Effect of Nanoparticle Distribution on Photothermal Absorption in Binary Mixtures of Colloidal Supraballs

Ti-based metal-organic frameworks (MOFs) are demonstrated as promising photosensitizers for photoelectrochemical (PEC) water splitting. Photocurrents of TiO2 nano wire photoelectrodes can be improved under visible light through sensitization with aminated Ti-based MOFs. As a host, other sensitizers or catalysts such as Au nanoparticles can be incorporated into the MOF layer thus further improving the PEC water splitting efficiency.

The propagation of light through biological tissues depends on its optical properties. These properties vary between individuals, tissues, and location; however, they are not considered to establish light dosimetry for therapies in clinical practice. In this context, this work aimed to use Monte Carlo (MC) simulations to evaluate how different skin phototypes influence light propagation and, consequently, the penetration depth. We use the Monte Carlo Extreme (MCX) implementation to simulate the photon trajectory. The skin model was composed of the following layers: living epidermis, papillary dermis, upper blood network dermis, reticular dermis, deep blood network, and subcutaneous fat. The skin layers’ optical properties were obtained directly from the literature, except for the absorption coefficient of the living epidermis, which was calculated based on the Petrov1 equation. This equation uses the wavelength, melanin and water concentrations, eumelanin/pheomelanin ratio, and other parameters to determine the absorption coefficient as a function of the melanin concentration. The melanin concentration value was varied from 0% to 50% to cover all six phototypes predicted on the Fitzpatrick scale. We also evaluated the effects at four different wavelengths: 410 nm, 630 nm, 780 nm, 850 nm. Our simulation results indicate that as the melanin concentration increases, the penetration depth decreases due to a higher absorption coefficient at the more superficial layers. This effect is more evident for lower wavelengths because biological components absorb more energy. They also show us that individual parameters can affect light propagation and need to be adjusted correctly. Thus, the development of individualized dosimetry can lead to a higher success rate for phototherapy. We also emphasize that skin phototype is not a parameter reported in most clinical studies papers, despite this being an important parameter that might influence clinical results, as this work shows. Thus, it is necessary to start paying attention to this characteristic and include it in phototherapy publications.

Brown carbon from biomass burning imposes strong circum-Arctic warming

Various defects during the manufacture of a high-energy laser monocrystalline silicon reflector will increase the energy absorption rate of the substrate and worsen the optical properties. Micron-scale or larger manufacturing defects have been inhibited by mechanism study and improvement in technology, but the substrate performance still fails to satisfy the application demand. We focus on the changes in the optical properties affected by nanoscale and Angstrom lattice defects on the surface of monocrystalline silicon and acquire the expected high reflectivity and low absorptivity through deterministic control of its defect state. Based on the first principles, the band structures and optical properties of two typical defect models of monocrystalline silicon—namely, atomic vacancy and lattice dislocation—were analyzed by molecular dynamics simulations. The results showed that the reflectivity of the vacancy defect was higher than that of the dislocation defect, and elevating the proportion of the vacancy defect could improve the performance of the monocrystalline silicon in infrared (IR) band. To verify the results of simulations, the combined Ion Beam Figuring (IBF) and Chemical Mechanical Polishing (CMP) technologies were applied to introduce the vacancy defect and reduce the thickness of defect layer. After the process, the reflectivity of the monocrystalline silicon element increased by 5% in the visible light band and by 12% in the IR band. Finally, in the photothermal absorption test at 1064 nm, the photothermal absorption of the element was reduced by 80.5%. Intense laser usability on the monocrystalline silicon surface was achieved, and the effectiveness and feasibility of deterministic regulation of optical properties were verified. This concept will be widely applied in future high-energy laser system and X-ray reflectors.

