Optical Absorption Characteristics Research Articles

Exploring the Post-Annealing Influence on Stannous Oxide Thin Films via Chemical Bath Deposition Technique: Unveiling Structural, Optical, and Electrical Dynamics

Stannous oxide (SnO2) thin films have garnered significant attention for their promising applications in various electronic and optoelectronic devices. In this study, we investigate the impact of post-annealing on the structural, optical, and electrical properties of stannous oxide thin films deposited using the chemical bath deposition (CBD) technique. The thin films were prepared on a Borosilicate glass substrate, followed by a controlled annealing process to enhance their performance. Structural analysis was conducted using techniques such as X-ray diffraction (XRD) to examine the cubic crystalline structure and the crystallite size increase induced by post-annealing. The results revealed alterations in grain size from the SEM and the purity of samples confirmed from EDX results. The optical properties of the Stannous oxide thin films were examined using UV-Vis spectroscopy. The optical absorption and bandgap characteristics were analyzed to understand how post-annealing influences the optical behavior of the thin films. Where the optical absorption was 320nm and the bandgap ranges were 3.86eV to 3.83eV. Furthermore, the electrical properties of the thin films were evaluated semiconducting nature, and conductivity increased with rising post-annealing. The findings from this study contribute to the understanding of the role of post-annealing in tailoring the properties of Stannous oxide thin films. The optimization of structural, optical, and electrical characteristics is crucial for their successful integration into electronic and optoelectronic devices.

Development and preparation of novel nano-enhanced organic eutectic phase change materials for low-temperature solar thermal applications

ABSTRACT Thermally reliable and stable eco-friendly Phase change materials are of significant aid in thermal energy storage technology, leading to improved energy utilization and reliability of the system. This study develops two novel organic eutectic PCM of Lauric acid – Margaric acid (LM) and Myristic acid – Margaric acid (MM), which are chemically stable and thermally compatible for latent heat energy storage. LM eutectic mixture had a melting temperature of 52.66°C with a latent heat of 163.68 J/g, and MM eutectic mixture had its melting temperature at 44.79°C and a latent heat of 197.31 J/g. The phase change temperatures were favorable for low temperature solar thermal applications with good latent heat capacity. The thermal characteristics of these eutectic mixtures are further enhanced with the dispersion of highly conductive Multi walled carbon nanotubes (MWCNT) at three different mass fractions (.5%, 1% and 1.5% by weight). Nano enhancement could achieve exceptional thermal conductivity enhancement in MM eutectic mixture by 110.6% and 83.73% in LM eutectic mixture. Thermogravimetric analysis and Fourier-transform infrared spectroscopy analysis ensured the thermal and chemical stability of the eutectic mixtures. The optical absorption characteristics were extensively enhanced with nano particle addition, which is highly preferable in solar thermal applications.

Dynamic two-dimensional covalent organic frameworks.

Porous covalent organic frameworks (COFs) enable the realization of functional materials with molecular precision. Past research has typically focused on generating rigid frameworks where structural and optoelectronic properties are static. Here we report dynamic two-dimensional (2D) COFs that can open and close their pores upon uptake or removal of guests while retaining their crystalline long-range order. Constructing dynamic, yet crystalline and robust frameworks requires a well-controlled degree of flexibility. We have achieved this through a 'wine rack' design where rigid π-stacked columns of perylene diimides are interconnected by non-stacked, flexible bridges. The resulting COFs show stepwise phase transformations between their respective contracted-pore and open-pore conformations with up to 40% increase in unit-cell volume. This variable geometry provides a handle for introducing stimuli-responsive optoelectronic properties. We illustrate this by demonstrating switchable optical absorption and emission characteristics, which approximate 'null-aggregates' with monomer-like behaviour in the contracted COFs. This work provides a design strategy for dynamic 2D COFs that are potentially useful for realizing stimuli-responsive materials.

Effects of Static Electric Fields on the Excitations of Silver Nanowire Dimers.

