Violet Region Research Articles

Impact of Annealing Time on Structural Evolution of Pure and Dy3+-Doped CeO2 Nanopowder, Rietveld Refinement and Optical Behavior

This work reports about annealing time effect on structural and optical properties of pure and Dy[Formula: see text]-doped CeO2 nanocrystallites. The nanopowders with an average grain size 13–15[Formula: see text]nm are successfully synthesized via a conducive and neoteric Pechini-type sol–gel technique. Surface morphology, composition, band gap and photoluminescence properties of the prepared samples are examined by multifarious characterization techniques like Rietveld refinement, FESEM, HRTEM, FTIR, UV–Vis spectroscopy and PL. The effects of annealing time on structural parameters including lattice parameter, bond distance, bond angle, strain, crystallite size and texture coefficient are computed for all prepared samples which are further ensured by Rietveld refinement. In absorption spectra, blue shift in the band gap of as-prepared samples has been observed due to well-known quantum size effect, however, red shift is noticed in further annealed samples. PL emission peaks are observed in violet, blue and green regions that are devoted to various defect levels and color centers such as F, F[Formula: see text], F[Formula: see text], etc. It is suggested that defects like oxygen vacancies play vital role in tailoring the band gap of prepared samples and therefore enhance its utility in photonics and oxygen storage appliances.

Indolo[3,2,1‐jk]carbazole Embedded Multiple‐Resonance Fluorophors for Narrowband Deep‐blue Electroluminescence with EQE≈34.7 % and CIEy≈0.085

AbstractMultiple‐resonance (MR) organic emitters bearing small full‐width at half‐maximum (FWHMs) are of general interest in organic light‐emitting diodes. Indolo[3,2,1‐jk]carbazole (ICz) embedded MR‐fluorophors have demonstrated extremely small FWHMs, yet in the violet region with low electroluminescence efficiency. Herein, a strategic implementation of ICz subunits into MR fluorophors is proposed by taking advantage of the synergetic effect of para‐positioned nitrogen atoms to enhance electronic coupling to decrease emitting energy gap. Deep blue emitters peaking at 441 and 447 nm with FWHMs of only 18 and 21 nm are thereof obtained, respectively, accompanied by ≈90 % photo‐luminance quantum yields. With the assistance of a thermally activated delayed fluorescence sensitizer to recycle excitons, the corresponding narrowband electroluminescent devices show unprecedent high maximum external quantum efficiencies of 32.0 % and 34.7 % with CIEy of 0.10 and 0.085, respectively.

Indolo[3,2,1-jk]carbazole Embedded Multiple-Resonance Fluorophors for Narrowband Deep-blue Electroluminescence with EQE≈34.7 % and CIEy ≈0.085.

Multiple-resonance (MR) organic emitters bearing small full-width at half-maximum (FWHMs) are of general interest in organic light-emitting diodes. Indolo[3,2,1-jk]carbazole (ICz) embedded MR-fluorophors have demonstrated extremely small FWHMs, yet in the violet region with low electroluminescence efficiency. Herein, a strategic implementation of ICz subunits into MR fluorophors is proposed by taking advantage of the synergetic effect of para-positioned nitrogen atoms to enhance electronic coupling to decrease emitting energy gap. Deep blue emitters peaking at 441 and 447 nm with FWHMs of only 18 and 21 nm are thereof obtained, respectively, accompanied by ≈90 % photo-luminance quantum yields. With the assistance of a thermally activated delayed fluorescence sensitizer to recycle excitons, the corresponding narrowband electroluminescent devices show unprecedent high maximum external quantum efficiencies of 32.0 % and 34.7 % with CIEy of 0.10 and 0.085, respectively.

