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In this work, the impact of the doping process on the photoluminescence emission of CaWO4 as a function of the concentration of Eu3+ cation (0.01 mol%, 0.02 mol%, 0.04 mol%, 0.06 mol%, 0.08 mol%, and 0.10 mol%) is discussed in detail. Ca1−xWO4:xEu3+ samples were successfully synthesized by a simple co-precipitation method followed by microwave irradiation. The blue shift in the absorption edge confirmed the quantum confinement effect and the band gap energy cover the range from 3.91 to 4.18 eV, as the amount of Eu3+ cations increases. The experimental results are sustained by first-principles calculations, at the density functional theory level, to decipher the geometry and electronic properties, thereby enabling a more accurate and direct comparison between theory and experiment for the Ca1−xWO4:xEu3+ structure. Funding for open access charge: CRUE-Universitat Jaume I

The article presents a new theory in physics which explains the interaction between gravity and light with mathematical results close to General Relativity (15 digits beyond the decimal point equal result) and unifies General Relativity with Quantum Physics by the fundamental elementary particle: the GEON. The GEON [1] is a fundamental solution of the relativistic quantum mechanical Dirac equation (Quantum Physics) and the confinement has been controlled by the fundamental interaction between Gravity and Light (General Relativity). The GEON is the most fundamental elementary particle and can be created by the compression of light into extremely high densities. The GEON appears when an equilibrium has been established between the expanding radiation pressure of light and the confining gravitational force of light. The GEON is the fundamental solution of the relativistic quantum mechanical Dirac equation. For this reason the GEON particle unifies Quantum Physics with General Relativity. The confinement of GEONS is only possible at discrete values. (Quantisation of Energy, Light and Gravity). The GEON carries the mass inside the structures of matter (Elementary Particles). The radius of a GEON with the mass of a proton (1.67×10-27 kg) equals 3 10-58 [m]. [30] PlotGraph 3, page 24 The new theory in physics has been based on the “divergence-free linear 4-dimensional stress-energy tensor in the Minkowski Space”. The difference between Einstein’s General Relativity and this theory is the different approach. Einstein has deformed (non-linear and non-divergence free) the “4-dimensional Stress-Energy Tensor” by introducing the curved 4-dimensional Riemannian Manifold to explain the interaction between Gravity and Light. The new theory describes the interaction between different fields (Electric, Magnetic and Gravitational) by identical interaction terms, generated by the separate divergence and the separate rotation of the different fields. (equation 24) The conclusion of the new theory is that “divergence-free” and “rotation-free” fields do not interact. When Isaac Newton published his 3 famous equations which became the foundation of Classical Dynamics, he was not aware that he was building the first elemental blocks for the Stress-Energy Tensor in the 4-dimensional Minkowski Space. When James Clerk Maxwell published his 4 famous equations which became the foundation for Classical Electrodynamics, he was not aware that he was building new blocks for the Stress-Energy Tensor in the 4-dimensional Minkowski Space. When Paul Dirac published his famous equation which became the foundation of Relativistic Quantum Physics, he was not aware that he was building further on blocks for the Stress-Energy Tensor in the 4-dimensional Minkowski Space. It was Albert Einstein who was one of the first physicists who discovered the importance of the Stress-Energy Tensor to describe in a mathematical way the interaction between Electromagnetic Radiation and a Gravitational Field. Because there was no match, Einstein deformed the Divergence-Free Linear “Stress-Energy Tensor” by deforming Space and Time. Using curved Riemannian manifolds, he deformed the fundamental Tensor in physics in such a way that he found a very special Mathematics to describe the interaction between Electromagnetic Radiation (Light) and a Gravitational Field. The Theory of General Relativity. This became a fundamental problem in physics. By deforming the fundamental building block in physics (the Divergence-Free Linear “Stress-Energy Tensor), there is no match anymore in the fundamental mainstreams in physics (classical mechanics, electrodynamics, quantum physics and general relativity). Classical Mechanics has no match with Classical Electrodynamics. Classical Electrodynamics has no match with Relativistic Quantum Physics. Relativistic Quantum Physics has no match with General Relativity. It is important to distinguish the “Physical Reality” from a Mathematical Description of it (which is in general an approach). The scalar curvature (or the Ricci scalar) is a measure of the curvature of a Riemannian manifold. Einstein used a curved Riemannian manifold to describe “Gravitational-Electromagnetic Interaction”. But the physics beyond this is the interaction between the different fields. It is possible to describe this in different ways. This new theory demonstrates a more direct approach in the force densities acting between different fields expressed by equation (24). This new theory starts with the Divergence-Free Linear “Stress-Energy Tensor” in the 4-dimensional Minkowski Space. And from this unique Divergence-Free “Stress-Energy Tensor” follows Classical Mechanics, Classical Electrodynamics, Relativistic Quantum Physics and General Relativity. Bringing back the necessary unity in physics. Theories which unify Quantum Physics and General Relativity, like “String Theory”, predict the non-constancy of natural constants. Accurate observations of the NASA Messenger [11] observe in time a value for the gravitational constant “G” which constrains until ( /G to be < 4 × 10-14 per year) . One of the characteristics of the New Theory is the “Constant Value” in time for the Gravitational Constant “G”. A second experiment to test the New Theory is the effect of “Gravitational RedShift” [2]. The “Gravitational RedShift” between an observatory on Earth (Radius = 6 106 [m]) and a Satellite in a Galileo Orbit (Radius = 23222 103 [m]) according “General Relativity”: The “Gravitational RedShift” between an observatory on Earth (Radius = 6 106 [m]) and a Satellite in a Galileo Orbit (Radius = 23222 103 [m]) according “The Proposed Theory”: &nbsp

