Optical Absorption Efficiency Research Articles

Two-dimensional pnictogen carbides and their Janus structures: Potential on visible-light photocatalytic water splitting for hydrogen production

This study explored eight novel and highly stable monolayer configurations: C3X2 (X = N, P, As, Sb, and Bi) and C3XY (X = P and As, YAs and Sb) by analyzing their electronic, optical, and photocatalytic properties based on first-principles density functional theory. The findings indicated that the C3X2 monolayers, except for C3Bi2, exhibit indirect band gap semiconductor properties, and their band gaps are 1.497, 1.862, 2.272, 1.448, and 1.561 eV, respectively. Notably, only C3P2 and C3As2 fulfilled the prerequisites for photocatalytic water splitting, boast high electron mobility (up to ∼103 cm2/Vs), strong absorption in the visible light range, and high solar-to-hydrogen (STH) efficiency (30.16% for C3P2 and 23.05% for C3As2). Moreover, the Janus C3PAs, C3PSb, and C3AsSb monolayers exhibited indirect band gaps ranging from 1.616 to 2.070 eV and satisfied the band structure criteria for photocatalytic water splitting. These three Janus monolayers outperformed C3X2 in terms of optical absorption, carrier mobility, and STH efficiency owing to their inherent electric fields. The STH efficiency of C3PSb and C3AsSb reach 31.26% and 29.17%, respectively, with electron mobility reaching up to 4642.01 and 11902.64 cm2/Vs, respectively, indicating their exceptional potential for photocatalytic water splitting.

Electronic and optical properties of two-dimensional MoS2/WX2 (X=S, Se, Te) heterostructures

Two-dimensional heterostructures have important applications in catalysis, field effect transistors, solar cells, and photodetectors due to their unique optical properties. In this work, two-dimensional MoS2/WX2 (X=S, Se, Te) heterostructures were constructed. The electronic and optical properties of two-dimensional MoS2/WX2 (X=S, Se, Te) were studied by first-principles calculation. The results show that MoS2/WS2 and MoS2/WSe2 are indirect band gap semiconductors and direct band gap semiconductors with type-Ⅱ band arrangement, respectively, and MoS2/WTe2 is a semi-metallic material with type-Ⅲ band arrangement. Compared with MoS2 and WX2, MoS2/WX2 has a higher absorption coefficient in the visible region and exhibits a stronger optical absorption response. Among them, MoS2/WS2 has the best optical absorption ability. Therefore, the construction of MoS2/WX2 heterostructure is an effective way to improve the optical absorption efficiency, which provides a valuable reference for the design of new optoelectronic devices.

Absorption and quantum efficiency of GeSn nanopillar arrays for infrared detectors

This research investigates the optical absorption and quantum efficiency of germanium-tin (GeSn) materials with a tin(Sn) content of 4.5%, and their potential applications in infrared optoelectronic systems. It has two forms which are crystalline(c-GeSn) and amorphous(a-GeSn) states. The finite-difference time-domain (FDTD) method was used to simulate the absorption of c-GeSn and a-GeSn. By optimising the period, radius and height of the nanopillars, the optimal parameters were determined, and it was found that the c-GeSn nanopillars in that case had a very stable and excellent absorption in the near-infrared (NIR) band. Calculated by MATLAB that the cylindrical nanopillars could reach a maximum quantum efficiency of 3.67% at 1350 nm. It is anticipated that this study will contribute to the further understanding of GeSn and provide a theoretical basis for designing high-performance infrared photodetectors.

