Optical Absorption Values Research Articles

Rapid and precise large area mapping of rare-earth doping homogeneity in luminescent materials

Doping of luminescent materials by rare-earth ions is common practice to achieve desired emission properties for a large variety of applications. As several rare-earths ions are frequently combined, it is subsequently difficult to effectively detect and control their homogeneous distribution within the host material. Here, we present a simple, rapid, large scale and precise method of rare-earth mapping using a commercial UV-Vis scanner. We discuss the influence of rare-earth distribution on the physical, optical and luminescent properties with no observable qualitative effect on photoluminescent properties and optical anisotropy. On the contrary, rare-earth-rich areas exhibit significantly higher values of refractive index and optical absorption, which allowed for their identification by the commercial scanner device. The presented method thus provides fast and accurate information about the rare-earth distribution in the material volume with high resolution (≈2.7 µm) and low limit of concentration difference detection (≈0.014 at.%) compared to other techniques, which makes it a promising candidate for high throughput measurements.

Continuously-tunable, compact, freespace notch-filter design using an all-dielectric metagrating capped with a low-loss phase change material

Abstract Active metasurfaces utilizing phase change materials (PCMs) are currently under investigation for applications in free-space optical communication, optical signal processing, neuromorphic photonics, quantum photonics, and compact LiDAR. Attention has now turned towards novel PCM like Sb2S3 which exhibit lower optical absorption and reasonable values of refractive-index contrast in comparison to traditional data-storage PCM. We propose and numerically study the class of all-dielectric metagratings capped with low-loss PCM and predict the possibility of continuously tunable resonances whose quality factors degrade gracefully during the amorphous-to-crystalline phase transition of the PCM. Specifically, we consider the CMOS-compatible silicon-nitride on silica substrate material platform for simple and asymmetric metagratings (in particular, the symmetric-broken dimerization) and Sb2S3 capping. Our numerical study predicts that notch-filters operating around the 1550 nm NIR wavelength window can be achieved with tuning range of over 76 nm with Q-factors ranging from 784 (amorphous-phase) to 510 (crystalline-phase) (a degradation in Q of about 35%) and insertion loss of about 0.9 dB. These performance figures are a significant improvement over previously published designs utilizing data-storage PCMs and other traditional notch-filter mechanisms. We examine the influence of grating dimerization and geometrical parameters on performance metrics of the notch-filter and predicts the possibility to trade-off rejection-band and in-band spectral transmission properties. Lastly, we perform a study of all-optical phase change mechanism. Our study is promising for the miniaturization of tunable notch-filter based optical systems.

First-Principles Calculations on Electronic, Optical, and Phonon Properties of γ-Bi2MoO6.

The wide band gap γ-Bi2MoO6 (BMO) has tremendous potential in emergent solar harvesting applications. Here we present a combined experimental-first-principles density functional theory (DFT) approach to probe physical properties relevant to the light sensitivity of BMO like dynamic and structural stability, Raman and infrared absorption modes, value and nature of band gap (i.e., direct or indirect), dielectric constant, and optical absorption, etc. We solvothermally synthesized wide band gap Pca21 phase pure BMO (≳3 eV) for two different pH values of 7 and 9. The structural parameters were correlated with the stability of BMO derived from elastic tensor simulations. The desired dynamical stability at T = 0 K was established from the phonon vibrational band structure using a finite difference-based supercell approach. The DFT-based Raman modes and phonon density of states (DOS) reliably reproduced the experimental Raman and infrared absorption. The electronic DOS calculated from Heyd-Scuseria-Ernzerhof HSE06 with van der Waals (vdW) and relativistic spin-orbit coupling (SOC) corrections produced a good agreement with the band gap obtained from diffuse reflectance spectroscopy (DRS). The optical absorption obtained from the complex dielectric constant for the HSE06+SOC+vdW potential closely resembled the DRS-derived absorption of BMO. The BMO shows ∼43% photocatalytic efficiency in degrading methylene blue dye under 75 min optical illumination. This combined DFT-experimental approach may provide a better understanding of the properties of BMO relevant to solar harvesting applications.

