Entire Visible Range Research Articles

Phosphorylated xanthan gum-Ag(I) complex as antibacterial viscosity enhancer for eye drops formulation

Topical instillation of eye drops represents the treatment of choice for many ocular diseases. Ophthalmic formulations must meet general requirements, i.e. pH, osmolality, transparency and viscosity to ensure adequate retention without inducing irritation and the development of eye infections. We developed a phosphorylated xanthan gum–Ag(I) complex (XGP-Ag) showing pH (pH = 7.1 ± 0.3) and osmolality values (311 ± 2 mOsm/kg) close to that of human tears (pH = 6.5–7.6 and 304 ± 23 mOsm/kg) thanks to the presence of phosphate moieties along the chain. The presence of phosphate groups covalently bound to the XG chains avoids their dispersion in fluid, thus reducing the risk of corneal calcification. 0.02% w/v XGP-Ag solution showed high transparency (higher than 95% along the entire visible range), adequate refractive index (1.334 ± 0.001) and viscosity in the range: γ 1 s-1-10,000 s- 1 (26.4 ± 0.8–2.1 ± 0.4 mPa·s). Its cytotoxicity and capability to hinder bacterial proliferation was also verified.

Processes of electroluminescence degradation of light-emitting structures based on thin silicon oxide and nitride films

SiO2 /Si, SiN1.2/SiO2 /Si and SiO2 /SiN0.9/SiO2 /Si structures have been fabricated by chemical vapor deposition and thermal oxidation of silicon. The elemental composition and thicknesses of dielectric layers have been studied using Rutherford backscattering spectroscopy, scanning electron microscopy, and spectral ellipsometry. The electroluminescence (EL) of the samples has been investigated in the “electrolyte–dielectric–semiconductor” system at a positive bias voltage applied to the silicon substrate. An intense band with maxima at 1.9 eV appears on the EL spectra of the SiO2 /Si sample, while the EL spectra of the SiN1.2/SiO2 /Si and SiO2 /SiN0.9/SiO2 /Si samples are characterized by the presence of bands with the maximum values of 1.9, 2.3 and 2.7 eV. The nature of these bands is discussed. Passing a charge in the range of 100–500 mC/ cm2 through the SiO2 /SiN0.9/SiO2 /Si sample, an increase in the EL intensity was recorded in the entire visible range. Passing a charge of 1 C/cm2 through a sample with a three-layer dielectric film resulted in the EL intensity decrease. It can be explained by the upper oxide layer degradation. It has been shown that silicon nitride deposited on top of the SiO2 layer protects the oxide layer from field degradation and premature breakdown. The most stable electroluminescence when exposed to a strong electric field is observed for the structure SiN1.2/SiO2 /Si.

Thiophene-benzothiadiazole based donor–acceptor–donor (D-A-D) bolaamphiphiles, self-assembly and photophysical properties

ABSTRACT Bolaamphiphilies with D-A-D type π-conjugated rigid cores composed by thiophenes as donors (D) and benzothiadiazole (BTD) as central acceptor (A) have been synthesised. Their self-assemblies and photophysical properties were investigated by polarising optical microscope, differential scanning calorimetry, X-ray diffraction and scanning electron microscopy. Such compounds can self-assemble into honeycomb cylinder mesophases with Colhex∆/p6mm and Colsqu/p4mm lattices in their pure states as well as organogels with different morphologies in organic solvents. Their absorption spectra cover nearly the entire visible light range and their band gaps are relatively low. Tetrathiophene BTD based bolaamphilphiles (BT4/n ) with higher D/A ratios than the bisthiophene BTD bolaamphilphiles (BT2/n ) can self-assemble into more ordered nanostructures in both bulk states and solution. Both the absorption and emission peaks of BT4/n are strongly red shifted. The influence of the molecular conformation, the conjugated core length, as well as the D/A ratio on the self-assemble and photophysical characteristics of such D-A-D bolaamphiphiles are discussed.