Computational study of LiAlSi, LiAlGe and LiGaSi Half-Heusler alloys for opto-electronic applications

In this comprehensive investigation, the structural, elastic, electronic, optical, thermodynamic and thermoelectric properties of Lithium-based ternary semiconductors, namely LiAlGe, LiAlSi, and LiGaSi were explored. Utilizing first-principle calculations, various material properties were accurately determined . The lattice constants, bulk modulus, and equilibrium total energies were obtained revealing that the three alloys are mechanically stable and show brittle behavior. Electronic band structures and density of states calculations, employing PBE+U, unveiled band gaps of 1.32 eV, 1.55 eV, and 1.47 eV for LiAlGe, LiAlSi, and LiGaSi, respectively, suggesting their suitability for photovoltaic applications. Analysis of the absorption spectra allowed the identification of the active window of the electromagnetic spectrum for these materials. Subsequently, the materials exhibited desirable optical properties, characterized by efficient optical absorption, with the highest peaks in the visible light and ultraviolet regions of the electromagnetic spectrum, low reflectivity, and a high dielectric constant. These collective findings indicate the potential of these materials for application in the field of opto-electronics. Furthermore, calculations of thermoelectric properties disclosed figure of merit values of 0.830, 1.046, and 0.697 at 950 K for the LiGaSi, LiAlSi, and LiAlGe HH alloys, respectively, further highlighting their potential for use in thermoelectric applications.

Strain-bandgap quasi-linear correlation applied to modulation of NiBr2 monolayer optical properties

Recently, two-dimensional transition metal dihalides have shown diverse applications in spintronics, quantum devices, and optoelectronic devices. In this work, density functional theory (DFT) is adopted to investigate the effect of biaxial strain upon the electronic structure and optical properties of NiBr2 monolayer. The results show that NiBr2 is an indirect semiconductor with band gap 2.62 eV (DFT + U) and 3.18 eV (HSE06), which could vary quasi-linearly from 2.73 eV to 1.71 eV modulated by biaxial strain (6 % to −10 %). Combined with the analysis of the density of states (DOS), the primary reason for the alteration in the band gap is that strain significantly affects the behavior of Ni 3d electrons. When the strain changes from positive to negative, the DOS of Ni 3d shifts towards the Fermi level, resulting in a reduction in the band gap. Within this strain range, all of the optical properties exhibit a quasi-linear tendency similar to the band gap variation. The optical peaks of NiBr2 under compressive strain are not only red-shifted into the visible light (VL) region but also significantly enhanced in the VL and ultraviolet (UV) regions. Applying strain can greatly boost the electrical and optical properties of NiBr2 monolayer, making it a promising candidate in the field of ultraviolet detectors.

Enhanced plasmonic absorption using MIM ring resonator structures for optical detector applications

This study delves into the design and analysis of plasmonic absorbers utilizing Metal-Insulator-Metal (MIM) ring resonator devices to achieve heightened optical absorption efficiency. Various ring resonator topologies, namely SRR-L and Ring-L, are investigated with the objective of amplifying absorption capabilities. Moreover, the examination extends to the influence of modifying the inner radius of the ring, resulting in discernibly diverse absorption levels. Through the integration of these ring resonators, absorption peaks are effectively brought into proximity, thereby yielding a broad-band absorption spectrum. Our discoveries underscore the promising potential of these devices as proficient optical detectors. The simulations were performed in three dimensions utilizing CST Microwave Studio.

Impacts of electric gating and divacancies on optical absorption spectra of zigzag buckling silicene nanoribbons

In this study, by combining the tight-binding description with the gradient approximation, we investigated the impacts of electric gating and divacancies on the optical characteristics of zigzag buckling silicene nanoribbons. Our results show that the back-gate electric potential tends to shift the peak structure to higher frequencies in the free-defective structures, while the side-gate electric potentials intensify the intensity of the excitation channels obeying the selection rule ΔJ=even. In particular, applying the potentials in a suitable range can improve the optical absorption efficiency at a certain frequency with the back gate or widen the threshold absorption intensity from Jv=1 to Jc=1 with the side gates. Besides, the defective structures' absorption spectra exhibit richer features than the perfect one, with the appearance of new optical excitations due to the transitions between the local minimum or maximum in the low-energy bands around the Fermi level. Moreover, applying electric gating in defective structures can also tune the absorption spectra with additional features.

