Indirect Electronic Transitions Research Articles

Charge transport properties and variable photo-switching of three-terminal Cs2AgBiBr6 device

In this study, we present an in-depth exploration of charge transport phenomena and variable photo-switching characteristics in a novel double-perovskite-based three-terminal device. The Cs2AgBiBr6 thin film (TF) was synthesized through a three-step thermal evaporation process followed by precise open-air annealing, ensuring superior film quality as confirmed by structural and morphological characterizations. Photoluminescence spectroscopy revealed distinct emissions at 2.28 and 2.07 eV, indicative of both direct and indirect electronic transitions. Our device exhibited space-charge limited current (SCLC) behaviour beyond 0.35 V, aligning with the relationship , where the exponent m transitioned from ≤1 to >1. Detailed analysis of Schottky parameters within the trap-filled limit (TFL) regime was conducted, accounting for variations in temperature and optical power. Significantly, the self-powered photodetector demonstrated outstanding performance under illumination. The sensitivity of the device was finely tunable via the applied bias voltages at the third terminal. Notably, an optimal bias voltage of ±100 μV yielded maximum responsivity (R) of 0.48 A/W and an impressive detectivity (D*) of 1.07 × 109 Jones, highlighting the potential of this double-perovskite-based device for advanced optoelectronic applications.

Effect of the behavior on direct–indirect electronic transitions of SrZrO3 nanowires grown in the crystallographic directions [100] and [110]: Ab-initio study

In the present work, we studied a set of strontium zirconate nanowires of different diameters oriented in the directions [100] and [110]. The density functional theory calculations were performed using the quantum espresso code, which confidently employs a combination of plane waves. In this study, we utilized a pseudopotential proposed by Perdew, Burke, and Ernzerhof to model the exchange–correlation energy using a generalized gradient approximation. In the study’s first phase, we performed a structural optimization of the nanowires by adjusting the atomic positions and lattice parameters. After calculating the electronic band structure and density of states, we found that the strontium zirconate nanowires in this study are semiconductors. The nanowires in the [100] direction have an indirect transition, while those in the [110] direction have a direct transition. Besides, the bandgap varies with diameter. We also calculated the density of states projected. Based on the results, it can be observed that the p orbital of oxygen is the primary contributor to the density of states in the valence region. On the other hand, in the conduction region, the density of states is mainly affected by the d and s orbitals of zirconium. Due to their exceptional electronic properties, strontium zirconate nanowires are up-and-coming candidates for photocatalysis and solar cell applications.

Preparation and Study of Structural, Optical and Electrical Properties of the Composite Films [PVA-PEO-MnCl2.4H2O

In the present paper, pure polymeric blend film [PVA-PEO] and the polymeric blend films reinforced by MnCl2.4H2O salt with different weight ratios (10, 20, 30, 40, 50 wt %) have been prepared by using the solution casting method. The effects of weight ratio of salt on structural properties for all reinforced polymeric blends films were studied. FTIR spectra were used to establish the interaction between the polymer (PVA) and the polymer (PEO) reinforced by MnCl2.4H2O salt, which causes some changes in the vibration modes and the position of the bonds. All inrestigated samples exhibited broad bonds at around (3310 cm-1). The results showed the asymmetric vibration of O-H group in the polymers matrix. The peaks around (2880 cm-1) can be attributed to the presence of C- H stretching vibration group. The C=C stretching vibration appears in the bonds at (1955 cm-1). The peak at (1096 cm-1) for all reinforced films is attributed to the stretching mode of C-O-C stretching. There is a shift of out-of-plane rings C-H bending vibration from 961.2 to 955 cm-1. These indicate the chemical interactions of MnCl2.4H2O salt with the polymeric blend [PVA-PEO]. The two strong bonds observed around (1471 cm-1 and 844 cm-1) are assigned to the bending and stretching vibration of the CH2 group, respectively. The change in the spectral intensities of polymeric blend [PVA-PEO] involves a shift in some bonds due to the MnCl2.4H2O salt addition. The effects of weight ratio of salt on optical properties for all reinforced polymeric blends films were studied, as the transmittance and absorbance spectra were recorded within the range of wavelengths (190-1100) nm, and it was found that the energy gap value decreases with an increase of the added salt’s weight ratio. Results showed that the indirect electronic transitions are allowed. Effects of salt’s weight ratio on electrical (dielectrical) properties for all reinforced polymeric blends films were studied, and the practical results showed a decrease in the dielectric constant (ε΄) with an increase in frequency for all polymeric blends films, while the practical results also showed an increase in the alternating electrical conductivity (σa.c) with increasing frequency for all polymeric blends films, as well as an increase in both the dielectric constant and alternating electrical conductivity with an increase in the added salt’s weight ratio at same frequency.

