Visible Region Research Articles

Tuning Excited State Character in Iridium(III) Photosensitizers and Its Influence on TTA-UC.

A series of mixed ligand, photoluminescent organometallic Ir(III) complexes have been synthesized to incorporate substituted 2-phenyl-1H-naphtho[2,3-d]imidazole cyclometalating ligands. The structures of three example complexes were categorically confirmed using X-ray crystallography each sharing very similar structural traits including evidence of interligand hydrogen bond contacts that account for the shielding effects observed in the 1H NMR spectra. The structural iterations of the cyclometalated ligand provide tuning of the principal electronic transitions that determine the visible absorption and emission properties of the complexes: emission can be tuned in the visible region between 550 and 610 nm and with triplet lifetimes up to 10 μs. The nature of the emitting state varies across the series of complexes, with different admixtures of ligand-centered and metal-to-ligand charge transfer triplet levels evident. Finally, the use of the complexes as photosensitizers in triplet-triplet annihilation energy upconversion (TTA-UC) was investigated in the solution state. The study showed that the complexes possessing the longest triplet lifetimes showed good viability as photosensitizers in TTA-UC. Therefore, the use of an electron-withdrawing group on the 2-phenyl-1H-naphtho[2,3-d]imidazole ligand framework can be used to rationally promote TTA-UC using this class of complex.

Near-Infrared Absorbing Aza-BODIPY Dyes for Optoelectronic Applications.

Organic dyes that absorb light in the visible to near-infrared region have garnered significant interest, owing to their extensive utility in organic photovoltaics and various biomedical applications. Aza-boron-dipyrromethene (Aza-BODIPY) dyes are a class of chromophores with impressive photophysical properties such as tunable absorption from the visible region towards near infrared (NIR) region, high molar absorptivity, and fluorescence quantum yield. In this review, we discuss the developments in the aza-BODIPYs, related to their synthetic routes, photophysical properties and their applications. Their design strategies, modifications in chemical structures, mode/position of attachment, and their impact on photo-physical properties are reviewed. The potential applications of aza-BODIPY derivatives such as organic solar cells, photodynamic therapy, boron-neutron capture therapy, fluorescence sensors, photo-redox catalysis, photoacoustic probes and optoelectronic devices are explained.

Experimental Study of White Light Interferometry in Mach–Zehnder Interferometers Based on Standard Single Mode Fiber

In this work, we experimentally analyzed and demonstrated the performance of an in-line Mach–Zehnder interferometer in the visible region, with an LED light source. The different waist diameter taper and asymmetric core-offset interferometers proposed used a single-mode fiber (SMF). The visibility achieved was V = 0.14 with an FSR of 23 nm for the taper MZI structure and visibilities of V = 0.3, V = 0.27, and V = 0.34 with FSRs of 23 nm, 17 nm, and 8 nm and separation lengths L of 2.5 cm, 4.0 cm, and 5.0 cm between the core-offset structure, respectively. The experimental investigation of the response to the temperature sensor yielded values from 50 °C to 300 °C; the sensitivity obtained was 3.53 a.u./°C, with R2 of 0.99769 and 1% every 1 °C in the transmission. For a range of 50 °C to 150 °C, 20.3 pm/°C with a R2 of 0.96604 was obtained.

Optoelectronic and transport properties of Lead-Free halide based Na2AgTlZ6 (Z = Cl, Br, I) double perovskites for energy harvesting applications

The bandgap engineering and deliberate band edge manipulation of perovskites make them potential candidates for the photovoltaic industry. Here we theoretically investigate the structure, density of states, and photovoltaic and thermoelectric characteristics of Na2AgTlZ6 (Z = Cl, Br, I) using WIEN2k code. The incorporation of Br and I at the Cl site caused the increase in lattice constant which leads to the decrease in bulk modulus and Debye temperature. The computed values of Poisson (<0.26) and Pugh (<1.75) ratio verified their brittle nature. The bandgap analysis reveals direct bandgap nature and bandgap value lie in the visible region for parent composition and infrared and far infrared when Cl is replaced with Br and I. The density of state plots uncovers the shifting of energy states in valence and conduction bands towards the Fermi level with the increasing number of electrons in the halogens. The increase in the value of dielectric constant, refractive index, and shifting of peaks towards lower energy value is witnessed with atomic number of halogen atoms. The viability of these compositions for thermoelectric devices is further confirmed when electrical conductivity and Seebeck coefficient dependent Figure of merit and power factor are evaluated in the temperature range of 200–800 K. In addition, the anisotropic nature of studied compositions is explored through the computation of the modulus of elasticity including Young’s modulus, Shear modulus in addition to compressibility, and Poisson’s ratio.

