Weak Band Research Articles

Investigation of gallium oxide thin film hetero-integrated with bulk diamond via atomic layer deposition

In this work, the characteristics of the gallium oxide (Ga2O3)/diamond heterostructure were thoroughly examined after the preparation of Ga2O3 thin film on bulk diamond via atomic layer deposition. The X-ray diffraction (XRD) analysis revealed the Ga2O3 film amorphous and diamond polycrystalline. The atomic force microscopy (AFM) mapping displayed remarkably smooth surfaces of the Ga2O3 film and diamond substrate (RMS of 0.184 and 0.508 nm, respectively). The scanning electron microscopy (SEM) images showed conspicuous grains formed on the diamond, and small crystallites on the surface of the film. The optical characteristics were investigated via spectroscopic ellipsometry (SE) and UV/Vis/NIR spectrophotometer. Raman spectroscopy suggested a sharp diamond-related (sp3) peak and an extremely weak bulge band around 1350–1620 cm−1. X-ray photoelectron spectroscopy (XPS) analysis indicated Ga2O3/diamond heterojunction to be staggered (type II) band alignment with valence band and conduction band offsets of around 1.18 eV and 2.09 eV, respectively. Moreover, according to time-domain thermoreflectance (TDTR) measurements, the thermal conductivity of Ga2O3 and the thermal boundary conductivity of the heterointerface were 5.13 W/(m·K) and 19.22 MW/(m2·K), respectively. These findings not only demonstrate the feasibility of Ga2O3-on-diamond hetero-integration but open up new prospects for the design and physical analysis of Ga2O3/diamond-based devices in the future.

Artificial coloration of ancient agate beads: a mineralogical study

The process of staining was frequently employed to enhance or alter the color of agate beads in ancient times. One of the key challenges in studying ancient beads is comprehending the intricate techniques employed to color agate stones. An understanding of the staining mechanism from a mineralogical standpoint offers insights into the level of technological advancement in different civilizations. In this study, the mineral structure of eight ancient agate beads from Xinjiang Uygur Autonomous Region, NW China, was analyzed using Micro X-ray fluorescence (µXRF), Raman spectroscopy, Scanning Electron Microscope (SEM), and Fourier Transform Infrared (FTIR) techniques. The color, transparency, mineral phase, and surface roughness of the beads were examined, revealing variations ranging from colorless to light violet to dark violet. Raman and FTIR spectroscopy were employed to determine the SiO2 phase and the changes in optical characteristics of agate beads after artificial staining. The black color of the beads was formed by carbon penetration, while the red color was produced by heating. The coexistence of α-quartz and moganite phases in the red, the dark red, the black, the idiochromatic white and the part translucent zones of the ancient beads was confirmed by the 464 cm−1 peak of α-quartz and the 502 cm−1 peak of moganite phase. The analyzed red, the dark red, the black, the idiochromatic white and the part translucent zones exhibited remarkably similar FTIR spectral features, with two prominent bands at ~ 1097 and ~ 1187 cm−1, as well as two weak bands at 798 and 778 cm−1, indicating the presence of moganite and α-quartz in the unetched ancient beads. In contrast to the idiochromatic white appearance of natural agate, the scattered white coloration in etched beads was generated by an etching reaction. Both Raman and FTIR spectroscopy indicated the absence of moganite in etched beads, indicating that the scattered white color was produced by the loss of moganite and a portion of α-quartz, resulting in a rough surface.

Down- and up-conversion luminescence processes in olivine-type ceramic phosphors Li2AGeO4:Er3+ (A = Zn, Mg)

Luminescence properties of olivine-type germanate phosphors with general formula Li2AGeO4:0.5Er3+ (A = Zn, Mg) have been studied. Olivine-type materials prepared via conventional solid-state reaction method were examined for down- and up-conversion luminescence processes. In the down-conversion process after 381 nm excitation, two strong green emission bands due to 2H11/2/4S3/2 → 4I15/2 transitions of Er3+ were registered, with a change in the intensity ratio depending on the ceramic matrix. Weak red emission bands related to 4F9/2 → 4I15/2 transition were also recorded. In contrast, luminescence bands behaved completely differently for the up-conversion process after infrared excitation at λexc = 980 nm. Red emission bands were much more significant than green emission bands. These effects are stronger for Li2MgGeO4:0.5Er3+ than Li2ZnGeO4:0.5Er3+. In the red and green spectral range, slope values for both matrices Li2AGeO4:0.5Er3+ (A = Zn, Mg) confirmed two-photon process.

