Blue-violet Region Research Articles

Effect of Lead:Halide Precursor Ratio on the Photoluminescence and Carrier Dynamics of Violet- and Blue-Emitting Lead Halide Perovskite Nanocrystals

Highly luminescent cesium lead halide (CsPbX3, X = Cl, Br, I) perovskite nanocrystals (NCs) are promising materials for a number of optoelectronic applications like LEDs and other display technologies. However, low photoluminescence (PL) quantum yield (QY) of the large-bandgap violet- and blue-emitting CsPbCl3 and CsPb(Cl/Br)3 NCs is an obstacle to the development of blue- and white-emitting LEDs. In this work, we show that these NCs with high PLQY can be obtained directly by employing an appropriate halide precursor and by optimizing the Pb:X precursor ratio. Specifically, employing N-chloro- and N-bromophthalimides as halide precursors and varying the Pb:X precursor ratio, we have obtained stable and highly luminescent (PLQY 80–99%) perovskite NCs emitting in the blue-violet region extending to green by direct synthesis. Time-resolved PL and ultrafast pump–probe studies of these systems reveal the effect of Pb:X precursor ratio on the carrier recombination processes. Rapid carrier trapping is found to be the dominant process that impairs the PLQY of the NCs obtained by using a stoichiometric (1:3) Pb:X precursor ratio. This trapping of carriers is effectively alleviated by using an excess amount of the halide precursor during the preparation of the NCs. The results brighten the potential utility of these high-quality perovskite NCs emitting in the blue-violet region in optical applications.

Influence of Pr3+ and CO32− Ions Coupled Substitution on Structural, Optical and Antibacterial Properties of Fluorapatite Nanopowders Obtained by Precipitation

Coupled substitution of fluorapatite (FAP) crystal lattice plays an important role in the engineering of optically active nanomaterials. Uniform fluorapatite nanopowders doped with praseodymium (Pr3+) and carbonate (CO32−) ions have been successfully synthesized by precipitation method under room temperature (25 °C). The structural, morphological, chemical and optical properties of monophase material were characterized by X-ray diffraction (XRD), Fourier Transform Infrared and Far Infrared Spectroscopy (FTIR and FIR, respectively), Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM/EDS), Transmission Electron Microscopy (TEM) and Photoluminescence Spectroscopy (PL). Coupled substitution of FAP crystal lattice with Pr3+ and CO32− reduces the crystallite size with a constant c/a ratio of 1.72. FTIR study showed that synthesized nanopowders were AB-type CO32− substitution, and FIR study revealed new Pr–O vibrations. TEM analysis was found that synthesized nanopowders were composed of irregular spheres in the nanometer range. The fluorescence of FAP nanoparticles was in the violet-blue region of the visible part of the spectrum. When Pr3+ was doped in a lattice, the violet-blue emission becomes sharper due to reabsorption. MCR–ALS analyses of fluorescence spectra indicated the shift of the maximum to the blue color with the increase in the concentration of Pr3+ ions. Additionally, luminescent nanopowders demonstrated significant antibacterial activity against Escherichia coli. As the obtained nanoparticles showed a good absorption of ultraviolet A light and reabsorption of blue-green luminescence, they are suitable for further development of optically active nanomaterials for light filtering. Optically active PrCFAP nanopowders with antibacterial properties may be promising additives for the development of multifunctional cosmetic and health care products.

Synthesis, structure, and photoluminescence of Zn(II) and Cd(II) complexes with N-[2-(diethylaminoalkyliminomethyl)-phenyl]-4-methylbenzenesulfonamides

Zn(II) and Cd(II) complexes based on N-[2-(diethylaminoalkyliminomethyl)-phenyl]-4-methylbenzenesulfonamide (HL) of composition ML2 and MHLCl2 were synthesized. The structures of the complexes were established by elemental analysis, IR, 1H NMR, UV spectroscopy, X-ray absorption spectroscopy (EXAFS), and X-ray crystallography. The complexes demonstrate photoluminescent properties in the blue-violet region of the spectrum with the maxima of the PL bands at 426–448 nm and quantum yields of 0.2–0.34.

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.”

