near-UV Region Research Articles

Fabrication of a uniform quantum dot film with a high quantum yield.

We present a method that uses viscosity-lowering materials to fabricate polydimethylsiloxane-based flexible quantum dot films with high quantum yield and improved uniformity. We found that the aggregation of individual quantum dots was prevented, and the quantum yield improved simultaneously in films that contained surfactants. These films showed an improved absorption of approximately 27% in the near-UV and blue light regions, along with an improved photoluminescence of approximately 18%, indicating improved light conversion from the UV to the visible frequency region.

Intense Circular Dichroism and Spin Selectivity in AgBiS2 Nanocrystals by Chiral Ligand Exchange.

Chiral semiconducting nanomaterials offer many potential applications in photodetection, light emission, quantum information, and so on. However, it is difficult to achieve a strong circular dichroism (CD) signal in semiconducting nanocrystals (NCs) due to the complexity of chiral ligand surface engineering and multiple, uncertain mechanisms of chiroptical behavior. Here, a chiral ligand exchange strategy with cysteine on the ternary metal chalcogenide AgBiS2 NCs is developed, and a strong, long-lasting CD signal in the near-UV region is achieved. By carefully optimizing the ligand concentration, the CD peaks are observed at 260 and 320nm, respectively, giving insight into the different ligand binding mechanisms influencing the CD signal of AgBiS2 NCs. Using density-functional theory, a large degree of crystal distortion by the bidentate mode of ligand chelation, and efficient ligand-NC electron transfer, synergistically resulting in the strongest CD signal (g-factor over 10-2) observed in chiral ligand-exchanged semiconductor NCs to date, is demonstrated. To demonstrate the effective chiral properties of these AgBiS2 NCs, a spin-filter device with over 86% efficiency is fabricated. This work represents a considerable leap in the field of chiral semiconductor NCs and points toward their future applications.

Electronic structure and theoretical exfoliation of non-van der Waals carbonates into low-dimensional materials: A case of Y2(CO3)3

The unique properties of two-dimensional (2D) materials make them highly versatile for a wide range of applications. Recently, low-dimensional structures obtained from bulk non-van der Waals materials have received particular interest. Yttrium carbonate is an example of such materials which hold the potential for creating 2D structures, however, its fundamental properties have been investigated only rarely. In this work, we demonstrate the possibility of obtaining 2D yttrium carbonate with the tengerite-(Y) structure. The electronic and optical properties of both bulk and two-dimensional Y2(CO3)3·2H2O are investigated using the PBE and HSE06 functionals. While the bulk material is predicted with a bandgap of 7.06 eV at the HSE06 level, the 2D Y2(CO3)3·2H2O material possesses a bandgap of, untypically, 0.4 eV narrower than the bulk material due to surface effects and different stoichiometry. The optical properties reveal that both the bulk and 2D forms are transparent in the visible and near-UV regions positioning them as promising candidates for various optical applications including doping-induced luminescent devices.

Machine learned analysis of pnictides based Sr3PnCl3 (Pn = P, As, Sb) halide perovskites for next-generation solar applications

This study provides an in-depth investigation into the structural, electronic, mechanical, and optical properties of Sr₃PnCl₃ (Pn = P, As, Sb) halide perovskites using QuantumATK tool. The computed equilibrium lattice constants for these materials are 6.28 Å, 6.32 Å, and 6.36 Å for Sr₃PCl₃, Sr₃AsCl₃, and Sr₃SbCl₃ respectively. The mechanical stability of these perovskites is confirmed by their elastic constants, adhering to the Born-Huang criteria with C₁₁ values of 45.21 GPa, 46.98 GPa, and 64.74 GPa for Sr₃PCl₃, Sr₃AsCl₃, and Sr₃SbCl₃ respectively. Their direct bandgaps of 2.137 eV, 1.950 eV, and 2.082 eV highlight their suitability for solar and optoelectronic applications. The absorption coefficients are notably high in the visible to near-UV region, with peak values of 406,483 cm⁻¹ for Sr₃PCl₃, 413,432 cm⁻¹ for Sr₃AsCl₃, and 435,860 cm⁻¹ for Sr₃SbCl₃. The refractive indices are reported as 1.76, 1.787 and 1.9 for Sr₃PCl₃, Sr₃AsCl₃ and Sr₃SbCl₃ respectively.

