cells and light-emitting devices to antibacterial coatings and gas-sensors. In this paper, the common BSi fabrication techniques are first reviewed, including electrochemical HF etching, stain etching, metal-assisted chemical etching, reactive ion etching, laser irradiation and the molten salt Fray-Farthing-Chen-Cambridge (FFC-Cambridge) process. The utilization of BSi as an anti-reflection coating in solar cells is then critically examined and appraised, based upon strategies towards higher efficiency renewable solar energy modules. Methods of incorporating BSi in advanced solar cell architectures and the production of ultra-thin and flexible BSi wafers are also surveyed. Particular attention is given to routes leading to passivated BSi surfaces, which are essential for improving the electrical properties of any devices incorporating BSi, with a special focus on atomic layer deposition of Al2O3. Finally, three potential research directions worth exploring for practical solar cell applications are highlighted, namely, encapsulation effects, the development of micro-nano dual-scale BSi, and the incorporation of BSi into thin solar cells. It is intended that this paper will serve as a useful introduction to this novel material and its properties, and provide a general overview of recent progress in research currently being undertaken for renewable energy applications.

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Black silicon: fabrication methods, properties and solar energy applications

https://pubs.rsc.org/en/content/articlepdf/2017/cc/c6cc06475b

Beyond methylammonium lead iodide: prospects for the emergent field of ns2 containing solar absorbers

As stated in the text, Figs. 3 and 4 (transmission versus probe laser detuning) were taken at an energy of 10 nJ in a 0.5-mm-diam beam. We should have noted that when the probe energy is increased to 150 n3 (— 10" W/cm ) the absorption cross section at the transmission maximum increases by a factor of approximately 2. At this energy density, with or without the coupling laser present, transmitted probe energy is no longer linear with incident probe energy.

Observation of Electromagnetically Induced Transparency in Collisionally Broadened Lead Vapor

Dans le present travail, nous avons analyse les caracteristiques optiques des couches minces de SnO2 et CuInS2 preparees par airless spray en vue de leur utilisation en tant que contact avant et absorbeur de la structure photovoltaique backwall CdS/CuInS2. Les donnees experimentales concernent la reflexion R et la transmission T dans les domaines du visible au proche infrarouge. L'interpretation de ces resultats a ete basee d'une part sur la methode d'analyse de R et T developpee par Tomlin et d'autre part sur la methode de resolution numerique d'equations non lineaires de Mueller. Nous avons ainsi obtenu les spectres de dispersion correspondants de n(A) et k(A). Dans le cas de la couche de SnO2, cette etude nous a permis de deduire la permittivite, la masse effective des electrons de conduction et l'energie de Fermi (e∞ = 3,74, m* = 0,34 m0 et EF = 0,64 eV). La loi de variation de e2(ω) en ω-4 obtenue dans la region ωτ >> 1, montre que les porteurs libres sont diffuses essentiellement par les impuretes ionisees. D'autre part, en considerant le materiau inhomogene CuInS2 contenant des inclusions d'air comme etant un milieu effectif, nous avons estime la densite de ces inclusions a environ 20 %. Enfin, cette etude a permis aussi d'evaluer les largeurs de bande interdite du SnO2 et CuInS2 qui sont respectivement de l'ordre de 3,9 eV et 1,4 eV.

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Propriétés optiques des couches minces de SnO2 et CuInS2 airless spray

http://www.fst.rnu.tn/lpmc/documents/publications/pub2006/29-06.pdf

Effect of pH on the properties of ZnS thin films grown by chemical bath deposition

http://www.fst.rnu.tn/lpmc/documents/publications/pub2002/2-02.pdf

Vapour-etching-based porous silicon: a new approach

β-In2S3 and β-In2−xAlxS3 thin films have been deposited on different substrates using the spray pyrolysis technique at 320 °C. X-ray diffraction, atomic force microscopy, and scanning electron microscopy were used to characterize the structure of the films; the surface compositions of the films were studied by Auger electrons spectroscopy and energy dispersive spectrometry (EDS), the work function and the photovoltage by the Kelvin method. Using these techniques, we have specified the effect of the nature of the substrate, of its surface morphology, of the introduction of small amounts of Al in the layer, on the properties of the films. The best crystallized of β-In2S3 were obtained for deposits on pyrex. This was improved by the introduction of Al atoms. The work function differences (φmaterial–φprobe) for β-In2S3 and β-In2−xAlxS3 deposited on steel were equal to −150 meV and to −180 meV, respectively. Putting Al atoms in the film increases φm (by about 30 meV) and induces the formation of a negative sur...

Structure, surface composition, and electronic properties of β-In2S3 and β-In2−xAlxS3

The electronic and optical properties of Sb2S3 are studied using the full potential linearized augmented plane wave (FP-LAPW) method as implemented in Wien2k. In this approach, the alternative form of the generalized gradient approximation (GGA) proposed by Engel and Vosko (EV-GGA) was used for the exchange correlation potential. The calculated band structure shows a direct band gap. The contribution of different bands was analyzed from total and partial density of states curves. Moreover, the optical properties, including the dielectric function, absorption spectrum, refractive index, extinction coefficient, reflectivity and energy-loss spectrum are all obtained and analyzed in detail.

Raouf Bennaceur

Papers

Propriétés optiques des couches minces de SnO2 et CuInS2 airless spray

Effect of pH on the properties of ZnS thin films grown by chemical bath deposition

Vapour-etching-based porous silicon: a new approach

Structure, surface composition, and electronic properties of β-In2S3 and β-In2−xAlxS3

Electronic structure and optical properties of Sb2S3 crystal