We theoretically studied the introduction of static electric fields to Ag10 nanowire dimer systems, including the effects of this field on optical absorption characteristics and the orbitals responsible for these excitations. Linear-response time-dependent density functional theory computations were performed on three distinct dimer systems: end-to-end, parallel, and 90° angle dimer systems separated by a closest interparticle distance of 7.0 Å. The calculations were performed in the presence of a 0.1 V/Å electric field strength applied in the z and y directions. The orientation of the dimer system and the direction of the applied static electric field each play a significant role in the resulting absorption spectra and the electronic structure of the nanowires. As a result, a dimer system can exhibit a blue shift for the longitudinal excitation and a red shift for the transverse excitation in the presence of one direction of the static electric field but not for the other direction. Notably, the electron density shifts from one nanowire to the other in the presence of the static electric field. Changes in optical characteristics and electronic structure suggest that the usage of a static electric field with a particular spatial configuration of nanowires provides a way to tune the optical properties of the system.

Revealing photoluminescence and nonlinear optical absorption characteristics of PbMo0.75W0.25O4 single crystal for optical limiting applications

Nonlinear absorption properties of PbMo0.75W0.25O4 single crystal fabricated by the Czochralski method were studied. The band gap energy of the crystal was determined as 3.12 eV. Urbach energy which represents the defect states inside the band gap was found to be 0.106 eV. PbMo0.75W0.25O4 single crystal has a broad photoluminescence emission band between 376 and 700 nm, with the highest emission intensity occurring at 486 nm and the lowest intensity peak at 547 nm, depending on the defect states. Femtosecond transient absorption measurements reveal that the lifetime of localized defect states is found to be higher than the 4 ns pulse duration. Open aperture (OA) Z-scan results demonstrate that the PbMo0.75W0.25O4 single crystal exhibits nonlinear absorption (NA) that includes two-photon absorption (TPA) as the dominant mechanism at the 532 nm excitations corresponding to 2.32 eV energy. NA coefficient (β eff ) increased from 7.24 × 10−10 m W−1 to 8.81 × 10−10 m W−1 with increasing pump intensity. At higher intensities β eff tends to decrease with intensity increase. This decrease is an indication that saturable absorption (SA) occurred along with the TPA, called saturation of TPA. The lifetime of the defect states was measured by femtosecond transient absorption spectroscopy. Saturable absorption behavior was observed due to the long lifetime of the localized defect states. Closed aperture (CA) Z-scan trace shows the sign of a nonlinear refractive index. The optical limiting threshold of PbMo0.75W0.25O4 single crystal at the lowest intensity was determined as 3.45 mJ/cm2. Results show that the PbMo0.75W0.25O4 single crystal can be a suitable semiconductor material for optical limiting applications in the visible region.

Correction to: Nonlinear Optical Refraction and Absorption Features of Methyl Orange Dye in Polar Solvents

Correction to: Nonlinear Optical Refraction and Absorption Features of Methyl Orange Dye in Polar Solvents

Passively mode-locked fiber laser based on ethylene glycol

A passively mode-locked Er-doped fiber laser employing ethylene glycol as a saturable absorber (SA) has been proposed and experimentally validated. The ethylene glycol-SA is fabricated by filling the space between the end facets of two optical patch cords inserted into a cannula with ethylene glycol. Utilizing such an SA with a modulation depth of 9.6 %, stable mode-locking operation are manifested in the laser cavity, including the production of bright pulse and bright-dark pulse pair. The generated bright pulse has a center wavelength at 1562.28 nm, a 3 dB bandwidth of 0.21 nm, a repetition frequency of 20.24 MHz, and a signal-to-noise ratio (SNR) of 57 dB. Through precisely manipulating the polarization state and the pump power in the laser cavity, the bright-dark pulse pairs can be successfully attained at the same repetition frequency. This is the first demonstration of a passively mode-locked fiber laser utilizing ethylene glycol as the saturable absorber. Due to their superior optical absorption characteristics, low cost, simplicity in fabrication and non-volatile nature, ethylene glycol-SAs have enormous potential in the field of nonlinear optics and ultrafast photonics.

