Visible Spectral Region Research Articles

Exchange-correlation effects on the structural, electronic, and optical properties of Sr2RuO4 using DFT calculations

We perform a first principle study on the electronic, structural, and optical properties of Sr2RuO4 by various functionals: LSDA, GGA, GGA-mBJ, PBE-D3, optB88-vdW, vdW-DF2 and HSE06 using the plane-wave method of density functional theory (DFT) in the presence of the spin-orbit coupling (SOC) and Coulomb interaction parameter, U. The dynamical stability and the thermal stability are calculated via phonon dispersions and ab initio molecular dynamics simulations, respectively. The band structure calculation and the orbital-resolved density of states of LSDA and the schemes of GGA reveal different ground state. For GGA-mBJ and the hybrid functional, there is an indirect gap in the band structure. In the case of vdW functionals, our findings are in agreement with GGA. We compute a variety of optical responses and compare them with existing experimental studies. The results of the dielectric function suggest that GGA-mBJ (LSDA and GGA) may better account for the experimental findings in the presence (absence) of SOC at the infrared spectral region (infrared and visible spectral regions). We observe that the optical responses are strongly influenced by SOC and intraband transitions. Among the optical spectra, we focus more on the electron energy loss spectrum, which depends on the excitations, the exchange-correlation effects, and the multiorbital nature of Sr2RuO4.

Impact of the thickness of phthalocyanine films and its metal complexes on optical and electrical properties

The paper presents the results of a study of the structural, optical and electrophysical characteristics of phthalocyanine films and its metal complexes with different thicknesses. Films of phthalocyanine and its metal complexes were obtained on the conductive surface of the FTO by thermal evaporation in vacuum. It is shown that the observed broadening of the B and Q bands and the hypsochromic shift of the maxima in the absorption spectra are associated with the central atom. With a decrease in the thickness of MPc films, there is a decrease in the value of the half-width of the absorption spectra. The effect of the thickness of phthalocyanine films on the efficiency of generation and transport of charge carriers in the FTO/MPc/Al cell was studied. It is shown that the VAC increases almost 2.5 times compared to a photocell based on a metal-free phthalocyanine. From the obtained impedance measurement data, it was found that the electrophysical parameters of phthalocyanines depend on the values of optical density, broadening of absorption bands in the short-wave and visible spectral regions, which is consistent with the data of the volt-ampere characteristic.

Beam profiles and radiation coherence at the output of solid-state and dye lasers with an intra-cavity immersion diffuser

Lasers on mixtures of solid particles and liquids have long been an attractive subject of research as they can serve as sources of low-coherent radiation and provide a good thermal management using a medium flow. One of such schemes is a laser with an intra-cavity cuvette-diffuser filled by a dense immersion mixture of activated solid micro-particles and a liquid (slurry), similar to the known Christiansen filter. The properties of perspective slurry lasers and features of beams formation in such media were studied in model experiments on bulk Nd:YVO4 and Nd:YAG active elements pumped by 808 nm diodes in quasi-continuous (1 ms, 10 Hz) regime, and on a Rhodamine 101 dye laser pumped by 20 ns, 532 nm light pulses. Laser media were tested in compact (7–50 mm) resonators using a diffuser on a mixture of non-doped LiF micro-particles and isobutanol. The laser spatial coherence was estimated by the contrast C of speckle patterns or by the visibility of Young interferograms γ. Near the threshold separate deformed Laguerre-Gaussian modes and concentric rings were observed at lasers’ output, indicating radiation coherence of C=0.5−0.7. At 100 W pumping Nd:YVO4 and Nd:YAG lasers with diffusers in plano-spherical (PS) resonators provided 1 ms pulses of 1–6 W multimode 1064 nm generation with smoothed beam profiles, divergence up to 0.11 rad and C=0.02−0.1. For a dye laser with a diffuser in PS resonators, 17 ns pulses of 627 nm multimode radiation with 1–3.5 mJ energy, beam divergence 60–280 mrad, γ=0.01−0.05 and up to 30% optical efficiency were obtained. Thus, an intra-cavity diffuser with an immersion mixture is a convenient and simple device to reduce the laser coherence. C and γ values, close to those for thermal light sources make it possible to use the developed lasers for speckles suppression at laser projection, in speed photography, etc. Promising solid-state and dye slurry lasers are discussed. The obtained results show the specific of beam formation in slurry media and give grounds to expect successful development and applications of low-coherent solid-state and dye slurry lasers operating in the visible and infra-red spectral regions.

