Stable Optical Properties Research Articles

Fabrication of highly conducting ZnO/Ag/ZnO and AZO/Ag/AZO transparent conducting oxide layers using RF magnetron sputtering at room temperature

Sputter deposition of multilayer ZAZ (ZnO/Ag/ZnO) and AAA (AZO/Ag/AZO) TCO coatings has been done using a magnetron sputtering system. The deposition has been performed by moving the substrate under the desired target (ZnO or AZO and Ag) using a movable arm. This movable arm allows the substrate movement in the required order through a controller in a forward or reverse direction. Using this arrangement, the fabrication of ZAZ and AAA multilayer TCOs has been done on glass substrates at room temperature and the layer properties are found to be comparable with the properties of commercial ITO film. The fabricated ZAZ and AAA multilayers (with thickness around 70 nm) exhibit better electrical properties as compared to the commercial ITO film. The electrical resistivities of the ZAZ 2 and AAA 2 layers are 3.78 × 10−5 and 3.71 × 10−5 Ω cm, respectively which are much lower than the ITO resistivity of 4.56 × 10−4 Ω cm. The sheet resistances of ZAZ 2, AAA 2 and commercial ITO layers are 5.4, 5.3 and 16.8 Ω/□, respectively. The figure of merit (FoM) for AAA 2 multilayer is 45.5 × 10−3 Ω−1, much higher than commercial ITO film (23.7 × 10−3 Ω−1). The high-temperature annealing shows almost stable optical and electrical properties of the fabricated TCO layers up to 200 °C. Therefore, these TCOs can be used as electrodes for the solar cell fabrication where high-temperature annealing is required.

A computational prediction of a novel quasi hexagonal Al2SSi semiconductor monolayer

Abstract In this article, we predicted a novel two dimensional (2D) quasi hexagonal Al2SSi semiconductor monolayer by using first principles calculations based on the density functional theory (DFT). At first, it is shown that 2D Al2SSi is energetically and dynamically stable suggests its promising experimental realization. As a possible stable 2D monolayer, its electrical and optical properties were investigated. To get more insight into the effect of external strains on the electronic property of the Al2SSi monolayer, we calculated the electrical properties of the structure under different strain conditions. We found that, the electron properties of the material can be effectively modulated by strain effect. According to our calculations, 2D Al2SSi monolayer is a semiconductor with a strain tunable direct band gap 0.344 eV (1.09 eV) obtained by DFT-PBE (DFT-HSE06) level of theory. Assessing its optical properties shows that the proposed monolayer shows optical sensitivity in the visible light region as well as the high absorption in the ultraviolet (UV) portion of the electromagnetic spectrum. These results, suggests 2D Al2SSi as a promising material for using in electrical and optical nano devices.

Synthesis, Spectral and Thermal Characteristics of Silica/PVP Nanofluids

Nanofluid is well known as smart fluid which has high ability to recover oil. Therefore, it gains more significant effect in oil and gas industry. With the low concentration of nanofiller in nanofluid is used to enhance the numerous characteristics for oil recovery applications. Then, the main feature is the size of reinforcing agent and properties along matrix medium. Nano dimensional particles suspension in polymeric matrix have major advantages are stable sedimentation, optical, mechanical, electrical, and rheological properties that can be affected during the synthesis of nanofluids. Therefore nanoparticles/polymeric nanofluid have exceptional characteristics over the conventional fluid. Mixed nanoparticles/polymeric nanofluid in the presence of surfactant have effective interfacial tension and wettability which is evident for the development of nanofluids for oil recovery. In this context, the designed experimental study of silica/PVP nanofluids is synthesized via two step methods and characterized by SEM, TG/DTA, contact angle measurement, centrifugal effect and sedimentation test intended for Enhanced Oil Recovery (EOR) system.