Synthesis of type-II TiO2 nanoparticle/ZnO nanorods heterostructure for enhanced photocatalytic activity

A type-II TiO2/ZnO heterostructure is fabricated by coating TiO2 nanoparticles (2, 4 and 6 layers) over ZnO nanorods using sol–gel method to obtain the optimized system with enhanced photocatalytic activity. TiO2/ZnO:6 layer exhibited a higher optical absorption and lowest bandgap value among the synthesized samples. A lower photoluminescence (PL) intensity is noticed for TiO2/ZnO:6 layer sample, ensuring efficient reduction of carrier recombination rate. Moreover, TiO2/ZnO:6 layer exhibited maximum methylene blue (MB) and phenolphthalein dyes degradation efficiency of 86.3% and 76.5% respectively under UV light illumination for 180 min. Our study proposes that formation of type-II heterostructure enhances the photocatalytic activity.

Material Synthesis, Spectral, Optical and Antimicrobial Activity of Imidazolium Based Aldehydic Ionic Liquids: 1–Ethyl-3-methyl-2-(2-oxo-ethyl)-3H-imidazol-1-ium bromide (I) and 1-butyl-3-methyl-2-(2-oxo-ethyl)-3H-imidazol-1-ium chloride (II)

We successfully produced imidazolium aldehydes from imidazolium alcohols for the first time using copper wire and no oxidizing agents. The findings of IR, UV, 1H-NMR, and 13C-NMR spectral examinations all indicated complete Oxidation of the alcohols, which was further demonstrated by those findings. The oxidation technique was used to create the ionic liquids 1-ethyl-3-methyl-2-(2-oxo-ethyl)-3H-imidazol-1-ium; bromide and 1-butyl-3-methyl-2-(2-oxo-ethyl)-3H-imidazol-1-ium; chloride. Using elemental and spectral analyses confirmed the structure of the synthesized compounds (I) and (II). FT-IR analysis was used to determine the presence of functional groups in the grown samples (I) and (II), and 1H-NMR and 13C-NMR spectral analysis were performed to confirm the environment of the elements (C, H). A UV-Visible-NIR spectrophotometer was implemented to determine the optical absorption value for samples (I) and (II). Using DSC analysis, the thermal stability and decomposition were seen. Bacillus Cereus, Staphylococcus Aureus, Enterobacter Coacae, and Staphylococcus Haemolytics were used in an antimicrobial study for samples (I) and (II), and the results are compared with control Ciprofloxacin.

Theoretical Insights into the Optical and Excited State Properties of Donor–Phenyl Bridge–Acceptor Containing Through-Space Charge Transfer Molecules

A comparative new strategy to enhance thermally activated delayed fluorescence (TADF) of through-space charge transfer (CT) molecules in organic light-emitting diodes (OLEDs) is investigated. Generally, TADF molecules adopt a twisted donor and acceptor structure to get a sufficiently small ΔEST and a higher value of the spin-orbit coupling matrix element (SOCME). However, molecules containing donor-phenyl bridge-acceptor (D-p-A) units and featuring π-stacked architectures have intramolecular CT contribution through space and exhibit high TADF efficiency. We have explored the insights into the TADF mechanism in D-p-A molecules using the density functional theory (DFT) and time-dependent DFT methods. The calculated optical absorption and ΔEST values are found to be in good agreement with available experimental data. Interestingly, we found the origin of the SOCME to be the twisted orientation of the donor and bridge moieties. Also, we predicted similar molecules with enhanced OLED efficiency with different substitutions.