The electronic and optical properties of InSe/ZnO van der Waals heterojunction:First principles study

The efficient, simple and low-cost photocatalysts has become a hot topic in the field of photocatalysis, ZnO has attracted the attention of researchers due to its high photocatalytic efficiency. Although, the broad band gap of around 3.4 eV in ZnO greatly limits its optical absorption efficiency. Based on this, two types of InSe/ZnO heterojunction models with different configurations are constructed, their electronic and optical properties are studied through first principles calculations. The results indicate that the II InSe/ZnO heterojunction has a band gap of 1.84 eV, which compensates for the shortcomings of ZnO monolayer broad band gap absorption of visible light and the difficulty of InSe monolayer in participating in water splitting oxidation reactions. The construction of heterojunctions using InSe and ZnO significantly improves the light absorption efficiency, especially in the visible spectral region, compared to ZnO monolayers, accelerating the generation and migration efficiency of photo generated electrons, thereby improving the catalytic efficiency of ZnO.

Optical solitons in hollow-core fibres

I review the historical observation and subsequent research on optical soliton dynamics in gas-filled hollow-core optical fibres. I include both large-core hollow capillary fibres, and hollow-core photonic-crystal or microstructured fibres with smaller cores, in particular photonic bandgap and antiresonant guiding fibres. I discuss how the optical guidance properties of these different fibre structures influence the soliton dynamics that can be obtained. The dynamics I consider include: soliton propagation at peak power levels ranging from the megawatt to terawatt level, and pulse energies from sub-microjoule to millijoule range; pulse self-compression, leading to sub-cycle and sub-femtosecond pulse duration; soliton self-frequency shifting due to both the Raman effect, and the influence of photoionisation and plasma formation; and resonant dispersive wave emission, leading to the generation of tuneable few-femtosecond pulses across the vacuum and deep ultraviolet, visible, and near-infrared spectral regions.

The effect of composition on the structure, optical, and room-temperature ferromagnetic properties of hydrothermally synthesized (ZnSn)1-xCuxO nanocomposites

(ZnSn)1-xCuxO nanocomposites (NCs) with nanorods and nanosheet morphologies were synthesized by a facile hydrothermal technique. (ZnSn)1-xCuxO NCs exhibited a gradual band gap redshift from UV to visible spectral region with increasing Cu-content. The room temperature magnetic hysteresis loop indicated the improvement of room temperature ferromagnetic (RTFM) behavior of (ZnSn)1-xCuxO NCs compared with nanostructured ZnSnO NCs induced by the exchange interaction of Cu-bound polarons with the localized spins and free carriers. The (ZnSn)60Cu40O NCs exhibited the highest saturation magnetization (Ms) of 0.539 emu·g−1. Further increase in Cu-content resulted in the deterioration of crystalline domains and the reduction of Ms to 0.259 emu·g−1. This behavior revealed that the electronic and magnetic properties of (ZnSn)1-xCuxO NCs were so sensitive to the dopant concentration that need to be utilized for improving their performance as good candidate NCs for spintronic applications.