Transparent titanium ions doped lead-borate glasses with optimized persistent optical features for optoelectronic applications

The detection of distinctive optical materials is still under investigation. Hence, here, the melt-quenching approach was used to create a series of PbO–B2O3–TiO2 (PBT) glass materials with improved optical features. The transmittance of this PBT glass system decreased, and its reflectivity increased, through titanium ions doping. Spectrophotometric studies show that the optical bandgap energy of the PBT glasses decreased from 2.60 eV to 2.44 eV, arising from the permitted indirect electronic transitions, whereas the Urbach energy augmented from 0.029 eV to 0.042 eV as the TiO2 content increased. The incorporation of titanium ions into the lead-borate glass improved the behavior of the optical parameters, optical constants, energy loss factor, and dispersion parameters, as well as controlling the sheet resistance, coverage density, figure of merit, and plasma resonance frequency. Additionally, the electronic parameters including the energies of Plasmon, Penn, and Fermi, and the number of active electrons were evaluated. It was theoretically confirmed that the refractive index and band gap were oppositely correlated. Metallization criteria values indicated that these glasses exhibited semiconductor characteristics. Obtained findings revealed that the PBT glasses are suitable for optoelectronic applications. Finally, this work offers meaningful reference for developing optoelectronic properties of glass materials.

Phonon-assisted carrier transport and indirect optical absorption of cubic boron nitride from first-principles

Inquiring the isotopically engineered carrier transport in polar materials remains an open question. Herein, the phonon-limited drift carrier mobility of single-crystal cubic boron nitride is presented using first-principles calculations. Natural c-BN has the predicted electron mobility of 1230 and 760 cm2/V s by solving the iterative Boltzmann transport equation and self-energy relaxation time approximation, respectively. The hole mobility under the Boltzmann transport equation and self-energy relaxation time approximation is 193 and 105 cm2/Vs, respectively. Subsequently, the electron and hole mobilities at the stable isotope levels of boron and nitride are predicted, and nitride isotopes are found to be more effective than boron for carrier mobility. Those carrier mobilities further decrease with increasing temperature due to the strengthened electron–phonon interactions. Moreover, the phonon-assisted indirect optical absorption of c-BN is investigated by considering the contribution of phonons to the indirect electronic inter-band transitions. The predicted imaginary part of the dielectric function is in better agreement with previous experiments. This work aims to understand the role of phonons in determining the carrier mobility and indirect optical absorption of c-BN.

Damping effect of longitudinal optical phonon—plasmon coupling on thermal radiation from surface micro-gratings on direct and indirect electronic transition type semiconductors

Thermal radiation properties of surface micro-Au-line and space structures on direct and indirect electronic transition-type semiconductors of n-type (n-) GaAs and GaP, respectively, are studied. The electron densities range from 0.62 to 1.0 × 1018 cm−3. The emission spectra of samples on n-GaAs wafers show peak energies significantly shifted from the longitudinal optical (LO) phonon energy due to the LO-phonon−plasmon coupling (LOPC) at 630 K, while partial decoupling is observed. The thermal emission from the sample on n-GaP is peaked at 395.9 cm−1, shifted only by 1.5 cm−1 from the LO-phonon energy, with a linewidth of 12.5 cm−1 at 630 K. The effect of LOPC on the emission from the sample on n-GaP is mostly suppressed because of the electron localization in the X-valley, suggesting an advantage of indirect transition-type semiconductors in LO-phonon resonant infrared emitters using the phonons generated via the electron energy relaxation.

Indirect and direct electronic transitions and electron transport properties of van der Waals NbOCl2.