Exploring nonlinear optical absorption in cobalt-doped Nickel–Zinc nanomaterials

This study emphasises on synthesis of ferrite nano powders via hydrothermal route within the compositional range of Ni0 65Zn0.35CoxFe(2-2x/3) O4 (x = 0.00 to 0.05 in steps of 0.01 wt%). Structural analysis via XRD and FTIR unveiled the cubic spinal structure, confirmed by signature absorption bands existence in the infrared spectra. The FESEM analysis revealed the morphological characteristics of ferrite crystals, while characterizations indicated a diminution in crystallite sizes from 53 to 37 nm. The magnetic behaviour displayed the existed correlation between Ms and Y–K angles along with finite size effects of the samples. Notably, low coercively values (0.13 Oe to 1.09 Oe) and magneto crystalline anisotropy pointed towards the magnetic quality of the ferrites with soft nature. Exhibited dielectric loss factor near 10−1, and ac-conductivity (σac) within the range of 10−5S/m to 10−4S/m of the samples indicates their improved dielectric properties. Further analysis from UV–vis. Diffuse reflectance (UV-DRS), PL spectroscopy, and Raman studies exhibits slight variations in optical band gaps, and vibrational modes due to varying cobalt doping concentrations. The evaluation of optical limiting characteristics using the Z-scan technique revealed absorption coefficients ranging from 1.40 to 4.80 × (10−10 m/W) and onset limiting values between 1.93 W/m2 and 1.11 W/m2. These findings position the Ni–Zn–Co ferrites as promising contenders for optical limiting applications owing to their optical nonlinearity and absorption characteristics.

Fundamental frequency and second harmonic mode-locked operations in an erbium-doped fiber laser based on Cr2Sn2Te6 saturable absorbers

With the rapid development of ultrafast photonics, the need for optical modulators is expanding. In particular, the optical modulator with a high damage threshold and the ability to generate multiple soliton states. This has prompted an ongoing search for optical modulators based on two-dimensional (2D) materials. Therefore, in this work, a novel 2D material Cr2Sn2Te6 (CSnT) with modulation depth of 6.17% and saturation intensity of 15.97 MW/cm2 is prepared as saturable absorber (SA). The nonlinear optical absorption characteristics and pulse modulation applications of CSnT are showed in the Erbium-doped fiber laser (EDFL). The fundamental frequency mode-locked operation and the second harmonic mode-locked operation are realized simultaneously in the ring cavity. Moreover, CSnT SA has a high damage threshold and high stability, the damage threshold reaches 467 mW and the signal-to-noise ratio (SNR) is higher than 70 dB. The experimental findings demonstrate that the CSnT-based saturable absorber possesses remarkable nonlinear optical properties, indicating its considerable potential in the realm of ultrafast photonics.

Electron‐Deficient Boron‐Doped g‐C3N4 as an Efficient and Robust Photocatalyst for Visible‐Light Driven Hydrogen Evolution from Water Splitting

AbstractElemental doping is considered to be a promising approach for altering the electronic structure, optical absorbance, and charge separation characteristics of graphitic carbon nitride (g‐C3N4, termed as CN), thus boosting its photocatalytic performance for practical applications. Herein, a series of boron (B) doped g‐C3N4 (named as BCN) photocatalysts are developed via one‐step pyrolysis of a mixture of urea and 3‐methoxycarbonyl‐5‐nitriophenylboronic acid (MCNPBA). The results show that B‐atoms have been successfully incorporated into the g‐C3N4 network. The as‐synthesized BCN‐x (x shows the weight content of MCNPBA) photocatalysts are evaluated in photocatalytic hydrogen (H2) evolution from water splitting under visible‐light (λ ≥ 420 nm). The optimized BCN‐10 sample shows a maximum H2 evolution rate of 1789.93 µmol h─1 g─1, which is 6.2 times higher than that of g‐C3N4 (289.73 µmol h─1 g─1). This is attributed to the fact that the electron‐deficient B‐atoms are lewis acids that trap electrons, which in turn expands visible‐light absorption, narrows the bandgap, and prevents the recombination of photogenerated charge carriers. Moreover, B‐doping can readily modify the valence and conduction band positions of g‐C3N4, therefore augmenting the photocatalytic H2 evolution activity. This paper presents a unique rational framework for developing other functionalized electron‐deficient elemental‐doping g‐C3N4‐based photocatalysts for practical applications in solar‐to‐fuel conversion.