Mid-infrared supermirrors with finesse exceeding 400 000

For trace gas sensing and precision spectroscopy, optical cavities incorporating low-loss mirrors are indispensable for path length and optical intensity enhancement. Optical interference coatings in the visible and near-infrared (NIR) spectral regions have achieved total optical losses below 2 parts per million (ppm), enabling a cavity finesse in excess of 1 million. However, such advancements have been lacking in the mid-infrared (MIR), despite substantial scientific interest. Here, we demonstrate a significant breakthrough in high-performance MIR mirrors, reporting substrate-transferred single-crystal interference coatings capable of cavity finesse values from 200 000 to 400 000 near 4.5 µm, with excess optical losses (scatter and absorption) below 5 ppm. In a first proof-of-concept demonstration, we achieve the lowest noise-equivalent absorption in a linear cavity ring-down spectrometer normalized by cavity length. This substantial improvement in performance will unlock a rich variety of MIR applications for atmospheric transport and environmental sciences, detection of fugitive emissions, process gas monitoring, breath-gas analysis, and verification of biogenic fuels and plastics.

Simulation and Analysis of Plasmonic Photodetector Based on Au Nanoparticles and HfO2 Interlayer With Improved Performance in Visible Spectral Region

Simulation and Analysis of Plasmonic Photodetector Based on Au Nanoparticles and HfO₂ Interlayer With Improved Performance in Visible Spectral Region

Modification of the optical and elastic properties of TlGaSe2 layered semiconductor produced by the memory effect

A comparative analysis of the temperature behaviors of optical and elastic properties of single crystals under a memory effect experimental condition are presented for the first time. A memory effect condition suggests that the sample is thermally annealed inside the incommensurate (INC) phase for a time interval the corresponding physical parameters is measured experimentally. From ultrasound velocity measurements, carried out before and after the thermal annealing process subjected to the sample, the noticeable changes in the temperature variation of the longitudinal ultrasonic wave velocity associated with the elastic constants of due to the memory effect was detected. Our results reveal that thermal annealing performed at the INC - phase has some influence on the optical absorption of crystals in the visible spectral region. We assumed that thermal annealing within INC - phase is accompanied with the appearance, inside samples, a new quasiperiodic frozen structure formed from the intrinsic defects migrated into the lowest energy diffusion barriers of the INC - modulation wave. Such structural modulation is incommensurate with the underlying lattice of and can lead to changes in the electronic band structure and the optical bandgaps of

High stability white light generation in water at multi-kilohertz repetition rates.

An efficient supercontinuum (SC) generation featuring high spectral intensity across a large bandwidth requires high peak powers of several megawatts from pulsed lasers. Under these conditions and at multi-kilohertz (kHz) repetition rates, the SC generated in most materials is unstable due to thermal effects. In this work, we leverage the superior dispersion properties of water to maximize the spectral width of the SC, while avoiding stability issues due to thermal loading by means of a constant laminar flow of the liquid. This flow is controlled by a differential pressure scheme that allows to precisely adjust the fluid velocity to an optimum value for maximum stability of the SC. This approach is successfully implemented for repetition rates of 50 kHz and 100 kHz and two different pump wavelengths in the visible (VIS) and near infrared (NIR) spectral region with stability of the SC signal only limited by the driving pulses. The resulting water SC spans more than one octave covering the VIS to NIR range. Compared to established materials, such as yttrium aluminum garnet (YAG) and sapphire, the spectral bandwidth is increased by 60% and 40% respectively. Our scheme has the potential to be implemented with other liquids such as bromine or carbon disulfide (CS2), which promise even wider broadening and operation up to the mid-infrared.

A comparative study of photoelectric performance of Ga2O3 solar-blind photodetectors with symmetric and asymmetric electrodes