The photothermal coupling of TiN@Au core-shell nanorods applied to near-infrared photothermal therapy

Thermal plasmonic nanoparticles offer a novel and significant approach for photothermal therapy in the medical field, which is photothermal therapy of cancer. This study introduces a type of core-shell nanorods with internal coupling of titanium nitride (TiN) and gold (Au) nanomaterials. The photothermal properties of these nanorods in the near infrared (NIR) band were investigated using COMSOL Multiphysics software and the finite element method. Results indicate that TiN@Au and Au@TiN core-shell nanorods exhibit superior photothermal properties in the NIR band compared to pure TiN nanorods of similar volume. Furthermore, core-shell nanorods with polarization angles of 0° and 45° demonstrate enhanced optical absorption properties in the near infrared range. Furthermore, the study on the tunability of localized surface plasmon resonance with variations in core diameter, shell thickness, and combined changes of core diameter and shell thickness for core-shell nanorods of equal volume suggests that TiN@Au core-shell nanorods with a 10 nm Au shell offer increased optical absorption efficiency and photothermal conversion capability. Ultimately, the TiN and Au core-shell nanorods proposed in this research offer valuable insights for the structural design and heat transfer control of nanoparticle heat generators to enhance fluid temperature, as well as provide practical guidance for the preparation of core-shell nanoparticles.

Strain-induced changes of electronic and optical properties of Zr-based MXenes

Zr-based MXenes recently attracted attention because of its experimental preparation showing temperature stability, mechanical strength, and promising energy, sensoric, and electrochemistry applications. However, necessary theoretical predictions at a precise/predictive level are complicated due to essential excitonic features and strong electron correlation (i.e., a necessity to go beyond standard density functional theory, DFT). Contrary to the prevailing focus on oxygen-terminated MXenes and standard predictions of other Zr-based MXenes as conductors, based on the hybrid DFT and GW many-body perturbational theory, we were able to find seven different semiconductors (five of them for their equilibrium geometry and two others under slight tensile biaxial strain) in the case of two- and three-layered Zr2CT2 and Zr3C2T2 configurations with various terminations (T = O, F, S, Cl). We observed semiconductor-to-conductor transition induced by strain in the majority of such Zr-based MXenes at an experimentally achievable strain range. Furthermore, using the Bethe–Salpeter equation (BSE), we demonstrated that selected semiconducting Zr-based MXenes possess high optical absorption efficiency (20%–30%) in the visible light range, underscoring their potential in photonic applications. The high sensitivity of Zr-based MXenes to external conditions and functionalization combined with the thermal stability makes the materials promising for applications at operational temperatures in electronic and optical technologies.

Predicting the electronic, optical, and thermometric properties of novel K2LiSbX6 (X = Cl, Br, I) semiconductors: A first-principles study

Due to their acceptable optical absorption efficiency, greater stability, adjustable bandgap, huge carrier mobility, non-toxicity, readily accessible raw materials, and low cost. The halide-based double perovskites (DPs) have demonstrated several advantages over halide-based perovskites. The Perdew-Burke-Ernzerhof (PBE) functional is used to compute the electrical, optical, mechanical, and thermal properties of halide-based DPs K2LiSbX6 (X = Cl, Br, I) in the Generalized Gradient approximation (GGA) framework of density functional theory (DFT). The objective of studying these materials is to compute the electronic, optical, and thermal properties, to use these materials in the solar cell and thermal applications. It is calculated what the structural parameters are, including the lattice parameter, cell volume, total energy, bulk modulus, pressure derivative, and tolerance factor. The compound’s semiconducting nature is revealed by the electrical density of states, and the band structure shows that the band gaps (3.7 eV, 2.9 eV, and 2.2 eV) are indirect in nature. To address the under-estimated band gap as found in the GGA-PBE functional, the mBJ functional is introduced. Electronic structures analysis and provide explanations for the actual and fictitious parts of the dielectric function ε (ω), absorption coefficient α(ω), energy loss function L(ω), reflectivity ℜ(ω), refractive index n (ω), and extinction coefficient K (ω) versus photon energy (eV). According to these criteria, Br, Cl, I-based materials are optically preferable to K-based compounds. Because of the above predicted outcomes, we conclude that these materials are good candidates for optoelectronics and thermal devices.