In this paper, the optical and electron transport properties of the two-dimensional (2D) van der Waals (vdW) niobium oxide dichloride (NbOCl2) crystal with extremely high second-order nonlinear coefficients are investigated theoretically. We found that the strong absorption of NbOCl2 in the infrared region is caused by the indirect transition accompanied by phonons and confirmed that the interaction between layers is very weak. However, the study of electron transport properties shows that the interlayer interaction of NbOCl2 has a certain degree of influence on the scalability of electrical and optical properties. Because of the strong anisotropy of the NbOCl2 material, it will be a more optimized choice for constructing on-chip photoelectric or thermal devices in the Nb-Cl-Nb direction.

PICOSECOND PULSED LASER DEPOSITION OF MOS2 THIN FILMS

MoS2 thin films were grown by the pulsed laser deposition technique using a picosecond laser at a wavelength of 1030 nm. The plasma ion mean kinetic energy and density were estimated from the time-of-flight distributions measured using a Langmuir planar probe. It has been found that the mean kinetic energy decreases with increasing the laser pulse energy. This unusual effect is explained by the difference in the volatility of the vaporized species. Samples were structurally characterized by Raman spectroscopy and grazing angle X-ray diffraction. It was found that thin films of amorphous matrices containing MoS2 nanocrystallites were grown. Optical characterization carried out by UV-vis spectroscopy yielded transmittance values above 90% in the visible spectral range and an indirect electronic transition at 1.4 eV. Chemical oxidation states for molybdenum and sulfur were analyzed by means of X-ray photoelectron emission spectroscopy, which revealed Mo-S bonding states, confirming the growth of MoS2.

2D Semiconducting Polymers Based on Aromatic 1,5‐Diheterocines with Oxygen and Nitrogen

AbstractA class of two‐dimensional polymers (2DP) based on aromatic oxygen‐ and nitrogen‐containing 1,5‐diheterocines is proposed. The diheterocines are interconnected via linkages with multiple bonds (─N═N─, ─C≡C─, ─N═CH─, ─CH═CH─) resulting in 30 polymers with 2D π‐conjugated network. According to DFT modeling nine of them are strictly planar species of monoclinic symmetry featuring either direct or indirect electronic transitions with HSE06 energies falling in the range [0.01–1.03] eV. The highest charge carrier velocity and corresponding lowest mass are estimated at 5.79 × 105 m s−1 and 9.45 × 10−3 m0, respectively. In addition to prospective optoelectronic applications, the polymers can be used in separation/filtration technologies. The proof‐of‐principle of N2/O2 separation is presented. Pore sizes of the 2DPs can be varied subject to the size of linkages. This study opens up new avenues for a design of multifunctional 2DPs.

Improved photocatalytic performance of Nb4TeO12 particles by the surface depositing α-Bi2O3

Mixed-metal oxides composed of Nb5+(d0) and Te4+(p-) cations generally exhibit excellent optoelectronic properties due to the stereoactive lone pair of electrons in the structure. In this work, a mixed-metal niobate tellurite Nb4TeO12 is prepared using solid state reaction method. The p-n junctions α-Bi2O3/Nb4TeO12 are prepared via soaking the as-prepared particles and post annealing treatments. Nb4TeO12 has indirect electronic transition characteristic with a band energy of 3.01 eV. The bottom of conduction band is − 0.55 eV and the top of valance band is + 2.46 eV. Surface deposits of α-Bi2O3 induce the recrystallization on the particle surface. The microstructure, electrical impedance, and photocurrent properties are analyzed. The p-n junction can significantly delay the recombination between photo-created h+/e− pairs. As a consequence, significant improvement of photocatalysis in p-n junction α-Bi2O3/Nb4TeO12 was realized. The rate constants of as-prepared Nb4TeO12 and p-n junction α-Bi2O3/Nb4TeO12 (30/100) are 4.21 × 10−3 min−3 and 1.82 × 10−2 min−1, respectively. The experimental results show that deposits of α-Bi2O3 on the surface is effective to improve the surface light absorption and photochemical properties of the Nb5+−Te4+ oxide semiconductors.

