Wavelength Values Research Articles

Ag@WO3 core-shell nanocomposite for wide range photo detection.

This study successfully synthesized high-performance photodetectors based on Ag-WO3 core-shell heterostructures using a simple and economical two-step pulsed laser ablation in water method and has investigated the electrical characteristics of the Ag@WO3 nanocomposite heterojunction. The Hall effect tests indicate that the synthesized Ag@WO3 exhibits n-type conduction with a Hall mobility of 1.25 × 103 cm2V-1S-1. Dark current-voltage properties indicated that the created heterojunctions displayed rectification capabilities, with the highest rectification factor of around 1.71 seen at a 5V bias. A photodetector's responsivity reveals the existence of two response peaks, which are situated in the ultraviolet and visible region. The photodetector demonstrates a rapid response time of less than 100ms. The detectivity values for wavelengths of 350nm and 490nm were 35 × 1013 Jones and 28 × 1013 Jones, respectively. The n-Ag-WO3/n-Si photodetector achieved a maximum EQE of 11.5% in the ultraviolet wavelength when subjected to 3V and illuminated with 350nm (26 mW/cm2) light. The devices demonstrate rapid switching behavior with a rise time of 0.32s and a fall time of 0.33s. The time-dependent light response of a photodetector under illumination at 26 mW/cm2 is seen at a bias of 3V. The light exhibits a rise and decay duration of 15s, while the photocurrent gain is measured at 9µA. The photocurrent of devices exhibited a positive correlation with the incoming light intensity, suggesting that the junction has the potential to function as a photo detector.

Antibiotic-Mediated Plasmonic Resonance on a Novel Nanopillar Metasurface Array.

This study demonstrates a silicon nanopillar metasurface coupled with localized surface plasmon resonance (LSPR) mediated by the presence of cephalexin antibiotics in solution for biosensing applications. A facile fabrication process was developed to create the metasurface on silicon wafers with a unique resonance signature. The resulting metasurface consists of periodic nanopillars approximately 180 nm in diameter, 210 nm deep, and with a controlled edge-to-edge separation of 200 nm. These dimensions were chosen based on a finite element method simulation that was used to investigate the ideal parameters to produce the desired resonance effect in the metasurface reflection spectra. Optimization of the nanopillar surface properties and the sidewall angle allowed for replication of the simulations. This metasurface was coupled with BSA-coated gold nanospheres (BSANS) to mediate the redshift of peak resonance wavelength values, occurring only in the presence of the antibiotic linker. The device fabricated herein exhibits a significant 22 nm wavelength shift resulting from changes to the local refractive index in the presence of the BSANS-antibiotic coupling. Further enhancement of the binding events is promoted by the LSPR hot spots formed between the nanoparticles and the metasurface allowing for sensitive and real-time detection.

Gamma radiation induced tailoring the structural, optical, surface and mechanical properties of UHMWPE

The present investigation examined how the resultant gamma radiation affected the ultra-high molecular weight polyethylene's (UHMWPE) mechanical, optical, surface, and structural characteristics. Different gamma doses of 75, 150, 250, and 350 kGy were applied to the UHMWPE samples. The study of physical and chemical qualities has involved a variety of spectroscopy techniques, including Fourier Transform Infrared spectroscopy, X-ray diffraction, mechanical property changes, and biocompatibility properties. New bands are formed, as indicated by FT-IR analysis, and this process is linked to the oxidation of irradiation polymer chains and the production of carbon dioxide. The crystallinity of irradiated samples increases as the gamma radiation increases, according to XRD patterns. The analyzed optical results exhibit improvements in the optical characteristics of the irradiated samples. The absorbance spectra of the irradiated samples showed a shift toward the high of wavelength values in the absorption edge as compared to the pristine sample. On the other hand, the optical absorption edge has an increasing tendency as the dose of gamma-ray radiation is increased. As the gamma-ray dose increases, the absorption edge moves toward the longer wavelength. The measurements of the contact angle indicate that the surface free energy rises with increasing gamma irradiation. It was detailed how the mechanical properties of the irradiated UHMWPE samples were measured. The mechanical measurements indicate that the mechanical properties are dose-dependent to some extent. Furthermore, as gamma doses rise, so does the hardness of irradiated UHMWPE.