Cyclic Azahelicene Dimers Showing Bright Circularly Polarized Luminescence and Selective Fluoride Recognition

Although helicenes are promising molecules, the synthetic difficulty and tediousness have often been problems, and only small amounts of optically pure helicenes have been obtained by using chiral HPLC in most cases. Herein, aza[7]helicenes or closed‐aza[7]helicenes with (1R)‐menthyl substituents were selectively synthesized via the intramolecular Scholl reaction, and the diastereomeric pairs were separated by silica gel column chromatography. The optically pure helicenes were further transformed into the corresponding cyclic dimers, and the chiroptical properties were investigated. The rigid p‐frameworks of the dimers led to the high molar extinction coefficients and fluorescence quantum yields, while the twisted helicene moieties induced clear Cotton effects and CPL in the visible region, and the high CPL brightness (BCPL) was achieved. Furthermore, the cyclic dimers were found to have the macrocyclic cavity with the two NH groups suitable for the selective binding of a fluoride anion, which induced significantly redshifted fluorescence and CPL in the red region.

Temperature-switchable anti-reflective structure based on vanadium dioxide phase transition in the visible and near-infrared wavelength regions

Abstract Nowadays, the anti-reflective (AR) structures are essential in many applications like display screens, photovoltaic structures and light detection and ranging. Traditionally, the AR surfaces are almost multilayer (ML) structures to minimize the reflection value by producing the destructive interference of reflected light beams at the layers' interfaces. In the new and advanced AR surfaces, nanostructures (NS) are proposed and used for minimizing the reflection. In this paper, we propose a temperature-switchable AR-ML-NS, based on vanadium dioxide (VO2) phase transition from semiconductor to metallic state around the critical temperature of 68º C. Here, a pyramidal NS of VO2 is considered on top surface of a ML which minimizes the light reflection of the structure. While some AR structures may work in some restricted light wavelengths, here our proposed structure's AR wavelength region can be tuned between the visible and near-infrared (NIR) region through the thermal phase transition of VO2. VO2 phase control leads to a temperature-switchable AR structure, which is of great importance for investigating different switchable AR structures.&amp;#xD;

Cyclic Azahelicene Dimers ShowingBright Circularly Polarized Luminescence and Selective Fluoride Recognition.

Although helicenes are promising molecules, the synthetic difficulty and tediousness have often been problems, and only small amounts of optically pure helicenes have been obtained by using chiral HPLC in most cases. Herein, aza[7]helicenes or closed-aza[7]helicenes with(1R)-menthyl substituents were selectively synthesized via the intramolecular Scholl reaction, and the diastereomeric pairs were separated by silica gel column chromatography. The optically pure helicenes were further transformed into the corresponding cyclic dimers, and the chiroptical properties were investigated. The rigidp-frameworks of the dimers led to the high molar extinction coefficients and fluorescence quantum yields, while the twisted helicene moieties induced clear Cotton effects and CPLin the visible region,and thehighCPL brightness (BCPL) was achieved. Furthermore, the cyclic dimers were found to have the macrocyclic cavity with the two NH groups suitable for the selective binding of a fluoride anion, which induced significantly redshifted fluorescence and CPL in the red region.