Intriguing electronic, optical and mechanical properties of the vertical and lateral heterostructures on the boron phosphide and GaN monolayers

Using the first-principles method, the structural, electronic, optical and mechanical properties of the vertical and lateral heterostructures based on the boron phosphide (BP) and GaN monolayers, named V-GaN@BP and L-GaN@BP, are investigated systematically. Our results revealed that the band structure of the V-GaN@BP is more sensitive than that of the L-GaN@BP to the strain and the external electric field (Efield). For the VD-GaN@BP, with the Efield and strain, the band structure not only undergoes a fascinating direct–indirect and semiconductor–metal transition, but also experiences a transition from type-I to type-II. However, the LNB-GaN@BP maintains a type-II semiconductor with an indirect band gap, though the band gaps can be strongly modulated by applied strain and the Efield. Moreover, the heterostructures are found to be mechanically stable presenting superior optical properties in the visible and UV light range. Consequently, we expect the GaN@BP heterostructures are novel architectures for the future development of efficient optoelectronic devices, due to the selective control of their bandgaps, the excellent optical and mechanical properties.

Red, green, and blue light-emitting carbon dots prepared from o-phenylenediamine.

Carbon dots (CDs), as the most important type of carbon-based material, have been widely used in many fields because of their excellent properties. In particular, multicolor fluorescent CDs with high photoluminescence quantum yield are the focus of active research. Herein, red, green and blue CDs (RGB CDs) were successfully synthesized by a solvothermal method from o-phenylenediamine under different reaction conditions. The RGB-CDs have stable optical properties and significant photoluminescence characteristics. Structural and elemental analyses propose a conjugated structure and the surface state of the CDs as the main causes for the different color emission of RGB-CDs. In addition, a white fluorescent CD solution was prepared by mixing these multicolor fluorescent CDs in appropriate proportions.

Evaluation of physical and radiation shielding properties of Bi2O3–B2O3 glass doped transition metals ions

Bismuth borate glasses of formula 60% Bi2O3 and 40% B2O3 doped 0.7 wt % of one of the transition metal oxides; TiO2, Cr2O3, V2O5 or Fe2O3 were prepared using melting-annealing method. The glasses optical transmittance spectra have been studied and reveal UV transmission bands related to the different valence states of the doped transition metal ions. Electrical conductivity and many physical parameters of the glasses were also investigated such as; optical bandgap (Eopt), refractive index (n), reflection loss (RL), molar refractivity (Rm), molar polarizability (αm), dielectric constants (ε), optical transmission coefficient (T) and metallization criterion (M Criterion).The effectiveness of the glasses as radiation protective shield was evaluated and calculated by Monte Carlo N-Particle Transport Code (MCNP) using the Medical Internal Radiation Dose (MIRD) of male human model. Many shielding parameters have been also deliberated such as; linear attenuation coefficient, effective removal cross section (ΣR), radiation protective efficiency (RPE %), tissue weighting factors (Wt), in addition to a comparison between the experimental and the simulated linear gamma attenuation coefficients at numerous energies. The glasses reveal high stable optical and physical properties in addition to high radiation shielding efficiency against gamma irradiation. The high concentration of heavy Bi3+ ions and presence of transition metal ions with their variable configurations, provide the shielding behavior of the glasses and decreased the life time risk for cancer by about five times.

Group-III quantum defects in diamond are stable spin-1 color centers

Color centers in diamond have emerged as leading solid-state artificial atoms for a range of quantum technologies, from quantum sensing to quantum networks. Concerted research activities are now underway to identify new color centers that combine stable spin and optical properties of the nitrogen vacancy (NV$^-$) with the spectral stability of the silicon vacancy (SiV$^-$) centers in diamond, with recent research identifying other group IV color centers with superior properties. In this Letter, we investigate a new class of diamond quantum emitters from first principles, the group III color centers, which we show to be thermodynamically stable in a spin-1, electric-field insensitive structure. From ab initio electronic structure methods, we characterize the product Jahn-Teller (pJT) effect present in the excited state manifold of these group III color centers, where we capture symmetry-breaking distortions associated with strong electron-phonon coupling. These predictions can guide experimental identification of group III vacancy centers and their use in applications in quantum information science and technology.