Effect Of Annealing Temperature On The Optical And Structural Properties Of Zinc-Doped Cd2SnO4 Thin Films Prepared By Dip-Coating Method

As demand for solar PV modules steadily increases studies on cheaper alternative TCO materials, with low resistivity and high transmittances in the visible spectrum to replace ITO are been undertaken. Among TCO materials considered as alternative to Indium Tin Oxide (ITO) is Cd2SnO4, owing to its availability in large quantities at relatively lower costs. Studies on optical properties of N2 and F2 doped Cd2SnO4 films have revealed increased transmittance 99%, and reduced band gap 3.3 eV. On the other hand Fe doped films have been observed to exhibit higher refractive indices, extinction and absorption coefficients with lower transmittance and optical band gap. Although studies have been carried out on Zinc doped Cd2SnO4 films, the effect of annealing temperature on the properties of the films have not been reported. This study investigated the effect of annealing temperature on the optical and structural properties of Zinc-doped Cd2SnO4 films. Thin films of Zincdoped Cd2SnO4 were prepared by mixing 0.1 M Cadmium Acetate with 0.1 M Tin II Chloride in ratio 1:1 to prepare Cd2SnO4 which was doped with 0.1 M Zinc Nitrate then dip-coated on clean glass substrates. The coated substrates were dried at room temperature and annealed in air the films annealed at 350 o C, 400 o C and 450 o C for 90 minutes Optical transmittance and reflectance were measured in wavelength range 200-1200 nm and with the results: prominent XRD peak oriented in the (2 0 0) direction, transmittance of 78.7% at 700 nm wavelength, absorption coefficient of 3.891 - 5.591 x 104 cm-1 , extinction coefficient of 0.1852 - 0.2126, refractive indices of 1.983-2.121 at 588 nm wavelength and band gap values range 3.45-3.65 eV. Annealing was observed to reduce refractive index and does not affect transmittance therefore doesn’t enhance suitability of films as TCO materials for Photovoltaic applications.

Characterization of SiNx grown at different nitrogen flow and prediction of refractive index using artificial neural networks

SiNx films were grown on silicon substrates by Radio Frequency (RF) magnetron sputtering deposition. The effect of nitrogen flow on the structural and optical properties of the obtained films was investigated using X-ray diffraction, Scanning Electron Microscopy (SEM), UV–Vis–NIR spectrophotometer and spectroscopic ellipsometer, respectively. XRD spectra of the films showed that all films belong to amorphous structure. SEM photographs of SiNx films were analyzed. As a result of the analysis, it was observed that the surfaces of the films had a homogeneous and smooth structure as the nitrogen flow increased. The total and diffuse reflectance spectra of the films were measured and the energy band gaps of the films were determined using the Kubelka-Munk function by using the diffuse reflectance. It was observed that the energy band gap changed as the nitrogen percentage increased. The refractive index of all films was obtained as a function of temperature using a spectroscopic ellipsometer. In the second part of this study, we focused on predicting the temperature dependent refractive indices of the nitrogen flow-dependent films using Artificial Neural Networks (ANN). For the training of the ANN model, wavelength and temperature values from experimental data were used as input and refractive index as output parameters. The simulation and prediction results obtained from this model are compared with the experimental data and interpreted. It is concluded that the ANN approach is suitable for simulating and predicting the temperature dependent refractive index. The models successfully trained with ANN will be especially preferred for predicting the refractive indices of SiNx films, which cannot be measured experimentally, thus providing predictions in non-experimental ranges. In particular, the results obtained by focusing on the ability of the developed artificial neural network (ANN) models to predict the optical properties of SiNx films and their potential to provide information in non-experimental conditions, offer a new approach to quickly and effectively evaluate the optical properties of SiNx films. This approach reveals the importance of artificial intelligence-based methods in materials characterization studies.

Study of mesomorphic, thermal and optical properties of 4-pentylbenzoic acid (5BA) and 4-n-alkyl-4́-cyanobiphenyl (nCB; n = 5, 6) supramolecular hydrogen bonded mesogenic complexes