Constraining z ≲ 2 ultraviolet emission with the upcoming ULTRASAT satellite

Context. The extragalactic background light (EBL) carries a huge astrophysical and cosmological content. Its frequency spectrum and redshift evolution are determined by the integrated emission of unresolved sources, with these being galaxies, active galactic nuclei, or more exotic components. The near-UV region of the EBL spectrum is currently not well constrained, yet a significant improvement can be expected thanks to the soon-to-be launched Ultraviolet Transient Astronomy Satellite (ULTRASAT). Intended to study transient events in the 2300–2900 Å observed band, this detector will provide wide field maps tracing the UV intensity fluctuations at the largest scales. Aims. In this paper, we suggest how to exploit the ULTRASAT full-sky map as well as its low-cadence survey in order to reconstruct the redshift evolution of the UV-EBL volume emissivity. We build upon the work of Chiang et al. (2019, ApJ, 870, 120), who used the clustering-based redshift (CBR) technique to study diffuse light maps from GALEX. Their results showed the capability of the cross correlation between GALEX and SDSS spectroscopic catalogs in constraining UV emissivity, highlighting how CBR is sensitive only to extragalactic emissions, avoiding foregrounds and Galactic contributions. Methods. In our analysis, we introduce a framework to forecast the CBR constraining power when applied to ULTRASAT and GALEX in cross correlation with the five-year DESI spectroscopic survey. Results. We show that these will yield a strong improvement in the measurement of the UV-EBL volume emissivity. For λ = 1500 Å non-ionizing continuum below z ∼ 2, we forecast a 1σ uncertainty ≲26% (9%) with conservative (optimistic) bias priors using the ULTRASAT full-sky map. Similar constraints can be obtained from its low-cadence survey, which will provide a smaller but deeper map. Finally, we discuss how these results will foster our understanding of UV-EBL models.

Chiral Nanostructured Glycerohydrogel Sol-Gel Plates of Chitosan L- and D-Aspartate: Supramolecular Ordering and Optical Properties.

A comprehensive study was performed on the supramolecular ordering and optical properties of thin nanostructured glycerohydrogel sol-gel plates based on chitosan L- and D-aspartate and their individual components in the X-ray, UV, visible, and IR ranges. Our comparative analysis of chiroptical characteristics, optical collimated transmittance, the average cosine of the scattering angle, microrelief and surface asymmetry, and the level of structuring shows a significant influence of the wavelength range of electromagnetic radiation and the enantiomeric form of aspartic acid on the functional characteristics of the sol-gel materials. At the macrolevel of the supramolecular organization, a complex topography of the surface layer and a dense amorphous-crystalline ordering of polymeric substances were revealed, while at the nanolevel, there were two forms of voluminous scattering domains: nanospheres with diameters of 60-120 nm (L-) and 45-55 nm (D-), anisometric particles of lengths within ~100-160 (L-) and ~85-125 nm (D-), and widths within ~10-20 (L-) and ~20-30 nm (D-). The effect of optical clearing on glass coated with a thin layer of chitosan L-(D-)aspartate in the near-UV region was discovered (observed for the first time for chitosan-based materials). The resulting nanocomposite shape-stable glycerohydrogels seem promising for sensorics and photonics.

Ab initio multireference calculation of electronic spectra of the osmium complexes, [Os(bpy) ] and [Os(phen) ] .

The spin-orbit coupling corrected absorption spectra of osmium complexes, [Os(bpy) ] and [Os(phen) ] , were calculated by using ab initio multireference perturbation method (NEVPT2) with relativistic effects taken into account throughout ZORA approximation and corresponding all-electron basis sets. For the same purpose, the time-dependent DFT techniques were used. A very good agreement between NEVPT2 and experimental spectra should be highlighted, especially for the MLCT transitions that occur in visible and near-UV regions ( cm ). Moreover, the present study offers description of excited states of titled osmium complexes and their spectra interpretation using molecular orbitals.

A Sacrificial Linker in Biodegradable Polyesters for Accelerated Photoinduced Degradation, Monitored by Continuous Atline SEC Analysis.