Relationships between optical and physical properties were examined on the basis of intensive sampling at a site on the New England continental shelf during late summer 1996 and spring 1997. During both seasons, particles were found to be the primary source of temporal and vertical variability in optical properties since light absorption by dissolved material, though significant in magnitude, was relatively constant. Within the particle pool, changes in phytoplankton were responsible for much of the observed optical variability. Physical processes associated with characteristic seasonal patterns in stratification and mixing contributed to optical variability mostly through effects on phytoplankton. An exception to this generalization occurred during summer as the passage of a hurricane led to a breakdown in stratification and substantial resuspension of nonphytoplankton particulate material. Prior to the hurricane, conditions in summer were highly stratified with subsurface maxima in absorption and scattering coefficients. In spring, stratification was much weaker but increased over the sampling period, and a modest phytoplankton bloom caused surface layer maxima in absorption and scattering coefficients. These seasonal differences in the vertical distribution of inherent optical properties were evident in surface reflectance spectra, which were elevated and shifted toward blue wavelengths in the summer. Some seasonal differences in optical properties, including reflectance spectra, suggest that a significant shift toward a smaller particle size distribution occurred in summer. Shorter timescale optical variability was consistent with a variety of influences including episodic events such as the hurricane, physical processes associated with shelfbreak frontal dynamics, biological processes such as phytoplankton growth, and horizontal patchiness combined with water mass advection.

Perovskite halides, owing to their environmental stability, non‐toxicity, and remarkable efficiency, are emerging as potential candidates for photovoltaic, solar cell, and thermodynamic applications. The electronic, optical, thermoelectric, and thermodynamic properties of cubic perovskite RbTmCl3 are studied using density functional theory (DFT). The electronic, optical, and thermoelectric properties are calculated both with and without spin‐orbit coupling (SOC) using the Tran and Blaha functional in the structure of the modified Becke Johnson (mBJ) exchange potential, while structural and mechanical properties are assessed using the exchange‐correlation functional calculated using the Perdew Burke Ernzerhof Generalized Gradient Approximation (PBE‐GGA). The negative formation energy (−592.39 KJ mol−1) and tolerance factor (1.17) for structural stability and current their existences in the cubic phase are found. Evaluation of the obtained data with and without SOC shows that the SOC effect causes the Tm‐d states to be shifted toward the level of Fermi, thereby decreasing the energy band gaps from 1.42 to 1.32 eV. Nevertheless, only the shift of the third variable peak to lower energies indicates the impact of SOC on optical properties. The effectiveness of RbTmCl3 in optical devices operating in the visible and ultraviolet regions is demonstrated by the exceptional absorption of light in these ranges. Using TB‐mBJ + SOC functional, the electronic band structure research reveals a direct semiconducting band gap of 1.32 eV in comparison to earlier calculations like LDA, PBE‐GGA, and TB‐mBJ. The absorption spectrum, reflectivity, extinction coefficient, refractive index, and dielectric function are displayed in addition to the electrical properties. Additionally, the quasi‐harmonic Debye model, which accounts for lattice vibrations, was used to study the corresponding volume, heat capacity, expansion of the heat coefficient, and Debye temperature of the RbTmCl3 crystal. We have calculated the thermoelectric parameters such as the Seebeck coefficient, thermal conductivity, electrical conductivity, and power factor as a function of temperature (100–900 K).