Within the scope of this study, the process of producing and analyzing a liquid crystalline substance (supramolecular hydrogen-bonded mesogen) is presented. The formation of this mesogen involves the use of two chemicals, namely 4-pentylbenzoic acid (5BA) and 4-n-alkyl-4́-cyanobiphenyl (nCB; n = 5, 6). Equimolar (1:1) 5BA/5CB and 5BA/6CB binary combination samples have been organized by using one at a time mixing 5CB and 6CB liquid crystal chemical substances with 5BA. Differential scanning calorimetry (DSC) and polarized optical microscopy (POM) are employed for the examination of phase transitions, and liquid crystalline phase texture properties of the produced mesogens. The phase transformation sequence that occurred during heating and cooling is Crystal (Cr) ↔ Smectic A (SmA) ↔ Nematic (N) ↔ Isotropic (I) with the 1st order or weakly 1st order transition. The nematic range value observed for 5BA/6CB is considerably smaller than the nematic range value observed for 5BA/5CB, but the thermal mesophase range value for both is approximately the same. Fourier-transform infrared (FTIR) evaluation of 5BA, 5CB, and their hydrogen-bonded combos (5BA/nCB; n = 5, 6) confirmed attribute peaks. The X-ray diffraction (XRD) study revealed that the produced mesogens possess a crystalline structure. In addition, UV–Vis experiments demonstrated that the increase in alkyl chain length in the combination resulted in a decrease in absorbance and wavelength values, while leading to an increase in absorbency and band gap energy values. These results propose workable purposes for the synthesized substances in liquid crystal displays and other optoelectronic devices. Overall, the findings display the feasibility and viability of these novel hydrogen-bonded liquid crystalline mesogens in various technological applications.

Polymerization‐Induced Emission and Specific Detection to Cu2+ Ions of Polyacrylates with Morpholine Structure

AbstractIn this investigation, the fluorescent poly(N‐hydroxyethyl morpholine acrylate) (PHEMA) and poly(N‐hydroxypropyl morpholine acrylate) (PHPMA) are prepared and applied as fluorescent probes for the specific detection of Cu2+ ions. Far different from the non‐fluorescent monomer, PHEMA and PHPMA emit a strong fluorescence at 410 nm due to the intramolecular aggregation of morpholine structures along macromolecular chains in the polymerization, indicating polymerization‐induced emission (PIE). The fluorescent emission of PHPMA shows the dependence on external factors including solution concentration, excitation wavelength, solvent, and pH value. PHPMA specifically detects Cu2+ ions even in the presence of 16 common metal ions and 6 anions, with an LOD of 0.077 µM. In the fluorescent quenching, the O atom from ─C═O and N atom from morpholine moiety on the PHPMA chain participate in the complexation with Cu2+ ions with the ratio of the structural unit and Cu2+ ion of 2:1, leading to the dynamic quenching of PHPMA solution. As for the application, PIE‐active PHPMA is easily made into a portable semi‐quantitative filter paper with recyclability. In brief, the PIE‐active PHPMA synthesized in this study can be used as a promising material for the specific detection of Cu2+ ions in industry, agriculture, and medicine fields.

Synthesis, intercalation reactions, and electrochemical studies for VO2/PEO/Chitosan

VO2 obtained by hydrothermal synthesis from V2O5 was used as a matrix to obtain hybrid compounds containing different proportions of polyethylene oxide and chitosan. The XRD results demonstrate that monoclinic VO2 was obtained, and hybrid compounds showed variation in the displacement of the lamella peak, indicating an intercalation of polymers into the matrix. The stretching and vibration bands show a variation towards higher wavelength values of the hybrid compounds, which indicates that the intercalation of the polymers occurred into the matrix. The UV–Vis spectra show the absorptions that can be attributed to the transitions of each material. Absorption in the visible region decreases for hybrid compounds in relation to VO2. The hybrid compounds presented lower bandgap values compared to VO2. From cyclic voltammetry, it was possible to observe anodic and cathodic peaks linked to the redox process of the VIV/VIII pair for both VO2 and VO2/polymers, which is derived from the insertion/disinsertion process of lithium ions, where the hybrid compound presented a different voltammetric profile compared to VO2. The total charge curves as a function of the number of cycles demonstrate better cycling stability and a greater total charge of the hybrid compounds compared to VO2. These results demonstrate that hybrid compounds have potential as cathode materials for lithium-ion batteries.

Spectral dispersion and thermo optic coefficient for Silicon material

In this study, the first derivatives of this equation with respect to temperature (thermo-optic coefficients) and wavelength (spectral dispersion) were derived in the MATLAB software, and a special code was written to solve the equations and found for temperatures that range from 100 to 750 K and wavelength range from 1.2 to 14 µm. The results of the computation were compared with previously published data, and showed a good agreement. Once that was done, the values of phase velocity and group velocity that depend on refractive index and spectral dispersion in the medium were found. The phase velocity and group velocity were plotted in three dimensions to show the overall change over different values of wavelengths and temperature.