The Mechanical Properties and Fracture Characteristics of Shale Layered Samples from the Lucaogou Formation Considering Natural Crack and Mineral Distribution.

Shale oil is one of the most promising alternative unconventional energies in the world, and recently the Lucaogou Formation showed significant exploration potential, becoming the primary target in northwestern China. This paper focuses on the mechanical properties and fracture characteristics of shale layered samples from the Lucaogou Formation, conducting uniaxial compressive tests with real-time micro-CT scanning, as well as mineral analysis after failure. It has been found that the mechanical and fracture features are both related to the composition, distribution, content and particle size of minerals, as well as natural fractures. The main crack tends to form in the weak mineral band, for example, calcite or clay band. Since the discontinuous stress usually forms at the interfaces of different minerals, the sample with several major minerals of close content is easier to break into a fractured zone, causing lower uniaxial compressive strength and elastic modulus, compared with the composition of only one dominant mineral. Also, the region will be more fractured after failure if the mineral particles there become smaller. Additionally, although natural cracks have a certain influence on the development of new fractures, not all of the natural ones will propagate into the final fracture network, some of them are just compacted and closed.

Influence of Al3+ co-doped ions for the improvement of orange-reddish light emitting photoluminescence characteristics of Gd2Ti2O7:Eu3+ pyrochlore

Series of Al3+ doped Gd1.92Ti2-xO7:Eu0.08Al3+x (where x = 0, 0.02, 0.04, 0.06, & 0.08), powdered samples had been successfully developed using the solid-state reaction strategy. The purity of the produced samples was confirmed using X-ray diffraction analysis, while through Raman spectroscopy analysis and deconvolution, it has been observed that high intensity vibrational bands exhibited a blue shift (from 312.3 to 313.9 cm−1 and 518.2–518.6 cm−1) upon the introduction of Al3+ substitution in the Gd1.92Eu0.08Ti2O7 host lattice. Photoluminescence excitation spectra showed absorption in the ultraviolet & near-ultraviolet regions for Gd1.92Eu0.08Ti2O7, monitored at a wavelength of 588 nm. On the other hand, the Al3+ doped Gd1.92Eu0.08Ti2O7 oxides exhibited distinct absorption bands in 250–500 wavelength region, in addition to the host excitation bands. Under 322 nm excitation, the Al3+ doped Gd1.92Eu0.08Ti2O7 pyrochlore oxides displayed a dominant orange-reddish emission spike at 588 nm occurring due to 5D0→7F1 transition, along with weak emission peaks at 612 nm originating from 5D0→7F2 transition of trivalent europium ions. Similarly, under 394 nm excitation, the whole series exhibited analogous emission spikes, with the highly intense peak centered at 588 nm and weak band at 612 nm but in this case the emission intensity for all the peaks are relatively low as compared to when excited to 322 nm. The energy transfer processes and their relative possible reasons for concentration quenching above a Al3+ ion concentration of 2.0 mol% were discussed in detail. The optimized sample showed CIE chromaticity coordinates of (0.605, 0.392) under 322 nm excitation, indicating its positioning in the orange-reddish region. The CIE coordinates measured, depends on the emission profile under 322 nm excitation closely matched those of the economic phosphor Y2O2S:Eu3+ (x = 0.622 and y = 0.351). Overall, these results highlight the potential of Al3+ doped Gd1.92Eu0.08Ti2O7 pyrochlore oxides as orange-reddish emitting components for luminescent devices.