In this paper, a new method for pesticide detection based on porous silicon microcavities was proposed. First, the aptamer of acetamiprid was fixed in the functionalized porous silicon microcavity. Then, the complementary strand of the aptamer modified with graphene quantum dots was hybridized with the aptamer, and the effective refractive index of the porous silicon microcavity increased. When acetamiprid was added, it bound to the aptamer due to its stronger specificity. The aptamer separated from the complementary strand of the coupled graphene quantum dots and bound to acetamiprid, resulting in a decrease in the effective refractive index, and its central wavelength of reflection spectrum was blue shifted, and the blueshift increased with the increase of acetamiprid concentration. The relationship between the change in central wavelength and the concentration of acetamiprid was analysed, and the detection limit of acetamiprid was 151 nm.

Hydrogen bonds (H-bonds) in the complexes between aldehydes and hydrogen chalcogenides, XCHO...nH2Z with X = H, F, Cl, Br, and CH3, Z = O, S, Se, and Te, and n = 1,2, were investigated using high-level ab initio calculations. The Csp2-H...O H-bonds are found to be about twice as strong as the Csp2-H...S/Se/Te counterparts. Remarkably, the S/Se/Te-H...S/Se/Te H-bonds are 4.5 times as weak as the O-H...O ones. The addition of the second H2Z molecule into binary systems induces stronger complexes and causes a positive cooperative effect in ternary complexes. The blue shift of Csp2-H stretching frequency involving the Csp2-H...Z H-bond sharply increases when replacing one H atom in HCHO by a CH3 group. In contrast, when one H atom in HCHO is substituted with a halogen, the magnitude of blue-shifting of the Csp2-H...Z H-bond becomes smaller. The largest blue shift up to 92 cm-1 of Csp2-H stretching frequency in Csp2-H...O H-bond in CH3CHO...2H2O has rarely been observed and is much greater than that in the cases of the Csp2-H...S/Se/Te ones. The Csp2-H blue shift of Csp2-H...Z bonds in the halogenated aldehydes is converted into a red shift when H2O is replaced by a heavier analogue, such as H2S, H2Se, or H2Te. The stability and classification of nonconventional H-bonds including Csp2-H...Se/Te, Te-H...Te, and Se/Te-H...O have been established for the first time.

Inorganic metal-halide perovskites hold a lot of promise for solar cells, light-emitting diodes, and lasers. A thorough investigation of their optoelectronic properties is ongoing. In this study, the accurate modified Becke Johnson generalized gradient approximation (mBJ-GGA) method without/with spin orbital coupling (SOC) implemented in the WIEN2k code was used to investigate the effect of mixed I/Br and Br/Cl on the electronic and optical properties of orthorhombic CsPb(I1-x Br x )3 and CsPb(Br1-x Cl x )3 perovskites, while the Perdew-Burke-Ernzerhof generalized gradient approximation (PBE-GGA) method was used to investigate their structural properties. The calculated band gap (Eg) using the mBJ-GGA method was in good agreement with the experimental values reported, and it increased clearly from 1.983 eV for CsPbI3 to 2.420 and 3.325 eV for CsPbBr3 and CsPbCl3, respectively. The corrected mBJ + SOC Eg value is 1.850 eV for CsPbI3, which increased to 2.480 and 3.130 eV for CsPbBr3 and CsPbCl3, respectively. The calculated photoabsorption coefficients show a blue shift in absorption, indicating that these perovskites are suitable for optical and optoelectronic devices.

With the blooming development of zero-dimensional nanomaterials, I-III-VI alloying quantum dots (QDs) with outstanding photoelectrical properties have emerged to attract much attention as promising environmentally-friendly substitutions for conventional binary Cd-based QDs. In this work, a facile one-pot method was introduced to synthesize unreported quaternary Ag-Cu-Ga-Se/ZnSe (ACGSe/ZnSe) QDs. A relatively high photoluminescence quantum yield (PL QY) of 71.9% and a tunable emission from 510 to 620 nm were successfully achieved. We explored the roles of alloying compositions in ACGSe/ZnSe QDs, inferring that increased Ag proportion would not only lower the Vdefect level which leads to the blue shift of emission, but also slow the ZnSe shelling process owing to the larger lattice distortion. At last, the white light-emitting diodes (WLEDs) were fabricated with ACGSe/ZnSe QDs as the conversion layer, indicating that the as-prepared QDs are a promising candidate for further applications.

ZnO QDs at different pH (8–12) concentrations were prepared using the hydrothermal method. The crystallite size decreases with the increase of pH concentration in the range of ~ 8 nm to ~ 4 nm. FESEM studies confirm the agglomerated highly dense homogeneous QDs. Optical studies reveal decrement in optical band gap with highly confined QDs. The detailed study of photoluminescence of ZnO QDs signifies the presence of the defect between the conduction band and the valence band. Drastic blue shift and enhancement in oxygen vacancies are obtained with more confined QDs as pH increases. The electrical conductance improves considerably and may be due to the increase in oxygen-related defects with increasing pH. With increasing pH the UV sensitivity increases but for all visible light decreases. Using density functional theory structural, electronic and electron localization functions have been determined. Hence a co-related study of experimental and theoretical work of prepared QDs is investigated.