Nonlinear Optical Refraction and Absorption Features of Methyl Orange Dye in Polar Solvents.

Herein, we report the nonlinear optical (NLO) refraction and absorption features of azo dye namely, methyl orange (MO) dissolved in ethanol, methanol, acetone, 1-propanol, DMF and DMSO. The UV-Visible absorption study reveals that the maximum absorption spectrum of MO dye appeared towards longer wavelength by increasing the solvent polarizability is the result of red shift or bathochromic shift. The Z-scan method is utilized to measure the third-order NLO features of MO dye in different polar solvents. A continuous wave laser with 5-mW power and an excitation wavelength of 405nm is employed in the Z-scan technique. The NLO features including nonlinear index of refraction (n2), nonlinear coefficient of absorption (β) and third-order NLO susceptibility (χ3) are calculated to be the order of 10-7 cm2/W, 10-2cm/W and 10-7 esu, respectively. The NLO index of refraction shows peak-valley transmittance is the result of self-defocusing and NLO absorption coefficient exhibits both positive and negative nonlinearity owing to saturable absorption (SA) and reverse saturable absorption (RSA). The effect of solvent polarizability and dipole moment on third-order NLO susceptibility of MO dye is discussed. Based on the experimental results, an azo dye MO appears to be a promising option for NLO applications in the future.

Optical properties of blue-light-emitting Y2 O3 :Ce nanophosphor for solid-state lighting application.

The structural, surface morphological, optical absorption and emission features of Y2 O3 :Ce (0%-5%) were studied. The samples had a body-centred cubic crystal structure. The undoped sample had a crystallite size of 29.03 nm, and it varied after doping with Ce. The grain size of the samples varied from 23.00 to 50.78 nm. All the samples exhibited a strong absorption band at 206 nm due to F-centre absorption and absorption involving the delocalised bands. In addition, the doped samples exhibited a secondary band at ~250 nm due to 4f → 5d transitions of Ce3+ ions. The optical bandgap of the undoped sample was found to be ~5.37 eV, and it decreased to 5.20 eV with an increase in Ce concentration to 5%. The undoped sample under 350-nm excitation exhibited a broad photoluminescence (PL) emission band with the maxima at 406 nm and a secondary band at 463 nm. In contrast, multiple PL peaks were centred at ~397, 436, 466, 488 and 563 nm in all the doped samples. The average lifetime of the emission band at 406 nm was 1.05 ns and that of the emission band at ~466 nm was 1.63 ns. The material has potential for solid-state lighting applications.

Excited State Calculations of Cu-Doped Anatase TiO2 (101) and (001) Nanofilms

Excited state calculations are performed to predict the electronic structure and optical absorption characteristics of Cu-doped anatase TiO2 nanofilms, focusing on their (101) and (001) surface terminations. Using model structures that successfully represent the equilibrium positions of deposited Cu atoms on the TiO2 surface, a comprehensive analysis of the absorption spectra for each considered model is made. The proposed modeling reveals phenomena when photogenerated electrons from TiO2 tend to accumulate in the vicinity of the deposited Cu atoms exposed to photon energies surpassing the band gap of TiO2 (approximately 3.2 eV). The crucial transition states that are essential for the creation of potential photocatalytic materials are identified through detailed calculations of the excited states. These insights hold substantial promise for the strategic design of advanced photocatalytic materials. The obtained results provide a base for subsequent analyses, facilitating the determination of heightened surface reactivity, photostimulated water splitting, and antibacterial properties.

Ultra-Broadband Ultraviolet-Visible Light-Short Wavelength Infrared InGaAs Focal Plane Arrays via n-InP Contact Layer Removal.