Host sensitization of luminescence of lanthanide activators in NaBi(WO4)2

The synthesis and luminescence of a series of NaBi(WO4)2 activated with trivalent lanthanides Tb, Sm and Nd using the solid-state reaction method is reported. All samples were characterised by X-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescence (PL). The XRD study confirmed the tetragonal phase without any secondary phase. Particles of irregular shape ranging between 5 and 20 µm were observed. Elemental composition was obtained from EDAX and results were found consistent with the formula NaBi(WO4)2. The formation of single-phase NaBi(WO4)2 was again confirmed through these results. Elemental mapping indicated that all elements were uniformly distributed. The band gap was evaluated using Tauc’s. formula and was found from 5.6 eV to 5.91 eV which is higher than reported values (3.6 eV). For NaBi(WO4)2:Tb, excitation was monitored for 545 nm emission. Emission spectra upon excitation by 488 nm showed prominent lines around 545 and 549 nm. These are due to the transition 5D4 7F5. 5 mol.% Tb yielded maximum PL intensity. When 405 nm excitation is used for Sm3+ doped phosphor, lines can be seen in three groups around 564, 600 and 647 nm. The highest emission intensity is observed for Sm3+ concentration of 5 mol.% and quenching was observed for high values. A weak band could be seen in the excitation spectra which is distinct from the f-f lines. The position of this band is close to that observed in the reflectance spectra. Hence it is proposed that there is host sensitization, even though weak, of the lanthanide luminescence in this host. Sensitization is most probably due to Bi3+ Ln3+ energy transfer.

Extraction and Modification of Cellulose Microfibers Derived from Biomass of the Amazon Ochroma pyramidale Fruit

Microfibers are important to several areas of human lifestyle, and the knowledge about their physicochemical characteristics allows for proposing new technological applications. The in natura microfiber of Ochroma pyramidale fruit (IN sample) and its extracted pulp (PU sample) were evaluated by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and Thermogravimetry and Differential Scanning Calorimetry (TG/dTG and DSC). Microfibers were composed mainly of (68 ± 1)% holocellulose, (35.8 ± 0.1)% cellulose, (32 ± 3)% lignin and (3.7 ± 0.3)% extractives. The XRD pattern of the PU sample revealed that the mercerization process resulted in the change of the cellulose crystal structure from Iα type (triclinic) to type II (monoclinic). The SEM technique showed that the IN sample presented regular cylindrical/hollow-shaped wire-like microfibers with diameters ranging from 5 µm to 25 µm. However, the mercerization process changed their natural morphology. A significant change in the FTIR spectra after the removal of hemicellulose and lignin components was observed: weak bands at 1739 cm−1 (C=O stretching of lignin and hemicellulose fractions), 1463 cm−1 (CH3 of lignin) and 1246 cm−1 (C-O of lignin) were still observed in the PU sample, indicating that the lignin was not completely removed due to the natural difficulty of isolating pure cellulose. The TG/dTG and DSC evaluation revealed a temperature increase of the second thermal event (starting at 235 °C) in the PU sample, which was assigned to the cellulose and residual hemicellulose degradation. Then, this work aimed to disseminate and characterize a microfiber with unusual characteristics still little explored by the scientific community, as well as its cellulosic pulp, providing information that may be useful in its application in different industries, enabling the positive development of new biocompatible, renewable and sustainable materials.

An algorithm for correction of atmospheric scattering dilution effects in volcanic gas emission measurements using skylight differential optical absorption spectroscopy

Differential Optical Absorption Spectroscopy (DOAS) is commonly used to measure gas emissions from volcanoes. DOAS instruments measure the absorption of solar ultraviolet (UV) radiation scattered in the atmosphere by sulfur dioxide (SO2) and other trace gases contained in volcanic plumes. The standard spectral retrieval methods assume that all measured light comes from behind the plume and has passed through the plume along a straight line. However, a fraction of the light that reaches the instrument may have been scattered beneath the plume and thus has passed around it. Since this component does not contain the absorption signatures of gases in the plume, it effectively “dilutes” the measurements and causes underestimation of the gas abundance in the plume. This dilution effect is small for clean-air conditions and short distances between instrument and plume. However, plume measurements made at long distance and/or in conditions with significant atmospheric aerosol, haze, or clouds may be severely affected. Thus, light dilution is regarded as a major error source in DOAS measurements of volcanic degassing. Several attempts have been made to model the phenomena and the physical mechanisms are today relatively well understood. However, these models require knowledge of the local atmospheric aerosol composition and distribution, parameters that are almost always unknown. Thus, a practical algorithm to quantitatively correct for the dilution effect is still lacking. Here, we propose such an algorithm focused specifically on SO2 measurements. The method relies on the fact that light absorption becomes non-linear for high SO2 loads, and that strong and weak SO2 absorption bands are unequally affected by the diluting signal. These differences can be used to identify when dilution is occurring. Moreover, if we assume that the spectral radiance of the diluting light is identical to the spectrum of light measured away from the plume, a measured clean air spectrum can be used to represent the dilution component. A correction can then be implemented by iteratively subtracting fractions of this clean air spectrum from the measured spectrum until the respective absorption signals on strong and weak SO2 absorption bands are consistent with a single overhead SO2 abundance. In this manner, we can quantify the magnitude of light dilution in each individual measurement spectrum as well as obtaining a dilution-corrected value for the SO2 column density along the line of sight of the instrument. This paper first presents the theory behind the method, then discusses validation experiments using a radiative transfer model, as well as applications to field data obtained under different measurement conditions at three different locations; Fagradalsfjall located on the Reykjanaes peninsula in south Island, Manam located off the northeast coast of mainland Papua New Guinea and Holuhraun located in the inland of north east Island.