Multicomponent oxide (GaxIn1−x)2O3 films are prepared on (0001) sapphire substrates to realize a tunable band-gap by magnetron sputtering technology followed by thermal annealing. The optical properties and band structure evolution over the whole range of compositions in ternary compounds (GaxIn1−x)2O3 are investigated in detail. The X-ray diffraction spectra clearly indicate that (GaxIn1−x)2O3 films with Ga content varying from 0.11 to 0.55 have both cubic and monoclinic structures, and that for films with Ga content higher than 0.74, only the monoclinic structure appears. The transmittance of all films is greater than 86% in the visible range with sharp absorption edges and clear fringes. In addition, a blue shift of ultraviolet absorption edges from 380 to 250 nm is noted with increasing Ga content, indicating increasing band-gap energy from 3.61 to 4.64 eV. The experimental results lay a foundation for the application of transparent conductive compound (GaxIn1−x)2O3 thin films in photoelectric and photovoltaic industry, especially in display, light-emitting diode, and solar cell applications.

The nanocrystalline Al-doped CdS semiconductors were produced accurately by the sol-gel calcination process. The aluminum was added with different percent’s (0, 1, 5, 10, 15, and 20 wt%) to the synthesized CdS. Both FT-Raman analysis and UV–VIS-NIR absorption measurements were utilized to characterize the studied semiconductors' structural and optical characteristics. The detected X-ray diffraction (XRD) patterns of the prepared CdS present a polycrystalline structure, and Al-doping does not significantly impact this range. Optical bandgaps were determined for undoped and Al-doped CdS, showing a significant change with the percentage of Al-dopants. With increasing Al-doping up to (20 percent), the optical bandgap for CdS (2.38 eV) grows to reach (2.47 eV) and the allowed transitions were found to be direct for the investigated samples. The blue shift may be the reason for the optical bandgap variations. Scanning Electron Microscope (SEM) micrographs were performed to establish the Al-doped CdS nanostructure to identify the morphological characteristics.

The structural and optical properties of polypyrrole-ZnO (PPy-ZnO) composites with different amount of ZnO are investigated. The nature of optical absorption and emission of the composites having agglomerated granular morphology is explored. Addition of ZnO slightly affects the conjugation of the polymer chain due to which the π-π* transition of PPy-ZnO composite shows some blue shift in the UV-Vis absorption spectra. The photoluminescence intensity of PPy-ZnO nanocomposite varies with variation of ZnO content. This tunability in the photoluminescence intensity of PPy-ZnO nanocomposite can be understood in terms of Forster Resonance Energy transfer (FRET) from ZnO (donor) to PPy (acceptor). The energy transfer efficiency, Forster radius and separation between donor and acceptor are predicted theoretically by using a FRET model. With the change in donor concentration, the energy transfer efficiency changes which affects the emission intensity of composites. The highest emission intensity is observed for 1.22 g of ZnO which indicates the highest energy transfer between ZnO and PPy. Thus, by tuning ZnO content the emission properties of the PPy-ZnO composite can be tuned.

Two dimensional (2D) van der Waals heterostructures from transition metal dichalcogenide (TMDC) semiconductors show a new class of spatially separate excitons with extraordinary properties. The interlayer excitons (XI) have been studied extensively, yet the mechanisms that modulate XI are still not well understood. Here, we introduce several organic-layer-embedded hybrid heterostructures, MoS2/organic/WSe2, to study the binding energy of XI. We discover that the dielectric screening of the quasi-particle is reduced with organic molecules due to decreased dielectric constant and greater separation distance between the TMDC layers. As a result, a distinct blueshift is observed in interlayer emission. We also find that the band alignment at the heterointerface is critical. When the organic layer provides a staggered energy state, interlayer charge transfer can transition from tunneling to band-assisted transfer, further increasing XI emission energies due to a stronger dipolar interaction. The formation of XI may also be significantly suppressed with electron or hole trapping molecules. These findings should be useful in realizing XI-based optoelectronics.

Electric field-induced antiferromagnets with ultrahigh resonant frequencies without current flow in insulating materials is highly desired. This paper reports the terahertz (THz) responses of Γ4 in rare-earth orthoferrite GdFeO3 ceramics, which were manipulated using thickening and thermal methods. As the thickness was increased, the noise was greatly reduced, and increased peak heights of both the ferromagnetic resonances and antiferromagnetic resonances were observed. For the thermal control of THz responses in GdFeO3, the resonant frequencies of both the ferromagnetic resonances and antiferromagnetic resonances experienced a blue shift, and their peak heights increased. The detected shifts of the responses were determined by the changes in thermodynamic potential. Moreover, macroscopic properties were collected to verify the coexistence of ferromagnetism and antiferromagnetism.

We investigated the structural and optical properties of nanoparticle-assisted pulsed laser-deposited ZnO microrods and Au-coated ZnO microrods grown on Si substrate. Our present study indicates that Au-coated ZnO microrods exhibit whispering gallery modes (WGM) in the near band edge region with significant splitting into two branches. Moreover, the WGMs exhibited blue shift with decrease in rod size. We found that the modes are well split in Au coated ZnO rods when compared with as-grown rods, resulted from the plasmon enhancement of WGM modes. We also found that the Au-coated ZnO was stable in the ambient when compared with uncoated ZnO. WGM resonance from the exciton related emission, the enhancement in WGMs, and stability in the ambient condition of the Au-coated ZnO microrods suggest great potential for small-volume devices and microlasers.