Enhancing Titania-Tantala Amorphous Materials as High-Index Layers in Bragg Reflectors of Gravitational-Wave Detectors

Amorphous mixed titania-tantala coatings are key components of Bragg reflectors in gravitational-wave detectors (GWDs). Attaining the lowest possible values of optical absorption and mechanical losses in coatings is of paramount importance for GWDs, and this requires a complex optimization of the coating deposition and postdeposition annealing. We present here a systematic investigation of the optical properties and internal friction of amorphous mixed titania-tantala coatings grown by ion beam sputtering. We consider coatings with six different cation mixing ratios─defined as Ti/(Ti + Ta)─and we study them both in the as-deposited and annealed states. All coatings have been subject to the same annealing of 500 °C for 10 h in air, which is the postdeposition treatment adopted so far for Bragg reflectors in GWD applications. By exploiting spectroscopic ellipsometry data and modeling, along with ancillary techniques, we retrieved the dielectric function of the coatings in a wide spectral range. When varying the mixing ratio and performing the annealing, we find monotonic─in some cases, almost linear─trends for most of the aforementioned properties. Remakably, the postannealing Urbach energy displays a definite minimum for a mixing ratio around 20%, very close to the composition of the coatings showing the lowest optical absorption for GWD applications. We suggest that the observed minimum in the Urbach energy depends not only on the mixing ratio but also on the annealing parameters. On the other hand, the minimum coating loss angle was found to be weakly dependent on the considered measurement frequency and to lie within a rather broad range of Ti content (cation ratios of 21 and 44%), suggesting that the search for an absolute minimum following postdeposition annealing should be rather sought in the study of the best annealing parameters for each specific cation ratio considered. This work constitutes a reference for the optical properties of the amorphous mixed titania-tantala coatings and highlights the relevance of the Urbach energy as an additional parameter to guide the optimization process of materials for high-performing Bragg reflectors.

Toxicity Stress of the Durah Power Plant Ash and its Effect on the Alga Chlorococcum humicola (Naeg) Rabenhorst 1868

Al-Naymi, N.A.Sh., H.A.S. AL-Nuaimi and M.R. Nashaat. 2022. Toxicity Stress of the Durah Power Plant Ash and its Effect on the Alga Chlorococcum humicola (Naeg) Rabenhorst 1868. Arab Journal of Plant Protection, 40(2): 188-192. https://doi.org/10.22268/AJPP-040.2.188192 This study illustrates the acute toxic effect of ash released from Durah power plant (DPP) on the biology of the phytoplankton species Chlorococcum humicola in Iraq. The results showed that the median lethal concentration for killing 50% of the Alga population (LC50) was 0.15 and 0.13 ppt (parts per thousand) for 24 and 48 hours exposure to crude ash concentrations, respectively. In contrast, no LC50 value was recorded for 72 and 96 hrs after exposure. The reduction in the optical density absorption value and the growth rate recorded was 0.083±0.121 cells for the highest ash concentration used, compared with 0.594±0.099 cells recorded for the control group. On the other hand, the doubling time for the control group was 1.16±0.652 an hour compared with 1.36±0.981 an hour recorded for 2 ppt ash exposure. The current study confirms that the crude ash concentrations tested had an adverse toxic effect on the biological parameters of the algal species Chlorococcum humicola in Iraq. Keywords: Algae, fly ash, pollutants, power plant, C. humicola

First principle and experimental investigations of monodispersed Au plasmonic nanoparticles on TiO2

Plasmonic nanostructures play an important part in improving the light absorption of semiconductors that are feasible for photovoltaic and other optical devices. In this context, we have synthesized TiO2 thin films with monodispersed Au nanoparticles. These metallic nanoparticles act as plasmonic structures over the smooth semiconductor surface thereby enhancing their properties. X-ray diffraction was done to confirm the formation of the rutile phase while electron microscope images reveal the presence of Au nanoparticles over the entire surface of TiO2 film. Electronic properties were performed to determine a direct bandgap of 2.8 eV which was reduced significantly to 0.3 eV. Thermoelectric calculations were performed to explore the various temeperature dependent physical properties. Optical properties were also enhanced as high values of optical absorption and refractive index were obtained for TiO2 thin film with monodispersed Au nanoparticles.