Zvěstovite-(Fe), Ag6(Ag4Fe2)As4S13, a new member of the tetrahedrite group from the Ulatayskoe Ag–Cu–Co occurrence, eastern Siberia, Russia

Abstract. The new mineral zvěstovite-(Fe), ideally Ag6(Ag4Fe2)As4S13, has been found in the small abandoned Ulatayskoe Ag–Cu–Co occurrence, Ovyurskiy District, Tuva Republic, eastern Siberia, Russia. It occurs as anhedral grains, up to 1 × 0.4 mm in size but usually much smaller, closely intergrown with native silver, in Mg-bearing siderite–quartz gangue. Other associated minerals include acanthite, cobaltite, As-rich members of the tetrahedrite group (kenoargentotennantite-(Fe), tennantite-(Zn), zvěstovite-(Zn)), gersdorffite, jalpaite, krutovite, löllingite, pearceite, safflorite, skutterudite, Br-bearing chlorargyrite, malachite, and muscovite. Zvěstovite-(Fe) is iron black and opaque and has a black streak and metallic lustre. It is brittle and has a conchoidal fracture. No cleavage or parting is observed. The Vickers micro-indentation hardness (Vickers hardness number, VHN; 25 g load) is 169 kg mm−2 (range of 149–187 kg mm−2, n=4), corresponding to a Mohs hardness of 3–3.5. The calculated density is 4.979 g cm−3. In reflected light, zvěstovite-(Fe) is light grey with a greenish tint and isotropic. Internal reflections are ubiquitous and deep red in colour. The reflectance values for wavelengths recommended by the Commission on Ore Mineralogy of the International Mineralogical Association are (R, %): 32.5 (470 nm), 31.1 (546 nm), 30.1 (589 nm), and 28.8 (650 nm). The chemical composition (wt %, electron microprobe data, mean of eight spot analyses) is as follows: Cu 1.81, Ag 56.02, Fe 4.60, Zn 0.01, As 13.85, Sb 2.63, S 21.50, total 100.42. The empirical formula, calculated on the basis of 16 atoms per formula unit, is Ag9.93Cu0.54Fe1.58As3.54Sb0.41S12.83. Zvěstovite-(Fe) is cubic and has a space group of I4‾3m, with a=10.8601(3), V=1280.86(11) Å3, and Z=2. The strongest lines of the X-ray powder diffraction pattern (d, Å (I, %) hkl) are 7.68 (11) 110, 3.136 (100) 222, 2.717 (12) 400, 1.984 (8) 521, 1.921 (23) 440, and 1.638 (11) 622. The crystal structure of zvěstovite-(Fe) was refined to R1=0.0551 for 400 unique reflections with Fo>4σ (Fo). The possible ordering of the split M(2) sites is discussed. The new mineral is the Fe isotype of zvěstovite-(Zn). Both these minerals form the zvěstovite series within the tetrahedrite group.

Improving the Transparency of a MgAl2O4 Spinel Damaged by Sandblasting through a SiO2-ZrO2 Coating

Transparent materials in contact with harmful environments such as sandstorms are exposed to surface damage. Transparent MgAl2O4 spinel used as protective window, lens or laser exit port, among others, is one of the materials affected by natural aggressions. The impact of sand particles can cause significant defects on the exposed surface, thus affecting its optical and mechanical behavior. The aim of this work is to improve the surface state of a spinel damaged surface by the deposition of a thin layer of SiO2-ZrO2. For this purpose, spinel samples obtained from different commercial powders sintered by Spark Plasma Sintering were sandblasted and further coated with a SiO2-ZrO2 thin layer. The coating was successfully synthesized by the sol/gel method, deposited on the sandblasted samples and then treated at 900 °C, reaching a final thickness of 250 nm. The results indicated that sandblasting significantly affects the surface of the spinel samples as well as the optical transmission, confirmed by UV-visible spectroscopy and profilometry tests. However, the deposition of a SiO2-ZrO2 coating modifies the UV-visible response. Thus, the optical transmission of the S25CRX12 sample presents the best transmission values of 81%, followed by the S25CRX14 sample then the S30CR sample at 550 nm wavelength. An important difference was observed between sandblasted samples and coated samples at low and high wavelengths. At low wavelengths (around 200 nm), sandblasting tends to improve significantly the transmission of spinel samples, which exhibit a low transmission in the pristine state. This phenomenon can be attributed to the healing of small superficial defects responsible for the degradation of transmission such as pores or flaws. When the initial transmission at 200 nm is high, the sandblasting worsens the transmission. Sandblasting reduces slightly the transmission values for long wavelengths due to the formation of large superficial defects like chipping by creation and propagation of lateral cracks. The coating of the sandblasted samples exhibits some healing of defects induced by sandblasting. The deposition of the SiO2-ZrO2 layer induces a clear increase in the optical transmission values, sometimes exceeding the initial values of the transmission in the pristine state.