Thermal and hydrothermal synthesis of WO3 nanostructure and its optical and photocatalytic properties for the degradation of Cephalexin and Nizatidine in aqueous solution

Pharmaceuticals have recently become a serious environmental concern due to the increase in the human population, industrial development and modern lifestyles. The optical property and photocatalytic degradation of Cephalexin and Nizatidine were investigated using nanostructured WO3 under visible photon irradiation. The WO3 nanostructures were synthesised through direct heating and hydrothermal method using WCl6 as a precursor for tungsten. The prepared WO3 was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS) analysis and Photoluminescence analysis (PL). The optical properties were investigated by UV–vis DRS and PL were WO3 nanostructures exhibited band gaps from 2.60 to 2.70 eV and an emission covering the blue-violet region. The photocatalytic activity studies revealed that the prepared WO3 exhibit good photocatalytic performance, degrading the aqueous pharmaceutical solutions of Cephalexin and Nizatidine under visible light illumination.

Influence of hydrothermal reaction time on crystal qualities and photoluminescence properties of β-Ga2O3 nanorods

The β-Ga2O3 nanorods were synthesized by the hydrothermal method, which were characterized in detail so as to explore the effects of the hydrothermal time on their final morphologies and photoluminescence properties. The X-ray diffraction pattern indicates that the synthesized GaOOH precursor is completely converted into the monoclinic β-Ga2O3 phase. The microscopic analysis shows that the single crystal β-Ga2O3 samples are of a slender shape, i.e., nanorods and microrods. The main element composition and their valence states were detected by X-ray photoelectron spectroscopy, whose result is consistent with that of XRD. The Raman spectrum for the sample obtained at the hydrothermal time of 10 h has the highest intensity and narrowest full width at half-maximum that indicates the highest crystallinity. The photoluminescence spectra show that the emission peaks of the three samples appear in the blue-violet region between 375 and 425 nm, which are greatly affected by the hydrothermal time.

Hydrothermal Preparation, Crystal Structure, Photoluminescence and UV-Visible Diffuse Reflectance Spectroscopic Properties of a Novel Mononuclear Zinc Complex

A novel mononuclear zinc complex [ZnL(Phen)(H2O)]·H2O containing the mixed ligands of Phen (Phen = 1,10-phenanthroline) and 3-hydroxy-2-methylquinoline-4-carboxylic acid (HL) was prepared by hydrothermal synthesis and its crystal structure was characterized by X-ray single-crystal diffraction method. The title complex crystallizes in the orthorhombic systems and forms monomeric units. The molecules in the title complex are connected through the interactions of hydrogen-bonding and ????? interactions to give a three-dimensional (3D) supramolecular structure. The fluorescence result discovers a wide emission band in the violet blue region. Time-dependent density functional theory (TDDFT) calculations reveal that this emission can be attributed to ligand-to-ligand charge transfer (LLCT). Solid-state diffuse reflectance shows there is a wide optical band gap.

Carbon Nanoparticles. Production, properties, perspectives of use

The paper is devoted to the study of the optical properties of carbon nanoparticles synthesized by the method developed during our experimental studies. The optimal conditions for the creation of carbon nanostructures with predetermined properties are defined. Nanoparticles of the size of about 100 nm were obtained, the maximum of absorption of which is localized at wavelengths in the violet-blue region of the spectrum, while the maximum of luminescence – in the green region of the spectrum. The assumption is made about the possibility of using the obtained particles for correlation diagnostics of optical speckle fields.

Fundamental Research on Electronic Image Recognition of Cylindrical Zno Nanorods Based on Deep Learning

ZnO is recognized as one of the most important photonic materials in the blue-violet region due to its straight-width band gap and large excitation bonding energy. Since ZnO nanorod array performs superior optical and field emission properties, a lot of efforts have been made in the fabrication of a vertically ordered ZnO nanorod array. The shape and size of ZnO nanorods have a significant effect on PEC property. In order to efficiently recognize and measure the shape and size of ZnO nanorods, a new method based on deep learning model mask r-cnn is proposed to detect cylindrical ZnO nanorods. The SEM images of ZnO nanorods were used as a data set for training. Adjust the size of the bounding boxes that model generated to make it more suitable for the data set. At the same time, improve the NMS (non-maximum suppression) algorithm to reduce the missing detection rate, and achieve a good detection effect on the SEM images of ZnO nanorods.