Highly accurate potential energy surface and dipole moment surface for nitrous oxide and 296K infrared line lists for 14N2 16O and minor isotopologues

To facilitate the data analysis of current and future high-resolution space telescope missions, we adopt ‘Best Theory + Reliable High-resolution Experiment’ (BTRHE) strategy to develop highly accurate infrared line lists for nitrous oxide (N2O). The ‘Ames-1’ potential energy surface (PES) is a CCSD(T)/aug-cc-pVQZ PES refined using selected HITRAN experimental data, with σ rms = 0.02–0.03 cm-1 for five isotopologues. The ‘Ames-1’ dipole moment surface (DMS) is fitted from CCSD(T)/aug-cc-pV(T,Q,5)Z dipoles extrapolated to one electron basis set limit. Using the Ames-1 PES and DMS, Ames-296K line lists are computed in the full range of 0–15,000 cm-1 for 12 N2O isotopologues, with S 296K ≥ 10−31 cm-1/molecule.cm-2. The reliability and consistency of Ames-296K intensity predictions (S Ames) are demonstrated through comparisons with HITRAN (S HITRAN), NOSL-296 (S NOSL), recent observed intensities (S obs) and Effective Dipole Model (EDM) intensities (S EDM). Agreements and discrepancies are discussed, along with preliminary uncertainty estimate for S Ames. The S Ames provides a good constraint to prevent substantial errors in intensity predictions (e.g. for weak bands and minor isotopologues) and can be further improved. Ames-296K and NOSL-296 may complement each other to provide improved input for future database updates, combining the strengths of EH/EDM and BTRHE approaches. Data available at https://doi.org/10.5281/zenodo.7888194 and https://doi.org/10.48667/9kmk-0334.

Exploring the properties of Dy2O3–Y2O3 Co-activated telluro-borate glass: Structural, physical, optical, thermal, and mechanical properties

The successful application of glass-based materials in a wide range of scientific fields depends on the associated physical, optical, thermal, and mechanical properties. This article investigate the structural, Physical, thermal, optical, and mechanical properties of Dy2O3, Y2O3 co-activated telluro-borate glass developed using the melt-quenching method. The glassy quality and the elements component of the specimens were observed using XRD and EDX analyses. The addition of Y2O3 rise the glass density from 2.956 to 3.303 g/cm3 the refractive index from 2.5 to 2.7. These changes are due to the increase in polarizability and non-bridging oxygen (NBO). The photoluminescence (PL) spectra revealed a broad peak at 550 nm and additional weak emission peaks at 573 and 664 nm, respectively. While the observed broader peak can be linked to the convolution of Bi3+ ions transitions corresponding to the non-centrosymmetric site respectively, the weak emission bands are due to 4F9/2 → 6H13/2 and 4F9/2 → 6H11/2 Dy3+ transitions. Hence, the low symmetrical features of both Bi3+ and Dy3+ ions were confirmed. The increase in the Vickers hardness of the glass from 536.7 to 1366.9 indicates the influence of Y2O3 addition on the mechanical properties of the glasses. The findings help to improve our understanding of the behaviour of the glass composition and its prospective applications in disciplines such as photonic, and laser optics.