PIN InGaAs short wavelength infrared (SWIR) focal plane array (FPA) detectors have attracted extensive attention due to their high detectivity, high quantum efficiency, room temperature operation, low dark current, and good radiation resistance. Furthermore, InGaAs FPA detectors have wide applications in many fields, such as aviation safety, biomedicine, camouflage recognition, and infrared night vision. Recently, extensive research has been conducted on the extension of the response spectrum from short wavelength infrared (SWIR) to visible light (VIS) through InP substrate removal and reserving the n-InP contact layer. However, there is little research on the absorption of InGaAs detectors in the ultraviolet (UV) band. In this paper, we present an ultra-broadband UV-VIS-SWIR 640 × 512 15 μm InGaAs FPA detector by removing the n-InP contact layer in the active area and reserving the InP contact layer around the pixels for n contact, creating incident light to be directly absorbed by the In0.53Ga0.47As absorption layer. In addition, the optical absorption characteristics of InGaAs infrared detectors with and without an n-InP contact layer are studied theoretically. The test results show that the spectral response is extended to the range of 200-1700 nm. The quantum efficiency is higher than 45% over a broad wavelength range of 300-1650 nm. The operability is up to 99.98%, and the responsivity non-uniformity is 3.28%. The imaging capability of InGaAs FPAs without the n-InP contact layer has also been demonstrated, which proves the feasibility of simultaneous detection for these three bands.

First-principles calculations for heterostructure studies Involving CsPbI3 perovskite and IV-VI semiconductors

The PbX(X = S, Se, Te)/CsPbI3 heterostructure, formed by lead chalcogenides and halide perovskite CsPbI3, holds promise for optoelectronic devices. Utilizing first-principles calculations with VASP software, this study investigates its structural, electronic, and optical properties. With confirmed appropriate lattice mismatch rates (4.6%, 2.4%, 3.8%) and similar octahedral frameworks, constructing the PbX/CsPbI3 heterostructure is feasible. Calculations of electronic properties reveal mechanisms to improve optical performance. The type-I band alignment at the PbX/CsPbI3 interface(−5.27 eV < PbX < −3.73 eV, −5.34 eV < CsPbI3 < −3.57 eV) reduces electron and hole recombination losses, enhancing energy transfer efficiency. This arrangement facilitates electron and hole transfer from CsPbI3 to PbX, supported by charge density differences. Among the three heterostructures, PbSe/CsPbI3 demonstrates superior charge transfer capabilities, with more pronounced electron clouds. The PbX/CsPbI3 heterostructure extends CsPbI3’s light absorption into the near-infrared via PbX influence. Spectral comparison reveals PbTe/CsPbI3 > PbSe/CsPbI3 > PbS/CsPbI3, with PbSe/CsPbI3 excelling in stability, charge density transfer, and optical properties. Furthermore, under the premise of ensuring stability, different optical absorption characteristics can be achieved by adjusting the composition of Se atoms in PbSe/CsPbI3. This work provides a theoretical basis for the physical mechanisms behind enhancing the performance of PbX/CsPbI3 heterostructures as visible-to-near-infrared optoelectronic materials. It offers a promising avenue for the design of high-performance visible-to-near-infrared optoelectronic materials.

Nonlinear and Negative Effective Diffusivity of Interlayer Excitons in Moiré-Free Heterobilayers.

Interlayer exciton diffusion is studied in atomically reconstructed MoSe_{2}/WSe_{2} heterobilayers with suppressed disorder. Local atomic registry is confirmed by characteristic optical absorption, circularly polarized photoluminescence, and g-factor measurements. Using transient microscopy we observe propagation properties of interlayer excitons that are independent from trapping at moiré- or disorder-induced local potentials. Confirmed by characteristic temperature dependence for free particles, linear diffusion coefficients of interlayer excitons at liquid helium temperature and low excitation densities are almost 1000 times higher than in previous observations. We further show that exciton-exciton repulsion and annihilation contribute nearly equally to nonlinear propagation by disentangling the two processes in the experiment and simulations. Finally, we demonstrate effective shrinking of the light emission area over time across several hundreds of picoseconds at the transition from exciton- to the plasma-dominated regimes. Supported by microscopic calculations for band gap renormalization to identify the Mott threshold, this indicates transient crossing between rapidly expanding, short-lived electron-hole plasma and slower, long-lived exciton populations.