Dependence of thermal stability in the composition of Ge-As-Te films

Ge5AsxTe95-x amorphous thin films (x=20∼60) have been deposited by thermal evaporation and the change of their optical parameters—like refractive index and optical bandgap as a function of thermal annealing time—have been studied with an aim to screen the composition of the film with stable optical and thermal properties for applications in optical waveguide devices. The film with a composition around x=38.0 was found to be stable, while the optical band gap and refractive index decreases in the films with x<38.0, and opposite changes can be observed in the film with x>38.0. Further structural characterization showed no any observable changes of the Raman spectra in the as-prepared and annealed Ge5.2As38.0Te56.8 film, confirming the stability of the optical and thermal properties in this composition.

Structural, electronic and optical properties of metalloid element (B, Si, Ge, As, Sb, and Te) doped g-ZnO monolayer: A DFT study

Stable geometries, electronic structure, and optical properties of ZnO monolayer doped with metalloid element (M = B, Si, Ge, As, Sb, and Te) atom have been studied using density functional theory. It is found that among these elements Ge, As, and Sb can be effectively doped at Zn site in the ZnO monolayer with the formation energies ranging from −1.02 to −0.96 eV. Except B element, all the metalloid atoms prefer to protrude out of the plane of the ZnO monolayer. The nonmagnetic nature of the ZnO monolayer is retained with the doping of B, Si, Ge, As, and Sb atom, while Te atom induces the magnetism in ZnO monolayer (2 μB). While doping of Si, As, Sb, and Te in ZnO monolayer resulted in a red shift in the absorption spectra of doped ZnO monolayer and the blue shift is observed for B and Ge doped ZnO. The static dielectric constant for ZnO monolayer is 1.49. With the doping of these metalloid elements in ZnO monolayer, the dielectric constant can be tuned from 1.36 to 2.84. These results are potentially useful for optoelectronic applications and the development of optical nanostructures.

Chemosensing Test Paper Based on Aggregated Nanoparticles of a Barbituric Acid Derivative

The development of sensitive, cheap, and portable methods for detecting nitroaromatics explosives has a profound significance and value for public health and environmental protection. For this purpose, a new D-π-A barbituric acid derivative CB-CYH with aggregation-induced emission (AIE) behavior was synthesized, which can interact with picric acid through photoinduced electron transfer (PET). Scanning electron microscopy (SEM) and dynamic light scattering (DLS) indicate that the enhanced emission of the compounds is related to the formation of nano-aggregates. It is well known that an important source of mechanochromic fluorescence (MCF) characteristic materials is the compound with AIE characteristics. The chemosensing test paper prepared by aggregated nanoparticles based on AIE properties is often subjected to external friction or squeeze during transportation or storage, resulting in changes of their optical properties, and destruction of test paper followed. Therefore, the development of compounds with AIE properties and stable optical properties in the presence of external stimuli is particularly important for chemosensing test paper. Molecular dynamics simulation (MDS) shows that the presence of hydrophobic cycloalkyl group in CB-CYH, which caused the molecules to be closely interspersed with each other; hence, it is difficult to change the microstructure and stacking mode of molecules by external stimulation simultaneously; the optical properties are not changed by external stimuli. Therefore, the test paper based on the AIE effect of CB-CYH was developed as chemosensing test paper for the detection of nitroaromatics.

Photoprogrammable Mesogenic Soft Helical Architectures: A Promising Avenue toward Future Chiro-Optics.

Mesogenic soft materials, having single or multiple mesogen moieties per molecule, commonly exhibit typical self-organization characteristics, which promotes the formation of elegant helical superstructures or supramolecular assemblies in chiral environments. Such helical superstructures play key roles in the propagation of circularly polarized light and display optical properties with prominent handedness, that is, chiro-optical properties. The leveraging of light to program the chiro-optical properties of such mesogenic helical soft materials by homogeneously dispersing photosensitive chiral material into an achiral soft system or covalently connecting photochromic moieties to the molecules has attracted considerable attention in terms of materials, properties, and potential applications and has been a thriving topic in both fundamental science and application engineering. State-of-the-art technologies are described in terms of the material design, synthesis, properties, and modulation of photoprogrammable chiro-optical mesogenic soft helical architectures. Additionally, the scientific issues and technical problems that hinder further development of these materials for use in various fields are outlined and discussed. Such photoprogrammable mesogenic soft helical materials are competitive candidates for use in stimulus-controllable chiro-optical devices with high optical efficiency, stable optical properties, and easy miniaturization, facilitating the future integration and systemization of chiro-optical chips in photonics, photochemistry, biomedical engineering, chemical engineering, and beyond.