ZnO:Eu thin film fabricated by pulsed laser deposition was treated by pulsed UV laser. The effect of laser fluence from 70 to 125 mJ cm−2 on film properties was investigated. The results showed that the surface morphology was clearly modified and the film treated at laser fluence of 70 mJ cm−2 was more densified compared to the other annealed films. Laser treatment led to a reduction of carbon content and to a stoichiometric ZnO:Eu composition on the surface. Refractive index significantly decreased and extinction coefficient was blue shifted for higher laser fluences. Strong characteristic Eu3+ transitions were obtained using excitation at 266 nm. The highest photoluminescence intensity was observed for the annealed film at a laser fluence of 70 mJ cm−2. The influence of ambient composition (N2 and O2) and temperature (room temperature and 150 °C) to photoluminescence response was examined for optical gas sensor application. The laser-untreated film showed higher sensitivity to the presence of oxygen at both temperatures compared to the treated film. The stability of photoluminescence intensity at elevated temperature was improved for laser-treated areas.

Mixed-valent metal-halides containing ns2 lone pairs may exhibit intense visible absorption, while zero-dimensional (0D) ns2-based metal-chlorides are generally colorless but have demonstrated promising optoelectronic properties suitable for thermometry and radiation detection. Here, we report solvothermally synthesized mixed-valent 0D metal-halides Rb23BiIII x SbIII 7-x SbV 2Cl54 (0 ≤ x ≤ 7). Rb23SbIII 7SbV 2Cl54 crystallizes in an orthorhombic space group (Cmcm) with a unique, layered 0D structure driven by the arrangement of the 5s2 lone pairs of the SbIIICl6 octahedra. This red material is likely the true structure of a previously reported monoclinic "Rb2.67SbCl6" phase, the structure of which was not determined. Partially or fully substituting SbIII with isoelectronic BiIII yields the series Rb23BiIII x SbIII 7-x SbV 2Cl54 (0 < x ≤ 7), which exhibits a similar layered 0D structure but with additional disorder that yields a trigonal crystal system with an enantiomorphic space group (R32). Second harmonic generation of 532 nm light from a 1064 nm laser using Rb23BiIII 7SbV 2Cl54 powder confirms the noncentrosymmetry of this space group. As with the prototypical mixed-valent pnictogen halides, the visible absorption bands of the Rb23BiIII x SbIII 7-x SbV 2Cl54 family are the result of intervalent SbIII-SbV and mixed-valent BiIII-SbV charge transfer bands (CTB), with a blueshift of the absorption edge as BiIII substitution increases. No PL is observed from this family of semiconductors, but a crystal of Rb23BiIII 7SbV 2Cl54 exhibits a high resistivity of 1.0 × 1010 Ω·cm and X-ray photoconductivity with a promising μτ product of 8.0 × 10-5 cm2 s-1 V-1. The unique 0D layered structures of the Rb23BiIII x SbIII 7-x SbV 2Cl54 family highlight the versatility of the ns2 lone pair in semiconducting metal-halides, pointing the way toward new functional 0D metal-halide compounds.

In the present study, we aimed to investigate the effects of pH and sodium chloride (NaCl) concentration on the structure of β‐casein (β‐CN) purified from buffalo milk using circular dichroism (CD), intrinsic tryptophan, and anilino‐8‐naphthalene sulfonate (ANS) fluorescence spectroscopy. We found that NaCl concentration played a critical role in the stability of the secondary structure of β‐CN. The CD negative peak had a redshift as the NaCl concentration was increased and accompanied by a decrease of β‐sheet content and an increase of α‐helix content. ANS fluorescence spectroscopy also indicated that higher NaCl concentration and lower pH significantly affected the tertiary structure of β‐CN. Dynamic light scattering (DLS) results showed that the particle size of buffalo β‐CN had a blueshift, and then a redshift within the pH range of 5.0–7.5, and it showed a redshift when the NaCl concentration was increased., This study aimed to investigate the effects of pH and NaCl concentration on purified β‐casein structure from buffalo milk using circular dichroism (CD), intrinsic tryptophan and ANS fluorescence spectroscopic. It was found that NaCl concentration was a critical factor in affecting stability of the secondary structure of β‐casein.

GaN nanorods (NRds) with axial InGaN/GaN MQWs insertions are synthesized by an original cost-effective and large-scale nanoimprint-lithography process from an InGaN/GaN MQWs layer grown on c-sapphire substrates. By design, such NRds exhibit a single emission due to the c-axis MQWs. A systematic study of the emission of the NRds by time-resolved luminescence (TR-PL) and power dependence PL shows a diameter-controlled luminescence without significant degradation of the recombination rate thanks to the diameter-controlled strain tuning and QSCE. A blueshift up to 0.26 eV from 2.28 to 2.54 eV (543 nm to 488 nm) is observed for 3.2 nm thick InGaN/GaN QWs with an In composition of 19% when the NRds radius is reduced from 650 to 80 nm. The results are consistent with a 1-D based strain relaxation model. By combining state of the art knowledge of c-axis growth and the strong strain relieving capability of NRds, this process enables multiple and independent single-color emission from a single uniform InGaN/GaN MQWs layer in a single patterning step, then solving color mixing issue in InGaN based nanorods LED devices.