Morphological and Physiological Responses of Pinus massoniana Seedlings to Different Light Gradients

Light intensity is a critical factor regulating photosynthetic capacity in plants. However, the effects of varying light intensity on morphological and photoprotective mechanisms in Pinus massoniana seedlings have not been explored in depth, especially those in the first seedling growing season. We measured the growth, photosynthetic physiology, biochemistry, and chlorophyll fluorescence of P. massoniana seedlings at four light gradients: 100% relative irradiance (RI, full sunlight), 70% RI, 50% RI, and 20% RI. The seedling height at 70% RI was 9.27% higher than that at 100% RI. However, seedling height was inhibited under low light intensity; at 20% RI, all seedlings died. The decreasing light intensity inhibited ground diameter growth but increased the height-diameter ratio. The secondary needle emergence rate was 53.4% higher at 70% RI than at 100% RI but was only 2% at 50% RI. The chlorophyll and carotenoid contents increased significantly with decreasing light intensity. The increased Chl b and Car contents promoted the photoreceptor potential of the violet (400~420 nm), blue (440~480 nm), and yellow-orange (597~655 nm) regions in leaves. Among the chlorophyll fluorescence parameters, Fv/Fm, Fv′/Fm′, Y(II), qp, and ETR all reached maximum values at 70% RI but were significantly lower at 50% RI than at 100% RI. However, decreasing the light intensity caused a reduction in NPQ. The 70% RI level increased POD and SOD activity and the contents of osmotic regulation substances and slowed MDA accumulation. Seedlings at 70% RI had a higher growth rate, higher photosynthetic activity and potential, and significantly greater stress resistance than the other seedlings. Therefore, appropriate shading measures were beneficial to the cultivation of vigorous seedlings. Furthermore, spectral reflectance indexes were found to be a suitable tool for monitoring the photosynthetic physiological characteristics, stress resistance characteristics, and growth status of P. massoniana seedlings in real time.

A novel class of Mx-Sr-Nb-Oy+δ (M = Cr3+, Cu2+, Zn2+, Ag+ and Cd2+) nanocomposites as catalyst for the synthesis of 2-amino-4H-chromene derivatives under ultrasound and microwave irradiations

Fabrication of some transitional metals doped into Nb2O5-Sr2Nb2O7-SrCO3 nanocomposites via a simple and low-cost solvothermal route is reported. Sr(NO3)2, Nb2O5, Cr(NO3)3.9H2O, Cu(NO3)2.3H2O, Zn(NO3)2.6H2O, AgNO3 and Cd(NO3)2.4H2O were used as raw materials at 200 °C for 96 h. Rietveld analysis data revealed that the synthesized nanocomposites were mainly crystallized in tetragonal (Nb2O5) and orthorhombic (Sr2Nb2O7) crystal systems. According to the data, it was found that Nb2O5 was the main phase and no dopant crystal phase was found separately in the mixture. Field emission scanning electron microscope (FESEM) images revealed that the synthesized materials had rod and particle morphologies. Vibrating-sample magnetometer (VSM) analysis showed that the as-synthesized nanomaterials had ferromagnetic behavior. Ultraviolet–visible (UV–Vis) spectra indicated that the synthesized nanocomposites had absorption in the ultraviolet and visible light regions. The photoluminescence (pL) spectra showed that the as-prepared nanocomposites had considerable optical emissions in violet, blue, green and yellow regions. The catalytic performance of the synthesized nanomaterials was studied for the synthesis of 2-amino-4H-chromene derivatives under ultrasound and microwave irradiations. The reaction parameters such as reaction time, temperature, solvent type and catalyst amount were optimized. The data showed that the optimum reaction time, temperature, catalyst amount, frequency and solvent type are 10 min, 60 °C, 10 mol%, 50 kHz and H2O under ultrasound and 11 min,10 mol% and solvent-free under microwave irradiation for model reaction. Studying the kinetic model of the chromene reactions revealed that the reactions followed a pseudo-first-order kinetic model in the two reaction conditions under ultrasound and microwave irradiations.

Engineering the Bandgap and Surface Structure of CsPbCl3 Nanocrystals to Achieve Efficient Ultraviolet Luminescence.

Herein, we report the design of novel ultraviolet luminescent CsPbCl3 nanocrystals (NCs) with the emission peak at 381 nm through doping of cadmium ions. Subsequently, a surface passivation strategy with CdCl2 is adopted to improve their photoluminescence quantum yield (PLQY) with the maximum value of 60.5 %, which is 67 times higher than that of the pristine counterparts. The PLQY of the surface passivated NCs remains over 50 % after one week while the pristine NCs show negligible emission. By virtue of density functional theory calculations, we reveal that the higher PLQY and better stability after surface passivation may result from the significant elimination of surface chloride vacancy (VCl ) defects. These findings provide fundamental insights into the optical manipulation of metal ion-doped CsPbCl3 NCs.