Broad intrinsic luminescence properties in Nb4TeO12 mixed-metal niobate tellurite

Mixed-metal oxides composed of Nb5+(d0) and Te4+(p-) cations generally exhibit excellent optoelectronic properties due to the stereoactive lone pair of electrons in the structure. In this work, a mixed-metal niobate tellurite Nb4TeO12 was prepared using solid state reaction method. The polycrystalline samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), optical absorption, photoluminescence (PL) and dynamic properties. This sample shows characteristic indirect electronic transitions with an interband energy of 3.01 eV. The bottom of conduction band and the top of valence band are +0.37 eV and +3.38 eV, respectively. Using a Nd:YAG pulsed laser as the excitation light source, the intrinsic luminescence of Nb4TeO12 was investigated over a wide temperature range of T = 10–300 K. The broad band emission peaking at 513 nm corresponds to the self-activating luminescence of the niobate octahedral group [NbO6]7−. The luminescence decay curve did not depend on the laser excitation energy, and it showed a non-exponential characteristic with two decay lifetime components. The experiments also preliminarily studied the performance of the luminescence application of Nb4TeO12.

Low cost novel PEO based nano-composite for semiconductor and He–Ne lasers beam attenuation: Structural and optical properties

This paper reports the synthesis of low cost polyethylene oxide (PEO) based polymer nanocomposites (PNCs) for laser beam attenuation. The experimental investigations revealed the novel optical properties and bandgap reduction of PEO upon insertion of the Pb3O4 nanofiller. The changes in structural and optical properties of the prepared PNCs were explored using the X-ray diffraction (XRD) method and the ultraviolet–visible (UV–Vis). A broad shift of absorption is evidenced upon the addition of Pb3O4 nanofiller. The optical parameter, including absorption coefficient (α), linear refractive index (n), and dielectric loss (εi), were calculated. The optical band gap reduced significantly from 5.4 eV (neat PEO) to 1.8 eV for PEO doped with 9% Pb3O4. The direct and indirect electronic transitions in pure PEO and PEO: Pb3O4 PNCs were determined based on Tauc's model. The type of electron transition is specified with the assistance of εi spectra. The nonlinear optical parameter, including first-order susceptibility (χ1), third-order susceptibility (χ³), and nonlinear refractive index (n2), were studied. In addition, Laser beam attenuation characteristics for prepared PNCs samples were investigated using both semiconductor laser and He–Ne laser. The PEO: Pb3O4 PNCs significantly attenuated the laser power for both laser systems.

One-pot synthesis of BaTi0.85Zr0.15O3/MOF-199 (HKUST-1) as a highly efficient photocatalytic nanocomposite for tetracycline degradation under UV irradiation

BaTi0.85Zr0.15O3/MOF-199 (HKUST-1) nanocomposite was prepared by a one-pot method and characterized via various methods such as XRD, FT-IR, TG and DTG, SEM equipped with an EDX analyzer, X-ray mapping, UV–Vis DRS, TEM, photoluminescence spectroscopy (PL), and N2 adsorption–desorption (for BET surface area measurement). The BaTi0.85Zr0.15O3/MOF-199 (30 wt%) exhibited best degradation efficiency of tetracycline (TC), BaTi0.85Zr0.15O3/MOF-199 (10 wt%) and BaTi0.85Zr0.15O3/MOF-199 (20 wt%).The photocatalyst used in this work is a novel, nanocomposite-based compound. The average crystallite size of the composite estimated by the Williamson-Hall equation was 41.7 nm. For the indirect electronic transitions of MOF-199 (HKUST-1), BaTi0.85Zr0.15O3, and BaTi0.85Zr0.15O3/MOF-199 (HKUST-1) nanocomposite, the band gap energies of 3.81, 3.20, and 3.00 eV, respectively, were obtained. The nanocomposite point of zero charges (pHpzc) was estimated at 5.5. The nanocomposite was then utilized in the photodegradation of tetracycline (TC). Due to the smallest electron/hole recombination process, the composite exhibited the smallest PL intensity and the maximum photocatalytic activity, owing to the smallest electron/hole recombination process. The result showed that in TC degradation, the pH of the solution, time-CTC interactions, irradiation times, and time-pH remained highly significant elements. The most suitable degradation extent was acquired at pH of 9, catalyst dose of 0.6 gL-1, TC concentration of 30 mgL-1, and irradiation time of 180 min. Between Z-scheme mechanisms and type II-heterojunction, the former played a major role in the photodegradation of TC.

