Optical properties

Résumé

The optical properties of a material define how it interacts with light. The optical properties of matter are studied in optical physics, a subfield of optics. The optical properties of matter include: *Refractive index *Dispersion *Transmittance and Transmission coefficient *Absorption *Scattering *Turbidity *Reflectance and Reflectivity (reflection coefficient) *Albedo *Perceived color *Fluorescence *Phosphorescence *Photoluminescence *Optical bistability *Dichroism *Birefringence *Optical activity *Photosensitivity A basic distinction is between isotropic materials, which exhibit the same properties regardless of the direction of the light, and anisotropic ones, which exhibit different properties when light passes through them in different directions. The optical properties of matter can lead to a variety of interesting optical phenomena. Properties of specific materials *Optical properties of water and ice *Optical properties of carbon nanotubes *Crystal optics Li

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https://en.wikipedia.org/wiki/Optical_properties

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First-principles investigation of the optical properties of gold and its alloys

Deniz Keçik

EPFL2013

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Cyanine dyes are organic semiconductor compounds with light absorption and emission properties useful for emerging technologies such as solar cells and light-emitting devices. The characteristics of these materials in the solid state depend on their organization of the constituting building blocks. This thesis focuses on controlling the morphology of cyanine dye thin films at different length scales and clarifying the resulting properties. When microstructures present features whose size matches visible light wavelengths, new properties may arise from light-matter interactions. Here the properties resulting from the light-matter interactions of cyanine droplet films cast from solution are studied. Based on experimental evidence, it is shown that dye droplet ensembles scatter light with different efficiencies and wavelength ranges depending on their dimensions. FDTD simulations are used to show that this effect results fromscattering enhancement at the absorption edge of the dye where the refractive index varies considerably. Simulations also provide a better understanding of individual dropletsâ interaction with light. While earlier work had hypothesized that the observed scattering phenomenon were due to crystalline clusters within the droplets, this work highlights the contribution of the dye filmmorphology. Cyanines also form single crystals whose fabrication induces molecular-scale order in the material. Previous work demonstrated that thin single crystals could be grown by solvent vapor annealing of dye droplets. Here it is shown that in uncontrolled conditions, cyanine single crystals destabilize to formdendritic crystals. In-situ microscopy observations highlight the solute reservoir role of the droplet distribution surrounding a growing crystal; when the distance between droplets and the crystal front is large, the solute supply is diffusion-limited. Moreover variations in local pressure equilibrium between the droplets and crystal front lead to advection fluxes which perturb the crystal growth. These observations help design configurations to either prevent crystal destabilization or take advantage of the dendritic growth in a controlled manner. In addition, the patterning of crystals on a substrate is relevant for their application in devices. A practical challenge is to induce single crystal growth at specific locations. Here, surfaces patterned with SAMs of hydrophilic and hydrophobic thiols are used to create dye droplet arrays from which crystals can be grown. This method is shown to yield local crystallization of the dye and to prevent crystal destabilization through better control of the droplet distribution. By varying the dye solution concentration, partial control over crystal density is achieved, however it proved difficult to control the number of nuclei per droplet. A more controlled evaporation and solvent vapor annealing system might be necessary to master the nucleation process. Finally the structure and optical properties of cyanine single crystals are addressed. The crystal structure was determined by X-ray diffraction. Structural aspects are shown to lead to excitonic couplings, which are evidenced by orientation-dependent spectroscopic measurements of single crystals. Although further investigation of the absorption band structure is necessary, the results are promising for photovoltaic devices as they might improve exciton transport compared to amorphous layers.

EPFL2018

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EPFL2003

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EPFL2018