Gallium oxide (Ga2O3) thin films were deposited on quartz substrates under different oxygen flow ratios (O2/[O2+Ar], 0%−5%) by radio-frequency (RF) magnetron sputtering technique followed by thermal annealing at 900 °C for 2 h under N2 atmosphere. The influence of the oxygen concentration on the structural and optical characteristics of Ga2O3 thin films was investigated. The Ga2O3 thin films prepared under an oxygen flow ratio of 1% exhibited optimum crystal quality and the lowest oxygen vacancy (VO) concentration according to X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) investigations. All as-prepared polycrystalline Ga2O3 thin film samples exhibited high average transmittance above 87.8% in the visible spectral region and the 0% and 1% thin films had optical bandgap energies of about 4.9 eV. We also fabricated metal−semiconductor−metal (MSM) photodetectors based on 1% Ga2O3 thin films by employing pairs of Ni−Ni symmetrical or Ni−Al asymmetrical interdigitated electrodes. The Ni−Ni photodetector had a high on/off current ratio (Ion/Ioff > 105), a responsivity of 88.7 mA/W, and specific detectivity of 4.81×1010 J at 10 V bias under ultraviolet light-C (UVC) illumination, and the Ni−Al photodetector exhibited self-driven behavior along with short rise and fall times (0.45 s and 0.69 s, respectively).

First-principles investigations on the electronic structure, optical properties, and giant magnetic-optical Kerr effect in double-perovskite Ba2NiBO6 (B = Os, Ir)

The hybrid 3d–5d transition-metal oxides have been frequently studied for their novel electronic and magnetic properties, in which the strong spin-orbit coupling (SOC) effect is added to the interplay among charge, spin, and orbital degrees of freedom. Recently, perfectly ordered 3d–5d double-perovskite oxides of Ba2NiOsO6 and Ba2NiIrO6 were synthesized: Ba2NiOsO6 was measured to be a rare ferromagnetic semiconductor and predicted to have a giant magneto-optical Kerr effect (MOKE); and Ba2NiIrO6 showed a competition between antiferromagnetic and ferromagnetic interactions. In this work, we systematically investigated the magnetic, electronic, and optical properties, as well as the MOKE of Ba2NiBO6 (B = Os, Ir) using density functional theory. The long-ranged B–B interaction was found to play a key role in determining the magnetism of the compounds. For Ba2NiOsO6, the experimentally observed semiconductive nature was reproduced only by taking into account both the electron correlation and SOC effect. In Ba2NiIrO6, however, the SOC effect on 5d Ir was weak. Owing to the d→d or p→d interband transitions, both materials had a strong absorption in the ultraviolet–visible spectral region. In particular, the absorption spectrum of Ba2NiIrO6 covered almost the entire visible region. They also exhibited considerable MOKE in the visible region. The maximum of Kerr rotation for Ba2NiOsO6 and Ba2NiIrO6 could reach 5.3° and 4.1°, respectively. The characteristics of the Kerr spectra were primarily dominated by the off-diagonal optical conductivity, which reflects the contributions of band exchange splitting and SOC to MOKE. The Ba2NiBO6 (B = Os, Ir) are very promising optoelectronic and magneto-optical materials.

Electronically preresonant stimulated Raman scattering microscopy in the visible

We report an experimental scheme for stimulated Raman scattering (SRS) microscopy with excitation in the visible spectral region. This allows electronically preresonant (epr) SRS microscopy of a broad range of chromophores with sensitivities as low as 1 μM. Our experiment is based on two synchronously near-infrared pumped optical parametric oscillators (OPO). One of the outputs is modulated at a fourth of the repetition rate with a novel broadband electro-optical modulator. Using a combination of spectral focusing and tuning of the OPO, we show the recording of epr-SRS spectra over the whole range of molecular vibrations at a speed up to 20 times faster than classical wavelength tuning. The imaging capabilities of this setup are demonstrated with material scientific and cellular samples.

Evaluating potential of leaf reflectance spectra to monitor plant genetic variation