Adjustment of optical absorption in phosphorene through electron-phonon coupling and an electric field.

This study investigates the optical absorption of monolayer phosphorene, focusing on its response to the electron-phonon coupling (EPC) and an electric field. Using a tight-binding Hamiltonian model based on the Barišic-Labbe-Friedel-Su-Schrieffer-Heeger model and the Kubo formula, we calculate the electronic band structure and optical absorption characteristics. The anisotropic dispersion of carriers along armchair and zigzag directions leads to distinct optical responses. Positive and negative EPC effects increase and decrease hopping parameters, respectively, enlarging and reducing/closing the band gap. Moreover, both EPCs cause an admixture of blue and red shift spectrum along the armchair direction, while a red (blue) shift spectrum is observed for positive (negative) EPC along the zigzag direction. Incorporating electric field effects in the EPC increases band gaps for both positive and negative EPC activities, resulting in shifted optical peaks along both directions.

Structural and opto-electrical properties of Y2O3 nanopowders synthesized by co-precipitation method

The synthesis-dependent structural-optical characteristics of nanomaterials have induced the critical optimization of parameters for nanoparticle synthesis. Considering the potential applications of yttria (Y2O3) in high-temperature IR windows and electro-optic devices, the present study describes the preparation of yttria nanopowders (YNPs) through co-precipitation method. Some special morphological and opto-electrical properties have been observed with a change in the precipitating agent concentration (R = NH5CO3/Y3+ = 1.5–5.5) without using any surfactant. Rietveld refinement confirmed the body-centered cubic (Ia-3 space group) structure of YNPs. Surface functionalities have been determined by Fourier transform infrared (FTIR) spectroscopy. Electron microscopy results confirmed the formation of agglomerated YNPs with R-dependent morphological modifications from flake-like shape to pseudo-spherical and rod-like particles. UV–visible and fluorescence (FL) spectroscopy confirmed the R-dependent optical absorption and emission (indigo, blue and green) characteristics. The dielectric measurement also confirmed the R-dependent variation in the dielectric constant values in the lower frequency range.

Research on the Structure Design of Silicon Avalanche Photodiode with Near-Ultraviolet High Responsivity

To improve the low responsivity of the silicon avalanche photodiode in the near-ultraviolet wavelength range, we designed a near-ultraviolet highly responsive Si-APD basic structure with a multiplication layer neighboring the photosensitive surface through the analysis of the optical absorption characteristics, junction breakdown characteristics, and avalanche multiplication characteristics. The dark current and electric field distribution of the device were investigated. Meanwhile, the structural parameters of the surface non-depleted layer, multiplication layer, and absorption layer were optimized. It was found that the breakdown voltage of the device is 21.07 V. At an applied bias voltage of 20.02 V, the device exhibits a responsivity of 6.79–14.51 A/W in the wavelength range of 300–400 nm. These results provide valuable insights for the design of silicon avalanche photodiode with high responsivity in the near-ultraviolet range.

Photovoltage and Photocurrent Absorption Spectra of Sulfur Vacancies Locally Patterned in Monolayer MoS2.

We report on the optical absorption characteristics of selectively positioned sulfur vacancies in monolayer MoS2, as observed by photovoltage and photocurrent experiments in an atomistic vertical tunneling circuit at cryogenic and room temperature. Charge carriers are resonantly photoexcited within the defect states before they tunnel through an hBN tunneling barrier to a graphene-based drain contact. Both photovoltage and photocurrent characteristics confirm the optical absorption spectrum as derived from ab initio GW and Bethe-Salpeter equation approximations. Our results reveal the potential of single-vacancy tunneling devices as atomic-scale photodiodes.