Colour tuning of garnet phosphor through codoping

Ca3Sc2Si3O12:Ce3+ is a well known green emitting phosphor for two phosphor converted LED lamp. It is shown that the emission colour can be tuned with the help of various co-dopents. For obtaining safer cyan emitting phosphor, partial substitution of Si by Ge found to be effective. Pr codoping is responsible for the addition of red component. The partial substitution of Y at Ca site and Mg at Sc site is the novel step into the work. This substitution converts the cyan emitting phosphor into yellow one. The colour changes are illustrated by calculating colour coordinates. Na codoping facilitates incorporation of the trivalent activator at Ca2+ site, as well as the grain growth, and enhances the PL intensity without changing emission colour. Addition of Cyan emitting phosphor in the blend can be useful for achieving super Colour Rendition Index (CRI > 95). Extended excitation in the violet region will result in removal of the harmful wavelengths from the LED lamp.

Structural, elastic, thermodynamic, electronic, optical and thermoelectric properties of MgLu2X4 (X= S, Se) spinel compounds from ab-initio calculations

Computational investigations, concerning structural, elastic, electronic, optical, and thermometric properties of the MgLu2X4 (X = S, Se) spinel compounds are performed. The calculations are carried out by employing the first-principles L(APW + lo) method designed within density functional theory (DFT). Our ground-state calculations are found to be consistent with experimental data wherever available. Similarly, calculations of the elastic constants demonstrate that both MgLu2S4 and MgLu2Se4 are brittle and anisotropic in nature. The dominant bonding between the atoms is found covalent and strongly favouring their mechanical stability. From the calculations of electronic band structure, both compounds are found direct bandgap semiconductors at Γ- Γ with bandgap energy of 3.119 eV for MgLu2S4 and 2.480 eV for MgLu2Se4. Our analysis of electronic and optical parameters suggest them suitable candidates for optoelectronic devices particularly from visible to extreme violet region applications whereas the calculated results of thermoelectric properties highlight their remarkable thermoelectric response for a workable range of temperature.

Theoretical investigation on bisarylselanylbenzo-2,1,3-selenadiazoles as potential photosensitizers in photodynamic therapy.

Density functional theory and time-dependent (TDDFT) calculations were carried out for recently reported bisarylselanylbenzo-2,1,3-selenadiazoles derivatives capable of producing singlet oxygen (1O2) under UV-Vis irradiation. Conformational behaviors, excitation energies, singlet-triplet energy gaps, and spin-orbit coupling constants were evaluated. The conformational analysis evidences that two different conformers have to be taken into consideration to completely describe the photophysical properties of this class of molecules. TDDFT results show that these compounds, though possessing absorption wavelengths that fall in the violet region, are characterized by singlet-triplet energy gaps greater than the energy required to excite the molecular oxygen, thus being able to produce the cytotoxic species, spin-orbit coupling constants large enough to ensure efficient singlet-triplet intersystem spin crossing, and even the highly reactive superoxide anion O2 •(-) by autoionization and subsequent electron transfer to molecular oxygen in its ground state.

Direct growth of tungsten disulfide on gallium nitride and the photovoltaic characteristics of the heterojunctions

Photovoltaic device construct with a 2D nanomaterial atop a 3D wide bandgap semiconductor enables van Hove singularity induced enhanced light absorption on the front surface in close proximity (few atoms above) to the depletion region. Here, thin layers of tungsten disulfide (WS2) varying from mono to few layers were grown directly on both n-gallium nitride (GaN) and p-GaN via low pressure chemical vapor deposition. The conditions for WS2 growth were optimized for a larger coverage of the GaN substrate. The WS2 film was characterized using confocal Raman spectroscopy and x-ray photoelectron spectroscopy. Ultraviolet photoelectron spectroscopy measurement was conducted to elucidate the electronic band structures of WS2 on top of GaN. Afterwards, WS2/GaN heterojunction photovoltaic devices were fabricated. The current density–voltage (J–V) tests were conducted to illustrate the electrical performance. The device showed an open circuit voltage of 0.53 mV and a short circuit current density of 60 µA cm−2, 85% higher than that of a WS2/Si solar cell. An external quantum efficiency was measured to be near 60% for red and infrared, and above 50% in the violet region.