金沢大学先端科学・社会共創推進機構, To produce a deep green (530 nm–570 nm) LED, the suitable indium (In) composition in the InxGa1-xN/GaN multi-quantum well (MQW) structure is crucial because a lower indium composition will shift the wavelength of emission towards the ultraviolet region. In this paper, we clarify the effects of an indium-rich layer to suppress such blue shifting, especially after the annealing process. According to characterizations by the uses of XRD and TEM, narrowing of the MQW layer was observed by the indium capping, while without the capping, the annealing results in a slight narrowing of MQW on the nearest layer to the p-type layer. By adding an indium capping layer, the blue shift of the photoluminescence was also suppressed and a slight red shift to keep green emission was observed. Such photoluminescence properties were consistent with the tiny change of the MQW as seen in the XRD and TEM characterizations.

This paper investigates the impact of dislocation density and active layer structure on the degradation mechanisms of 1.3 $\mu \text{m}$ InAs Quantum Dot (QD) lasers for silicon photonics. We analyzed the optical behavior of two sets of samples, having different dislocation densities and different number of quantum dot layers in the active region. The samples were subjected to a short-term step-stress experiment and to long-term constant current operation in order to investigate the dominant degradation processes. The results indicate that: (i) the temperature stability is much higher in the devices grown on native substrate, thanks to the lower defect density; (ii) the roll-off current is considerably higher for the devices with higher number of layers, due to the lower density of carriers in the QDs; (iii) in nominal ground-state operating regime, the degradation rate is limited by the density of dislocations, that may serve as preferential paths for the diffusion of non-radiative recombination centers; (iv) at extreme injection levels and operating temperatures, the devices exhibit a blue shift of the spectral emission; possible explanations for this process are discussed in the paper.

The strongly anisotropic properties of phosphorene makes it an attractive material for applications in deciding the specific direction for different purposes. Here we have particularly reported the competition between strain and electric field stimuli in evaluating the band gap and electron energy loss spectrum (EELS) of single-layer black phosphorus using the tight-binding method and the Kubo conductivity. We construct possible configurations for this competition and evaluate the interband optical excitations considering the corresponding band gap variations. The band gap increases with the individual electric field, while it increases (decreases) with tensile (compressive) uniaxial in-plane strain. Contrary to the in-plane strains, the uniaxial out-of-plane strain shows a critical strain at which the system suffers from a phase transition. Furthermore, the presence of these stimuli simultaneously results in an extraordinary band gap engineering. Based on the EELS response in the electromagnetic spectrum, the armchair (zigzag) direction is classified into the infrared and visible (ultraviolet) region. We report that the electric field gives rise to the blue shift in the interband optical transitions along the armchair direction, while the compressive/tensile (tensile/compressive) in-plane/out-of-plane strain provides a red (blue) shift. Moreover, we observe an inverse behavior of EELS response to the individual and combined effects of electric field and strains compared to the band gap behavior except at critical out-of-plane strain for which the physical theory of interband excitation is simply violated. Our results provide a new perspective on the applicability of phosphorene in stimulated optical applications.

Strain in two-dimensional (2D) materials induces shifts in the visible spectrum due to strained binding energies, an accurate study of which is critical for materials engineering in the design of optoelectronic applications. Different from previous studies that employed computationally demanding theoretical approaches, we present an analytical approach, based on the difference method to calculate the impact of strained binding energy on the optical gap in mono-layer $${\hbox {MoS}}_{2}$$ by exploiting an existing tight binding (TB) and a fractional Coulomb potential model, for strained band gap and binding energy calculation, respectively. The inclusion of strained binding energy, changing at a rate of $$-8.1 \, \hbox {meV}/\bigtriangleup 1\%$$ of biaxial in-plane tensile strain accompanied with a variation of $$-110 \, \hbox {meV}/\bigtriangleup 1\%$$ of strain in the TB band gap, causes the optical gap to alter at a rate of $$-105.3 \, \hbox {meV}/\bigtriangleup 1\%$$ of strain, supported by first-principles calculations and is benchmarked with reported experimental and theoretical values. The effect of strained binding energies causes a blueshift in the optical gap by a correction factor, increasing from $$\approx 0.5\%$$ to $$\approx 12\%$$ , with an increase in equi-biaxial in-plane tensile strain from 1% to 11%, respectively. Furthermore, binding energy sensitivity to strain decreases linearly with a structural change from a mono-layer to a few layers in the 2D regime and saturates in the bulk regime. The presented framework can be used for the calculation of strained binding energies and optical gaps of other 2D materials and thus allows us to tune optical properties of 2D nanomaterials that are sensitive to lattice deformations.

Mechanical tuning of a 3D-printed, polymer-based one-dimensional photonic crystal was demonstrated in the terahertz spectral range. The investigated photonic crystal consists of 13 alternating compact and low-density layers and was fabricated through single-step stereolithography. While the compact layers are entirely polymethacrylate without any intentional internal structures, the low-density layers contain sub-wavelength sized slanted columnar inclusions to allow the mechanical compression in a direction normal to the layer interfaces of the photonic crystal. Terahertz transmission spectroscopy of the photonic crystal was performed in a spectral range from 83 to 124 GHz as a function of the compressive strain. The as-fabricated photonic crystal showed a distinct photonic bandgap centered at 109 GHz, which blue shifted under compressive stress. A maximum shift of 12 GHz in the bandgap center frequency was experimentally demonstrated. Stratified optical models incorporating simple homogeneous and inhomogeneous compression approximations were used to analyze the transmission data. A good agreement between the experimental and model-calculated transmission spectra was found.