Sensitive Water Probing through Nearly Monochromatic Red Emission in Er3+-Enriched Core-Shell Upconversion Nanoparticles

Introduction Water is not only the most precious resource on earth, but also the most important component of the organism, which is vital to life. However, sometimes even a very small amount of water is dangerous. When water is present in fuels, organic solvents, it can sometimes cause serious consequences. Therefore, moisture monitoring and measurement play a very important role in basic research, industrial synthesis and etc.At present, the standard method for detecting moisture is the Karl Fischer method[1], which is complicated and time-consuming, therefore is not suitable for rapid determination and repeated measurement of moisture. The optical moisture sensor has the advantages of simple operation, fast response, etc. The rare earth-doped upconversion nanoprobes have the advantages of stable chemical properties, large anti-Stokes shift, and stable optical properties, which has attracted great attention in the sensor field[2-3].Here, a water detection probe based on LiErF4: 0.5% Tm@LiYF4 under 808nm excitation was constructed to detect the trace water in DMF. Method TmCl3·6H2O (0.0025mmol) and ErCl3·6H2O (0.4975 mmol) were added to 3 mL oleic acid and 7 mL 1-octadecene. The solution was heated to 150℃ and stirred for 30 minutes before cooled down to 30℃. NH4F (2mmol ) and LiOH (1.25 mmol) dispersed in 5 mL methanol were added to the mixture, then heated to 80℃ lasted for 30 min to remove the methanol. The solution was then heated to 300℃ and keep for 90 min before cool down to room temperature. Finally, the LiErF4:0.5%Tm nanoparticles were washed by acetone and anhydrous ethanol and dispersed in 4ml cyclohexane.YCl3·6H2O (0.25 mmol) was added to a mixture of 3 mL OA and 7 mL ODE and stirred continuously for 30 min. The solution was heated to 150℃ for 30min, then cooled down to 30℃, 5mL methanol containing NH4F (1mmol) and LiOH (0.625mmol) was added and then heated to 80℃ for 30min to remove the methanol, 2ml cyclohexane containing the core LiErF4:0.5%Tm nanoparticles was added and then heated to 90℃ lasted for 30min to remove the cyclohexane. Finally, the mixture was heated to 305℃ lasted for 90min. The LiErF4: 0.5% Tm@LiYF4 nanoparticles were obtained and washed with acetone and ethanol respectively, then dispersed in 4ml cyclohexane.Nitrogen protection and continuous stirring are required throughout the experiment.The oleic acid coated nanoparticles were dispersed in DMF(10mL) containing 0.2mmol NOBF4 and then ultrasonicated for 10 min to remove the oleic acid. The ligand-free nanoparticles were collected by centrifugation at 13000 rpm for 15 min, washed with DMF two times, and redispersed in DMF. Results and Conclusions Because of the high concentration of Er3+ ions in the nanoprobe, the interaction among Er3+ ions is very strong and easy to be affected by the environment. When there is water in the solution, the nanoprobe will transfer energy to the water molecules, leading to the upconversion emission quenching. The response sensing of water molecules was realized by detecting the red emission of nanoprobe with the change of water content in DMF.The results showed that the red emission intensity of the nanoprobe was weakened obviously with the increase of water content in the solution and there is a good linear relationship between the logarithm of the change in emission intensity (ln(F/F0)) and water content (vol%) . The limit of detection in DMF can be down to 60ppm. The results are of great significance for the development of reusable water test strips and highly sensitive detection instruments.