The Effect of Gamma Ray (γ) Irradiation on Optical Absorption of Polymer Film Blend

Polymer films have become a material for research recently because polymer films have an important role in the application of basic sciences. The polymer film has good mechanical, electrical and optical properties to be used in many applications, one of which is a polymer film that has the potential to be irradiated into a dosimeter. Therefore, modification of polymer film one of which is gamma ray irradiation is important to be further explored. This study aims to explore the effect of gamma ray irradiation on the optical absorption of polymer film blend PVA (polyvinyl alcohol) -trichloroacetid acid (TCA) -methylene blue (MB). Preparation of polymer films by chemical processes using the solvent-casting method. Each polymer film was irradiated with gamma rays with radiation doses ranging from 0 kGy to 14 kGy. Optical absorption was measured using a UV-VIS spectrophotometer with a range of wavelengths ranging from 200 nm to 700 nm. The results showed that three optical absorption peaks were formed on the polymer film PVA-TCA-MB due to gamma ray radiation at wavelengths of 360 nm, 440 nm, and 560 nm. Gamma ray radiation has an effect on optical absorption, where the optical absorption value of polymer film for the first peak (360 nm) and second peak (440 nm) decreased along with the increase in the dose of gamma ray irradiation, but for the third peak (560 nm) there was an increase in the optical absorption value along with an increase in the dose of gamma ray irradiation. The results of further studies are described in this article.

Tunable intersubband absorption spectrum between Landau levels in GaAs/AlGaAs quantum well

Intersubband optical absorption spectrum was studied in quantum well structures in quantizing magnetic field tilted with respect to the structure layers. Violation of the selection rule forbidding optical intersubband transitions in structures made of quantum wells with an asymmetric potential is proposed. The importance of asymmetric structure design to achieve considerable values of optical absorption is demonstrated.

Photoacoustic optical semiconductor characterization based on machine learning and reverse-back procedure

This paper introduces the possibility of the determination of optical absorption and reflexivity coefficient of silicon samples using neural networks and reverse-back procedure based on the photoacoustics response in the frequency domain. Differences between neural network predictions and parameters obtained with standard photoacoustic signal correction procedures are used to adjust our experimental set-up due to the instability of the optical excitation source and the state (contamination) of the illuminated surface. It has been shown that the changes of the optical absorption values correspond to the light source wavelength fluctuations, while changes in the reflexivity coefficient, obtained in this way, correspond to the small effect of the ultrathin layer formation of SiO2 due to the natural process of surface oxidation.

Density Functional Theory Studies of Zn12O12 Clusters Doped with Mg/Eu and Defect Complexes

We report a density functional theory study of ZnO cluster doped with Eu and Mg along with native point defects using the generalized gradient approximation including the Hubbard parameter. The Zn atomic positions are found to be energetically more favorable doping sites than O. The Eu has a lower formation energy than Zn and O vacancies, helps in lowering the formation energy of point defects and induces spin polarization. Mg is less favorable dopant energetically and is not inducing any magnetism in the cluster. Presence of Eu and point defects along with Mg can help in sustaining spin polarization, implying that transition metal and rare earth dopant is a favorable combination to invoke desirable properties in ZnO based materials. Eu–Eu doping pair prefers ferromagnetic orientation and a spin flip is induced by Eu in the Eu–Mg configuration. Further, Eu doping increases the value of static refractive index and optical absorption in the UV region compared to the undoped ZnO cluster.