Decay time dynamics of red and blue luminescence of surface-functionalized silicon quantum dots

Controlling the emission wavelength by the quantum confinement or the size effect of silicon quantum dots (Si QDs) has a limitation in that it can be only approximately 600 nm or above. To overcome this limitation, in the recent decade, numerous studies have been conducted for reproducing the entire visible range from blue to red from Si QDs by their surface functionalization. In this study, we fabricated alkyl- and amine-passivated Si QDs and investigated their emission mechanism following surface functionalization. We interpreted the emission mechanism of the surface-functionalized Si QDs by combined experimental analysis of the decay time dynamics and density functional theory-based model calculation of the highest occupied molecular orbital-lowest unoccupied molecular orbital electronic structures. Our comprehensive studies could provide insight into the debated problems of the luminescence mechanism of surface-functionalized Si QDs.

Widely tunable optical properties via oxygen manipulation in an amorphous alloy

The ability to widely tune the optical properties of amorphous alloys is highly desirable especially for their potential applications in optoelectronic devices. In this work, we demonstrate that introducing oxygen into an amorphous alloy system of Co-Fe-Ta-B enables the formation of various amorphous derivatives ranging from metals to semiconductors, and eventually to insulators. These oxygen-containing amorphous derivatives gradually become transparent with the opened bandgaps, leading to a continuous increase in their optical transmittance. Furthermore, the reflective metal-type amorphous alloy and transparent insulator-type amorphous oxide of the system can be integrated together to realize the full-color tuning over the entire visible spectral range. This provides a new way to develop large-area color coatings with high design flexibility and full-color tun-ability. We envisage that the design concept proposed in this work is also applicable to many other amorphous alloy systems, from which all types of amorphous materials including alloys, semiconductors and insulators may be developed to show unprecedented optical functionalities.

Piperazine-based zirconium oxy-chloride (PzZrOCl) single crystal: a third-order nonlinear optical material for optoelectronic device applications

Single crystals of piperazine zirconium oxy-chloride (PzZrOCl) are grown successfully by slow evaporation technique for optoelectronic device applications. The suitability of the material was estimated and reported as follows. For device compatibility crystal habits, purity, crystallite size, microstructure, and bulk crystals structures are essential parameters and hence they were examined with basic characterization techniques. The average dimensions of as-grown crystals are up to $$10 \times 10 \times 7 {\text{mm}}^{3}$$ grown within a period of $$35$$ days. The grown single crystals were subjected to powder X-ray diffraction (XRD) to confirm the crystalline quality. The single crystal X-ray diffraction indicates that the PzZrOCl crystal belongs to the tetragonal system (P), with unit cell parameters $$a = 6.46{{ {\AA}}},{ }b = 12.81{{ {\AA}}}$$ , $$c = 12.85{{ {\AA}}}$$ , $$\alpha = 89.95^\circ$$ , $$\beta = 89.96^\circ ,$$ and $$\gamma = 90.03^\circ$$ . The volume of the unit cell was found to be V = 1063 $${\text{\AA}}^{3} .$$ The analysis on the microstructure of grown single crystals shows layered-like growth pattern. The functional groups of a molecule, their bond vibration frequencies, and mode of alignments have been examined by Fourier-transform infrared spectroscopy (FT-IR). The transmittance (98%) in the entire visible range with lowest cutoff wavelength (215 nm) and green emission (545 nm) are another evidence of suitability for industrial applications. The thermal properties of PzZrOCl single crystals were analyzed from TG–DTA curves and the compound is thermally stable up to $$162\,^{ \circ } {\text{C}}$$ . The mechanical strength hardness, Mayer index, yield strength, and elastic stiffness constant were evaluated. These values indicate that the sample is mechanically strong and belongs to soft category. The laser-induced damage was estimated by using Nd:YAG laser of wavelength 1064 nm and the observed values is three times higher than KDP ands 1.2 times higher than LAPP. The optical nonlinear nature and its efficiency are examined by using Z-scan technique. The analysis is discussed in detail, and the results strongly recommend that PzZrOCl single crystals are suitable for optical and electronic device applications.

Multiresponsive Photonic Microspheres Formed by Hierarchical Assembly of Colloidal Nanogels for Colorimetric Sensors