Structure, Morphology Features and Photocatalytic Properties of α-Ag2WO4 Nanocrystals-modified Palygorskite Clay

Aims: In the present study, we investigate the photocatalytic properties of α-Ag2WO4 nanocrystals- modified Palygorskite (PAL) clay synthesized by the impregnation method. The PAL clay was chemically purified and heat-treated (500 ºC for 2 h), which served as an excellent supporting matrix for loading α-Ag2WO4 (α-AWO) nanocrystals. Background: Water contamination is one of the most serious problems affecting human health, ecosystem survival, and the economic growth of societies. Industrial effluents, such as textile dyes, when not treated and improperly discharged into water resources are considered the main cause of water pollution. Thus the scientific community has been developing effective remediation technologies based on advanced oxidative processes to reduce the harmful effects of these organic pollutants. Objective: This study aimed to improve the photocatalytic activity of PAL clay with α-AWO nanocrystals to degradation of Rhodamine B (RhB) dye. Methods: We purify and heat-treated the PAL clay, synthesize nanocrystals ofα-AWO nanocrystals and modify PAL clay with 30% α-AWO nanocrystals by the impregnation method. The modified PAL clay was able to improve RhB dye degradation. The materials were characterized by XRD, RAMAN,FE-SEM, FT-IR, XRF, etc. The samples were used as photocatalysts under UV-C lamps for the degradation of RhB dye in order to analyze its catalytic performances. Results: The PAL clay modified with 30% α-AWO nanocrystals showed a catalytic efficiency of 79%, and degradation kinetics about 16 times higher when compared to PAL-500 only purified and heat-treated at 500 ºC. In this way, this PAL-modified is an alternative as a low-cost photocatalyst for the degradation of RhB dye. Conclusion: Ultraviolet-visible spectra revealed that our materials have optical band gap energies controlled by indirect and direct electronic transitions and suitable to be activated under ultraviolet illumination. The adequate amount (30 wt.%) of α-Ag2WO4 nanocrystals added to PAL brought significant improvement in the photocatalytic activity for the degradation of rhodamine B. Finally, a photocatalytic mechanism was proposed in detail.

Au-Al intermetallic compounds: A series of more efficient LSPR materials for hot carriers-based applications than noble metal Au

Abstract Hot carriers generated by the non-radiative decay of localized surface plasmon resonance (LSPR) of noble metal nanoparticles are widely investigated in applications ranging from solar energy conversion to photocatalysis, and photodetection. From the perspective of sustainable development of the LSPR based applications, it is important to find metallic materials that are cheap and plentiful and show excellent hot carrier properties. In this context, we investigate the possibility of alloying Au with Al to develop efficient LSPR materials for hot carriers-based applications. Taking thermodynamically stable AuAl2 and AuAl as examples, we study their electronic structures, generation rates, energetic distribution, relaxation times, and mean free paths of hot carriers originating from direct and phonon-assisted indirect electronic transitions, which are two of the main channels for generating high-energy hot carriers from the decay of LSPR, and compare the results with that of Au and Al metals. It is found that both AuAl2 and AuAl show larger hot carrier generation rates than Au and the resulting hot carriers are energetically higher than that in Au. Meanwhile, the transport properties of hot carriers in AuAl2 and AuAl outperform that of Au, which is manifested through comparable or even longer relaxation times and mean free paths. Consequently, it is believed that the Au-Al intermetallic compounds should be a series of efficient LSPR materials for hot carriers-based applications, which is comparable with or even better than the noble metal Au. These results are helpful for the sustainable development of related fields.

Innovative Incorporation of Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) as Hole Carrier Transport Layer and as Anode for Organic Solar Cells Performance Improvement.