Remote sensing of vegetation by spectroscopy is increasingly used to characterize trait distributions in plant communities. How leaves interact with electromagnetic radiation is determined by their structure and contents of pigments, water, and abundant dry matter constituents like lignins, phenolics, and proteins. High-resolution (“hyperspectral”) spectroscopy can characterize trait variation at finer scales, and may help to reveal underlying genetic variation—information important for assessing the potential of populations to adapt to global change. Here, we use a set of 360 inbred genotypes of the wild coyote tobacco Nicotiana attenuata: wild accessions, recombinant inbred lines (RILs), and transgenic lines (TLs) with targeted changes to gene expression, to dissect genetic versus non-genetic influences on variation in leaf spectra across three experiments. We calculated leaf reflectance from hand-held field spectroradiometer measurements covering visible to short-wave infrared wavelengths of electromagnetic radiation (400–2500 nm) using a standard radiation source and backgrounds, resulting in a small and quantifiable measurement uncertainty. Plants were grown in more controlled (glasshouse) or more natural (field) environments, and leaves were measured both on- and off-plant with the measurement set-up thus also in more to less controlled environmental conditions. Entire spectra varied across genotypes and environments. We found that the greatest variance in leaf reflectance was explained by between-experiment and non-genetic between-sample differences, with subtler and more specific variation distinguishing groups of genotypes. The visible spectral region was most variable, distinguishing experimental settings as well as groups of genotypes within experiments, whereas parts of the short-wave infrared may vary more specifically with genotype. Overall, more genetically variable plant populations also showed more varied leaf spectra. We highlight key considerations for the application of field spectroscopy to assess genetic variation in plant populations.

Effects of Gd3+-doping on the fabrication and performances of highly transparent (Lu,Gd)2O3:Eu solid-solution ceramics

By pre-treating and component design of the ceramic powders, cubic (Lu,Gd)2O3:Eu solid-solution ceramics with high optical quality were achieved by the solid-state reaction method combined with vacuum sintering. The effects of Gd3+ doping (x = 0.05–0.6) on powder characteristics, phase compositions, microstructures and optical performances of the (Lu0.95-xGdxEu0.05)2O3 ceramics were systematically investigated to obtain the optimum Gd3+ content. The results indicated that the incorporation of moderate amounts of Gd3+ (5–50 mol%) effectively promoted mass diffusion and grain growth during sintering. The 50 mol% Gd3+-doped Lu2O3:Eu transparent ceramic (using the powder calcined at 1200 °C) sintered at 1750 °C for 5 h exhibited the optimum transmittance of 77.0 % in the visible spectral region (∼1 mm in thickness), which was significantly higher than the reported transmittance of vacuum sintered (Lu,Gd)2O3:Eu ceramics (less than 65.0 %). Owing to the lower electronegativity of Gd3+ relative to Lu3+, the bandgap energies of the final ceramics decreased gradually with increasing Gd3+ substitution, and the redshift of the CTB centre was observed with more Gd3+ addition. Under CTB excitation, the incorporation of Gd3+ enhanced the red emission intensity and shortened the fluorescence lifetime.

Color adjustable CsPbX3 (X=Cl, Br, I) perovskite quantum dots germanate glass

CsPbX3 (X = Cl, Br, I) perovskite quantum dots (QDs) have attracted extensive attention due to their great application prospects in the photoelectronic field. However, the poor long-term stability still limits their practical use. In this work, a whole series of CsPbX3 QDs were precipitated in a germanate glass matrix by a melt quenching method. The emission wavelength can be tunable in the entire visible spectral region by adjusting of the halide ions and the thermal treatment process. The photoluminescence quantum yield of CsPbBrxI3-x QDs glass can reach up to 38.24%. The exciton binding energies of CsPbBrxCl3-x, CsPbBr3 and CsPbI3 QDs glass are about 67 meV, 160 meV and 290 meV, respectively. Additionally, the influence of the thermal treatment temperature on photoluminescence properties of CsPbBrxI3-x QDs glass was investigated in detail. These results will be of benefitting to their practical applications, such as display devices and WLEDs.