High-pressure ice polymorphs are important for our understanding of hydrogen bonding and exist in the interior of the earth and icy moons. Nonetheless, spectroscopic information about them is scarce, where no information about their optical properties in the near-infrared (NIR) region is available at all. We here report NIR spectra of six ice polymorphs differing in terms of their density and O-atom topology, namely, ices II, IV, V, VI, IX, and XII, in comparison with the known spectra of ice Ih. By contrast to earlier work, we do not use mulling agents or transmission of thin films but use diffuse reflectance on powdered samples in liquid nitrogen. The first overtone of the OH-stretching mode is identified as the marker band most suitable to distinguish between these ices. There is a clear blue shift of this band that increases with increasing topological density in addition to a significant narrowing of the band.

Travel time anomaly in the communicatin of spatial instruments installed in solar planets and Earth are investigated in a model of gravity impact on radio signal propagation. Resulting travel times anomaly shows variations less than 10-3 seconds to and from Venus and Mars while Sun provides anomaly travel times of about -2 × 10-2 sec as backward signal needs more times than emitted signal from Earth. In the current explorations on Mars, the travel time anomaly may reach 1.8 × 10-4 sec as orbital Mars position pass through its minimum distance with respect to Earth. Implications of the difference between one and two-way travel times may be related to redshift/blueshift while travel time of received signal is less or greater than emitted signal.

Photochemical synthesis under visible light irradiation is a novel approach in the field of green chemistry, and composites with abundant active centers for electrochemical detection are highly attractive. Herein, a meso-tetra(4-sulfonatophenyl)porphyrin silver/Ag nanoparticles/graphene phase C3N4 nanosheets (Ag2TPPS4/AgNPs/ng-C3N4) material with a sandwich-like structure was synthesized using a two-step photocatalytic reaction at room temperature (25 °C). In the first visible light irradiation step and in the presence of a hole capture agent, Ag+ ions were photocatalytically reduced onto the surface of ng-C3N4 that was used as a photocatalyst. Then, the protons (H+) in the core of H2TPPS4 were substituted in situ by photo-oxidized Ag+ during the second visible light irradiation step and in the presence of an electron capture agent. The electrochemical response of Ag2TPPS4 and ng-C3N4 to ractopamine (RAC) results in the unique double-faced active centers of Ag2TPPS4/AgNPs/ng-C3N4, and the cores (AgNPs) are beneficial as bridges for the connection between Ag2TPPS4 and ng-C3N4 and for high-efficiency electron transfer. Hence, as-synthesized Ag2TPPS4/AgNPs/ng-C3N4 exhibits high sensitivity (a low detection limit of 5.1 × 10−8 M, S/N = 3.0), a wide linear range (1 × 10−7 to 1.2 × 10−5 M), and long-term stability. Based on the experimental verification of the electrochemical dynamics and electrostatic attraction at the interface between the dual-active-center surface and RAC, the electrochemical mechanism has been clarified. Specifically, in the multi-cycle oxidation of RAC, the blue shift of specific UV-vis peaks also confirms the electrocatalytic oxidation of the two terminal hydroxyl groups of RAC. In brief, Ag2TPPS4/AgNPs/ng-C3N4 with a sandwich-like structure and double-faced active centers enhances the detection sensitivity and electrocatalytic efficiency towards RAC.

ZnO nanoparticles co-doped simultaneously with Ni and Cu at concentrations varying between 0 and 10% were synthesized by wet chemical method. The resulting nanoparticles were less than ~ 60 nm. At 5% Ni + 5% Cu co-doping, enhanced visible luminescence between 380 nm – 460 nm is seen. Coupled with a low bandgap of 3.4 eV, they result in conducive optical properties for application of this material as UV Photodetector. Marginal changes in bond length (~ 0.003 A) and c/a ratio (~ 0.002 A), along with absence of impurity phases reflect its microstructural superiority. Morphological studies indicate marginal reduction of interplanar spacing due to doping, thus, forming uniform crystalline nanoparticles. The nominal composition of Zn, O, Ni and Cu without any impurity phases remains intact. An overall blue shift in absorption peak for all samples than bulk ZnO is observed, emerging due to size effects. However, at doping concentrations higher than 5%, Cu (111) and Ni (200) phases are seen due to clustering. Electrical studies under UV exposure are in agreement with the characterization studies on the sample, showing highest responsivity, current gain and high quantum efficiency values of 10.003 mA, 1.0421 and 3.146% respectively. These properties enable 5% Ni + 5% Cu co-doped ZnO nanoparticles to be explored for use as a material for optoelectronic devices like UV Photodetector.