Circular dichroism induced by tunable symmetry breaking in vertical Q-shaped nanostructure

Circular dichroism (CD) is widely used in bio-sensing, pharmaceuticals, and molecular chemistry. Symmetry breaking is an important method of achieving CD signals. However, the relationship between the magnitude of CD and symmetry breaking remains unclear. In this study, we introduce nanorods into symmetric nanostructures comprising vertical Q-shaped nanostructure arrays (VQNAs) to prove the relativity of the symmetry breaking. The numerical simulations results show that the CD spectra of VQNAs present four modes in the visible spectrum. The coupling between nanorods differs under left- and right-handed circular polarized illuminations, leading to the production of the CD. The CD magnitude is not monotonic when the parameters of VQNAs change, and it is the largest for the structure at an appropriate scale. Besides, VQNAs have stable optical properties. Results can help to understand more deeply the CD mechanism produced by symmetry breaking, and design chiral plasmonic nanostructures.

Heat-Stable and Moisture-Proof CsPbBr3 Quantum Dots Under Dual Protection: Coordination of Non-Crystalline SiO2 and Crystalline h-BN Nanosheets

It’s hard for pure perovskite quantum dots (QDs) to maintain long-term and stable optical properties in practical conditions. Here, CsPbBr3 QDs were first stabilized in amorphous SiO2 and crystalline hexagonal boron nitride (h-BN) nanosheets. The transmission electron microscopy (TEM) images display the laminated structure consisting of CsPbBr3/SiO2 nanospheres and h-BN nanosheets. Besides, the photoluminescence (PL) intensity of CsPbBr3/SiO2/h-BN nanohybrid only has a slight decrease than CsPbBr3/SiO2 nanocomposite. But, dual protection of SiO2 and h-BN give perovskite QDs better humidity stability and thermal stability. Besides, CsPbBr3/SiO2/h-BN block exhibits excellent water-resistance. This work provides a novel method to accelerate the application of perovskite QDs in optoelectronic devices.

Photoluminescence Enhancement: Over 1000‐Fold Enhancement of the Unidirectional Photoluminescence from a Microsphere‐Cavity‐Array‐Capped QD/PDMS Composite Film for Flexible Lighting and Displays (Advanced Optical Materials 24/2019)

A Tai Chi patterned microsphere-cavity array on a flexible quantum dot film to enhance and direct white-light emission is demonstrated here. Two aspects of a material, i.e. rigidity and flexibility, are implied by the symbol. The microsphere cavity is rigid with stable optical properties, while the microsphere array is flexible due to the weak connection between the microspheres. The cover image, referring to article number 1901228 by Yinzhou Yan and co-workers, combines Chinese traditional culture with modern science to motivate new ideas in flexible nanophotonics.

Calibration of Spectral Imaging Devices With Oxygenation-Controlled Phantoms: Introducing a Simple Gel-Based Hemoglobin Model

An optical phantom model with stable oxygen saturation (StO2) and optical properties (OPs) is the key for quick and accurate calibration of spectral imaging devices. Toward this goal, we have developed gel-based phantoms using Agarose, polystyrene microsphere, purified hemoglobin and yeast. Theoretical values of OPs were calculated by applying Beer Lambert law and Mie theory whereas a robust fitting algorithm was used to extract StO2. Stability of OPs and StO2 in the phantoms was validated experimentally over a period of two weeks and the effect of pre-heating at 65o C degrees on StO2 was observed. Multi-spectral imaging (750, 780, 850 and 945 nm) of the phantoms were also performed on the FDA-approved commercial system to demonstrate the utility of the phantoms.

In Situ Green Synthesis of Nitrogen-Doped Carbon-Dot-Based Room-Temperature Phosphorescent Materials for Visual Iron Ion Detection

Room-temperature phosphorescent (RTP) materials show great potential for ion detection due to a long lifetime and a high signal-to-noise ratio. Most RTP materials are limited to organometallic or organic compounds that are costly, toxic, and complex. Here, an in situ green synthesis of carbon dot (CD)-based RTP materials using Schisandra chinensis polysaccharide as the only carbon source, which has a natural nitrogen-containing structure for endogenous nitrogen-doping, is performed. RTP measurements show that the CD-based RTP materials had lifetimes up to 271.2 ms under 350 nm excitation and with a smaller energy gap (0.32 eV). In addition, they exhibit adequate quenching in the presence of iron ions (Fe3+). The visible RTP intensity is inversely proportional to the Fe3+ concentration over the range of 0.1–2 mM, with a 0.57 μM detection limit. Further, the prepared CD-based RTP materials have highly stable optical and physical properties, which open a new perspective as luminescent sensors for Fe3+ detection with inexpensive and green raw materials.