Modulation of components toward blue light emission and scintillation properties of Eu2+ activated Sr1-xLaxMgxAl12-xO19 crystal

The development of Eu2+-activated oxide materials with high efficiency, fast decay and narrow bandwidth emission in the visible region is still challenging for the field of luminescence and scintillation applications. Generally, Eu2+ in oxide hosts can emit intense and broad 5d-4f emission in the visible region, but efficient emitting with stable bivalence of Eu is rare in inorganic oxide system. In this work, a series of ASL:Eu2+ (Sr1-xLaxMgxAl12-xO19) powder samples with various La, Mg doping ratios were designed and synthesized to modulate the UV or X-ray excited luminescence properties, including redshift, quantum yield, and decaying lifetime. Moreover, an ASL:Eu2+ crystal with the optimal ratio x = 1/3 was grown, its scintillation performance was compared with standard Bi4Ge3O12 crystal sample and evaluated in detail. These results indicate that the ASL:Eu2+ crystal is potential scintillator as a kind of X-ray detection and provide a reference for the further development of high-performance Eu-activated oxide scintillation materials.

Formation of a potential barrier by a ZnSXSe1−X electron-blocking layer to improve the efficiency of CdSe0.3S0.7/CdSe quantum dot sensitized solar cells

We designed and fabricated multilayer quantum dots sensitized solar cells (QDSCs) with TiO2 NPs/CdSe0.3S0.7/CdSe/ZnSXSe1−X, X = S/S + Se = 0, 0.7, 0.8, 0.9, and 1 photoelectrodes to achieve optimum power conversion efficiency (PCE). In the corresponding structure, incoming light is absorbed by the CdSe0.3S0.7 and CdSe quantum dots (QDs), while the ZnSXSe1−X QDs act as an electron blocking layer or passivation layer, forming an energy barrier that restricts electron mobility from the light absorbers to the polysulfide electrolyte. The beneficial effect of the alloyed ZnSXSe1−X layer is the adjustability of its nanoparticle size/bandgap energy proportional to variations in the concentration of anionic precursors X, according to optical results. The PCE value of the reference cell with the TiO2 NPs/CdSe0.3S0.7/CdSe photoanode is 4.15 %. Following the coating of ZnSe, ZnS0.7Se0.3, ZnS0.8Se0.2, ZnS0.9Se0.1, and ZnS QDs via two successive ionic layer adsorption and reaction (SILAR) cycles (2Sc) on the CdSe0.3S0.7/CdSe co-sensitized photoelectrode increasing stability and improving the PCE value to 4.9 %, 5.40 %, 5.70, 5.25 %, and 5.05 %, respectively. Next, by modifying the thickness of the champion cell's passivation layer, the QDSCs with TiO2 NPs/CdSe0.3S0.7/CdSe/ZnS0.8Se0.2 (3Sc) photoelectrode exhibit maximum photovoltaic performance parameters of short circuit current density (JSC) = 26.25 mA/cm2, open circuit voltage (VOC) = 560 mV, fill factor (FF) = 0.42 % and PCE = 6.15 %. This improvement in performance is the result of decreased internal energy loss and recombination of charge carriers at the interface between the electrolyte and photoelectrode, which increases electron collection efficiency and electron injection efficiency in the visible region according to the external and internal quantum efficiency curves.

Theoretical Study of the Ternary Compound Monolayer CuP2Se for Photocatalytic Water Splitting with Efficient Optical Absorption.

Utilizing photocatalytic method to produce hydrogen by splitting water is an efficient strategy to solve the hotspot issues of energy crisis and environmental pollution. Herein, we systematically investigate the corresponding properties of the reported Cu-bearing ternary compound monolayer CuP2Se by using the first-principle calculations. The monolayer CuP2Se has quite small cleavage energy of 0.51 J/m2, indicating it can be easily produced by the mechanical exfoliation method experimentally. In addition, it is an indirect bandgap semiconductor material which has a moderate value of 1.91 eV. The conduction band minimum (CBM) and valence band maximum (VBM) can perfectly straddle the redox potentials of water when a biaxial strain of -4% to 4% is applied, unveiling the high photocatalytic thermodynamic stability of monolayer CuP2Se in response to the effect of solvent tension. Remarkably, the monolayer CuP2Se also demonstrates significant sunlight capturing ability in the visible region. The outstanding electronic and optical properties suggest that the monolayer CuP2Se is undoubtedly a viable material for photocatalytic water splitting.