The Effects of Pheophytin a on Absorption Properties of Phytoplankton in Dalian Bay, China

We examined the effects of pheophytin a (Phe-a) on absorption properties of phytoplankton obtained from the red tide prone area of Dalian Bay in the North Yellow Sea, China, in June 2007 and July 2011. When the proportion of Phe-a relative to chlorophyll-a (Chl-a) increased, the absorption peak in the blue-violet region shifted from 438nm to 409nm. The relationship between blue-violet absorption maximum and Phe-a concentration is more tightly correlated than the relationship between blue-violet absorption maximum and Chl-a concentration. However, we found the opposite results for the red absorption maximum. These findings suggest that Phe-a mainly effects the blue-violet absorption maximum, while Chl-a primarily controls the red absorption maximum. Our results are determined by specific absorption coefficients of Phe-a and Chl-a in living algae cells. A multivariate linear regression analysis revealed that the specific absorption coefficients of Phe-a accounts for the absorption peaks at 407 nm and 673 nm, and specific absorption coefficient of Chl-a accounts for the absorption peaks at 440 and 673 nm, furthermore, the specific absorption coefficients of Phe-a are much larger than those of Chl-a in the blue-violet region, but they are lower in the red region.

Preparation and luminescent properties of zinc sulfoselenide thin films

The preparation of zinc sulfoselenide heterolayers is considered. The possibility of obtaining a hexagonal modification of the crystal lattice by the method of isovalent substitution was shown. The λ-modulated optical reflection was studied and the parameters of the energy structure of α-ZnSe, α-ZnS, α-ZnS0.45Se0.55 were determined. It has been established that the obtained heterolayers are characterized by intense photoluminescence with a quantum yield η = 8–12% in the blue-violet region. It is formed by constituent bands, the nature of which is determined by the annihilation of bound excitons and interband transitions of free charge carriers. It is shown that the selection of temperature regimes allows obtaining radiation with ħωm maxima in the violet 2.80 eV, blue 2.70 eV and green 2.45 eV spectral regions. It is determined by the generation-recombination transitions involving donor and acceptor states formed by intrinsic point defects of the crystalline lattice , і Zni, respectively. The models of radiative recombination are discussed.

Application of Satellite Image Processing Methods for Hydrocarbon Field Search

The object of the study is software methods of the Earth surface images processing obtained from the VRSS-2 satellite to determine the spectral composition of the vegetation cover to detect the presence of carotenoids during prolonged exposure to hydrocarbons.The photosynthetic pigments of higher plants (chlorophylls, carotenoids and phytobiliproteins) were analyzed. In the chloroplasts of higher plants, chlorophyll and carotenoids are present in a ratio of about 3:1. The presence of hydrocarbons increases the amount of carotenoids. Carotenoids have absorption bands in the blue-violet region from 400 to 500 nm and a high reflection coefficient in the red-orange and yellow spectral regions, which corresponds to the multispectral MSS operating mode (B2) of the VRSS-2 satellite camera. An analysis of the vegetation growing in the study area of the Puerto Kumarebo settlement showed that the best indicator of the presence of hydrocarbons in the soil is Prosopis juliflora – CUJI with a deep root system of up to 50 m, growing in the study area.Using ENVI software, a comparative evaluation of the efficiency of photographs image processing was carried out using the normalized relative vegetation index (NDVI) and the structure-insensitive pigment index (SIPI) to detect changes in the color of green vegetation. It has been established that the SIPI index is more applicable for hydrocarbon search tasks. Moreover, the recorded index fluctuations in the area of uniform vegetation at the level of 2.5 % are characteristic of normal growing conditions and cannot serve as evidence of the presence of factors indicating the presence of hydrocarbons in the soil. For a more detailed assessment of the presence of carotenoids in the foliage and the presence of hydrocarbons in the soil, photographs with high optical resolution of objects on the surface are required.

Cyanobacterial Secondary Metabolite Scytonemin: A Potential Photoprotective and Pharmaceutical Compound

Scytonemin is a lipid-soluble, highly stable, yellow–brown-coloured secondary metabolite that is accumulated in the extracellular polysaccharide sheath of several but not all members of cyanobacteria. Chemically, scytonemin is an indole alkaloid composed of two heterocyclic units symmetrically connected through a carbon–carbon bond. Thus, scytonemin is unique among natural products due to its special structure, location in a cell, as well as strong absorption maxima in UV-A in addition to the violet–blue region. Traditionally, scytonemin is a well-established photoprotective compound against ultraviolet radiation. Its accumulation in the cyanobacterial sheath has been suggested to be a strategy adopted by several cyanobacteria to protect their cellular components against damaging effects of UVR. Additionally, recent studies have also established the importance of scytonemin in reactive oxygen species scavenging as well as in controlling the growth of cancerous cells. Thus, scytonemin is both ecologically as well as pharmaceutically important metabolite. Recent developments made in the biochemistry and genetics of this compound have paved the way for its application and commercialization for human welfare. This review aims to present a brief history of the compound with chronological developments made in the study of scytonemin and emphasizes its physiochemistry, analytical chemistry, biochemistry, and genetics. We provide a separate section for metabolic engineering and potential applications of scytonemin, mainly as sunscreen and anti-cancerous drugs. We also discuss the future research directions which need to be worked out.