Soft photonic materials formed from nanoscale colloidal crystals are versatile platforms for sensing and signaling in biomedical, chemical, and mechanical application scenarios. A particularly leveraged attribute of such materials is structural coloration; when applied in reconfigurable systems, dynamic coloration can be achieved, akin to the ability of chameleons to change their color appearance through nanocrystal structures beneath their skin. To date, many hybrid photonic materials composed of hard, passive, and soft adaptable systems have been explored for their dynamic color-changing performance; however, a lack of multifunctional and fully adaptable systems with sufficient control of properties on nanoscale persists. In addition, in hybrid systems with multiple stimuli-responsive components, interactions among components tend to be overlooked. Here, we propose a facile and scalable method to prepare multiresponsive photonic materials composed of soft and adaptable components, to tune the structural coloration over the entire visible spectral range. Temperature-responsive hydrogel microspheres of diameters of several tens of microns host an array of pH-responsive colloidal nanogels; the hierarchical assembly of nanogels scaffolded within the hydrogel microspheres form soft photonic microspheres that display a dynamic color change spanning the entire visible spectral range, through a variation in pH or temperature. pH change triggers a volume change in the nanogels, as does temperature change in the scaffolding hydrogel. A model predicting the equilibrium sizes of the microspheres as a function of temperature and pH has been proposed and validated. We also discuss the mutual interactions between the colloidal nanogels and the scaffolding hydrogel. These photonic microspheres could be applied as optically interrogated sentinels in label-free multiplexed chemical, thermal, and mechanical sensing with sub-millimeter resolution.

Ultrastable low-cost colloidal quantum dot microlasers of operative temperature up to 450\u2009K

Quantum dot microlasers, as multifunctional optical source components, are of great importance for full-color high-pixel display, miniaturized coherent lighting, and on-chip integrated photonic and electronic circuits. Since the first synthesis of colloidal quantum dots (CQD) in the 1990s, motivation to realize high-performance low-cost CQD micro-/nanolasers has been a driving force for more than three decades. However, the low packing density, inefficient coupling of CQDs with optical cavities, and the poor thermal stability of miniaturized complex systems make it challenging to achieve practical CQD micro-/nanolasers, especially to combine the continuous working ability at high temperatures and the low-cost potential with mass-produced synthesis technologies. Herein, we developed close-packed CQD-assembled microspheres and embedded them in a silica matrix through the rapid self-aggregation and solidification of CdSe/ZnS CQD. This technology addresses the core issues of photoluminescence (PL) quenching effect and low optical gain in traditional CQD laser research. High-efficiency low-threshold CQD microlasers are demonstrated together with long-playing (40 min) working stability even at 450 K under pulsed laser excitation, which is the highest operational temperature for CQD lasers. Moreover, single-mode CQD microlasers are obtained with tunable wavelengths across the entire visible spectral range. The chemosynthesis process supports the mass-produced potential of high-density integrated CQD microlasers, promoting CQD-based low-cost high-temperature microdevices.

Self‐Assembled Plasmonic Coaxial Nanocavities for High‐Definition Broad‐Angle Coloring in Reflection and Transmission

AbstractResonant spectral scattering from metallic nanostructures is an attractive alternative approach to produce colors instead of using chemical pigments. Here, a technological platform based on self‐assembled arrays of coaxial plasmonic resonators is developed for generating a bright color gamut over the entire visible spectral range in both reflection and transmission, offering the potential for ultrahigh definition coloring over large areas. Unlike the approaches using the nanostructure periodicity to define colors, the developed method employs color engineering based on the localized plasmon resonances in nanocavities, therefore, providing a broad angular response and viewing angles of up to 40°. With the nanoscale dimensions of color pixels and an increased viewing angle range, the proposed approach allows achieving large‐area color patterns with local coloring controlled by postprocessing, important for display technology, anticounterfeiting and artistic applications.

Recrystallization of CsPbBr3 Nanoparticles in Fluoropolymer Nonwoven Mats for Down- and Up-Conversion of Light.

Inorganic halides perovskite CsPbX3 (X = Cl, Br, and I or mixed halide systems Cl/Br and Br/I) nanoparticles are efficient light-conversion objects that have attracted significant attention due to their broadband tunability over the entire visible spectral range of 410–700 nm and high quantum yield of up to 95%. Here, we demonstrate a new method of recrystallization of CsPbBr3 nanoparticles inside the electrospun fluoropolymer fibers. We have synthesized nonwoven tetrafluoroethylene mats embedding CsPbBr3 nanoparticles using inexpensive commercial precursors and syringe electrospinning equipment. The fabricated nonwoven mat samples demonstrated both down-conversion of UV light to 506 nm and up-conversion of IR femtosecond laser radiation to 513 nm green photoluminescence characterized by narrow emission line-widths of 35 nm. Nanoparticle formation inside nonwoven fibers was confirmed by TEM imaging and water stability tests controlled by fluorimetry measurements. The combination of enhanced optical properties of CsPbBr3 nanoparticles and mechanical stability and environmental robustness of highly deformable nonwoven fluoropolymer mats is appealing for flexible optoelectronic applications, while the industry-friendly fabrication method is attractive for commercial implementations.