Graphene and ZnO NPs-enhanced photodetectors based on SiO NWs: Synthesis, characterization, and applications

In this study, we successfully synthesized and characterized silicon oxide nanowires/graphene/zinc oxide nanoparticles (SiO NWs/Graphene and ZnO NPs) hybrid nanostructures using pulsed laser deposition (PLD) technique. The characterization of the crystalline phase, morphology, and optical properties of the synthesized hybrid nanostructure systems revealed that the addition of graphene and ZnO NPs led to increased roughness values and changes in the surface topography of the films. The optical properties showed that the addition of graphene and zinc oxide enhanced the reflectivity in specific regions, including the UV and visible ranges, and improved the collection of charge carriers. The SiO NWs/Graphene and ZnO NPs was assessed as a photodetector and exhibited excellent performance, with high quantum efficiency, detectivity, and responsivity in the visible and near-infrared regions, making it a promising platform for the development of next-generation optoelectronic devices in various fields, including security, environmental monitoring, and medical diagnostics.

First-principles study of the effect of strain on the structural and optoelectronic properties of flexible photovoltaic material Cs2AgInBr6

The lead-free double-perovskite halide materials are promising materials for photovoltaics. Recently, Cs2AgInBr6 (CAIB) has been synthesized with the estimated direct nature of a band gap value of 1.57 eV. To cover the wide solar spectrum for photo-conversion, the applied strain is one of the promising approaches to achieve it through band gap tuning. The density functional theory is used to investigate the effect of compressive strain on the structural, electronic, and optical properties of CAIB. The elastic constants follow the Born–Huang stability criterion and show the mechanical stability of the composition even under compressive strain. The Poisson’s ratio in the range of 0.23–0.26 and B/G > 1.75 indicate the ductile and soft nature of the material. The band gap increases monotonically without changing the direct nature of the band gap by increasing the compressive strain. However, the larger value of strain reproduces more dispersive conduction band minima and valence band maxima, resulting in lower effective masses and consequently larger carrier mobilities. The variations in the optical properties of CAIB are explored under compressive strain. The structural, electronic, and good photo response of the material in the visible and ultraviolet regions indicate the suitability of the material for flexible photovoltaics.

First-principle simulation of inorganic Na2CuSbX6 (X = Cl, Br, I) halides for photovoltaic and energy conversion applications

The exceptional flexibility of optoelectronic attributes exhibited by inorganic Na2CuSbX6 (X = Cl, Br, I) halides has sparked significant interest in recent research. Our approach involves the utilization of Wien2k and BoltzTrap coding to scrutinize the mechanical, thermoelectric and optoelectronic attributes of studied halides. Structural stability have been investigated through Born stability criteria employing generalized gradient approximation (GGA-PBEsol). In addition, negative formation energy (−2.15 eV for Cl-halide, −1.88 eV for Br-halide and −1.68 eV for I-halide) indicate all halides are thermo-dynamical stable. For accurate calculation of optoelectronic properties, modified Becke and Johnson (mBJ) potential has been employed. Band structure indicate all halides are semiconductor with indirect bandgap nature having bandgap values 1.7 eV for Cl-halide, 1.34 eV for Br-halide and 0.85 eV for I-halide respectively. Substituting Cl-halide with Br and I-halide results in enhanced optical absorption predominantly in the visible region, causing a shift in the absorption edge from visible light to IR. Further, electronic thermoelectric properties are discussed against temperature 300 K to 800 K. The computed higher Seebeck coefficient observed in Na2CuSbI6 suggests that a narrower band gap is more suitable for thermoelectric applications in comparison to Na2CuSbBr6 and Na2CuSbCl6. In a broader context, the computational analysis of thermoelectric and optical properties indicates that Li2CuSbX6 halides is generally well suited for use in solar cell devices and energy conversion applications.

First principle study of X2GaAgCl6 (X = Cs, Rb) double perovskites: structural, mechanical, vibrational, electronic, optical, SLME, thermoelectric, and thermodynamic properties for solar cell applications.