Improving Electrical and Optical Properties of ZnO/p-Si Optical Sensor

The main purpose of this study is to investigate the influence of Ga doping ratio on the electrical and optical properties of ZnO. Pure ZnO and Ga-doped ZnO solutions were procured using sol–gel spin coating technique. Next, this solution was deposited onto the p-Si substrate to obtain homogenous thin films. After that, photodiodes were produced using these films. When the process was complete, the morphological structure of the thin films and the electrical and optical properties of the photodiode were studied. Within this scope, while absorbance and transmittance of the thin films were characterized using UV–Vis spectrophotometry, the morphological properties of the thin films were analyzed using atomic force microscope (AFM) and the roughness and fiber size were analyzed using AFM analysis software. On the other hand, the band gap of the thin films was determined using optical absorption values. Additionally, the photocurrent of the ZnO/p-Si photodiode was studied under dark conditions and under various illumination intensities. Likewise, the capacitance and conductance of the photodiode were studied. In addition to these parameters, the Rs–V, C–V, Cadj–V, and Gadj–V characteristics of the photodiode were also studied and the obtained results illustrated graphically. The results showed that the electrical and optical properties of ZnO can be improved and controlled via Ga doping ratio. Therefore, the produced photodiode can be used in optical electronics for different applications as either a photodiode or photosensor.

Na-Based monolayer photocatalysts with an extremely high intrinsic electric-field for water splitting.

A strong built-in electric field, high carrier mobility and a wide range of optical absorption values are the key parameters for photocatalysts used in water splitting. The design and preparation of photocatalysts possessing simultaneously these characteristics have always been the main tasks in the water splitting field. Here, we report a new family of 2D Na-based photocatalysts, NaAB2 (A = Al, Ga, In; B = S, Se, Te) monolayers, which may achieve this goal. First-principles calculations show that most of the NaAB2 monolayers are semiconductors with a suitable direct band gap ranging from visible to near-infrared light, exhibiting good optical absorption. The electron mobilities of the NaAB2 monolayers are up to 103 cm2 V-1 s-1, meaning the rapid migration of electrons can promote photocatalytic overall water splitting. Importantly, the electrostatic potential differences between the top surface and the bottom surface are larger than 1.23 eV for all the studied NaAB2 monolayers, meaning a high intrinsic built-in electric field that is present in these Na-based photocatalysts can promote the overall water splitting irrespective of their band gaps and band edges. Our studies show that the NaAB2 monolayers may be ideal photocatalysts for use in water splitting and may initiate a new round of experimental studies.

Multinary CdZnIn2(SeTe)5 thin films produced by arrested precipitation technique for photoelectrochemical solar cells

Chemically synthesized multinary CdZnIn2(SeTe)5 thin film used as photoanodes in solar cell have been systematically investigated. The indium ion concentration dependent morphological evolution and its consequent effect on photoelectrochemical properties were studied. The growth mechanism for the morphological evolution of CdZnIn2(SeTe)5 thin films has been proposed. Optical absorption values varied with the indium concentration and the band gap energy is found in the range 1.87eV to 1.72 eV. The X-ray diffraction (XRD) patterns reveal the formation of rhombohedra, cubic and hexagonal CdZnIn2(SeTe)5 thin films with the preferred (110), (138) and (220) orientation for CdZnIn2(SeTe)5 microflower, which is further supported by the analysis of the high resolution transmission electron micrographs (HRTEM). The SEM image revealed that the surface morphology of multinary thin films have been changed to microflower by systematic control of indium ion concentration. Finally, current-voltage measurements at different concentration for solar cell with maximum efficiency were carried out in order to find out the dominant transport mechanisms. The solar cell fabricated shows the best conversion efficiency of 1.28%. The deposition of a certain amount of indium was beneficial to the improvement of photoelectrochemical conversion efficiency. To the best of our knowledge, it is the highest efficiency for CdZnIn2(SeTe)5 based photoanode solar cells fabricated from APT.

Synthesis and characterization of Bi doped ZnO thin films using SILAR method for ethanol sensor

Pure and Bi doped ZnO thin films prepared by Successive Ionic Layer Adsorption and Reaction (SILAR) method. The structural analysis shows that prepared films are polycrystalline in nature with preferential orientation along (100), (002) and (101) planes. Scanning electron microscope shows the morphological changes of the films with respect to increase in doping concentration. The average optical absorption value of all films was in the near visible range and the band gap of the films varies from 3.21 to 3.17 eV. The gas sensing study shows a maximum response of the films at 1000 ppm of ethanol was found to be around 60% with an operating temperature of 400 °C.

