Violet Region Research Articles

Synthesis of 2,4-Diamino-6-arylpyridine-3,5-dicarbonitriles and Study of Their Optical Properties

2,4-Diamino-6-arylpyridine-3,5-dicarbonitriles were synthesized by the nucleophilic substitution of bromine in 4-amino-2-bromo-6-arylpyridine-3,5-dicarbonitriles. The optical properties of the synthesized compounds were studied to show that they fluoresce in solution and in the solid state in the violet region of the spectrum.

Lead-free violet-emitting K2CuCl3 single crystal with high photoluminescence quantum yield

Abstract Lead halide perovskites have attracted great attention on their promising luminescent properties. However, their practical use is hampered by the toxicity of Pb, and also the photoluminescence efficiency in violet region is much lower than green and red emitters. Herein, a new copper (I) halide with nontoxicity and efficient violet emission was synthesized and characterized. The major emission peak locates at 386 nm, the photoluminescence quantum yield reaches 98.8%, and the Stokes shift is as high as 1.15 eV K2CuCl3 crystal consists of one dimensional [CuCl4]3- tetrahedral ribbons, which are isolated by K+ ions. The one dimensional crystal structure and the formation of self-trapped excitons, benefit the large thermal activation energy of 1090 meV, which contributes to the observed efficient emission.

Mn-doped Cu3Se2 nanosheets: Impact of physical characteristics on the photovoltaic performance

The un- and manganese (Mn)-doped Cu3Se2 nanosheets were prepared by the electrodeposition method. X-ray diffraction (XRD) patterns revealed that polycrystalline Cu3Se2 nanostructures were at the tetragonal phase. Field emission scanning electron microscopy (FESEM) images showed that all samples had a sheet-like structure. The photoluminescence (PL) spectra showed that the un- and Mn-doped Cu3Se2 nanosheets had three emission bands in violet, green, and red regions. The absorption spectra also demonstrated that the band gap energy of the Mn-doped samples was increased relative to the un-doped sample. Solar cell evaluation showed that addition of Mn dopant was effective on increasing the solar cell efficiency. Further investigations indicated that these changes were close to different physical properties such as increase in the surface-to-volume ratio, absorption intensity, and carrier concentration with the lowest value of strain.

Dielectric and optical properties of Ln0.8Lu0.2TiNbO6 (Ln = Ce, Pr, Nd & Sm) ceramics

Ln0.8Lu0.2TiNbO6 (Ln = Ce, Pr, Nd & Sm) are synthesized through conventional solid state ceramic route. The XRD, FT Raman and FT IR studies revealed that the samples have aeschynite orthorhombic symmetry. The samples are sintered at 1230 ∘C. Using SEM technique, microstructure of the sintered samples is analyzed. The dielectric properties of all the samples in the radio as well as microwave frequencies are studied. UV spectra of the samples are recorded and the optical band gap is estimated from the Tauc's plots. The samples are found to be photoluminescent materials with emissions at violet and green regions.

Investigation of electronic and optical properties of novel graphene-like GeS2 monolayer by density function theory

Electronic and optical properties of pentagonal GeS2 monolayer are investigated by first principles calculations in the framework of the density functional theory. The stability of the nanostructure is confirmed by cohesive energy calculation, as well as phonon dispersion calculation. The electronic properties simulation indicates that GeS2 monolayer is an indirect band gap semiconductor with a band gap of about 0.9 eV. Furthermore, the optical properties investigation reveals that the material exhibits a very low absorption and reflectivity in visible region of the electromagnetic spectrum. However, it has a considerable absorption and reflectivity in the ultra violet region. The results of this study, therefore, suggest that the considered structure has a good potential application in the new generation of opto-electronic devices, especially as a UV protection layer.

Tuning of metal oxides photocatalytic performance using Ag nanoparticles integration

Water contamination is increasingly an important issue in developing and under developed countries. The main cause of water contaminations are industrial dyes and toxic chemicals. Hence many technologies are being developed to de-contaminate the toxic materials. The photocatalytic de-contamination of dyes is an effective and simple technology to purify water. Among various photocatalysts, the transition metal based oxides (TiO2, NiO and ZnO) being the state-of art photocatalytic material. But, the metal oxides have large band gap and suffers from the fact that it predominantly absorbs the Ultra Violet region of irradiation. But, any viable photocatalytic technology demands absorption in the visible light region, so as to utilize the cost-free sun light. Herein, we tune and utilize the metal oxides through the integration of Ag metal nanoparticles. The synthesized materials were completely analyzed by PXRD, HRTEM, UV, XPS and BET instruments. All TiO2/Ag, NiO/Ag and ZnO/Ag nanocomposites were subjected to photocatalytic degradation using visible light. The nanocomposites acted as photocatalyst and degrade the colorful methyl orange and colorless toxic 4-chlorophenol. Among the aforementioned three samples, TiO2/Ag exhibited best performance than ZnO/Ag and NiO/Ag. We attributed the enhancement of photocatalytic activity due to Plasmons assistance and nanoscale regime of photocatalyst. In summary, we tuned the metal oxide photocatalytic performance using the Ag nanoparticle surface Plasmon resonance.