Bodipy−corrole tetrads as heavy−atom−free triplet photosensitizers: Study of the energy transfer and application in triplet−triplet annihilation upconversion

Free base corrole can generate triplet state without invoking of heavy−atom effect, however, its weak and narrow absorption band in the visible spectral range make corrole not an ideal triplet photosensitizer. Herein, novel Bodipy−corrole tetrads were prepared by attaching visible light-harvesting antennae of Bodipy or electron spin converter with fullerene units (2B−Tur−Cor and B−C60−Tur−Cor) to solve the above problems, which show a stronger and broader absorption band in the visible region, and the maximum molar absorption coefficient is up to 2.58 × 105 M−1 cm−1 at 504 nm for 2B−Tur−Cor. By using of fluorescence spectroscopy, steady-state and time-resolved transient absorption spectroscopic methods, the singlet energy transfer progress from the Bodipy moiety to the corrole moiety was confirmed. Through fluorescence lifetimes and fluorescence excitation spectrum study, the rate constant of the singlet energy transfer was calculated as 9.58 × 107 s−1 for 2B−Tur−Cor and 2.45 × 108 s−1 for B−C60−Tur−Cor, respectively. The TD−DFT computation suggests that the first and second triplet state is localized in the corrole moiety and the Bodipy moiety for 2B−Tur−Cor, respectively, and the triplet state energy was calculated to be 1.37 eV and 1.61 eV, respectively. Nanosecond time−resolved transient difference absorption spectra show that the triplet excited states of these tetrads are localized on corrole unit, the lifetime of 2B−T−Cor is up to 143 μs, however, the lifetime of B−C60−Tur−Cor is only 3.3 μs. Long-lived triplet excited states play important role in applications of the triplet photosensitizers in photocatalysis or other photophysical processes concerning triplet–triplet−energy−transfer. As a proof of concept, these tetrads were used as heavy−atom−free organic triplet photosensitizers for triplet−triplet annihilation based upconversion. The upconversion quantum yield was up to 5.86% for 2B−Tur−Cor, however, it is only 0.52% for B−C60−Tur−Cor.

SYNTHESIS AND PHOTOCHEMICAL PROPERTIES OF NOVEL AZOQUINOLINE CONTAINING POLYMERS

The development of modern technologies are constantly requires seeking new low-cost, efficient materials and establish new technical methods for application these materials. Synthesis of polymers with predicted and expected properties on the one hand and using specific features of interaction light with photoactive fragments in polymers, on the other hand, opens new prospects of application for new materials based on these polymers. The side chain methacrylic polymers with different active functional group have been well studied and widely applied in many fields, such as optoelectronics, nonlinear optics, optical storage materials, biochemicals, and medicine.
 The present work focused on synthesis new azostyrylcontaining methacrylic monomers and copolymers with methylmetacrylate (MMA) based on these monomers. The pre­sent study is a first reported notice of the synthesis and photochemical properties of methacrylic polymers with 6-azo-phenylquinoline frag­ments in side chain. Moreover in this work the features of syntheses have been described in detail for monomers and polymers based on new azocompounds. Absorption spectroscopic properties for new quinoline polymers with azo fragment were investigated with UV-Vi­sible spectrophotometry in THF solutions. All studi­ed polymers show a strong absorption band in the range of 300–375 nm resulting from π-π* electronic transition and a weak absorption band in the range of 400–490 nm assigned to n-π* transitions. Electron donating and electron withdrawing substituents at quinoline moity of azo-quinoline polymer solutions lead to bathochromic shift of the π-π*absorption band which agrees well with the result of work. We found that this red-shift increases with an increase of electron donating strength of the substituent as well as with an increase of electron withdrawing strength of the substituent. Based on of the result achieved we can suppose that irradiation of polymers with azo fragment lead to photoinduced trans-cis-isomerization.
 From the obtained and presented results one can conclude that novel quinoline polymers with azo fragment can be considered as promising materials for applications requiring photosensitivity in certain of range of wavelength.