Polymeric materials that undergo photoinduced degradation have wide application in fields such as controlled release. Most methods for photoinduced degradation rely on the UV or near-UV region of the electromagnetic spectrum; however, use of the deeply penetrating and benign wavelengths of visible light offers a multitude of advantages. Here we report a lactone monomer for ring-opening copolymerizations to introduce a sacrificial linker into a polymer backbone which can be cleaved by reactive oxygen species which are produced by a photocatalyst under visible light irradiation. We find that copolymers of this material readily degrade under visible light. We followed polymer degradation using a continuous flow size exclusion chromatography system, the components of which are described herein.

Luminescent Behavior of Zn(II) and Mn(II) Halide Derivatives of 4-Phenyldinaphtho[2,1-d:1',2'-f][1,3,2]dioxaphosphepine 4-Oxide and Single-Crystal X-ray Structure Determination of the Ligand.

The two enantiomers of chiral phosphonate 4-phenyldinaphtho[2,1-d:1',2'-f][1,3,2]dioxaphosphepine 4-oxide, O=PPh(BINOL), were synthesized from the proper 1,1'-bi-2-naphtol (BINOL) enantiomer and characterized. The structure of the (S)-enantiomer was elucidated by means of single-crystal X-ray diffraction. The reaction with anhydrous ZnBr2 afforded complexes having the general formula [ZnBr2{O=PPh(BINOL)}2] that showed intense fluorescence centered in the near-UV region rationalized on the basis of TD-DFT calculations. The corresponding Mn(II) complexes with the general formula [MnX2{O=PPh(BINOL)}2] (X = Cl, Br) exhibited dual emission upon excitation with UV light, with the relative intensity of the bands dependent upon the choice of the halide. The highest energy transition is comparable with that of the Zn(II) complex, while the lowest energy emission falls in the red region of the spectrum and is characterized by lifetimes in the hundreds of microseconds range. Although the emission at lower energy can also be achieved by direct excitation of the metal center, the luminescence decay curves suggest that the band in the red range is possibly derived from BINOL-centered excited states populated by intersystem crossing.

Effect of Plasma Treatment on the Luminescent and Scintillation Properties of Thick ZnO Films Fabricated by Sputtering of a Hot Ceramic Target

The paper presents the results of a comprehensive study of the structural-phase composition, morphology, optical, luminescent, and scintillation characteristics of thick ZnO films fabricated by magnetron sputtering. By using a hot ceramic target, extremely rapid growth (~50 µm/h) of ZnO microfilms more than 100 µm thick was performed, which is an advantage for the industrial production of scintillation detectors. The effects of post-growth treatment of the fabricated films in low-temperature plasma were studied and a significant improvement in their crystalline and optical quality was shown. As a result, the films exhibit intense near-band-edge luminescence in the near-UV region with a decay time of <1 ns. Plasma treatment also allowed to significantly weaken the visible defect luminescence excited in the near-surface regions of the films. A study of the luminescence mechanisms in the synthesized films revealed that their near-band-edge emission at room temperature is formed by phonon replicas of free exciton recombination emission. Particularly, the first phonon replica plays the main role in the case of optical excitation, while upon X-ray excitation, the second phonon replica dominates. It was also shown that the green band peaking at ~510 nm (2.43 eV) is due to surface emission centers, while longer wavelength (>550 nm) green-yellow emission originates mainly from bulk parts of the films.

Photoelectrochemical UV Detector Based on High-Temperature Resistant ITO Nanowire Network Transparent Conductive Electrodes: Both the Response Range and Responsivity Are Improved.

UV transparent conductive electrodes based on transferable ITO nanowire networks were prepared to solve the problem of low UV light utilization in conventional photoelectrochemical UV detectors. The mutually cross-linked ITO nanowire network achieved good electrical conductivity and light transmission, and the novel electrode had a transmission rate of more than 80% throughout the near-UV and visible regions. Compared to Ag nanowire electrodes with similar functionality, the chemical stability of the ITO nanowire transparent conductive electrode ensured that the device worked stably in iodine-based electrolytes. More importantly, ITO electrodes composed of oxides could withstand temperatures above 800 °C, which is extremely critical for photoelectrochemical devices. After the deposition of a TiO2 active layer using the high-temperature method, the response range of the photoelectrochemical UV detector was extended from a peak-like response between 300-400 nm to a plateau-like response between 200-400 nm. The responsivity was significantly increased to 56.1 mA/W. The relationship between ITO nanowire properties and device performance, as well as the reasons for device performance enhancement, were intensively investigated.