Computation of the Dielectric and Optical Properties of Dimethylammonium Tin Triiodostanate (II) Perovskite for Solar Cell Application

Hybrid halide perovskites are promising photovoltaic materials for use in solar cells. The ongoing research on perovskites have shown that these materials are potential light-harvesting mediums. The optical properties of dimethylammonium triiodostanate (II) (DASnI3) a hybrid halide perovskites needs to be studied because it can be a good light absorber material due to the wide band gap exhibited. The real and the imaginary parts of the dielectric is a measure of the extent of light absorption. The GGA+U exchange-correlation implemented in Quantum ESPRESSO was used basing on density functional theory to obtain the optical properties. The DASnI3 has a direct band gap of 2.7 eV with the real part of the dielectric diagram indicating that the maximum value of ε1 (ω) is in the visible range of (3.0–3.5 eV). High absorption peaks were also observed in the visible spectral region at energy of around (3.5–4.5 eV) with several weak peaks observed in the energy range of (4.5–14.0 eV). The band structure and the dielectric functions are important in the study of optical properties. These properties expresses the interaction of light with the material medium and thus the luminescence of the device which are important in the use of DASnI3 as a solar cell material in photovoltaics.

High‐Performance Filterless Blue Narrowband Organic Photodetectors

AbstractModern image sensors necessitate three color‐selective photodetectors: red, green, and blue (RGB) sensing units. Among those, blue light‐specific photodetectors are comparably much less reported. Here, a fully thermal‐evaporated organic photodetector (OPD) with narrowband blue detection based on exploring the dual role of the hole‐transporting layer is elegantly demonstrated. By incorporating a MoO3‐doped underlayer, the narrowband OPD achieves high external quantum efficiency up to 50% at 0 V with thin‐film devices. By adopting an intrinsic underlayer in planar junction configuration along with efficient hole and electron blocking layers, an ultralow dark current (2.46 × 10−12 A cm−2 at −0.1 V) is achieved. The device has a calculated specific detectivity (D*) reaching a record‐high value of 6.35 × 1014 Jones, outperforming commercial silicon photodetectors, and an ultrahigh linear dynamic range of 205 dB. This work paves the way for high‐sensitivity narrowband organic photodetectors in the visible spectral region.

Two‐Stage, Low Noise Quantum Frequency Conversion of Single Photons from Silicon‐Vacancy Centers in Diamond to the Telecom C‐Band

AbstractThe silicon‐vacancy center in diamond holds great promise as a qubit for quantum communication networks. However, since the optical transitions are located within the visible red spectral region, quantum frequency conversion to low‐loss telecommunication wavelengths becomes a necessity for its use in long‐range, fiber‐linked networks. This work presents a highly efficient, low‐noise quantum frequency conversion device for photons emitted by a silicon‐vacancy (SiV) center in diamond to the telecom C‐band. By using a two‐stage difference‐frequency mixing scheme, spontaneous parametric down‐conversion (SPDC) noise is circumvented and Raman noise is minimized, resulting in a very low noise rate of 10.4 ± 0.7 photons per second as well as an overall device efficiency of 35.6%. By converting single photons from SiV centers, it demonstrates the preservation of photon statistics upon conversion.

Thioxanthonation of 2-naphthalene-thioacetic acid as a visible-light photoinitiator: The investigation of photophysical and photochemical properties

Thioxanthonation of naphthalene thioacetic acid (TXNPSCH2COOH) resulted a visible light photoinitiator with the high molar absorptivity (ε405: 5680 L.mol−1.cm−1) in the visible spectral region and made this compound an attractive photoinitiator for free radical polymerization reactions. Low fluorescence quantum yield (ΦF: 0.06 in 2-MeTHF) and comparatively low triplet energy (186 kJ/mol in 2-MeTHF) was in favorable for efficient intersystem crossing to the triplet state which is necessary for production of initiating radicals. Indeed, photopolymerization of methyl methacrylate along with TXNPSCH2COOH (1 × 10−3 M) and a tertiary amine namely MDEA yielded nearly 25% conversion of monomer to polymer. All spectrophotometric studies including laser flash photolysis which gives triplet lifetime of initiator which is very important information for initiation mechanism of photoinitiators, indeed a long enough triplet lifetime of TXNPSCH2COOH (τT: 1000 ns) allows for efficient reactions with co-initiators to generate radicals.