Enhancing the optoelectronic properties of V2O5 thin films through Tb doping for photodetector applications

Using highly economical and scalable nebulizer-aided spray pyrolysis approach, a high-quality terbium (Tb) doped vanadium pentoxide (V2O5) thin film-based optical sensor was developed. To investigate the effects of various terbium doping concentrations on its growth and optoelectronic features, the structural properties as well as its elemental composition, surface morphology, photoluminescence, optical, and current-voltage (I-V) characteristics were examined. An orthorhombic structure with orientation along the (010) plane was found to be existing in the X-ray diffraction pattern of Tb-doped V2O5 thin films with increase in the crystallite size upto 3 % Tb-doped V2O5 films. The prevalence of dense nanorods is observed in all the films while analyzing their micrograph from a field emission scanning electron microscope. Also it is noted that the addition of 3 % Tb dopants increases UV absorption by lowering its energy gap from 2.43 to 2.37 eV. A strong green emission peak at 530 nm and weak UV bands were noted in the PL spectrum due to higher crystalline quality, free from defects and native flaws for the 3% Tb-doped V2O5. Terbium-doped V2O5 films exhibited elevated UV photo response and photoelectric properties than their pristine form. Among various doping concentrations, 3 % terbium in V2O5 thin film exhibited a maximum response (4.72 × 10−1 A/W), detectivity (7.82 × 1010 Jones), external quantum efficiency (110 %), and high photo-switching characteristics. This study confirms the optimal 3 % Tb dopant concentration plays a significant role in enhancing the UV–visible photo-sensing behavior of the V2O5 thin films. Data availability statementThe raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.

Unveiling the Intimate Mechanism of the Crocin Antioxidant Properties by Radiolytic Analysis and Molecular Simulations.

The successive steps of the oxidation mechanism of crocin, a major compound of saffron, by the free OH• radical are investigated by pulse radiolysis, steady-state (gamma) radiolysis methods, and molecular simulations. The optical absorption properties of the transient species and their reaction rate constants are determined. The absorption spectrum of the oxidized radical of crocin resulting from the H-abstraction presents a maximum of 678 nm and a band of 441 nm, almost as intense as that of crocin. The spectrum of the covalent dimer of this radical contains an intense band at 441 nm and a weaker band at 330 nm. The final oxidized crocin, issued from radical disproportionation, absorbs weaker with a maximum of 330 nm. The molecular simulation results suggest that the OH• radical is electrostatically attracted by the terminal sugar and is scavenged predominantly by the neighbor methyl site of the polyene chain as in a sugar-driven mechanism. Based on detailed experimental and theoretical investigations, the antioxidant properties of crocin are highlighted.

The vacuum UV photoabsorption spectrum of 1,1-dibromo-2,2-difluoroethylene (1,1-Br2C2F2) in the 5-15 eV photon energy range. Combining experimental and theoretical investigations

Using synchrotron radiation, we have measured the vacuum UV photoabsorption spectrum (PAS) of 1,1-Br2C2F2 for the first time between 5 eV and 15 eV photon energy. Quantum chemical calculations have been performed for the determination of excitation and ionization energies. At low energy a weak broad band spreads between 5.2 eV and 6.0 eV and is assigned to nBr→Rpz (31B2) valence transition. A broad continuum starting at 6.18 eV corresponds to the π(3b1)→5s (41B1) Rydberg transition. Starting at Eexcad=6.595 eV a group of four narrower peaks likely corresponds to the vibrational excitation of the characteristic π(3b1)→π*(71A1) valence transition. The features evenly spaced by 1315 cm−1 are assigned to the C=C stretching vibration. Between 7.0 eV and 11.5 eV, several weak or very strong sharp features are observed. The 3b1→5p Rydberg transition is characterized by a short progression starting at 7.208 eV. A longer progression, assigned to 3b1→4d Rydberg transition, is observed up from 7.932 eV. Both Rydberg states converge to the X˜2B1 ionic ground state calculated at IEad=9.40 eV with quantum defects δ=2.51 and δ=0.96 respectively. The vibrational analysis provides vibrational wavenumbers ω1=1525±20 cm−1, ω2=975±40 cm−1, ω3=620±40 cm−1, ω4=355±20 cm−1 and ω5=185±30 cm−1 averaged over the 5p and 4d Rydberg states. An interaction has likely to be considered between the 6s and 4d Rydberg states. Above 11.5 eV, several strong sharp and broad bands are tentatively assigned to transitions to Rydberg states converging to excited ionic states of 1,1-Br2C2F2+. For one of these a vibrational structure is observed and a tentative assignment is proposed.