Photometric flow system for the determination of serum lactate dehydrogenase activity

The routine method for LDH (Lactate dehydrogenase) activity determination is to monitor the increase of NADH concentration at 340 nm. There are some inconvenience in taking measurements in the near-UV region, especially in the case of serum samples analysis. In this work, two modifications of the routine LDH activity assay based on the use of reducing properties of NADH have been compared. Both methods involved the reduction of compounds that can be easily determined by well-known methods, ferric ion (with ferrozine) and nitrotetrazolium blue (NBT). A fully-mechanized Multicommutated Flow Analysis-Paired Emitter Detector Diode (MCFA-PEDD) system based on solenoid devices was developed and applied for both methods. The linear ranges obtained for Fe-ferrozine and NBT methods are 6.0–200.0 U L−1 and 10.0–250.0 U L−1 with estimated detection limits at 0.2 U L−1 and 4.5 U L−1, respectively. The low LOQ values enabled 10-fold sample dilutions, which is advantageous for samples with limited available volume. The Fe-ferrozine method is more selective for LDH activity in the presence of glucose, ascorbic acid, albumin, bilirubin, copper and calcium ions than NBT method. To confirm the analytical usefulness of the proposed flow system, the analysis of real human serum samples was carried out. The statistic tests showed satisfactory correlation between the results obtained for both developed methods and those received using the reference method.

Exploring electronic, optical, and phononic properties of MgX (X = C, N, and O) monolayers using first principle calculations

The electronic, the thermal, and the optical properties of hexagonal MgX monolayers (where [Formula: see text] = [Formula: see text], [Formula: see text], and [Formula: see text]) are investigated via first principles studies. Ab-initio molecular dynamic, AIMD, simulations using NVT ensembles are performed to check the thermodynamic stability of the monolayers. We find that an MgO monolayer has semiconductor properties with a good thermodynamic stability, while the MgC and the MgN monolayers have metallic characters. The calculated phonon band structures of all the three considered monolayers show no imaginary nonphysical frequencies, thus indicating that they all have excellent dynamic stability. The MgO monolayer has a larger heat capacity then the MgC and the MgN monolayers. The metallic monolayers demonstrate optical response in the IR as a consequence of the metal properties, whereas the semiconducting MgO monolayer demonstrates an active optical response in the near-UV region. The optical response in the near-UV is beneficial for nanoelectronics and photoelectric applications. A semiconducting monolayer is a great choice for thermal management applications since its thermal properties are more attractive than those of the metallic monolayer in terms of heat capacity, which is related to the change in the internal energy of the system.

Iron(II) Complexes with Porphyrin and Tetrabenzoporphyrin: CASSCF/MCQDPT2 Study of the Electronic Structures and UV-Vis Spectra by sTD-DFT.

The geometry and electronic structures of iron(II) complexes with porphyrin (FeP) and tetrabenzoporphyrin (FeTBP) in ground and low-lying excited electronic states are determined by DFT (PBE0/def2-TZVP) calculations and the complete active space self-consistent field (CASSCF) method, followed by the multiconfigurational quasi-degenerate second-order perturbation theory (MCQDPT2) approach to determine the dynamic electron correlation. The minima on the potential energy surfaces (PESs) of the ground (3A2g) and low-lying, high-spin (5A1g) electronic states correspond to the planar structures of FeP and FeTBP with D4h symmetry. According to the results of the MCQDPT2 calculations, the wave functions of the 3A2g and 5A1g electronic states are single determinant. The electronic absorption (UV-Vis) spectra of FeP and FeTBP are simulated within the framework of the simplified time-dependent density functional theory (sTDDFT) approach with the use of the long-range corrected CAM-B3LYP function. The most intensive bands of the UV-Vis spectra of FeP and FeTBP occur in the Soret near-UV region of 370-390 nm.