Practical design of an optical filter for thermal management of photovoltaic modules

AbstractThis work presents a practical approach to designing an optical filter for thermal management for photovoltaic modules. The approach emphasizes the practicality of manufacturing over optical performance. Simulation work demonstrates that, for an interdigitated back contact solar cell architecture, complete rejection of infrared radiation offers limited thermal benefits requiring highly complex optical filter designs. An alternative approach consists of reducing thermalization losses by providing reflectance at lower wavelength values. An optical filter design that fulfills this requirement is possible using simple structures based on two materials and taking advantage of the harmonics present in quarter wavelength optical thickness designs. The filter is later optimized for angular performance via second‐order algorithms, resulting in a device consisting of only 15 thin‐film layers. Performance simulations on two locations, Delft (the Netherlands) and Singapore, estimate a temperature reduction of 2.20°C and 2.45°C, respectively. In a single year, the optical loss produced by the filter is not compensated via temperature reduction. However, improvements in the annual degradation rate show that in Singapore, the overall effect of the filter on the lifetime DC energy yield is positive.

Theuerdankite, Ag3AsO4, a new mineral from the Alter Theuerdank Mine, St. Andreasberg, Germany

Abstract The new mineral theuerdankite, ideally Ag3AsO4, was found in the Alter Theuerdank Mine, Beerberg, St. Andreasberg, Goslar District, Lower Saxony, Germany. Theuerdankite occurs as aggregates of anhedral grains up to 3 mm in size, growing in cavities of strongly supergene-weathered material consisting of native silver and chlorargyrite (but with calcite present). It is dark violet, changing to reddish and black when exposed to the air and light. It has a grey to violet grey streak; when readily fresh, its streak is brownish-red. The Mohs hardness is ~2. It is brittle with no observable cleavage or parting and with a conchoidal fracture. The calculated density is 6.620 g⋅cm–3. In reflected light, theuerdankite is dark grey with a pinkish tint, with no observable bireflectance, pleochroism, or anisotropy. It shows dark red internal reflections. The reflectance values for wavelengths recommended by the Commission on Ore Mineralogy of the International Mineralogical Association are (R, %): 13.3 (470 nm), 12.8 (546 nm), 12.7 (589 nm) and 12.5 (650 nm). The empirical formula (based on 4 apfu) is Ag3.00As1.00O4. Theuerdankite is cubic, space group P $\bar{4}$ 3n, a = 6.144(2) Å, V = 231.93(13) Å3 and Z = 2. The six strongest powder X-ray diffraction lines are [dobs in Å, (I) hkl]: 3.0736, (22) 200; 2.7502, (100) 210; 2.5106, (55) 211; 1.7050, (36) 320; 1.6249, (44) 321; and 1.3412, (17) 421. The crystal structure of theuerdankite (R1 = 1.69% for 519 reflections having I > 3σ(I)), is isotypic to those of synthetic Ag3AsO4 and Ag3PO4. The Gram–Charlier development describing the higher-order tensors representing the atomic displacement parameters of the silver atom was implemented, documenting that silver tends to behave anharmonically in the theuerdankite structure at room temperature.

SrO–ZnO–PbO–B2O3 glassy insights: Unveiling the structural and optical features for gamma ray shielding efficacy

The melt-quenching approach was utilised to synthesize amorphous SrO–ZnO–PbO–B2O3 glasses, with FTIR spectroscopy applied to the samples to reveal the various bonds' stretching and bending vibrations. With PbO introduced to the network, the UV–Vis absorption spectrum's absorption peak shifts towards the higher wavelength values, while Tauc plot analysis of the UV–Vis spectra reveals a 2.957–2.569 eV decrease in the band gap energy. The radiation shielding properties are examined via Phy-X program. The mass attenuation coefficient (MAC) has an inverse relation with the energy, which demonstrated the greater penetration ability of radiation that contains higher energy. In terms of the MAC values at low energies the results revealed a greater difference, while they are almost identical at higher energies. The linear attenuation coefficient (LAC) was evaluated and the chemical composition's influence discussed, with the LAC values in the order of SZPB1 <SZPB2 <SZPB3 <SZPB4. This confirms that the PbO addition leads to increased LAC values. The half value layer (HVL) decreases with increased concentration of PbO. This suggests that the higher the glass system's PbO content, the thinner the glass system needs to be to attenuate half of the incoming photons.