The spin coating method was employed to fabricate Yb-doped ZnO thin films at 0, 3, 5, 7, and 9 at.% over a glass substrate at low temperature. X-ray diffraction analysis revealed that the hexagonal wurtzite structure was retained even at high doping contents. With the incorporation of Yb+3 ions, a slight decrease in the lattice parameters and crystallite size was observed as the ytterbium content increased. X-ray photoelectron spectroscopy confirmed the presence of ytterbium in the doped ZnO films, and the oxidation state of ytterbium was 3+ for all the samples. Morphological studies revealed a surface microstructure formed by micro islands, which tended to be denser as the ytterbium content increased. Optical transmittance was observed at approximately 75–85%, a blueshift was observed, and consequently, an increase in the bandgap, which varies from 3.0 to 3.2 eV, was observed. The refractive index and extinction coefficient decreased as the ytterbium dopant concentration increased. The photoluminescence results exhibited a strong ultraviolet emission, allowing the use of these thin films in optoelectronic applications.

Author(s): Babbe, F; Masquelier, E; Zheng, Z; Sutter-Fella, CM | Abstract: Wide band gap mixed halide perovskites such as MAPb(I1-xBrx)3 sparked great research interest because of their outstanding optoelectronic properties, ease of fabrication, and band gap tunability. Their application thus far is however limited by light-induced halide segregation in which microscopic clusters with a high iodide content are formed and act as recombination centers. The key mechanism(s) underlying this halide segregation process are still debated. Here, we present a study on the photoluminescence evolution in MAPb(I1.5Br1.5) perovskites with varying microstructures under constant illumination at room temperature and at elevated temperature. Our findings reveal a more complicated picture of the segregation mechanism occurring in three stages instead of two as commonly reported. The process starts with a flash formation of I-rich domains. Following is a rapid blue shift before the gradual and typically observed red shift occurs. The evolution of the three stages is fully reversible in the dark and is also present at elevated temperatures (50 °C). We explain the existence of multiple stages during light-induced halide segregation by natural compositional fluctuations of the halides and the formation of halide clusters with a dynamically changing distribution in I-Br content. The variation in the I-Br ratio depends on the grain size and film heterogeneity. These findings add further details in the quest of unraveling the underlying segregation mechanism(s), which need to be identified to stabilize halides in wide band gap perovskites.

The existence of surface organic capping ligands on quantum dots (QDs) has limited the potential in QDs emission properties and energy band gap structure alteration as well as the carrier localization. This drawback can be addressed via depositing a thin layer of a semiconductor material on the surface of QDs. Herein, we report on the comparative study for photoluminescent (PL) properties of PbS and PbS/MnS QDs. The carrier localization effect due to the alteration of energy band gap structure and carrier recombination mechanism in the QDs were investigated via PL measurements in a temperature range of 10-300 K with the variation of the excitation power from 10 to 200 mW. For PbS QDs, the gradient of integrated PL intensity (IPL) as a function of excitation power density graph was less than unity. When the MnS shell layer was deposited onto the PbS core, the PL emission exhibited a blue shift, showing dominant carrier recombination. It was also found that the full width half-maximum showed a gradual broadening with the increasing temperature, affirming the electron-phonon interaction.

Photoluminescence (PL) and Raman spectra of GaAs1-xBix samples grown at different rates (0.09 to 0.5 µm/h) were investigated. The PL peak wavelength initially redshifted with the increase of growth rate and reached the longest wavelength (1158 nm) for sample grown at 0.23 µm/h. This is followed by PL peak wavelength blueshift for higher growth rates. The Raman data show peaks at 162, 228, 270, and 295 cm-1 which can be attributed to GaAs like phonons. GaBi like vibrational modes were also observed at 183 and 213 cm-1. However, the intensity of Bi induced phonons is significantly weaker compared to GaAs due to low concentration of Bi compared to As and thin GaAs1-xBix epilayer. The PL data and GaAs transverse optical (TO) to longitudinal optical (LO) phonons intensity ratio indicate that Bi concentration is highly dependent on the growth rate and the highest Bi concentration was obtained by sample grown at 0.23 µm/h. It is found that the full-width-at-half-maximum (FWHM) of GaAs LO mode increases significantly for samples grown at high growth rates suggesting crystal quality degradation due to lack of surfactant effects.

Real-time monitoring of the vital signals using flexible and portable biosensors plays an important role in future human life. However, there is most often a tradeoff between the improvement of the mechanical properties of these sensing chips and their sensitivity. In this study, we proposed 2-D polydimethylsiloxane (PDMS)–Au and silk–Au chips with microhole and microparticle patterns performing in an integrated platform of plasmonic ellipsometry. Under an external sinusoidal signal, we observed the regular dependence of the optical responses and plasmonic resonances on the frequency and not on the current. Using integrated plasmonic-ellipsometry technique and the phenomenon of active plasmonics, PDMS–Au microhole chip has demonstrated that $\Delta $ and $\Psi $ parameters became lesser by increasing the frequency and the resonance wavelength underwent a redshift. However, for silk–Au chip with inverse pattern of microparticle bumps, $\Delta $ and $\Psi $ had augmentation trend with respect to the frequency and the resonance wavelength shifted to shorter wavelengths. By optical and thermal analyses, we have demonstrated that this study can provide new insights into fabricating optically phase and amplitude sensitive biosensors based on conformal substrates with thermo-optical properties that can behave in redshift and blueshift regimes.