A comparative analysis of UV–vis transitions in hetaryl and ferrocenyl thioketones

Electronic transitions in a series of symmetrical and nonsymmetrical hetaryl- and/or ferrocenyl-functionalized thioketones have been studied using quantum chemistry methods. An in-depth theoretical characterization was carried out for low-energy electronic transitions. The effects of hetaryl and ferrocenyl groups on the energy of these transitions were recognized and elucidated in terms of atomic and molecular orbital contributions involved in the transitions. A comparison was drawn between the low-energy transitions in the thioketones and in their carbonyl counterparts. The effect of solvents on the position of UV–vis absorption bands, in particular, on those originating in the low-energy transitions, is discussed. The theoretical calculations indicate that the introduction of ferrocenyl group into the hetaryl-functionalized thioketones changes the character of their first two electronic transitions from n → π* and π → π* into dominant d → π*. The most intense band of all studied thioketones appears in the near-UV region and undergoes a redshift upon solvation.

Homoleptic Alkynylphosphonium Au(I) Complexes as Push-Pull Phosphorescent Emitters.

A series of compounds P1-P4 bearing terminal alkynyl sites connected with a phosphonium group via different π-conjugated linkers have been synthesized. The compounds themselves are efficient push-pull emitters and exhibit bright fluorescence in blue and near-UV regions. P1-P4 were used as alkynyl ligands to obtain a series of homoleptic bis-alkynyl Au(I) complexes 1-4. The complexes demonstrate bright phosphorescence and dual emission with dominating phosphorescence (2-4). Terphenyl derivative complex 3 exhibits warm white emission in DMSO solution and pure white emission in PMMA films. Time-dependent density functional theory calculations have shown that the T1 excited state has a hybrid MLCT/ILCT nature with a dominant contribution of charge transfer across a ligand-centered "D-π-A" system. The variation of linker allows tuning the effect of intermolecular charge transfer and thus changing the electronic and photophysical properties of the organogold "D-π-A" system. The results presented unambiguously display the advances of the conception of organometallic "D-π-A" construction.

Optical characterization of rare-earth activated La2-xLnx (MoO4)3 (Ln=Dy, Sm) phosphors

Dysprosium and Samarium doped Lanthanum molybdate (La2-xLnx(MoO4)3, Ln=Dy/Sm) powders were synthesized by the conventional solid-state ceramic route. X-ray diffraction studies confirmed the monoclinic phase of the samples with space group c2/c. Diffuse reflectance and photoluminescence spectrum revealed the optical properties of La2-xLnx(MoO4)3 samples. The band gap of doped La2-x(MoO4)3:x(Dy/Sm) shows a linear dependence on the doping concentration of rare-earth up to an optimum concentration. Low-symmetry site of Dy3+within the La2(MoO4)3 host resulted in a sharp yellow emission peak (575 nm) that dominates over blue emission (481 nm). Sm3+ doped samples showed intense orange-red emissions under an excitation wavelength of 404 nm. The variation of the lifetime of the luminescence peaks was studied in detail and the CIE colour coordinates and correlated colour temperature were calculated for varying rare-earth concentration as well as excitation wavelength to ascertain their suitability in phosphor applications. Dy3+ doped La2(MoO4)3 powders showed near white light emission and Sm3+ doped La2(MoO4)3 powders showed sharp emission in the orange-red region. Sharp excitation bands in near-UV (NUV) region in the luminescence spectra of La2-xDyx(MoO4)3 and La2-xSmx(MoO4)3 compounds establish the prospects of using these samples in NUV -LED applications. To investigate the effect of Sm3+ and Dy3+ co-doping on Lanthanum molybdate, a series of compounds of composition La1.8-xDy0.2Smx(MoO4)3 (x = 0.005, 0.02, 0.04 and 0.06) and La1.925-xSm0.075Dyx(MoO4)3 (x = 0.005, 0.02 and 0.04) were synthesized by the solid-state ceramic route. The effect of co-doping on the luminescence, CIE colour coordinates, correlated colour temperature and colour purity were studied.