In this work, we present a comparative study of benzoid poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) as electrode and as hole carrier transport layer (HTL) in the manufacture of organic photovoltaic devices using Fischer metal-carbene complexes. The performance of the different devices was evaluated for solar cell applications. Scanning electronic microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the thin films that integrated the devices. A more ordered and crystallized active film microstructure is observed when using benzoid PEDOT:PSS as nucleation layer. The optical gap for both direct and indirect electronic transitions was evaluated from ultraviolet-visible spectroscopy data (UV-vis), as well as the absorption coefficient (α), and the values are in the range of 2.10–2.93 eV. Photovoltaic devices with conventional architecture, using two different chromium carbenes as active layers, were manufactured, and their electrical behavior was studied. The devices were irradiated with different wavelengths between the infrared and ultraviolet regions of the electromagnetic spectrum. Using the PEDOT:PSS film as hole carrier transport layer (HTL) decreases the slope on the ohmic and space charge limited current (SCLC) regions and eliminates the trap-charge limited current (T-CLC) mechanism. Furthermore, a saturation current of ~1.95 × 10−10 A and higher current values ~1.75 × 10−2 A at 4 V, ~4 orders in magnitude larger were observed. The PEDOT:PSS films as HTL in the devices reduced the injection barrier, thus showing a better performance than as anodes in this type of organic solar cells.

Effects of Eu2+ doping on the structure and luminescence properties of strontium borosilicate glasses

Eu2+-doped SiO2-SrO-B2O3 glasses (abbreviated as GE) were successfully prepared and the structure and luminescence properties were detailed investigated. The results show that the GE glass with 0.4 mol% Eu2+ has the most compact structure owing to its low molar volume, high density. The GE glasses exhibit broad luminescence band centered at approximately 469 nm and 0.4 mol% Eu2+ is the optimum doping concentration. The absorption and emission spectra show redshift as increasing Eu2+ concentration. The optical band gap decreases from 2.86 to 2.68 eV and the Urbach energy decreases from 0.2241 to 0.1737 eV. The 5d-4f transition of Eu2+ is an indirect electronic transition. Concentration quenching occurs with the increase of Eu2+ content and the mechanism is belong to the type of electric dipole-dipole interaction. The luminescence intensity decreases with increasing temperature and the thermal quenching activation energy is 0.26 eV. The chromaticity shift is lower than Eu2+-doped commercial phosphors.

Surface Properties of Precipitated Aerosol Microparticles of Indium(III) Oxide under Conditions of Ambient Air

Adsorption and photosorption properties of precipitated indium(III) oxide aerosol particles are studied under conditions close to those of ambient air. The composition of the adsorbed surface layer of precipitated aerosol particles is analyzed. The quantum yields and their spectral dependences of oxygen photosorption and carbon monoxide photocatalytic oxidation are determined. Photocatalytic activity in the reaction of carbon monoxide oxidation is detected during the absorption of light quanta from the region of indirect electron transitions (quantum energy of <2.9 eV).

Effect of Indirect Electronic Transitions in Indium Oxide on Photoadsorption of Oxygen and Photocatalytic Oxidation of Carbon Monoxide

The photocatalytic activity of indium(III) oxide in the oxidation of carbon monoxide upon absorption of light quanta from the region of indirect electronic transitions (quantum energies <2.9 eV) has been found. The quantum yields and spectral dependences of the quantum yields of photocatalytic oxidation of carbon monoxide and photoadsorption of oxygen have been determined. The adsorption, photoadsorption, and photocatalytic properties of indium oxide microparticles have been studied.

Strain-engineered p-type to n-type transition in mono-, bi-, and tri-layer black phosphorene

Using density functional theory, a detailed computational study is performed to explore the structural and electronic properties of a black phosphorene monolayer, bilayer, and trilayer under a uniaxial strain along the armchair (b axis) and zigzag (a axis) directions. In the case of a monolayer black phosphorene, it is found that strain along the armchair direction slightly affects the a lattice parameter and the puckering height (Δ). Along the zigzag direction, however, variation of the a lattice parameter is compensated by both the a and b lattice variations while the parameter Δ remains unaffected. In the case of bilayer and trilayer black phosphorene, a similar behavior is observed where the layer-spacing “d” acts as an additional degree of liberty for strain compensation. In terms of electronic properties, strain along the armchair and zigzag directions changes the nature of the Γ point in the bandgap from a direct to an indirect electronic transition as a function of the strain value. In the strain range from −14% to +6%, all black phosphorene structures behave similarly to classical semiconductors. However, the size and strain combined effect significantly affects the Fermi energy position. Around 0% strain, all black phosphorene structures are of p-type, while they switch to an n-type semiconductor in the range of strain values from +2% up to +14%. This p-type to n-type transition may have a major technological impact in fields where mono- and hetero-junctions are considered.