Effect of Al Incorporation on the Structural and Optical Properties of Sol-Gel AZO Thin Films.

ZnO and Al-doped ZnO (AZO) thin films were prepared using the sol-gel method and deposited on a Silicon (Si(100)) substrate using the dipping technique. The structure, morphology, thickness, optical constants in the spectral range 300-1700 nm, bandgap (Eg) and photoluminescence (PL) properties of the films were analyzed using X-ray diffractometry (XRD), X-ray fluorescence (XRF), atomic force microscopy (AFM), scanning electron microscopy (SEM), spectroscopic ellipsometry (SE), Raman analysis and PL spectroscopy. The results of the structure and morphology analyses showed that the thin films are polycrystalline with a hexagonal wurtzite structure, as well as continuous and homogeneous. The PL background and broader peaks observable in the Raman spectra of the AZO film and the slight increase in the optical band gap of the AZO thin film, compared to undoped ZnO, highlight the effect of defects introduced into the ZnO lattice and an increase in the charge carrier density in the AZO film. The PL emission spectra of the AZO thin film showed a strong UV line corresponding to near-band-edge ZnO emission along with weak green and red emission bands due to deep-level defects, attributed to the oxygen-occupied zinc vacancies (OZn lattice defects).

A Merger‐Formation Bow Echo Caused by Low‐Level Mesovortex in South China

AbstractThis work studied a high winds‐producing bow echo that occurred over South China in the pre‐rainy season using radar observations and high‐resolution analyses from the Variational Doppler Radar Analysis System. The bow echo developed from a quasi‐linear convective system (QLCS) and acquired a well‐defined bow shape after merging with a pre‐line convective cell (CC). Interestingly, the rear‐inflow jet (RIJ), which has been well recognized to play a key role in the formation of a bow echo, was not found in this merger‐formation bow echo (MFBE). The reason is that the QLCS developed in the monsoon environment of high humidity and weak vertical wind shear, leading to a weak cold pool and line‐end vortices. A new pathway of bow echo formation was proposed which highlighted the importance of the low‐level mesovortex (MV) on the leading edge of the QLCS. Vertical vorticity budget analyses revealed that the MV originated from a weak vertical vorticity band ahead of the QLCS and grew rapidly during the merger, because of the enhanced low‐level convergence in between which led to vortexgenesis via vertical stretching of vertical vorticity. The up‐scale growth of the MV produced a RIJ‐like flow wrapping cyclonically from north of the QLCS which forced the system to bulge out and finally evolve into a bow echo. This MV contributed foremost to the near‐surface gales as well. These findings shed light on the diverse formation mechanisms of bow echoes and associated high winds in the moist monsoon environment of South China.

Efficient Zn2+ doping into CsBr nanocrystals using benzoyl bromide

The potential route to induce effective metal doping into the colloidal nanocrystal (NC) lattice is still limited due to the unfavorable energy cost and needs further investigation for colloidal chemistry involved in the optical properties and device development with optimized NC design. In this study, we reports a bright blue emitting Zn2+-doped CsBr NCs (6.7 at.%) by introducing reactive benzoyl bromide to promote a preferential reaction with metal cations that are not favorably incorporated into the CsBr lattice. In particular, the acyl group (R-C = O-) of benzoyl bromide is more effective to adopt additional metal cations into the crystal lattice during the nucleation and growth process of colloidal CsBr NCs compared to alkylammonium bromides with long hydrocarbon chains, providing a new synthetic route for metal doping into the metal halide perovskites NCs. Zn2+-doped CsBr NCs exhibit a blue PL emission at 425 nm with a Stokes shift of 113 nm for the weak absorption band edge.