Visible‐Light Absorbing TiO2 : Curcumin Thin Films with ALD/MLD

AbstractCurcumin is known for its antimicrobial effects. Here we use the atomic/molecular layer deposition (ALD/MLD) thin‐film technique to embed monomolecular curcumin layers within a photocatalytic TiO2 matrix into different superlattice structures with the anticipation of intriguing synergistic effects. We demonstrate the extension of the light absorption to the entire visible range which could pave the way for the use of these films for light‐driven destruction of pathogens.

Data on the refractive index of freshly-excised human tissues in the visible and near-infrared spectral range

We report on the experimental determination of the refractive index for eleven freshly-excised human tissue types, acquired from 16 patients. Measurements are based on a prism-coupling refractometer that is pumped by five individual laser sources emitting monochromatic radiation at 450 nm, 532 nm, 633 nm, 964 nm and 1551 nm, respectively. A simple Cauchy model reproduces accurately experimental data and enables the prediction of tissue’s index within the entire visible and near-infrared spectral range, as well the estimation of dispersion-related parameters, such as group velocity dispersion.

Design of narrowband or broadband absorber by heterostructures including TMDCs and spacers

Two-dimensional transition metal dichalcogenides materials (TMDCs) have gathered attention because of their special features like absorption. In order to increase absorption in narrowband or broadband wavelength, heterostructures, which consist of two TMDC, monolayers, and spacers, are suggested and probed in the entire visible wavelength range. In this paper, the effectiveness of TMDC monolayers permutation, spacer number, spacer place, spacer thickness, incident angle, and polarization on absorption have been investigated, and concluded that usage of the spacer would almost double the absorption comparing to having no spacer, while the structure is simple. The suggested structure is able to invite attentions to utilize them in devices like optoelectronic and nanophotonic.

First-principles study of graphenylene/MoX2 (X = S, Te, and Se) van der Waals heterostructures.

New van der Waals (vdW) heterostructures obtained by stacking monolayers of recently synthesized graphenylene (Gr) and two-dimensional 1H-MoX2 (X = S, Te, and Se) are proposed and analyzed using ab initio calculations. These heterostructures are stable under normal conditions and have unique crystalline lattices. The study of electronic properties shows that the proposed materials are direct-gap semiconductors with a narrow band gap, which can be controlled by in-plane tensile strain or a transverse electric field. The considered vdW heterostructures demonstrate the transition of band alignments between types I, II and III, when in-plane stress or a transverse electric field is applied, and hold great potential for creating multifunctional devices for stretched electronics. Computations based on the non-equilibrium Green's function method indicate a high rectification factor of the order of 103-104 for a diode based on the Gr/MoS2 vdW junction. The studied structures exhibit broad optical absorption across the entire visible range and represent a promising material for optoelectronic applications.

Формирование и оптические свойства нанорешеток на поверхности фторида кальция, генерируемых при фемтосекундном лазерном воздействии

Femtosecond laser structuring of dielectrics is an urgent problem for the creation of optical elements. In this work, we performed femtosecond laser nanostructuring of the calcium fluoride surface with the formation of self-organizing periodic gratings with subwavelength periods of the order of 200 and 350 nm. During the work, the dependence of the period of the structures on the wavelength of laser radiation was established, which was confirmed by the simulation results. The structures show a decrease in transmission over the entire visible range, predominantly due to diffraction and light scattering. Keywords: direct laser recording, femtosecond laser pulses, surface functional nano- and micro-optical structures, diffraction.

Large area coverage and controlled photoluminescence from vertically aligned ZnO nanorods on Cu substrates

ZnO nanorods were deposited on large area Cu foil using cathodic electrodeposition technique. The growth time was used as a control parameter for tuning the crystallinity as well as the length of nanorods. It is observed that the crystallinity improves with deposition time and the nanorods grow with a preferred orientation of 〈002〉. A typical circular area of 4 cm diameter was uniformly coated with ZnO nanorods. The contact angle decreases gradually from 108° to 71° as deposition time increases from 3 to 15 min. This marks the enhanced wettability of the surface. Further, the room temperature Photoluminescence (PL) spectra of these rods reveal that the near band edge UV emission (~3.3 eV) increases at the cost of defects induced visible emission, signifying improved crystallinity. The color rendering index of the 10-minute deposited sample is 90 and it shows a near white color temperature of 9013 K due to optimum emission coverage over the entire visible wavelength range.

