We analyze the uncertainty of the coefficient of band-to-band absorption of crystalline silicon. For this purpose, we determine the absorption coefficient at room temperature (295 K) in the wavelength range from 250 to 1450 nm using four different measurement methods. The data presented in this work derive from spectroscopic ellipsometry, measurements of reflectance and transmittance, spectrally resolved luminescence measurements and spectral responsivity measurements. A systematic measurement uncertainty analysis based on the Guide to the expression of uncertainty in measurement (GUM) as well as an extensive characterization of the measurement setups are carried out for all methods. We determine relative uncertainties of the absorption coefficient of 0.4% at 250 nm, 11% at 600 nm, 1.4% at 1000 nm, 12% at 1200 nm and 180% at 1450 nm. The data are consolidated by intercomparison of results obtained at different institutions and using different measurement approaches.
In this study, we explore for the first time the capabilities of nanoporous anodic alumina gradient-index filters (NAA-GIFs) functionalized with titanium dioxide (TiO) photoactive layers to enhance photon-to-electron conversion rates and improve the efficiency of photocatalytic reactions by "slow photon" effect. A set of NAA-GIFs was fabricated by sinusoidal pulse anodization, in which a systematic modification of various anodization parameters (i.e., pore widening time, anodization period, and anodization time) enables the fine-tuning of the photonic stopband (PSB) of these nanoporous photonic crystals (PCs) across the spectral regions. The surface of NAA-GIFs was chemically modified with photoactive layers of TiO to create a composite photoactive material with precisely engineered optical properties. The photocatalytic performance of TiO-functionalized NAA-GIFs was assessed by studying the photodegradation of three model organic dyes (i.e., methyl orange, Rhodamine B, and methylene blue) with well-defined absorption bands across different spectral regions under simulated irradiation conditions. Our study demonstrates that when the edges of characteristic PSB of TiO-modified NAA-GIFs are completely or partially aligned with the absorption band of the organic dyes, the photodegradation rate is enhanced due to "slow photon" effect. A rational design of the photocatalyst material with respect to the organic dye is demonstrated to be optimal to speed up photocatalytic reactions by an efficient management of photons from high-irradiance spectral regions. This provides new opportunities to develop high-performing photocatalytic materials for efficient photocatalysis with broad applicability.
Optical sensors are a class of devices that enable the identification and/or quantification of analyte molecules across multiple fields and disciplines such as environmental protection, medical diagnosis, security, food technology, biotechnology, and animal welfare. Nanoporous photonic crystal (PC) structures provide excellent platforms to develop such systems for a plethora of applications since these engineered materials enable precise and versatile control of light–matter interactions at the nanoscale. Nanoporous PCs provide both high sensitivity to monitor in real-time molecular binding events and a nanoporous matrix for selective immobilization of molecules of interest over increased surface areas. Nanoporous anodic alumina (NAA), a nanomaterial long envisaged as a PC, is an outstanding platform material to develop optical sensing systems in combination with multiple photonic technologies. Nanoporous anodic alumina photonic crystals (NAA-PCs) provide a versatile nanoporous structure that can be engineered in a multidimensional fashion to create unique PC sensing platforms such as Fabry–Pérot interferometers, distributed Bragg reflectors, gradient-index filters, optical microcavities, and others. The effective medium of NAA-PCs undergoes changes upon interactions with analyte molecules. These changes modify the NAA-PCs’ spectral fingerprints, which can be readily quantified to develop different sensing systems. This review introduces the fundamental development of NAA-PCs, compiling the most significant advances in the use of these optical materials for chemo- and biosensing applications, with a final prospective outlook about this exciting and dynamic field.
A comprehensive study on the engineering of titanium dioxide-functionalized nanoporous anodic alumina distributed Bragg reflectors (TiO 2-NAA-DBRs) for photocatalysis enhanced by the "slow photon" effect is presented. The photocatalytic performance of these composite photonic crystals (PCs) is assessed by monitoring photodegradation of a variety of organic molecules with absorbance bands across the spectral regions. This study demonstrates that photocatalytic performance of TiO 2-NAA-DBRs is enhanced by the "slow photon" effect when the edges of the PC's photonic stopband (PSB) fall within the absorbance band of the organic molecules. The photocatalytic performance is significantly enhanced when the PSB's red edge is in close proximity to the absorbance band of the organic molecules. Overall photocatalytic degradation is also dependent on the total pore length of the PC structure, charge of the organic molecules, percentage of vis-NIR irradiation and matrix complexity (i.e. interfering ions and molecules) when the PC's PSB is partially or entirely misaligned with respect to the absorbance band of the organic molecules. Finally, the real-life application of TiO 2-NAA-DBRs to degrade pollutants such as pesticides in environmental matrices is
An extensive study on the structural engineering of titanium dioxide-functionalized nanoporous anodic alumina optical microcavities (TiO2-NAA-μQVs) for photocatalysis enhanced by light confinement is presented.
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