Influence of Synthesis Conditions on the Photoluminescence of Poly(methyl methacrylate)/(ZnxCd1 –x)S Compositions

Quantum dots (QDs) synthesized by combining semiconductors are characterized by more stable optical properties. Introducing them into polymeric matrices can lead to optical compositions with predictable physical and chemical properties. These properties are largely determined by the method and conditions of synthesis of compositions. It has been demonstrated how the composition of reaction mixtures, the sequence of their preparation, and heating have an effect on the composition, structure, and photoluminescence properties of (ZnxCd1 –x)S QDs in polymeric compositions based on poly(methyl methacrylate) (PMMA). The QDs have been synthesized in situ in a methyl methacrylate (MMA) medium. Sulfides are formed during the destruction of thioacetamide metal complexes. The formation of QDs continues during thermal curing of the compositions to the glassy state. As a response to changes in the synthesis conditions, the changes in the photoluminescence and photoluminescence excitation spectra of PMMA/(ZnxCd1 –x)S compositions have been considered. The deactivation of excited electronic states occurs with the participation of energy levels of defects located on the energy diagram of the compositions in the band gap of semiconductor QDs. The luminescence spectrum is predominantly determined by CdS and defects on the surface of its crystals. Based on the data obtained, formulas are proposed that reflect the composition and structure of composites formed under various synthesis conditions.

Ultrahighly Photosensitive and Highly Stretchable Rippled Structure Photodetectors Based on Perovskite Nanocrystals and Graphene

Stretchable optoelectronic devices are the need of the hour when it comes to making present day technologies user-friendly. These devices when placed conformably on the human skin or any other artificial intelligence products must function in all their capacities to get a durable and highly sensitive device performance. Stretchable photodetectors are the core fundamental constituents that fall under the umbrella of flexible optoelectronic devices. Although a significant amount of research has been reported on stretchable photodetectors, good performance still remains a challenge. Nanometer-sized methylammonium lead bromide ((MA)PbBr3) perovskite nanocrystals can significantly emit and absorb light in the visible spectrum. With high quantum yield and stable optical and electronic properties, when they are subjected to mechanically tunable two-dimensional (2D) composites, we obtain better performance from stretchable optoelectronic devices. Here, a hybrid photodetector composed of perovskite nanocrystals and graphene of rippled geometry is demonstrated, where a thin film of photon-absorbing perovskite nanocrystals is placed on rippled graphene that contributes to a photoresponsivity on the order of ∼6 × 105 A W–1. The large photoresponsivity value places this hybrid stretchable device in the highest position among devices with similar functionality. It is found that the photoresponsivity of the perovskite nanocrystals and graphene hybrid rippled structure photodetector is strain tunable with a stretchability up to 100%. In addition, the hybrid rippled structure photodetector has wearability and durability. All of these superior functionalities lead the way toward fabricating stretchable optoelectronic devices suitable for applications in the fields of biomedicine, defense systems, fire detection, and flexible display panels.

Peptide-gold nanocluster synthesis and intracellular Hg2+ sensing

Peptide-gold nanoclusters (AuNCs) are often used in biosensing due to their stable physicochemical properties, adjustable functionality, and good biocompatibility. Hg2+ ions are widely distributed in soil and water, which can easily enter the human body through the food chain. Hg2+ pollution in the ecological environment is mainly through the conversion of inorganic mercury into methylmercury, which seriously threatens our normal physiological functions. It is necessary to develop a biosensor for detecting intracellular Hg2+. In this study, a novel fluorescent AuNCs were synthesized using the peptide CCYRRRRRRHHHH as a protective agent. The synthesized CCYR6H4-AuNCs had stable optical properties, high quantum yield (12%), and emitted red fluorescence under ultraviolet light. The synthesized AuNCs showed high selective for Hg2+ and the detection limit of Hg2+ could reach 30 nM in aqueous solution. At the same time, because of its good biocompatibility and low cytotoxicity, it has also been successfully used for live cell imaging and intracellular Hg2+ detection.