An improved plasmonic Au–Ag/TiO2/rGO photocatalyst through entire visible range absorption, charge separation and high adsorption ability

Plasmonic nanohybrids for visible light absorption: the combination of small alloyed AuAg NPs, TiO2 NPs and rGO nanosheets provides wide visible light absorption improving the photocatalytic efficiency towards water pollutant remediation.

White-light emission from zinc chalcogenide alloy quantum dots with gradient compositions

Zn(Te1−xSx) quantum dots (QDs) surrounded by a ZnS shell were synthesized using a standard hot-injection method. The obtained Zn(Te1−xSx) QDs consisted of a Te-rich center and an outer layer with a gradient composition in which the S concentration increased with increasing distance from the center. The Te-rich portion of the Zn(Te1−xSx) QDs had a composition range of 0.2 ≤ x ≤ 0.5 and a diameter <2 nm, while the compositionally graded S-rich region had a thickness of ~0.5 nm. The optical gaps of the Zn(Te1−xSx) QDs were smaller than that of unalloyed ZnTe QDs owing to the large band gap bowing that appears in ZnTe–ZnS alloys. The Zn(Te1−xSx)/ZnS core/shell QDs exhibited photoluminescence (PL) covering the entire visible range, with a narrow band emission at the blue region arising from exciton recombination and a broad band emission centered in the region from green to red. The alloying level, x, moved the values of the chromaticity coordinates (CIE 1931), where both x = 0.10 and x = 0.18 corresponded to warm white-light and daylight with the CIE color coordinates of (0.405, 0.408) and (0.318, 0.352), and a correlated color temperature of ~3400 and 6000 K, respectively. Based on the point defects that commonly appear in zinc chalcogenides and PL emission decay trace, the electronic transition responsible for the broad band emission was attributed to the recombination of the electron at the 1Se quantum level and the hole at the localized zinc vacancy acceptor level.

Modeling and Epitaxial Growth of Homogeneous Long-InGaN Nanowire Structures.

One-dimensional nanowires based on Group III-nitride materials are emerging as one of the most promising structures for applications of light-emitting diodes (LEDs), laser diodes (LDs), solar cells, and photocatalysts. However, leading to the so-called “green gap” in photonics, the fabrication of high concentration indium gallium nitride (InGaN) and long-InGaN structures remains still challenging. In this study, we performed simulations for structural modeling of uniform temperature distribution in a nanowire epitaxy, and have successfully developed high-concentration InGaN and long-InGaN nanowire heterostructures on silicon (Si) substrate using molecular beam epitaxy (MBE) system. From scanning electron microscope (SEM) and transmission electron microscope (TEM) results, it was confirmed that the various doped-InGaN nanowire structures show much higher crystal quality compared to conventional nanowire structures. By introducing a new three-step modulated growth technique, the n-/p-InGaN active regions were greatly increased and the optical properties were also dramatically improved due to reduced phase separation. In addition, a multi-band p-InGaN/GaN heterostructure was successfully fabricated with the core–shell nanowire structures, which enable the emission of light in the entire visible spectral range, and protect the InGaN surface from surface recombination. This paper offers important insight into the design and epitaxial growth of InGaN nanowire heterostructures.

Dynamically tunable transmissive color filters using ultra-thin phase change materials.

Structural color filters (i.e. plasmonics and nano-cavities) provide vivid and robust color filtering in applications such as CMOS image sensors but lack simplicity in fabrication and dynamic tuning. Here we report a dynamically tunable, transmissive color filter by incorporating an ultra-thin phase change layer inside a thin-film optical resonator. The transmitted color spectrum can be designed over the entire visible range and shifted by around 50 nm after phase transition. Angle dependence shows little color variation within a ±30° viewing angle. Crucially, only film deposition is required to fabricate our phase change color filter, showing great potential for large-scale and inexpensive production. The dynamically tunable color filter, described in this paper, could be a promising component in display, CMOS sensor, and solar cell technology.