Proton Beam Induced Modification of Luminescence Properties of Polystyrene/Al2O3 Polymer Nanocomposites.

Polystyrene polymer (PS)/Al2O3 nanocomposite films were synthesized from PS:Al2O3 (1-x):x mixtures (x = 3wt%) via solution casting method. These nanocomposite films were exposed to 5MeV proton beam of different fluences. The proton beam induced changes in optical and luminescence properties of PS and PS:Al2O3 films have been investigated using FTIR, UV-visible, Photoluminescence and thermoluminescence studies. FTIR studies concede reduction in the peak intensity due to doping of Al2O3 and proton irradiation. The UV-visible spectra show shifting of absorption edge with increasing fluence. This can be attributed to creation of conjugated system of bonds. The band gap of PS and 3wt% Al2O3 doped PS is observed to be 4.38eV and 4.34eV, respectively, whereas the band gaps of proton irradiated 3wt% Al2O3 doped PS films are found to be 4.28eV and 4.23eV at the fluences of 1 × 1012 ions/cm2 and 1 × 1013 ions/cm2, respectively. The photoluminescence emission spectra show three peaks, wavelength at 411nm, 435nm and 462nm corresponding to the PS in violet-blue region when excited with near UV wavelength of 380nm. The intensity of emission peaks was found to increase with increasing fluence. The thermoluminescence curves of PS/Al2O3 were analysed using glow curve deconvolution method (GCD). The increase in TL peak intensity of the glow curve was observed as fluence increase.

Creation and application of fluoropolymer photoconversion films for greenhouses: Concept.

The purpose of this investigation is to create a scientific basis and technology of the production of fluoropolymer photoconversion films for greenhouses to improve the performance of greenhouses in the area of risk farming. The aim basis of photoconversion technology in greenhouses is reduced to photoconversion of UV radiation into blue-violet, and green and yellow light into red light necessary for plants. In other words, when sunlight passes through fluoropolymer photoconversion films, the intensity of the blue-violet and red regions of the spectrum should increase, and the intensity of the UV, green and yellow regions of the spectrum should drop. The article presents the manufacturing technology of fluoropolymer photoconversion films and examples of its use in greenhouses.

Blue emitting Ce3+-doped CaYAl3O7 phosphors prepared by combustion route

The solution-combustion route was used to synthesize series of Ce3+-ion-activated CaYAl3O7 (CYO) blue-light-emitting phosphors. Formation of the tetragonal CYO structure was confirmed by the powder X-ray diffraction (XRD) studies. On substitution of Ce3+ ion to Ca site in CaYAl3O7 system, the photoluminescence spectra recorded at ultraviolet-light (360 nm) excitation. Photoluminescence excitation spectra at 360 nm showed the characteristic emission at 434 nm of the Ce3+ ion caused by 5d → 4f transitions. Increase in intensity can be seen up to 1 mol % of Ce3+ followed by quenching due to dipole-dipole interaction. The Commission Internationale de l’Eclairage (CIE - 1931) coordinates x = 0.1484 and y = 0.0987 of this phosphor are in the violet–blue region. The blue-color purity was found to be maximum 90% for 1 mol% Ce3+-doped phosphor. The obtained CIE, CCT, and color-purity results illustrate the potentiality of Ce3+-activated CYO phosphor for household-lighting and display-device applications.

A near-ultraviolet (NUV) converting blue-violet Mg2SiO4:Ce3+ phosphor for white light-emitting-diodes (w-LEDs)

Ce3+-doped silicate phosphors (Mg2-xSiO4:xCe3+, x = 0.001–0.007 mol) for NUV w-LEDs have been synthesized by solid-state reaction method at 1450°C. The as-prepared samples have been characterized by XRD and fluorescence spectrophotometer, respectively. The XRD results show that the aim phase has been synthesized and doping Ce3+ has not resulted in impurity phase. This phosphor material exhibits a strong blue-violet emission (330–520 nm) under the near-ultraviolet radiation excitation. The average colorimetric coordinate of Mg2-xSiO4:xCe3+ (x = 0.0025 mol) is (0.1508, 0.0694), locating in blue-violet region. We have obtained bright blue-violet light via pumping the sample by NUV light (λ ≈ 365 nm), suggesting that this material can be potential as a NUV converting blue-violet phosphor for the NUV w-LEDs.