IntroductionAtmospheric dust has large-scale effects on planetary radiation, global climate, and biogeochemical cycles, and is therefore a critical component of the Earth’s climate. However, the dynamics and impact of the dust is poorly understood (e.g., [1]). Particularly two strong absorbers of solar energy, magnetic minerals and giant particles, have been neglected in aerosol and climate models (e.g., [2][3]). The effects of magnetic (nano)particles can be comparable to black and brown carbon, they promote ice nucleation and play a role in cloud formation (e.g., [4]). It has been recently discovered that strong winds are able to carry even the giant particles (≥ 100 μm) long distances, from Sahara to Iceland [5]. Despite their global importance, both the magnetic nanoparticles and the giant particles remain poorly described. The optical and light scattering properties and the exact mechanism by which these particles initiate ice nucleation are not yet understood.Our project combines experimental and theoretical approaches to enhance our understanding of giant particles and magnetic minerals in atmospheric dust, utilising methods from both geosciences and physics. Ultimately, our work aims to contribute to characterising the particles and their source areas, long-range transport, and scattering effects, to be utilised in emission, transport, and deposition modelling, and in climate models.Dust samplesThe research material consists of Saharan dust that was deposited in Finland and collected as citizen science samples by the Finnish Meteorological Institute during 2021. The citizen science initiative yielded samples from 525 locations, with one or more samples collected from each site. The first results regarding some of the dust samples were published in 2023 [6]. The multidisciplinary study showed that the Saharan dust deposited in Finland originated from the Sahel desert (south of Sahara), based on the magnetic properties of the particles, and the System for Integrated modeLling of Atmospheric coMposition (SILAM) model (silam.fmi.fi). These results are an encouraging starting point for a more detailed analysis of the remaining > 500 samples.MethodsThis study begins by using mineralogical, geochemical, and magnetic methods to identify and characterise the particles in the Saharan dust samples. The particle grain-size and shape distribution are fundamental for understanding and predicting atmospheric residence times, optical properties, transport, and settling processes. Laser grain-size analyser and both dynamic and static image analyses will be used to determine the grain-sizedistributions and the particle shape (incl. sphericity, roundness, and aspect ratio). Bulk petrography and heavy mineral analysis provides the framework for the geological classification and yields information on the source, and both sedimentary and the pre-aeolian transport processes.Magnetic mineral characterisation is fundamental for source discrimination and for understanding both atmospheric optical and cloud formation properties. Magnetic methods are non-destructive and powerful in characterising the type, particle size, and quantity of magnetic materials. Measurements will be carried out in order of increasing magnetic field: initial susceptibility with two frequencies, NRM demagnetisation, anhysteretic remanence, and isothermal remanence.The research then focuses on the scattering and absorption of light by these particles, both experimentally and theoretically. The scattering matrix measurements will be conducted to analyse the physical and chemical characteristics, such as shape and composition, of the particles. The experimentally obtained information will then be used for developing the theoretical modelling of the particles, using numerical methods [7][8][9][10]. This is the first time when the scattering studies will culminate in an analysis of radiative effects of both the giant and magnetic particles in the Earth’s atmosphere.For bulk material optical properties, the modular integrating-sphere spectrometer will be used to determine the reflection and absorption spectra of particles in the ultraviolet-visual-near-infrared wavelength range. The spectral directional scattering from a particle layer will be measured with a goniometer. For light scattering properties, the 4 × 4 scattering matrix of a dust particle relates the Stokes parameters (intensity with linear and circular polarisation) of the incident light to the Stokes parameters of the scattered light. In Helsinki, the unique acoustic levitator facility allows for measurements of the upper left-hand 2 × 2 block of the scattering matrix for a large particle in controlled position and orientation. The aim of the measurements is to develop profound shape, structure, and compositional models for these particles. The scattering matrix and bulk optical property measurements will be matched with particle models of varying sophistication and a study follows on the implications of the particle absorption and scattering properties in atmospheric radiative energy transfer.

Recent studies have shown that gold nanorods are highly effective agents for conversion of visible and near infrared (NIR) light into heat. Thermal therapy that utilizes this effect is called Plasmonic Photohermal Therapy (PPTT), where light absorption by photothermal agents (plasmon-resonant gold nanorods) caused kinetic energy to increase, resulting in heating of the area surrounding the agent. A primary understanding of optical and thermal properties of gold particles at nonscale level is still unclear. Due to the limitations of current equipment for nanoparticle characterization, numerical methods and computational models are widely used to understand the physic at the nanoscale. In this thesis fininte element analysis and spatial modulation spectroscopy were used to develop and test a computational model to characterize optical properties of a single gold nanorod.