Influence of xylenol orange dye on structural, vibrational, thermal and luminescence properties of TGS crystals

Dye can induce positive change in crystal. Pure and xylenol orange-dyed triglycine sulphate (TGS) large single crystals (> 14 cm2) were grown by solution technique in which dye inclusion pattern along preferred crystallographic planes were visible. Rietveld refinement was used to confirm monoclinic phase with space group P21 in XRD analyses. The crystallite size of both grown crystals were calculated by Scherrer method. In FTIR and Raman analyses, all the observed functional groups were explained. Thermal stability of dyed TGS crystal was increased. UV–Vis–NIR spectra showed that grown crystals were highly transparent with the lower cut off at 230 and 228 nm for pure and dyed crystals, respectively. The characteristics luminescence properties, including hyperluminescence and additional luminescence nature in dyed crystal, were explained. Pure TGS fell in violet region which shifted in blue region in CIE diagram after dyeing. Changes in PL, Raman, UV–Vis and thermal behavior due to dye doping established the TGS crystal as a better candidate for optical applications.

Asma Su Stresinin Hiperspektral Analizi

Viticulture is very sensitive to water stress, which is critical and influenced by all environmental factors, relating to the crop quality and productivity of vineyards. In this study, water stress was examined in veraison and harvest stages for nine different species with spectroradiometric measurements. Leaf water potential (LWP) values from field measurements and original spectra-based (OSB) and continuum removed spectra-based (CRSB) curves were analyzed with correlation and regression analysis to find the highest related wavelengths. The analysis was done for both specific dates of field measurements (i.e. 08.08.2012 and 06.09.2012) and also in aggregate i.e. all measured data. The specific date wavelength-based analysis revealed the “red edge region” as a major water stress indicator. The highest correlated wavelength was found to be 684 nm of CRSB curves with R=0.988. For the aggregate wavelength-based water stress analysis, the “violet and green regions” were identified as the best indicators. The highest correlated wavelength was found to be 410 nm of OSB curves with R=0.820. Furthermore, the Analysis of Variance (ANOVA) testing indicates that the results are significant at relatively high confidence levels. The spectral-based method performed in this study provides fast, flexible, and non-destructive water stress measurements of grapevines when compared to classical methods.

Sun light driven photocatalytic performance of Ag decorated TiO2 nanocomposite thin films by sol gel method

High performance, low cost photocatalysts are essential for water treatment applications. However the existing majority of the photocatalysts limited to Ultra violet and visible region only. Besides the fabrication of photocatalysts, there is a huge demand for low cost, recyclable and solar light trapping photocatalysts, thereby effectively remove the organic pollutants present in water. Here, we have synthesized the solar light active Ag loaded TiO2 nanocomposite thin films by sol gel method. X ray diffraction, scanning electron microscopy and UV–visible spectroscopy were applied to characterizing the product. The results show that we successfully synthesized the silver doped titanium dioxide thin films. The silver doped titanium dioxide thin films show red shift and broad absorption band in the whole UV visible region in comparison with bare titanium dioxide. The results show that the Ag-TiO2 nanocomposite exhibit best photocatalytic efficiency under direct sun-light irradiation due to increased electron transfer and charge separation. The photodegradation activities of the Ag doped TiO2 were studied with model organic pollutants. Ag doped TiO2 sample showed 98% degradation efficiency in just 70 min under sun light irradiation. Repeated cycle runs revealed that these catalysts exhibit reusability and excellent stability, able to trap solar light efficiently and suitable for degradation of many organic pollutants. The performances of the Ag-TiO2 nanocomposites indicate that, these catalysts can find potential applications in photocatalytic water treatment plants.