Highly-increased photoluminescence of Pr3+ due to the Eu2+→ Pr3+ energy transfer in Al2O3 coatings formed by plasma electrolytic oxidation

In this paper, photoluminescence (PL) properties of Pr3+ single doped and Pr3+/Eu2+ co-doped Al2O3 coatings formed by plasma electrolytic oxidation of aluminum were investigated. The PL spectra of Al2O3:Pr3+ coatings feature bands ascribed to 4f-4f transitions of Pr3+. PL excitation spectra contain three broad bands in the violet and blue regions which correspond to the direct excitation of the Pr3+ ground state 3H4 into higher levels 3PJ (J = 0, 1, 2), while PL emission spectra contain several bands attributed to transitions of Pr3+ from excited levels 3P0 and 3P1 to the lower multiplets 3HJ (J = 4, 5, 6) and 3FJ (J = 2, 3, 4). Among these transitions, 3P0→3F2 transition in the red region (644 nm) is the most intense. PL emission intensity of Pr3+ increases by co-doping Eu2+ into Al2O3:Pr3+ coatings due to the energy transfer from Eu2+ to Pr3+, occurring due to the overlap between PL emission spectra of Eu2+, excited by middle ultraviolet radiation, and PL excitation spectra of Pr3+ in Al2O3 host. Under middle ultraviolet excitation, 3P0→3F2 transition of Pr3+ in Al2O3:Pr3+/Eu2+ coatings is 62 times more intense than without co-doping and 16 times if comparison is made with Al2O3:Pr3+ excited by 446 nm. The total luminescence intensity of Al2O3 co-doped with Pr3+/Eu2+ and doped with Pr3+ is 3.6 times more intense of the former if both samples are excited by 446 nm. The gains are linearly increasing with Eu2+ doping concentration. Al2O3:Pr3+/Eu2+ poses as an alternative phosphor to YAG:Ce3+ for the creation of neutral white LEDs by excitation with InGaN semiconductors.

Effective synthesis of green nano‐sized ceramic pigments by co‐doping Zn2+, Cr3+ and Sm3+ into the cobalt‐aluminate

AbstractA green nano‐sized ceramic pigment Co0.6Zn0.4Al0.8Cr1.2‐xSmxO4 has been successfully prepared by doping ions Zn2+, Cr3+, and Sm3+ into the crystalline CoAl2O4 spinel and using the complex‐gel method along with agar as complexing and combustion agent. The Infrared Spectroscopy, X‐ray diffraction, Thermo‐gravimeter, High resolution transmission electron microscopy, Automatic color reader, and UV Vis diffuse reflectance were applied to characterize the pigment power and its gel precursor. The results reveal that the introduction of Zn2+, Cr3+, and Sm3+ could change the occupation status of ions in the tetrahedral and octahedral framework of CoAl2O4 spinel, leading to the colorant variation of the blue cobalt pigment CoAl2O4, With increasing the content of Sm3+ ion, the reflection peak position of the pigments in visible spectrum appeared a red‐shift, ie the color transition from blue green to yellow green, and the average reflectivity in the violet region decreased to 13.31%, and the band gap energy also changed from 3.47 to 3.20 eV. This illustrates the better UV absorption of this green pigment and can be used as UV shielding material. With the hydrochloric acid or sodium hydroxide solution treatment, this pigment was found to be durable in chemical stability.

Long‐Standing Optically Excited Magnetic States in ZnO Nanoparticles

The spectral dependence of the light‐induced magnetic states generated in zinc oxide nanoparticles by illumination during an electron paramagnetic resonance (EPR) experiment is studied for three incident light wavelengths (451, 405, and 370 nm). The minimal wavelength excitation is found to be in the visible violet region, very close to 405 nm for all of the light‐induced EPR lines. This points to a close relationship between their originating centers, despite the difference in their dynamics previously revealed by saturation recovery measurements. The study of the light‐induced signals decay with time (after illumination removal) and with temperature (under constant illumination) confirms the existence of two groups of lines characterized by different dynamics. The quite unusual persistence of these magnetic states after excitation removal opens promising possibilities for encoding information within semiconducting nanoparticles.