Recent studies have shown that gold nanorods are highly effective agents for conversion of visible and near infrared (NIR) light into heat. Thermal therapy that utilizes this effect is called Plasmonic Photohermal Therapy (PPTT), where light absorption by photothermal agents (plasmon-resonant gold nanorods) caused kinetic energy to increase, resulting in heating of the area surrounding the agent. A primary understanding of optical and thermal properties of gold particles at nonscale level is still unclear. Due to the limitations of current equipment for nanoparticle characterization, numerical methods and computational models are widely used to understand the physic at the nanoscale. In this thesis fininte element analysis and spatial modulation spectroscopy were used to develop and test a computational model to characterize optical properties of a single gold nanorod.

Surface segregation in binary colloidal mixtures offers a simple way to control both surface and bulk properties without affecting their bulk composition. Here, we combine experiments and coarse-grained molecular dynamics (CG-MD) simulations to delineate the effects of particle chemistry and size on surface segregation in photonic colloidal assemblies from binary mixtures of melanin and silica particles of size ratio (D large /D small) ranging from 1.0 to ~2.2. We find that melanin and/or smaller particles segregate at the surface of micrometer-sized colloidal assemblies (supraballs) prepared by an emulsion process. Conversely, no such surface segregation occurs in films prepared by evaporative assembly. CG-MD simulations explain the experimental observations by showing that particles with the larger contact angle (melanin) are enriched at the supraball surface regardless of the relative strength of particle-interface interactions, a result with implications for the broad understanding and design of colloidal particle assemblies.

NIR absorptive croconic acid/quercetin/CaO2 nanoplatform for tumor calcium overload therapy combined mild photothermal therapy

By executing the Generalised Gradient Approximation (GGA) based on the Pethew Burke Emzerhof (PBE), the structural geometry, electronic band structures, total density of states (DOS), partial density of states (PDOS) and optical properties for both of undoped and doped ZnAg2GeTe4 were investigated. The calculated band gap of ZnAg2GeTe is 1.06 eV, indicating strong photocatalyst for organic pollutants. To explain the photocatalytic effect owing to hybridisation of orbitals, the DOS were simulated to assess the characteristics of 4s, 3d for Zn, 5s, 4d for Ag, 4s, 3d, 4p for Ge and 4s, 5s 4d 5p for Te orbitals travelling from the highest occupied valance bands to the lowest occupied conduction bands. The optical properties, for instance absorption, reflectivity, dielectric function and loss function may be indicated the increased absorption of visible light, as well as corresponds to electronic structure. For better photocatalytic activity, Fe metal was doped by replacing Ge at 7%. After doping, the band gap was decreased from 1.06 eV to 0.09 eV, and DOS was also increased. Nevertheless, optical properties, especially absorption, were also increased which indicates higher photocatalytic activity. It can be concluded that ZnAg2Ge0.93Fe0.07Te4 shows more photocatalytic activity than ZnAg2GeTe4 with the evidences from the band gap and optical properties.

The course for improving the stability and electronic transport properties of electrode materials is crucial for obtaining high-performance organic solar cells and warrants attention. The current study explores the potential of graphite as an anode-based counter electrode material for organic solar cell applications using a first-principles calculations approach. The study focuses on the effect of chitosan molecules on the charge transfers and optical response properties of graphite. The adsorption of chitosan onto graphite showed a negligible lattice mismatch and decreased cohesive energies, suggesting improved stability. The increased density of states of graphite with chitosan incorporation suggests the presence of delocalized electronic states near the Fermi level. The optical response properties show increased absorption with chitosan adsorption on graphite surface, suggesting the introduction of surface dipoles and light absorption. The variation of the refractive index of graphite ( ) with chitosan adsorption suggests significant interfacial charge transfers. The bulk of the charge transfer behaviour can be attributed to the π-π and n-π transitions. Hence, chitosan-supported graphite heterostructures can act as potential anode electrode materials for organic solar cells and other optoelectronic applications. METHODS: All computations were performed using density functional theory (DFT) as implemented in the CASTEP code, the DMol package, and the adsorption locator tool. The geometric structures were optimized using the generalized gradient approximation (GGA) with the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional. The electronic and optical properties were studied using the same norm-conserving pseudopotentials of the CASTEP code.