A Novel Boron Dipyrromethene-Erlotinib Conjugate for Precise Photodynamic Therapy against Liver Cancer.

Photodynamic Therapy (PDT) is recognized for its exceptional effectiveness as a promising cancer treatment method. However, it is noted that overexposure to the dosage and sunlight in traditional PDT can result in damage to healthy tissues, due to the low tumor selectivity of currently available photosensitizers (PSs). To address this challenge, we introduce herein a new strategy where the small molecule-targeted agent, erlotinib, is integrated into a boron dipyrromethene (BODIPY)-based PS to form conjugate 6 to enhance the precision of PDT. This conjugate demonstrates optical absorption, fluorescence emission, and singlet oxygen generation efficiency comparable to the reference compound 7, which lacks erlotinib. In vitro studies reveal that, after internalization, conjugate 6 predominantly accumulates in the lysosomes of HepG2 cells, exhibiting significant photocytotoxicity with an IC50 value of 3.01 µM. A distinct preference for HepG2 cells over HELF cells is observed with conjugate 6 but not with compound 7. In vivo experiments further confirm that conjugate 6 has a specific affinity for tumor tissues, and the combination treatment of conjugate 6 with laser illumination can effectively eradicate H22 tumors in mice with outstanding biosafety. This study presents a novel and potential PS for achieving precise PDT against cancer.

Ab initio calculations on magnetic and optical characteristics of pure ZnO and Mn(II)-doped ZnO monolayers with and without neutral charged vacancies defects

At high Curie temperatures, diluted magnetic semiconductors exhibit induced ferromagnetism and spin-dependent interactions, making them useful in magneto-electronic devices. In spite of the fact that ferromagnetism and optical emission dynamics are characterized by intricate microstructural and compositional features, the origins of these phenomena are not yet completely understood. Here, we used first principles calculations to study how vacancy defects affect the electrical, optical, and magnetic properties of pure ZnO and Mn@ZnO monolayers. In the pristine monolayer, the Zn vacancy produces magnetism with a total magnetic moment of 2 μB, but the oxygen vacancy does not. The magnetic semiconducting characteristic of the Mn substitution at the Zn site is shown by a total magnetization of 5 μB. The magnetic ground state of the ZnO monolayer doped with Mn is significantly influenced by the presence of native defects. More specifically, Zn vacancies are essential for stabilizing the FM states due to the bound magnetic polarons (BMPs) formation, but O vacancies have no influence on the magnetic ground state of the Mn(II)@ZnO monolayer. Based on the optical study, we discovered that Zn and O vacancies in the ZnO ML produce optical absorption peaks at 1.92 eV and 2.90 eV, respectively. The substitution of Mn(II) at Zn site not only increases the band gap of the ZnO monolayer but also produces d-d transition bands at lower energy side of fundamental energy gap peak. The Zn vacancies in the Mn(II)@ZnO ML produce an infrared absorption band around 1.13 eV, which could be due to the formation of the BMP, and enhance the optical absorption efficiency. The ZnO ML’s energy gap and Mn ion’s d-d transition bands exhibit a blueshift in AFM systems and a redshift in the FM systems. In far configuration, the Mn(II)@ZnO monolayer show no shift in the fundamental bandgap and intra-band transition of the Mn(II) spins due to the Mn(II) ion’s paramagnetic nature.

Facile synthesis of hierarchical W18O49 microspheres by solvothermal method and their optical absorption properties

In this study, a simple route for the synthesis of hierarchical W18O49 assembled by nanowires is reported. The morphologies and formation of W18O49 single-crystal could be controlled by changing the concentration of WCl6-ethanol solution. This synthesis strategy has the advantages that the hierarchical W18O49 microspheres could be economic synthesized at 180 °C without adding additives. Furthermore, efficient optical absorption properties in ultraviolet, visible and near-infrared region were obtained for the hierarchical W18O49 microspheres comparing with nanowires. These results will further promote the research of tungsten-based oxide nanomaterials.Graphical abstract

Effect of Surface Functional Groups on the Electronic Behavior and Optical Spectra of Mn2N Based MXenes.