An UV/Vis/NIR optical absorption spectroscopic and color investigation of transition-metal-doped gahnite (ZnAl2O4 spinel) crystals grown by the flux method

Abstract Synthetic flux-grown end-member gahnite, ZnAl2O4, and several different colored crystals doped with one or more transition metals including Mn, Ni, Cr, Co, and Fe were studied by electron microprobe methods and UV/Vis/NIR single-crystal optical absorption spectroscopy. The first major objective was to measure and assign the various electronic absorption features. The second was to analyze quantitatively the crystal colors using the experimental spectra and the CIE 1931 color-space-chromaticity diagram. The microprobe results show that the doped gahnites have transition metal concentrations between about 0.001 and 0.1 cations per formula unit. The spectrum of colorless, nominally pure ZnAl2O4 displays no absorption in the visible region. Microprobe analysis of a light-blue gahnite crystal reveals small amounts of Ni and Mn. The UV/Vis/NIR spectrum does not indicate any dd-electronic transitions relating to Mn. All absorption features also cannot be fully interpreted using Tanabe-Sugano diagrams for Ni2+ in either octahedral or tetrahedral coordination. A series of seven slightly different colored gahnites with differing concentrations of Cr3+ and most also containing smaller amounts of Ni was investigated. The spectrum of a one pink crystal shows two intense absorption features in the visible region. They are assigned to spin-allowed 4A2g → 4T2g (4F) and 4A2g → 4T1g (4F) transitions of VICr3+. Other spectra display additional weak bands and lines that are most probably spin-forbidden dd-transitions of Ni2+. These gahnites with Ni and Cr show varying purple colorations depending on the concentrations of both metals. Two more deeply blue gahnites contain Co2+ as demonstrated by their UV/Vis spectra but not by microprobe analysis. Two intense absorption features at ~7440 and ~16 850 cm–1 are observed and assigned to the spin-allowed transitions 4A2 → 4T1 (4F) and 4A2 → 4T1 (4P) of Co2+, respectively. Complex absorption fine structure, caused by spin-orbit and/or vibronic interactions, is also observed. Three different gahnites with yellow to orange colorations contain measurable Mn. Their spectra are similar in appearance and display several weak IVMn2+ spin-forbidden transitions located above 20 000 cm–1. The spectra of two green gahnites show several Fe spin-forbidden electronic transitions arising from single, isolated IVFe2+ and VIFe3+ cations between 10 000 and 25 000 cm–1. The intensities of some of the VIFe3+-related bands can be increased through exchange-coupled interactions with next nearest IVFe2+ neighbors. The colors of various doped gahnites and the end-member galaxite are analyzed using their single-crystal absorption spectra in the visible region. Their dominant wavelength, λk, and hue saturation, pc, values are given on the CIE 1931 color-space-chromaticity diagram and are discussed. The Hex colors of all crystals are calculated and can be compared to those of the studied crystals.

Infrared ellipsometry study of the charge dynamics in K3p -terphenyl

We report an infrared ellipsometry study of the charge carrier dynamics in polycrystalline ${\mathrm{K}}_{x}p$-terphenyl samples with nominal $x=3$, for which signatures of high-temperature superconductivity were previously reported. The infrared spectra are dominated by two Lorentzian bands with maxima around 4000 and $12 000 {\mathrm{cm}}^{\ensuremath{-}1}$ which, from a comparison with calculations based on a H\"uckel model, are assigned to intramolecular excitations of $\ensuremath{\pi}$ electrons of the anionic $p$-terphenyl molecules. The intermolecular electronic excitations are much weaker and give rise to a Drude peak and a similarly weak Lorentzian band around $220 {\mathrm{cm}}^{\ensuremath{-}1}$. A dc resistivity of about $0.3 \mathrm{\ensuremath{\Omega}}\phantom{\rule{0.16em}{0ex}}\mathrm{cm}$ at $300\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ is deduced from the IR data, comparable to values measured by electrical resistivity on a twin sample. The analysis of the temperature dependence of the low-frequency response reveals a gradual decrease of the plasma frequency and the scattering rate of the Drude peak below $300\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ that gets anomalously enhanced below $90\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. The corresponding missing spectral weight of the Drude peak appears blueshifted towards the Lorentz band at $220 {\mathrm{cm}}^{\ensuremath{-}1}$. This characteristic blueshift signifies an enhanced localization of the charge carriers at low temperatures and contrasts the behavior expected for a bulk superconducting state for which the missing spectral weight would be redshifted to a delta function at zero frequency that accounts for the loss-free response of the superconducting condensate. Our data might still be compatible with a filamentary superconducting state with a volume fraction well below the percolation limit for which the spatial confinement of the condensate can result in a plasmonic resonance at finite frequency.