Nanosized Titania-Nickel mixed oxide for visible light photocatalytic activity

Colourful dyes are primarily used in the textiles, toys, food, inks, paper and plastics. These dyes are water soluble and contaminate the water. The dyes are not bio-degradable and sustain in the water for long time create diseases like bladder tumour and chromosomal damage. Hence dyes are the major cause of pollution and must be removed from domestic and drinking water. The photocatalysts are energy-less technology for dye degradation and expected to solve clean water problems. Most of the photocatalysts are metal oxides and absorbed in the ultra violet region. But, sun light mostly consists of visible light, hence to use the sunlight effectively the absorption spectrum of the photocatalysts must be tuned to the visible region. Herein, we proposed visible light absorbed new TiO2/NiO nanocomposite for methyl orange dye degradation. The integration of NiO modified the TiO2 nanocomposite UV absorption spectrum into visible light region. The photocatalyst was prepared using mechano-thermal method and characterised using PXRD, TGA, FT-IR, HR-TEM, EDS, UV, PL and DRS methods. The photocatalytic property was explored using the degradation of methyl orange and compared the activity with different time intervals and wide range of pH. Within 60 min of irradiation, 98% of degradation was observed. Similarly, at all pH range more than 50% of degradation was observed, but the best performance (98%) was observed at pH = 7 (neural). Thus, the TiO2/NiO nanocomposite catalyst was effective in neutral, acidic and basic polluted water treatment. The synthesized TiO2/NiO nanocomposite is tuneable to visible light and degrade the methyl orange dye in all pH range.

Use of antimicrobial photodynamic therapy in the treatment of chronic tonsillitis

An effective method for treatment of chronic tonsillitis has been developed. It is based on combined (sequential) exposure of the tonsils to laser radiation of violet (405 nm wavelength) and red (650 wavelength) spectral regions at a power density of 25 mW/cm 2 for 3 minutes for each amygdala for 7 days. It was shown that laser therapy according to the above method has positive anti-inflammatory, decongestant and antimicrobial effects. Moreover, the antimicrobial effect of laser radiation is due to the excitation of endogenous porphyrin and flavin photosensitizers, localized mainly in pathogenic microflora. The high efficiency of generation of singlet oxygen by these compounds is capable of realizing the bactericidal action of light without introducing exogenous photosensitizers.

Strain tunable electronic and optical properties of 2D orthorhombic lithium sulfur monolayer

The stability, electronic and optical properties of possible two-dimensional (2D) Li2S monolayer with orthorhombic atomic configuration denoted as O-Li2S monolayer is theoretically investigated. It is shown that the proposed 2D O-Li2S monolayer exhibits the space group of 59_Pmmn and is energetically and kinetically stable. Our electronic properties computations indicate that 2D Li2S monolayer is a wide band gap (WBG) semiconductor with a strain tunable direct band gap of 4.13 eV obtained from HSE06 level of theory. Calculating its optical properties show that this newly designed 2D O-Li2S monolayer has high absorption property in ultra violet region of light.

Single crystal growth of l-tartaric acid and its characterization for optical applications

An optical material is a fundamental in the field of information along with measurement of laser applications. Crystals of organic compounds are very well known for its highly efficient behavior towards the optical activities. In the present study, slow evaporation solution growth technique has been adopted for the growth of l-tartaric acid (LTA). The phase and structural information was assessed with powder X-ray diffraction and grown single crystal’s quality was tested through high resolution X-ray diffraction and found to be reasonably good. The composition bonding between the molecules was revealed out by Fourier-Transform Infrared Spectroscopy method. The Ultraviolet–Visible spectroscopy exposes the excellent transmittance properties of LTA crystal. Photoluminescence spectrum shows strong emission in the violet region. Optical properties are measured to know its behavior towards electromagnetic spectrum which is further analyzed by ultrafast pump probe spectrometry and the determination of non-linear optical absorption coefficient was also taken into account with respect to the absorbance spectra. Moreover, Vickers microhardness studies were carried out to check its mechanical behavior.