The extensive applications of MXenes, a novel type of layered materials known for their favorable characteristics, have sparked significant interest. This research focuses on investigating the influence of surface functionalization on the behavior of Mn2NTx (Tx=O2, F2) MXenes monolayers using the "Density functional theory (DFT) based full-potential linearized augmented-plane-wave (FP-LAPW)" method. We elucidate the differences in the physical properties of Mn2NTx through the influence of F and O surface functional groups. We found that O-termination results in half-metallic behavior, whereas the F-termination evolves metallic characteristics within these MXene systems. Similarly, surface termination has effectively influenced their optical absorption efficiency. For instance, Mn2NO2 and Mn2NF2 effectively absorb UV light ~50.15×104 cm-1 and 37.71×104 cm-1, respectively. Additionally, they demonstrated prominent refraction and reflection characteristics, which are comprehensively discussed in the present work. Our predictions offer valuable perspectives into the optical and electronic characteristics of Mn2NTx-based MXenes, presenting the promising potential for implementing them in diverse optoelectronic devices.

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.

Monolithic integrated chip of AWG and PD for an FBG interrogation system

To advance the development of a compact and highly integrated fiber Bragg grating (FBG) interrogation system, to the best of our knowledge, this paper is the first to present the design and fabrication of a monolithic integration chip based on silicon-on-insulator (SOI), which is specifically intended for application in fiber grating sensing interrogation systems. By considering the impact of coupling structure dimensions on coupling efficiency as well as the effect of the photodetector (PD) parameters on the optical absorption efficiency of the device, we refine the structure of the monolithic integrated chip for arrayed waveguide grating (AWG) and PD. The test results reveal that the coupling loss between AWG and PD is -2.4 dB. The monolithic integrated interrogation chip achieves an interrogation accuracy of approximately 6.79 pm within a dynamic range of 1.56 nm, accompanied by a wavelength resolution of 1 pm. This exceptional performance highlights the potential of the monolithic integrated chip to enhance the integration of AWG-based fiber grating interrogation systems.

First principles study of thermo-physical and opto-electronic properties of NaCuTe, NaCuSe and NaScSn as potential photovoltaics

In this comprehensive study, we delved into the electronic, structural, elastic, optical and thermodynamic properties of sodium-based ternary semiconductors i.e NaCuTe, NaCuSe and NaScSn. Employing first-principle calculations, we precisely determined various material properties. The lattice constants, bulk modulus and equilibrium total energies were derived using the Murnaghan equation of state and demonstrate a good agreement with other theoretical methods. Analysis of the absorption spectra allowed us to identify the active window of the electromagnetic spectrum for these materials. The determination of elastic constants provided crucial insights into the materials’ ability to withstand external stress, revealing that the materials meet stability criteria with a ductile behavior. Electronic band structures and density of states calculations unveiled band gaps of 1.40 eV, 1.03 eV and 1.15 eV for NaCuTe, NaCuSe and NaScSn, respectively. This suggests their suitability for photovoltaic applications. Additionally, the materials exhibited desirable optical properties, characterized by efficient optical absorption with the highest peaks in the visible light and ultraviolet region of the electromagnetic spectrum, low reflectivity and a high dielectric constant. These findings collectively indicate the materials’ potential for utilization as solar photovoltaics

Environmental-Friendly Ag2S QD-Multilayer MoSe2 van Der Waals Heterostructure for High-Performance Broadband Photodetection.