The structural, mechanical, vibrational, electronic, optical, SLME, thermoelectric, and thermodynamic properties of X2GaAgCl6 (X = Cs, Rb), a double perovskite material, were computed by employing Density Functional Theory (DFT). CASTEP and Quantum ESPRESSO were used to perform first-principles calculations. X2GaAgCl6 possesses a cubic structure with the space-group symmetry Fm-3m. The lattice parameters of Cs2GaAgCl6 and Rb2GaAgCl6 were optimized using the energy-volume curves, resulting in values of 7.357Å and 7.365Å, respectively. The population analysis confirmed the charge transfer among transition metals and halogen atoms. The stability of crystal X2GaAgCl6 (X = Cs, Rb) is effectively demonstrated by analyzing phonon dispersion curves with no negative frequencies. The band structure calculations indicated the semiconducting nature of compounds with energy gaps of 0.96eV and 0.88eV for Cs2GaAgCl6 and Rb2GaAgCl6, respectively. The optical characteristics results confirm that the examined materials are suitable for devices working, primarily in the electromagnetic spectrum's visible region. SLME results showed that Cs2GaAgCl6 has 30% and Rb2GaAgCl6 has 27% efficiency, respectively, suggesting their use in photovoltaics. The thermoelectric properties of X2GaAgCl6 (X = Cs, Rb) were calculated by using the BoltzTraP code in the temperature range of 300 to 800K. The quasi-harmonic Debye model was applied to calculate the thermodynamic characteristics.

Emission Spectra of Uranium Particulates at High Temperature.

The emission spectrum of micron-scale uranium particulates at high temperatures in the ultraviolet, visible, and near-infrared spectral regions is investigated using a heterogeneous shock tube. Temperatures from 3000 to 9000 K are characterized in an inert argon environment and with incremental amounts of added oxygen. Atomic line spectra do not emerge above the continuum emission spectrum until between 4500 and 5000 K in pure argon, and 6100 and 6600 K in 1% oxygen. For 5% oxygen, however, the threshold for atomic emission drops below 3800 K. Uranium monoxide molecular emission in the strongest visible band at 595.4 nm is not observed at any condition. Uncertainties in particle temperature determination in high-temperature shock tube environments are discussed, and limitations to such measurements are presented, such as those from experimental factors such as the powder loading method and expected detection limits of uranium species in relevant conditions.

Uv–vis spectroscopy for simple chloride content analysis in edible oil using charged amino-functionalized carbon quantum dots fluorophore reagent

The utilization of UV–Vis spectroscopy with amino-functionalized carbon quantum dots (NCQD) as a positive fluorophore reagent for chloride sensing in oil marks a notable advancement in analytical spectroscopy chemistry. This approach streamlines the detection process by eliminating the need for lengthy procedures and pretreatment steps typically associated with chloride detection in edible oil. By incorporating NCQD in chloride detection within the oil matrix, the wavelength analysis transitions from the UV to the visible region. This shift eliminates interference from oil matrix interactions, ensuring more accurate results. Molecular analysis of NCQD reveals significant shifts in its Fourier Transformation Infrared and photoluminescence spectroscopy peaks due to interaction with chloride in edible oil. It has two impressive sensitivity ranges spanning from 0.1–1.0 to 1.0–8.0 ppm, with a value of −0.4656 au. ppm−1 (R2 = 0.998) and −0.0361 au. ppm−1 (R2 = 0.931), respectively, the technique meets regulatory standards while achieving a low limit of detection (LOD) of 0.1 ppm. This places it on par with conventional methods and commercial sensors. The NCQD-UV–Vis spectroscopy method not only enhances the efficiency and accuracy of chloride detection but also holds promise for various industrial applications requiring simple and precise monitoring of chloride levels in oil samples.

Strain modulated optical properties of MoSi2P4 monolayer – insights from DFT

Strain plays a very important role in tuning the properties of the materials for the desired applications. In the present work, we have investigated the variation of strain on the electronic and optical properties of a recently synthesized class of compound MoSi2P4 monolayer using the first principle methods. The MoSi2P4 monolayer is found to be dynamically and thermally stable at room temperature. The electronic structure of studied monolayer indicates a direct bandgap (at K-point) of 0.685 eV and 1.177 eV using the PBE and HSE06 hybrid functionals, respectively. To tune the electronic bandgap and optical properties, mechanical strain was applied (up to ±10%). A high optical absorption coefficient of the order of 105 cm−1 is observed. The absorption starts in the infrared and visible region covering a large part in the ultraviolet region. The absorption coefficient is found to decrease (increase) under tensile (compressive) strain. Our study indicates the potential application of MoSi2P4 monolayer in flexible optoelectronic devices for absorption and detection in the infrared, visible and ultraviolet region.