Highly fluorescent lipophilic 2,1,3-benzothiadiazole fluorophores as optical sensors for tagging material and gasoline adulteration with ethanol

Lipophilic 2,1,3-benzothiadiazoles were obtained in a short synthesis with excellent yields by a Sonogashira coupling reaction followed by a 1,3-dipolar cycloaddition reaction with alkyl azides. The obtained compounds presented high solubility in a wide range of solvents with different polarities. The benzothiadiazoles present absorption in the violet region due to fully spin- and symmetry-allowed π-π* electronic tansitions and an emission located in the blue-green region with a large Stokes shift. The high solubility in apolar media, along with their photophysical properties allowed their use as tagging materials up to a detection limit of 0.005 ppm. Moreover, their application as chemosensors for the detection of fuel adulteration in commercial gasoline in the range of 5–50 % ethanol/gasoline (v/v) was also sucesfully presented and discussed.

ZnSe:Te/ZnSeS/ZnS nanocrystals: an access to cadmium-free pure-blue quantum-dot light-emitting diodes.

Cadmium-free quantum dots (QDs) are attracting considerable research attention because of their low toxicity. However, the bandgap of most cadmium-free QDs avoids the pure-blue region, which leads to difficulty in realizing pure-blue quantum-dot light-emitting diodes (QLEDs). In this work, we successfully tuned the emission wavelength of ZnSe/ZnS quantum dots from the violet region (∼420 nm) to the pure-blue region (450-460 nm) by doping Te into the ZnSe core. The ZnSe:0.03Te/ZnSeS/ZnS QD sample with emission at 450 nm and a quantum yield of 30% was the most balanced formula. To overcome the energy gap between the hole-transfer layer and QD layers, a specific hole-transfer layer was developed for normal-structure QLEDs. A QLED with such a structure with ZnSe:0.03Te/ZnSeS/ZnS QDs achieved the pure-blue light emission at 455 nm, a low turn-on voltage of 4.4 V, and an external quantum efficiency of 0.33%. Overall, our cadmium-free QLED achieved pure-blue emission, revealing the potential of ZnSe-based pure-blue QLEDs for future displays.

Photodynamic therapy in 2D and 3D human cervical carcinoma cell cultures employing LED light sources emitting at different wavelengths

Light of different wavelengths can be used to obtain a more profitable outcome of photodynamic therapy (PDT), according to the absorption bands of the photosensitizer (PS). Low-grade cervical intraepithelial neoplasias (CINs) are superficial lesions that can be treated with light of shorter wavelength than red because a large light penetration depth in tissue is not necessary. We report a comparative investigation performed to evaluate the efficacy of light-emitting diodes (LEDs) of different wavelengths in the photodynamic treatment applied to both 2D and 3D HeLa cell spheroid cultures. The spheroids are utilized as a PDT dosage model, and cell viability is evaluated at different sections of the spheroids by confocal microscopy. Cells incubated with m-tetrahydroxyphenyl chlorin are illuminated with LED systems working in the low fluence range, emitting in the violet (390–415 nm), blue (440–470 nm), red (620–645 nm) and deep red (640–670 nm) regions of the light spectrum at various exposures times (tI) comprised between 0.5 and 30 min. PDT experiments performed on both 2D and 3D cell cultures indicate that the PDT treatment outcome is more efficient with violet light followed by red light. Dynamic data from the front displacement velocity of large 2D-quasi-radial colonies generated from cell spheroids adhered to the Petri dish bottom as well as the evolution of the 3D growth give further insight about the effect of PDT at each condition. Results from 3D cultures indicate that the penetration of the violet light is appropriate to kill HeLa cells several layers below, showing cell damage and death not only in the outer rim of the illuminated spheroids, where a PS accumulation exists, but also in the more internal region. Results indicate that violet LED light could be useful to treat CINs involving superficial dysplasia.

The effects of varying the annealing period on the structure, morphology and optical properties of MgAl2O4:0.1% Mn2+ nanophosphors

In this study, magnesium aluminate nanopowders doped with manganese ions (MgAl2O4:0.1% Mn2+) were prepared by citrate sol–gel technique. The consequences on the structural, morphological and optical properties when varying the annealing period (AP) at a fixed annealing temperature of 800 °C and dopant concentration (0.1% Mn2+) were investigated. The AP was varied at the range of 1–6 h. X-ray powder diffraction (XRD) results showed that doping with 0.1% Mn2+ and varying the AP did not influence the crystal structure of the host (un-doped) material. The scanning electron microscope (SEM) images suggested that doping does not influence the morphology of the prepared nanopowders and varying the AP slightly influence the particle size. Transition electron microscopy (TEM) image suggested that the crystallite sizes were below 15 nm. The ultraviolet–visible (UV–Vis) diffuse reflection spectroscopy showed that the band gap of the MgAl2O4:0.1% Mn2+ can be tuned from 5.04 to 4.58 eV with varying AP. Photoluminescence (PL) results showed two emission peaks located at around 413 and 655 nm. They were attributed to the defect levels within the host material and to the (4T1 → 6A1) transitions of Mn2+, respectively. Increasing the AP significantly influences the luminescence of the prepared powders. The CIE coordinate results showed that the bluish emission colour can be changed to the violet region when AP was increased.