Study of structure and optical properties of magnesium ammonium phosphate hexahydrate crystal known as struvite is presented. Experimentally determined infrared (IR) and ultraviolet–visible (UV–vis) spectra are compared with the theoretical predictions of density functional methods. Examination of the interatomic bond lengths, Mulliken atomic charges, and binding energies of water in the magnesium hexahydrate cation, together with the analysis of the hydrogen bond pattern have allowed us to explain a special feature of the IR spectrum of struvite, a blueshift of the band corresponding to the O–H stretching mode. This mode has been assigned to a “dangling” hydroxyl group in one of the water molecules in magnesium hexahydrate. Using experimentally obtained UV–vis spectrum and performing Tauc plots analysis, optical bandgap of struvite has been narrowed to a range from 5.92 to 6.06 eV.

The layered van der Waals magnetic insulator chromium bromine (CrBr3) has excellent optical properties and it provides an interesting platform for investigating light–matter interactions. Here, we focused on its self-modulated photoluminescence (PL) spectrum. We find that there are interference fringes superposed on the PL curves due to the Fabry–Perot resonance between the front and rear interfaces of CrBr3 flakes. Moreover, there is a huge Stokes shift between the PL spectrum and lowest absorption band, which can prevent reabsorption of PL and is a benefit for enhancing the resonant intensity of the PL spectrum. In addition, we investigate the PL spectrum variation under suppressing thermal vibration with decreasing temperature from 300 to 80 K, which shows the significant increase of PL intensity and blue shift of PL maximum peak. This work gives details of CrBr3 self-modulated PL properties and creates opportunities for using CrBr3 in optical devices and lasing components in future applications.

Molecular dopants are of great importance in nano-chemical compounds by improving the function of inorganic electronic devices. In this article, Cu:ZnS (CZS) powders were made using the chemical method. Thin films were deposited by the physical method. The CZS films showed cubic crystal structures with a single hexagonal peak. The impact of an increase in Cu2+ dopants was investigated not only in reducing the grain size but also in reducing the optical energy gap and deviation parameters of the lattice constants. The estimated energy gaps of CZS nanostructures (NSs) were (3.70, 3.66, 3.0, and 3.76 eV) for Cu dopant (0, 1.5, 3.0, and 4.5 at.%); an indication of a blueshift. Redshift was also noticed for Cu dopant 4.5% due to interstitial sites. Moreover, the transmittance for all specimens was (70–95%) in the visible and near IR-region and reduced in the UV range (

Full visible spectrum photonic droplets and consequent microcapsules with nano-in-micro structure were prepared through microfluidic technique. Photo-curable resin and suspension of monodispersed soft nanogels were used as shell and core of the microcapsules, respectively. Upon UV irradiation, the droplets can be subsequently transformed into photonic microcapsules with an ultrathin polymeric shell. The shell thickness of the photonic microcapsules was found to be approximately 700 nm. Due to the ultrathin shell and soft core, the photonic microcapsules with nano-in-micro structure display dramatic changes both in shapes and photonic property under the impact of osmosis effect or temperature stimulus. Typically, the shell and core parts of nano-in-micro structure could respectively undergo a size expansion/even rupture and a size decrease/buckling under hypotonic and hypertonic condition. Correspondingly, the peak value of the reflection spectra of the microcapsules showed a redshift and blue shift, respectively. The mechanism to the structure and optical properties variation involves the osmotic pressure induced the volume-fraction change of the nanogel-based photonic dispersion and the shell buckling of the core/shell microcapsules.

We investigate the strain state of ensembles of thin and nearly coalescence-free self-assembled GaN nanowires prepared by plasma-assisted molecular beam epitaxy on Ti/Al2O3(0001) substrates. The shifts of Bragg peaks in high-resolution X-ray diffraction profiles reveal the presence of a homogeneous tensile strain in the out-of-plane direction. This strain is inversely proportional to the average nanowire radius and results from the surface stress acting on the nanowire sidewalls. The superposition of strain from nanowires with different radii in the same ensemble results in a broadening of the Bragg peaks that mimics an inhomogeneous strain on a macroscopic scale. The nanowire ensembles show a small blueshift of the bound-exciton transitions in photoluminescence spectra, reflecting the existence of a compensating in-plane compressive strain, as further supported by grazing incidence X-ray diffraction measurements carried out at a synchrotron. By combining X-ray diffraction and photoluminescence spectroscopy, the surface stress components fx and fz of the air-exposed GaN { 1 1 ¯ 00 } planes that constitute the nanowire sidewalls are determined experimentally to be 2.25 and − 0.7 N/m, respectively.

The control of defect states is becoming a powerful approach to tune two-dimensional materials. Black phosphorus (BP) is a layered material that offers opportunities in infrared optoelectronics. Its band gap depends strongly on the number of layers and covers wavelengths from 720 to 4000 nm from monolayer to bulk, but only in discrete steps and suffering from poor photostability. Here, we demonstrate tunable and stable infrared emission from defect states in few-layer BP. First, we demonstrate a continuous blue shift of the main photoluminescence peak under laser exposure in air due to the creation of crystal defects during photo-oxidation. The tunable emission spectrum continuously bridges the discrete near-infrared energies of few-layer BP for a decreasing number of layers. Second, using plasma-enhanced encapsulation, we report the creation and protection of defects with peak emission energy between bilayer and trilayer BP. The emission is photostable and has an efficiency comparable to that of pristine layers while retaining the strong polarization anisotropy characteristic of BP. Our results put forward defect engineering in few-layer BP as a flexible strategy for stable and widely tunable infrared sources and detectors in integrated spectrometers and hyperspectral sensors.