Optimization of Reduction Time for Chemically Synthesized rGO

Introduction: This article presents structural and morphological analysis for graphene oxide (GO) synthesized via Hummers' method and for reduced Graphene Oxide (rGO) prepared by chemical reduction. Graphene Oxide is synthesized from graphite powder at room temperature. Hydrazine hydrate is used as a reducing agent to reduce the accumulated GO. Method: To understand the impact of reduction time on structural parameters of produced rGO, three different time limits, i.e. 4, 5, and 6 hrs at 800 °C are used. FTIR spectra show the presence of all functional groups to confirm the authenticity of rGO samples. The XRD peaks are utilized to calculate different structural parameters for all the samples to identify the effect of reduction time. A change in the band gap energy may be noticed from UV-Vis absorption spectra. Result: It indicates that with the increase in reduction time, the absorption edge shifts to a lower wavelength value. FESEM micrographs reveal a flake-like random growth of rGO with prominent wrinkled structures, which is a signature of graphene-like 2D material. Conclusion: Hence, from the structural and absorption studies, it can be concluded that an increase in reduction time will produce smaller rGO flakes in the Hummers synthesis method.

Automatic non-destructive estimation of polyphenol oxidase and peroxidase enzyme activity levels in three bell pepper varieties by Vis/NIR spectroscopy imaging data based on machine learning methods

The browning process of food products if often formed upon cutting and damage during their processing, transport, and storage, amongst other potential sources and reasons. Enzymic browning can be mainly due to polyphenol oxidase (PPO) and peroxidase (POD) enzymes. Visible/near-infrared (Vis/NIR) imaging spectroscopy in the range of 350–1150 nm was used in this study for automatic and non-destructive evaluation of PPO and POD activity levels in three bell pepper varieties (red, yellow, orange; N = 30), with a total of 30 inputs samples in each variety. The spectral data were then modeled by the partial least squares regression (PLSR) throughout the whole spectral range, without using any subset of the most effective wavelength (EW) values. Regression determination coefficient (R2) values for the estimation (prediction) of POD enzyme activity levels were 0.794, 0.772, and 0.726 for red, yellow, and orange bell peppers, respectively, all over the validation set. At the same time, the activity levels of PPO enzyme over bell peppers showed R2 values of 0.901, 0.810, and 0.859, for red, yellow, and orange bell peppers, respectively, all over the validation set. In addition, a combination of support vector machine (SVM) with either genetic algorithms (GA), particle swarm optimization (PSO), ant colony optimization (ACO), or imperialistic competitive algorithms (ICA) hybrid machine learning (ML) techniques were used to select the optimal (discriminant) spectral EW wavelength values, and regression performance was consistently improved, to judge from higher regression fit R2 values. Either 14 or 15 EWs were computed and selected in order of their discriminative power using previously mentioned ML techniques. The hybrid SVM-PSO method resulted the best one in the process of selecting the most effective wavelength values (nm). On the other hand, three regression methods comprising PLSR, multiple least regression (MLR), and neural network (NN), were employed to model the SVM-PSO selected EWs. The ratio of performance to deviation (RPD), the R2 and the root mean square error (RMSE), over the test set, for the non-linear NN regression method exhibited better results as compared to the other two regression methods, being closely followed by PLSR, and therefore NN regression method was selected as the best approach for modeling the most effective spectral wavelength values in this study.