Spectroscopic Determination of C, N, and O Abundances of Solar-analog Stars Based on the Lines of Hydride Molecules

Photospheric C, N, and O abundances of 118 solar-analog stars were determined by applying the synthetic-fitting analysis to their spectra in the blue or near-UV region comprising lines of CH, NH, and OH molecules, with an aim of clarifying the behaviors of these abundances in comparison with [Fe/H]. It turned out that, in the range of −0.6 ≲ [Fe/H] ≲ +0.3, [C/Fe] shows a marginally increasing tendency with decreasing [Fe/H] with a slight upturn around [Fe/H] ∼ 0, [N/Fe] tends to somewhat decrease toward lower [Fe/H], and [O/Fe] systematically increases (and thus [C/O] decreases) with a decrease in [Fe/H]. While these results are qualitatively consistent with previous determinations mostly based on atomic lines, the distribution centers of these [C/Fe], [N/Fe], and [O/Fe] at the near-solar metallicity are slightly negative by several hundredths of dex, which is interpreted as due to unusual solar abundances possibly related to the planetary formation of our solar system. However, clear anomalies are not observed in the [C, N, O/Fe] ratios of planet-host stars. Three out of four very Be-deficient stars were found to show anomalous [C/Fe] or [N/Fe] which may be due to mass transfer from the evolved companion, though its relation to the Be depletion mechanism is still unclear.

Effect of Thickness on Electrical and Optical Properties of ZnO:Al Films

Zinc oxide (ZnO:Al) films were prepared on a substrate of different thicknesses by sputtering at 1×10−2 mbar argon gas pressure and 200 W power. The effect of film thickness on the structural, electrical, and optical properties was investigated by X-ray diffraction (XRD), 4-point probe technique, and ultraviolet-visible spectroscopy. The XRD film crystal structure study revealed that all sample films at thicknesses of 66, 106, 150 and 193 nm, respectively, exhibited planar Hexagonal wurtzite crystal structure (002), and ZnO crystals were grown along the c-axis. The ZnO:Al film at a thickness of 66 nm had the highest strain and the smallest crystal size compared to other films. The electrical resistivity decreases with increasing film thickness. The sample at 193 nm has the lowest resistivity (1.37 Ω.m). The results showed that light transmission revealed that all sample films had high transparency in the white and near-UV region at a wavelength of 350 to 800 nm, with an average light transmittance shift of 85 - 95 %. The energy band gap increased with the film thickness of 3.49(66 nm), 3.55(106 nm), and 3.59(150 nm) eV, and decreased to 3.57 eV at 193 nm, respectively. HIGHLIGHTS The different thicknesses Zinc oxide (ZnO:Al) films were prepared by sputtering at 1×10-2 mbar argon gas pressure and 200 W power was used to study the effect of film thickness on the structural, electrical, and optical properties The electrical resistivity changing of ZnO:Al film depends on the film thickness. The electrical resistivity is reduced with increasing ZnO:Al film thickness The ZnO:Al film are highlighted by their characteristics for light transmission at the wavelengths between 350 and 800 nm, and exhibited exceptional transparency in the white and near-UV range GRAPHICAL ABSTRACT

Influence of the Coordinated Ligand on the Optical and Electrical Properties in Titanium Phthalocyanine-Based Active Films for Photovoltaics.

Tetravalent titanyl phthalocyanine (TiOPc) and titanium phthalocyanine dichloride (TiCl2Pc) films were deposited via the high-vacuum thermal evaporation technique and subsequently structurally and morphologically characterized, to be later evaluated in terms of their optoelectronic behavior. The IR and UV-vis spectroscopy of the films displayed α- and β-phase signals in TiOPc and TiCl2Pc. Additionally, the UV-vis spectra displayed the B and Q bands in the near-UV region of 270-390 nm and in the visible region between 600 and 880 nm, respectively. The films presented the onset gap (~1.30 eV) and the optical gap (~2.85 eV). Photoluminescence emission bands at 400-600 nm and 800-950 nm are present for the films. One-layer ITO/TiCl2Pc or TiOPc/Ag and two-layer ITO/PEDOT:PSS/TiCl2Pc or TiOPc/Ag planar heterojunction devices with poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) deposited by the spin-coating technique were constructed. In these devices, an electrical activation energy between 0.18 and 0.21 eV and a refractive index between 1.14 and 1.44 were obtained. The devices presented a change in the J-V curves for the illuminated and darkness conditions, as much as 1.5 × 102 A/cm2, related to the device architecture and phthalocyanine ligand. The latter indicates that the films should be used for optoelectronic applications.