An Optical Microbial Biosensor Based on Whole Cell of Acidithiobacillus thiooxidans for Hydrogen Sulfide Determination

Due to its corrosive and highly toxic character, the generation of hydrogen sulfide is a serious problem for the environment, human health, and the industry. This paper reported a new and simple methodology for aqueous hydrogen sulfide determination through the development of an optical microbial biosensor. The principle of detection was based on the aerobic and chemolithotrophic metabolism of Acidithiobacillus thiooxidans bacterial cells. Under low oxygen concentration and acidic conditions A. thiooxidans can rapidly oxidize H2S to elemental sulfur. The biochemical formation of elemental sulfur can be spectrophotometrically detected and the increase in absorbance at 620 nm exhibited a linear relationship to an H2S concentration up to 100 mg.L-1. The parameters concerning the analytical performance of the biosensor such as cell harvesting time and pH influence were measured and optimized through the optical absorption value. The biosensor was selective to H2S with no important disturbance by tested species except thiosulfate ion (11.5% error). Biosensor response expressed good repeatability (RSD = 4.46 %) and reproducibility (RSD = 4.66 %). The low cost of cell cultivation and the absence of the immobilization step make feasible the optic biosensor application.

Synthesis and studying of structural, surface topography and optical properties of Mgx Zn1-xO thin Films by spray pyrolysis method

In the present paper, MgxZn1-xO thin films were synthesized with a wide composition range x=(0.25, 0.5, 0.75) using a spray polyposis technique at 450 °C. The X-ray data analysis revealed that the films were polycrystalline with hexagonal and cubic structures. The preferential orientation of all films was absorbed along (002). Structural parameter such as average crystallite size, dislocation density and micro-striation were also investigated. AFM results show that the surface topography and the surface quality of the deposited thin film can be controlled by the Mg2+ content of MgxZn1-xO thin films. The UV-Visible analysis show that the optical absorption values decrease with the increase of Mg2+ concentration. It is observed that the band gap increases as the Mg2+ concentration increases. The reflectance spectra of MgxZn1-xO thin films shifted towards the lower wavelength with the increase of Mg2+ concentration. The extinction coefficient was slightly decreased and shifted towards higher energies with the increase of Mg2+ contents. These results demonstrate the high quality of single crystal MgxZn1-xO films and their potential in high-performance deep ultraviolet optoelectronic devices.

A study of microstructure and optical absorption properties of Cu(In,Ga,Al)Se2 powders

CuInxGayAl1‐x‐ySe2 powders were prepared using a solvothermal reaction technique in ethylenediamine at 290°C for 20 hours. The microstructure and optical absorption properties of the powders were investigated by XRD, SEM, TEM, XPS and UV‐Vis‐NIR spectra. The results indicated that the Al atom was successfully incorporated into the CuInxGa1‐xSe2 lattices, and Al doping had a significant effect on the microstructure, especially at the (112) crystal orientation. It was found that the peak of (112) shifted obviously to higher 2θ values with the increasing aluminum content. Transmission electron microscope observation revealed that the size of the CuInxGayAl1‐x‐ySe2 nanoparticles could be adjusted by varying the stoichiometric ratio of the In, Ga and Al, and the proper Al incorporation could reduce the density of the stacking faults and nanotwins in the CuInxGayAl1‐x‐ySe2 materials. XRD analysis indicated that the Al incorporation could effectively substitute In and Ga atoms. Finally, the band gap was obtained by UV‐Vis‐NIR spectra, and the results implied that the optical absorption value decreased and optical band gap increased significantly with the incorporation of Al, and it is close to the optimal band gap (1.37 eV) of solar cells when the stoichiometric ratio of the Al was between 0.2 and 0.3.