Illuminating the Inner Retina of Vertebrates: Multiple Opsins and Non-Visual Photoreceptors

Throughout evolution, the need to detect light has generated highly specialized photoreceptor cells that in vertebrates are mainly located in the retina. The most studied photodetectors within these cells are the visual photoreceptors “cones and rods” responsible for day and night vision, respectively. These cells contain photosensitive molecules consisting of a protein part called “opsin” that binds a chromophore derived from vitamin A, retinaldehyde, capable of photoisomerizing from 11-cis retinal to all-trans retinal form, and triggering the light responses that lead to vision. However, other cells of the inner retina of vertebrates [retinal ganglion cells (RGCs), horizontal cells (HCs), and Muller’s glial cells] are currently known to express non-visual photopigments such as melanopsin (Opn4), encephalopsin (Opn3) and neuropsin (Opn5), which would be involved in diverse functions not associated with imaging. Melanopsin is the most widely studied of them, it is expressed in intrinsically photosensitive RGCs (ipRGCs) and HCs of the chicken retina and participates in setting the biological clock, the pupillary light reflex, and presumably in other reflex and subconscious functions, in addition to the lateral interaction between visual photoreceptors and HCs. It is noteworthy that these non-visual photopigments (Opn3, Opn4 and Opn5) respond to blue and/or near violet region light. This particular photosensitivity may provide individuals with a broader spectrum of response to light stimulation within the visible beyond the scope of the visual photoreceptors, regulating an important number of functions not yet completely identified. We can conclude that “a constellation of cells and photoreceptor molecules are present in the inner retina of vertebrates, and from very early stages of development, even before any sign of vision may occur.”

2,5-Diaryl-1,3,4-oxadiazoles: synthesis, spectral-luminescent properties, and complexation with beryllium(ii)

Cyclization of aroylbenzohydrazides in SOCl2 was used to obtain 2,5-diaryl-1,3,4-oxadiazoles, and to study their spectral-luminescent properties. Oxadiazoles with phenyl or 2-methoxyphenyl substituents at position 2 of the oxadiazole ring have a luminescence with a high quantum yield in polar and nonpolar solvents (λflmax = 378−424 nm, φ = 0.88−0.98). Replacement of these groups with a 2-phenol substituent results in a ligand with strong emission only in highly polar aprotic DMSO (λflmax = 397 nm, φ = 0.18). Based on this ligand, a chelated beryllium complex with the composition L2Be was obtained, which has a strong luminescence in the violet region of the visible spectrum (λflmax = 410−414 nm, φ = 0.34−0.48).

Electro-Optical Properties of AZO Thin Films with Deposition & Heat treatment Conditions

AZO thin films are grown on a p-Si(111) substrate by RF magnetron sputtering. The characteristics of various thicknesses and heat treatment conditions are investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Hall effect and room-temperature photoluminescence (PL) measurements. The substrate temperature and the RF power during growth are kept constant at 400 ℃ and 200 W, respectively. AZO films are grown with a preferred orientation along the c-axis. As the thickness and the heat treatment temperature increases, the length of the c-axis decreases as Al3+ ions of relatively small ion radius are substituted for Zn2+ ions. At room temperature, the PL spectrum is separated into an NBE emission peak around 3.2 eV and a violet regions peak around 2.95 eV with increasing thickness, and the PL emission peak of 300 nm is red-shifted with increasing annealing temperature. In the XPS measurement, the peak intensity of Al2p and Oll increases with increasing annealing temperature. The AZO thin film of 100 nm thickness shows values of 6.5 × 1019 cm−3 of carrier concentration, 8.4 cm−2/V·s of mobility and 1.2 × 10−2 Ω·cm electrical resistivity. As the thickness of the thin film increases, the carrier concentration and the mobility increase, resulting in the decrease of resistivity. With the carrier concentration, mobility decreases when the heat treatment temperature increases more than 500 ℃.

Genetic variability of the sws1 cone opsin gene among New World monkeys.