Two mononuclear zinc(II) complexes constructed by two types of phenoxyacetic acid ligands: syntheses, crystal structures and fluorescence properties

Abstract Two new mononuclear complexes, [Zn(3-Hcpa)2(H2O)4] (1) and [Zn(3,5,6-tcpa)2(H2O)4] [Zn(3,5,6-tcpa)2(H2O)2] (2) (3-H2cpa = 3-carboxy-phenoxyacetic acid, 3,5,6-Htcpa = 3,5,6-trichloro pyridine-2-oxyacetic acid), were synthesized and structurally characterized. The single-crystal X-ray diffraction analysis showed that in 1 the ZnII ion lies on an inversion center of an octahedron formed by four aqua ligands and two carboxy oxygen atoms of two unidentate 3-Hcpa− anions in trans-arrangement. Complex 2 is a co-crystal consisting of two discrete and stereochemically different complexes: one with an octahedrally, and the other a tetrahedrally coordinated zinc center. The six-coordination about the first ZnII ion comprises four oxygen atoms from water (H2O) molecules and two from the carboxy groups of monodentate trans-related 3,5,6-tcpa− ligands. The four-coordination about the second ZnII ion is comprised of two H2O ligands and two unidentate carboxy oxygen atoms from 3,5,6-tcpa− ligands. O–HLO hydrogen bond and/or ClLCl halogen bond interactions play an important part in construction of the three-dimensional (3D) networks for 1 and 2. The photoluminescence spectra reveal that both 1 and 2 display luminescent properties in the violet region.

New cardo silylated poly(azomethine)s containing 9,9′‐diphenylfluorene units as materials with Brønsted acid‐dependent fluorescence

AbstractAromatic poly(azomethine)s have been studied due to their attractive properties such as high thermal stability, semiconducting behavior and the ability to coordinate species with their imine units (CN). In this paper, the synthesis and characterization of two novel silylated poly(azomethine)s containing cardo units are reported. These materials were highly soluble in organic solvents such as chloroform and m‐cresol and were thermally stable, and PAzMC1 exhibited a high glass transition temperature value (287 °C), while that for PAzMC2 was not observed. UV–visible spectrophotometry revealed absorption bands related to the aromatic backbone of both PAzMCs, 300–285 nm in tetrahydrofuran and 310–301 nm in dimethylsulfoxide, and bands attributed to the conjugated imine unit at around 350 nm. In order to investigate the phenomenon of the emission of fluorescence promoted by dopant agents with regard to potential optoelectronic applications, the materials were doped with H2SO4 and their optical and electrochemical properties investigated. Thus, the absorption band of the imine group was suppressed due to the nitrogen atoms being protonated. Fluorescence spectroscopy analysis developed in dilute solutions of polymers showed no emission from the undoped polymers, whereas the acid‐doped species emitted fluorescence in the UV and violet regions (322 nm). Cyclic voltammetry measurements were carried out and HOMO–LUMO energies were estimated. This study provides a starting point for the development of new poly(azomethine)s with doping‐dependent emission. © 2019 Society of Chemical Industry

Jet nebuliser spray pyrolysed indium oxide and nickel doped indium oxide thin films for photodiode application

Indium oxide thin films at different substrate temperatures (250−450 °C) and nickel doped indium oxide films with various doping concentration of 10 and 15 wt% were coated (at 400 °C) using jet nebulizer spray pyrolysis technique confirmed the cubic phase of the films from X-ray diffraction analysis. The micro-strain effects were also verified by Williamson-Hall method. Field emission scanning electron microscopy (FE-SEM) confirmed temperature dependence in the formation of octahedron layered geometry. The influence of temperature on surface irregularity and its effect on band gap shift confirmed using optical characterization was attributed to Burstein-Moss shift. The influence on doping was reinforced with the emission peak shift of photoluminescence spectra in ultra violet, violet and blue regions (394, 421 and 467 nm). Based on confirmations from these characterizations, n-In2O3/p-Si junction diodes were fabricated for as prepared In2O3 and 10 and 15 wt% concentrations nickel doped In2O3 at 400 °C. P-N junction diodes fabricated and analyzed showed high sensitivity for 15 wt% nickel doped indium oxide under illumination condition. On account of this 15 wt% nickel doped junction diode is a good candidate for optoelectronic devices.