Visible-Photocatalytic performance of TiO2 particles simply achieved by surface nitridation and coatings fabricated by electrophoretic deposition (EPD) process

Originally, surface-nitridated TiO2 particles were prepared by urea decomposition under hydrothermal treatment. After the surface nitridation, the absorption onset was extended to the visible region due to narrowed band gap of ∼ 3.10 eV comparable to that of ∼ 3.28 eV for pristine TiO2. Due to narrowed band gap, the surface-nitridated TiO2 distinguishably had the visible photocatalytic ability under 440 nm. The visible-photocatalytic nitridated TiO2 particles was successfully fabricated as dense coatings with controllable transparency by electrophoretic deposition (EPD) process.

2D-3D heterostructure of PtS2-x/Ga2O3 and their band alignment studies for high performance and broadband photodetector.

For deep ultraviolet (UV-C) photodetectors, Gallium oxide (Ga2O3) is a suitable candidate owing to its intrinsic ultra-wide band gap and high stability. However, its detection is limited within the UV-C region, which restricts it to cover a broad range, especially in visible and near-infrared (NIR) region. Therefore, constructing a heterostructure of Ga2O3 with an appropriate material having a narrow band gap is a worthwhile approach to compensate for it. In this category, PtS2 group-10 transitional metal dichalcogenide (TMDC) stands at the top owing to its narrow band gap (0.25-1.65 eV), high mobility, and stability for heterostructure synthesis. Moreover, heterostructure with Ga2O3 sensing in UV and PtS2 broad response in visible and IR range can broaden the spectrum from UV to NIR and to build broadband photodetector. In this work, we fabricated a 2D-3D PtS2-x/Ga2O3 heterostructure based broadband photodetector with detection from UV-C to NIR region. In addition, the PtS2-x/Ga2O3 device shows a high responsivity of 38.7 AW 1 and detectivity of 4.8×1013 Jones under 1100 nm light illumination at 5V bias. A fast response of 90 ms /86 ms illustrates the device's fast speed. An interface study between the PtS2-x and Ga2O3 was conducted using X-ray photoelectron spectroscopy and Ultraviolet photoelectron spectroscopy (UPS) which confirmed type-I band alignment. Finally, based on their band alignment study, a carrier transport mechanism was proposed at the interface. This work offers a new opportunity to fabricate large-area high-performance 2D-3D heterostructures based photodetectors for future optoelectronics devices.

First-principles calculations of electronic, optical and thermoelectric properties of the Ge2SeS/GeSe van der Waals heterostructure

In this research, we systematically investigate the electronic structure, optical and thermoelectric properties of the Ge2SeS/GeSe van der Waals (vdW) heterostructure in comparison to the Ge2SeS and GeSe monolayers by using density functional theory (DFT) implemented in Quantum ESPRESSO. We have constructed two configurations of the Ge2SeS/GeSe heterostructure by stacking the Ge2SeS monolayer on top of the GeSe monolayer (Stacking A1 and A2). According to our calculations, the calculated indirect electronic band gaps of both Stacking A1 and Stacking A2 are Eg = 0.80 eV and 0.88 eV, respectively. The transfer of charges from the Ge2SeS to the GeSe monolayer for both configurations has been predicted. By Bader charge analysis, the charge transfers for Stacking A1 and A2 are approximately 0.013 e and 0.020 e, respectively. The coefficient of absorption for the Ge2SeS/GeSe heterostructure is higher than that for Ge2SeS and GeSe monolayers in both regions of the spectrum (visible, and UV). Moreover, the Ge2SeS/GeSe heterostructure has a very good absorbing capability of light in the visible region up to 85 × 104 cm−1. Our calculations yielded a high thermoelectrical electronic figure of merit (ZTe) of 12.64 and 2.27 for Stacking A1 and A2, respectively. As a result, our findings show that the Ge2SeS/GeSe heterostructure is a promising material for thermoelectric and optoelectronic applications.