Vision is a major sense for Primates and the ability to perceive colors has great importance for the species ecology and behavior. Visual processing begins with the activation of the visual opsins in the retina, and the spectral absorption peaks are highly variable among species. In most Primates, LWS/MWS opsins are responsible for sensitivity to long/middle wavelengths within the visible light spectrum, and SWS1 opsins provide sensitivity to short wavelengths, in the violet region of the spectrum. In this study, we aimed to investigate the genetic variation on the sws1 opsin gene of New World monkeys (NWM) and search for amino acid substitutions that might be associated with the different color vision phenotypes described for a few species. We sequenced the exon 1 of the sws1 opsin gene of seven species from the families Callitrichidae, Cebidae, and Atelidae, and searched for variation at the spectral tuning sites 46, 49, 52, 86, 90, 93, 114, 116, and 118. Among the known spectral tuning sites, only residue 114 was variable. To investigate whether other residues have a functional role in the SWS1 absorption peak, we performed computational modeling of wild-type SWS1 and mutants A50I and A50V, found naturally among the species investigated. Although in silico analysis did not show any visible effect caused by these substitutions, it is possible that interactions of residue 50 with other sites might have some effect in the spectral shifts in the order of ~14 nm, found among the NWM. We also performed phylogenetic reconstruction of the sws1 gene, which partially recovered the species phylogeny. Further studies will be important to uncover the mutations responsible for the phenotypic variability of the SWS1 of NWM, and how spectral tuning may be associated with specific ecological features such as preferred food items and habitat use.

Effects in Band Gap for Photocatalysis in TiO2 Support by Adding Gold and Ruthenium

One of the key features of a nano catalyst for photocatalysis is the band gap, because, through its analysis, the potential of the catalyst can be determined. In this investigation, the impact on the band gap of different catalysts made by the sol–gel method, compared with TiO2 P25 Sigma-Aldrich, showing the effect of using gold or ruthenium as a metal supported on TiO2, with two different dosage percentages of 1 and 3 percent, was analysed. Additionally, two oxidation states of the catalyst, the reduced form and the oxidized form of the metal, were used to see the effect on the band gap. The experiments show that the gold addition has a higher beneficial effect on the band gap for the UV region (ultra violet region), and the ruthenium addition has a higher beneficial effect for the UV/visible region. The preferred oxidation state for the band gap was the oxidized state. The characterisation of the catalyst provided an insight into the relation between the band gap and the catalyst itself.

Prediction of a new 2D B2CO monolayer from density functional theory

In this study, a novel two-dimensional (2D) B2CO monolayer is theoretically predicted. According to our results 2D B2CO monolayer indicates significant structural, energetically and kinetically stabilities. These stabilities are confirmed by calculating its cohesive energy and phonon dispersion spectra. It is found that fully relaxed and optimized unit cell of the predicted monolayer possesses a buckled hexagonal crystal structure (space group: 156_P3m1) and is an indirect semiconductor with a band gap of 1.69 eV (2.81 eV) calculated by DFT-PBE (HSE06) level of theory. We further examined the effects of biaxial strains on the electronic properties of the monolayer and found its electronic properties can be effectively modulated by external strain effects. The optical aspects of the monolayer and found that proposed 2D material were also investigated. It has been shown that the monolayer shows very low absorption in visible region of electromagnetic spectra while it exhibits high absorption and reflection characters in UV region. These obtained results propose that the monolayer can be considered as a transparent material for the visible lights and a useful shielding material in ultra violet region.

The unique UV–Vis reflection features of the nacre of Hyriopsis cumingii shells, and its formation mechanisms

UV–Vis reflectance spectroscopy, combined with field emission scanning electron microscope (FE-SEM), was used to comparatively characterize nacre areas with milky-white and pink-violet coloration from the same Hyriopsis cumingii shell. Although the mean thicknesses of the aragonite platelets in the nacre from the pink-violet area were similar, the reflection spectra obtained from different locations within this area were not uniform. This indicated that the vivid color appearing on the inner surface of the shell was not completely derived from the one-dimensional photonic structure. We proposed that the absorption peak in the ultraviolet region was associated with carotenoids. The strength of the absorption peak increased with carotenoid concentration. The inner surface of the shell was not flat, leading to obvious frequency shifting in the reflection peak of the violet region. More importantly, our findings suggested that the vivid color of the inner surface of the shell was caused by the combined effects of organic pigment and one-dimensional photonic band. This present study advances our understanding of coloration mechanisms. Furthermore, we expect that our work may provide basis for further studies of pearl culture or quality grading and might inform further investigations of the design and synthesis of advanced functional materials for optical, biomedical, and mechanical applications.