Band gap tuning in nanocrystalline SrTi0.9Fe0.1O2.968 perovskite type for photocatalytic and photovoltaic applications

In the present work and for the first time, tuning of the band gap width of the SrTiO3 (STO) perovskite to a value suitable for photocatalytic (PC) and photovoltaic (PV) applications is accomplished by the incorporation of Fe cation. Nanocrystalline SrTi0.9Fe0.1O2.968 (STFO) was prepared by a modified solid state reaction process including successive sequences of milling and calcinations at high temperature. The X-ray diffraction (XRD) pattern revealed the formation of a single cubic perovskite phase of STFO with average crystallite size equaling ⁓30 nm. The local lattice strain on (h00) and (hh0) planes was found to decrease by Fe doping. The absorption spectrum deduced from diffused reflectance showed high intense broad structure extending over the range ⁓0.5 – ⁓6 eV, whereas pure STO gave strong absorption only at the UV region (λ < 400 nm). The deduced band gap width of the STFO sample was 1.43 eV; an ideal value for PC and PV applications. Deconvolution of the broad absorption band revealed the presence of four absorption structures attributed to Fe defect centers. The narrowing of the band gap was also confirmed through the photoluminescence study where many emission lines covering the violet-blue region were detected. The type of the Fe species and the relative abundance of Fe3+ and Fe4+ were determined by Mössbauer spectroscopy. The presence of oxygen vacancies and Fe-OV complexes were also supposed as lattice defects located above the O2p and below the Ti-3dt2g states. The novel electronic structure researched in this study offers a new avenue in the field of band gap engineering for future application in the field of photocatalytic materials.

Neutron irradiation of flint glasses for optics in ITER

Radiation-resistant optics, which is necessary to transfer light from plasma to detectors in ITER, will be exposed to neutron fluxes at D-T stage. Achromatic lenses located in the interspace and in the port cell areas must have a sufficient optical radiation hardness to sustain a neutron irradiation without significant degradation of transmittance in as wide spectral range as possible. They will be made of two types of glass: KU1 fused silica and a flint glass. The radiation hardness of the candidate flint glasses under neutron irradiation to ITER-relevant doses has to be investigated.Six types of the commercial Ce-doped flint glasses have been irradiated in a nuclear reactor up to fluencies of the fast neutrons (E > 0.1 MeV) within the range of 1012 − 1016 n/cm2. F108 and TF200 types have demonstrated the most prominent results. F108 type has a high transmittance in the visible region and a sufficient radiation hardness to be recommended for use in the port cell. TF200 type has a limited spectral range, but it has shown the best radiation hardness at a fluence of 1016 n/cm2. It can be used in the interspace area if a low transmittance in the violet-blue region is not an issue.

Ultra-highly fluorescentN doped carbon dots-CdTe QDs nanohybrids with excitation-independent emission in the blue-violet region.

Luminescent carbon dots (CDs) are of significant practical application interest such as in optoelectronic devices and sensitive probing in the life science and environment fields. In this study, N doped CDs-CdTe quantum dots (QDs) nanohybrids (CdTe/N-CDs) were synthesized by a plasma heating process using silk fibroin and CdTe QDs as precursors. The synthesis, doping, hybridizing and passivation of the CdTe/N-CDs were carried out in a single-step process. The as-synthesized CdTe/N-CDs dispersed in ethanol exhibited blue-violet photoluminescence with excitation-independent emission characteristics (strong emissions at 405 nm and 429 nm, and a weak emission at 456 nm). Additionally, the optimal excitation wavelength for the CdTe/N-CDs was found at 360–380 nm, which very closely matches the intrinsic wavelength of GaN-based LEDs. Furthermore, the obtained CdTe/N-CDs exhibited a very high quantum yield of ∼84%, showing great potential in developing chip-based high performance optoelectronics devices. The emission mechanism and emission enhancement by related factors including N-bonded configurations in the carbon base and the transfer of photo-excited electrons from the CdTe QDs to the N doped CDs were studied, as well.