Optical non-linearities and applications of ZnS phosphors

Optical non-linearities play a crucial role in enabling efficient and ultrafast switching applications that are essential for next-generation photonic devices. ZnS phosphor material produces the best results in terms of increased luminescence quantum yield when doped with certain impurities. Nevertheless, the investigation of the third-order non-linear optical susceptibility of the phosphor materials can be exploited for various switching applications. In this regard, we review the recent advancements in the investigation of non-linear optical properties of ZnS phosphors, where the knowledge of absorption and refraction is utilized in various optical and detector applications. Furthermore, the review highlights strategies employed to enhance the non-linear optical response of phosphor materials as well as a general discussion of an attosecond optical switching scheme which can be used to fabricate devices with petahertz speeds. Consequently, we provide a solution to the unsolved problem of the significant extension of optical limiting applications to switching applications by developing design strategies to manipulate conventional ZnS phosphor material. The potential challenges and future prospects of utilizing phosphor materials for switching applications are also addressed. The strategies for manipulating ZnS phosphor can be generalized for a broad range of other materials by minimizing linear and non-linear losses, while enhancing the values of the non-linear refractive index coefficient. We propose that the figure-of-merit of ZnS material can be enhanced by using a suitable combination of pump and probe wavelength values, which can be useful for optical switching applications.

Negative refractive index enhancement with zero absorption in a concentric chiral metal-atomic nanoshell

We investigate the electromagnetic chirality and negative refraction in a concentric nanoshell of a chiral metal sphere and a chiral atomic shell. The medium of the atomic shell with a four-level system is driven by a laser field and an incoherent pump field in a diamond configuration. We show that the electric and magnetic absorption spectra connecting through the chiral coefficients of the respective dipole moments of the two media, produce five and three lines spectral profiles. We explain that the spectral lines separated by dips are the manifestation of the classical (quantum) coherence effect of the wave field excitation in the medium of the metal sphere (atomic shell), and the interaction of the respective dipole moments at the interface of the two media. Furthermore, we show negative refraction with zero absorption without requiring permittivity (ϵ) and permeability (μ) simultaneously negative, where for all values of the incident wavelength, Re [μ] ≈ 1, representing a strong chiral electromagnetic behavior. Consequently, the negative refractive index enhances sufficiently beyond n = −1 for a wide range of parameters depending on the coupling parameters, chiral coefficients, and the radii ratio of the concentric metal-atomic nanoshell.

DFT study of the intrinsic electronic, optical, NBO, transport, and thermodynamic properties of 12,12-dimethyl-7-phenyl-7,12-dihydrobenzo[a]acridine-3-carbonitrile (BACN)

In this study, we investigate the structural, vibrational, electronic, optical, transport, and thermodynamic properties of pure BACN using density functional theory (DFT). The B3LYP, B3PW91, CAM-B3LYP and ωB97XD functionals associated with the basis sets 6-31G(d,p) and 6-311G(d,p) were used. With regard to the electronic and transport properties, analysis of the HOMO and LUMO frontier orbitals, the gap values obtained and the reorganisation energies show that BACN is a good donor-acceptor semiconductor and has a good hole transport capacity. The study of non-linear optical properties shows that BACN is a good candidate for applications in nonlinear optics (NLO) because of its first-order hyperpolarisability, which is higher than that of urea. The time density functional theory (TD-DFT) approach was used for the photophysical analysis of BACN. It was found that BACN exhibits a maximum absorption in the near-UV range, peaking at 222.42 nm, and strong emission in the near-UV range with a maximum wavelength value of 229.75 nm through TD-CAM-B3LYP/6-311G(d,p). The Stokes shift values obtained indicate that the molecule is chemically stable. The full width at half-maximum (FWHM) and radiative lifetime values for this molecule are 19.924 nm and 16.071 ns, respectively. These results show that BACN is a fluorescent material that can be used as an emitter material for designing and improving the colour purity of organic light-emitting diodes (OLEDs).

In Situ Center Wavelength Control of AlInN/GaN Distributed Bragg Reflectors with In Situ Reflectivity Spectra Measurements

An in situ control of a center wavelength in a 40‐pair AlInN/GaN distributed Bragg reflector (DBR) for GaN‐based vertical‐cavity surface‐emitting lasers (VCSELs) with an in situ reflectivity spectra measurement is proposed and developed. A procedure of the in situ control consists of the following three steps: 1) to grow an initial 5‐pair DBR; 2) to obtain the center wavelength value just after the initial DBR growth by the in situ reflectivity spectra measurement; and 3) to adjust growth times as a result of the obtained center wavelength value and continue the remaining 35‐pair DBR. It is experimentally demonstrated that the in situ control of the center wavelength in the 40‐pair DBRs with the ±2% thickness deviations in the initial 5‐pair DBR results in reductions of the deviation down to ±0.3%. The in situ DBR center wavelength control is a key technique for highly reproducible GaN‐based VCSELs.