In order to expand the use of titania indoor as well as to increase its overall performance, narrowing the band gap is one of the possibilities to achieve this. Modifying with rare earths (REs) has been relatively unexplored, especially the modification of rutile with rare earth cations. The aim of this study was to find the influence of the modification of TiO2 with rare earths on its structural, optical, morphological, and photocatalytic properties. Titania was synthesized using TiOSO4 as the source of titanium via hydrothermal synthesis procedure at low temperature (200 °C) and modified with selected rare earth elements, namely, Ce, La, and Gd. Structural properties of samples were determined by X-ray powder diffraction (XRD), and the phase ratio was calculated using the Rietveld method. Optical properties were analyzed by ultraviolet and visible light (UV-Vis) spectroscopy. Field emission scanning electron microscope (FE-SEM) was used to determine the morphological properties of samples and to estimate the size of primary crystals. X-ray photoelectron spectroscopy (XPS) was used to determine the chemical bonding properties of samples. Photocatalytic activity of the prepared photocatalysts as well as the titania available on the market (P25) was measured in three different setups, assessing volatile organic compound (VOC) degradation, NOx abatement, and water purification. It was found out that modification with rare earth elements slows down the transformation of anatase and brookite to rutile. Whereas the unmodified sample was composed of only rutile, La- and Gd-modified samples contained anatase and rutile, and Ce-modified samples consisted of anatase, brookite, and rutile. Modification with rare earth metals has turned out to be detrimental to photocatalytic activity. In all cases, pure TiO2 outperformed the modified samples. Cerium-modified TiO2 was the least active sample, despite having a light absorption tail up to 585 nm wavelength. La- and Gd-modified samples did not show a significant shift in light absorption when compared to the pure TiO2 sample. The reason for the lower activity of modified samples was attributed to a greater Ti3+/Ti4+ ratio and a large amount of hydroxyl oxygen found in pure TiO2. All the modified samples had a smaller Ti3+/Ti4+ ratio and less hydroxyl oxygen.

Polymethyl methacrylate (PMMA), commonly known as acrylic or plexiglass, is a widely used thermoplastic polymer renowned for its excellent optical clarity, mechanical properties, and ease of fabrication. However, its intrinsic optical properties, such as limited light absorption and scattering capabilities, pose challenges for advanced photonic applications. This paper explores the integration of metamaterials into PMMA to enhance its optical performance, leveraging the unique electromagnetic properties of metamaterials. The review systematically examines mechanisms of enhancement, including light manipulation, plasmonic effects, and refractive index modification, and highlights various integration techniques like doping with nanostructures, incorporating plasmonic nanoparticles, and using advanced synthesis methods. Fourteen key studies are analyzed to demonstrate the significant improvements achieved in PMMA’s optical properties, including enhanced light absorption, scattering, and UV resistance, as well as increased flexibility and energy efficiency. The paper also discusses current research gaps, such as achieving uniform nanoparticle distribution, ensuring long-term stability, and developing scalable fabrication techniques. Future research directions emphasize the need for advanced fabrication methods, long-term performance studies, exploration of new metamaterials, and the development of multifunctional composites. By addressing these challenges and leveraging technological advancements in nanotechnology, machine learning, and scalable manufacturing processes, PMMA-metamaterial composites can be optimized for a wide range of applications, from optoelectronics and energy harvesting to medical devices and smart technologies. This comprehensive review highlights the transformative potential of PMMA-metamaterial composites and provides valuable insights into their future development and application in various high-performance fields.