Broadband photodetectors have drawn intensive attention owing to their wide application prospects in optical communication, imaging, astronomy, and so on. Two-dimensional transition-metal dichalcogenides (TMDs) are considered as highly potential candidates for photodetection applications, benefiting from their excellent photoelectric properties. However, most of the photodetectors based on TMDs suffer from low performance in the near-infrared (NIR) region due to the weak optical absorption efficiency near their absorption band edge, which severely constrains their usage for broadband optoelectronics. Here, by taking advantage of the high absorption coefficient and environment-friendly property of Ag2S quantum dots (QDs), the hybrid of multilayer MoSe2/Ag2S QDs is demonstrated with a high-performance broadband photodetection capability (532-1270 nm). The favorable energy band alignment of MoSe2/Ag2S QDs facilitates effective separation and collection of photogenerated carriers, and the heterostructure device exhibits significant enhancement of performance compared to the bare MoSe2 device. High responsivity, detectivity, and external quantum efficiency of 25.5 A/W, 1.45 × 1011 Jones, and 1070% are obtained at a low working voltage of 1 V under 980 nm illumination. The responsivity of the device can reach up to 1.2 A/W at 1270 nm wavelength, which is competitive to the commercial NIR photodetectors. Meanwhile, broadband imaging capability is demonstrated. Our work may open up a facile and eco-friendly approach to construct high-performance broadband photodetectors for next-generation compact optoelectronic applications.

Reveal long-lived hot electrons in 2D indium selenide and ferroelectric-regulated carrier dynamics of InSe/α-In2Se3/InSe heterostructure.

As typical representatives of group III chalcogenides, InSe, α-In2Se3, and β'-In2Se3 have drawn considerable interest in the domain of photoelectrochemistry. However, the microscopic mechanisms of carrier dynamics in these systems remain largely unexplored. In this work, we first reveal that hot electrons in the three systems have different cooling rate stages and long-lived hot electrons, through the utilization of density functional theory calculations and nonadiabatic molecular dynamics simulations. Furthermore, the ferroelectric polarization of α-In2Se3 weakens the nonadiabatic coupling of the nonradioactive recombination, successfully competing with the narrow bandgap and slow dephasing process, and achieving both high optical absorption efficiency and long carrier lifetime. In addition, we demonstrate that the ferroelectric polarization of α-In2Se3 not only enables the formation of the double type-II band alignment in the InSe/α-In2Se3/InSe heterostructure, with the top and bottom InSe sublayers acting as acceptors and donors, respectively, but also eliminates the hindrance of the built-in electric field at the interface, facilitating an ultrafast interlayer carrier transfer in the heterojunction. This work establishes an atomic mechanism of carrier dynamics in InSe, α-In2Se3, and β'-In2Se3 and the regulatory role of the ferroelectric polarization on the charge carrier dynamics, providing a guideline for the design of photoelectronic materials.

Analysis of photothermal coupling of titanium nitride nanorods applied to near-infrared photothermal therapy

Titanium nitride (TiN) serves as an ideal reagent for photothermal therapy due to its cost-effectiveness, stability, and biocompatibility. This study investigates the optical and thermal properties of TiN nanoparticles in the near-infrared (NIR) region. Specifically, we employ the COMSOL Multiphysics software to solve Maxwell's equations using a finite element method, enabling us to investigate the photothermal characteristics of individual TiN nanorods. To ensure accurate photothermal coupling calculations, we utilize the Fourier steady-state heat conduction equation. The results demonstrate that the nanorod photothermal properties exhibit significantly enhanced effects when the incident light is polarized along the long axis of the rod, while the thermal properties of the nanorods are primarily influenced by their optical absorption efficiency. The tunability investigation of the nanorods demonstrates that an increase in aspect ratio (AR) results in a red-shift of the absorption peaks. Concurrently, there is an expansion in the bandwidth corresponding to the absorption peak, accompanied by an augmentation in its peak value. It is evident that at AR = 5, the TiN nanorods exhibit enhanced photothermal properties in the NIR region, resulting in a temperature increase of 43 K in the surrounding medium through efficient heat transfer. Consequently, this accomplishment enables achieving the desired temperature range for effective photothermal therapy. The significance of this study lies in providing a valuable reference and theoretical guidance for exploring the utilization of TiN nanorods in photothermal therapy, with a specific focus on attaining a more precise understanding of temperature elevation and distribution during the treatment process.