Doped System Research Articles

First-principles study of the effect of alkali metals on the electronic and optical properties of SnS2

In this paper, the photovoltaic properties of alkali metal atom X ( X is Li, Na, K, and Rb) doped monolayer SnS2 system have been investigated based on first principles calculations. After the doping of alkali metal atoms, the bond lengths of the doped systems increase compared to the pure SnS2 system. When alkali metal atoms are doped in the pure SnS2 system, the band gap of the doped systems increases and the SnS2 system changes from an indirect band gap to a direct band gap. It is found that the density of states in the valence band near the Fermi energy level of all doped systems is primarily contributed by S atoms, and the conduction band is primarily contributed by Sn and S atoms. The ionic bonds are formed between X and S atoms. The polarizability of the doped SnS2 systems is enhanced. Moreover, the absorption and reflection peaks of the SnS2 doping systems are redshifted, which improves the effective utilization rate of the infrared light region.

Highly Sensitive Gas Sensor for Detection of Air Decomposition Pollutant (CO, NOx): Popular Metal Oxide (ZnO, TiO2)-Doped MoS2 Surface.

When partial discharges occur in air-insulated equipment, the air decomposes to produce a variety of contamination products, resulting in a reduction in the insulation performance of the insulated equipment. By monitoring the concentration of typical decomposition products (CO, NO, and NO2) within the insulated equipment, potential insulation faults can be diagnosed. MoS2 has shown promising applications as a gas-sensitive semiconductor material, and doping metal oxides can improve the gas-sensitive properties of the material. Therefore, in this work, MoS2 has been doped using the popular metal oxides (ZnO, TiO2) of the day, and its gas-sensitive properties to the typical decomposition products of air have been analyzed and compared using density functional theory (DFT) calculations. The stability of the doped system was investigated using molecular dynamics methods. The related adsorption mechanism was analyzed by adsorption configuration, energy band structure, density of states (DOS) analysis, total electron density (TED) analysis, and differential charge density (DCD) analysis. Finally, the practical application of related sensing performance is evaluated. The results show that the doping of metal oxide nanoparticles greatly improves the conductivity, gas sensitivity, and adsorption selectivity of MoS2 monolayer to air decomposition products. The sensing response of ZnO-MoS2 for CO at room temperature (25 °C) reaches 161.86 with a good recovery time (0.046 s). TiO2-MoS2 sensing response to NO2 reaches 3.5 × 106 at 25 °C with a good recovery time (0.108 s). This study theoretically solves the industrial challenge of recycling sensing materials and provides theoretical value for the application of resistive chemical sensors in air-insulated equipment.

Effect of O-doping on electronic and optical properties of monolayer MoSe2 under shear deformation.

In this study, the electronic structures and optical properties of the pure MoSe2 and O-doped MoSe2 systems under different shear deformations are calculated based on the first-principles approach. It is hoped to provide new possibilities for the design of novel controllable optoelectronic devices and to provide guidance for the application of MoSe2 in the field of optoelectronic devices. The findings indicate that both pure MoSe2 and O-doped MoSe2 systems are somewhat impacted by shear deformation. The pure MoSe2 undergoes a transition from direct to indirect and then to direct bandgap under shear deformation, but still maintains the semiconductor properties. The bandgap of the doped system changes from a direct to an indirect bandgap at 8% shear deformation. According to the examination of the density of states, we find that the density of states of the pure MoSe2 system is mainly contributed by the Mo-d and Se-p orbitals, and the total density of states of the system after O-atom doping mainly originates from the results of the contributions of the Mo-d, Se-p, and O-p orbitals. Optical property analysis reveals that the conductivity and peak value of the pure MoSe2 system are gradually red-shifted toward the low-energy region with the increase of shear deformation. The dielectric function of the O-doped MoSe2 system is red-shifted in the region of 6~10% shear deformation, and the degree of red-shift rises with deformation amount. The findings demonstrate that the electrical structure and optical characteristics of the O-doped MoSe2 system may be modulated effectively by shear deformation, providing a theoretical foundation for expanding the usage of MoSe2 materials in the field of optoelectronic devices. This study is founded on the CASTEP module in the Materials-Studio software within the first-principles of the density-functional theory framework. The photoelectric properties of the intrinsic and doped systems under shear deformation are calculated using the Perdew-Burke-Ernzerh (PBE) of generalized function under the generalized gradient approximation (GGA). The Monkhorst-Pack special K-point sampling method is used in the calculations, and a 5 × 5 × 1 K-point grid is used for the calculations with a plane-wave truncation energy of 400 eV in the optimization of the structure of each model. After geometrical optimization, the energy convergence criterion for each atom is 1 × 10-5 eV/atom, the force convergence criterion is 0.05 eV/Å, and a vacuum layer of 20 Å in the c-direction is set.

Ab-initio calculation of magnetic properties of doped methylammonium lead chloride

ABSTRACT Magnetic properties of 3d transition metal ion doped methylammonium lead chloride (MAPbCl3) have been studied by ab-initio calculations in the framework of density functional theory. The study of spin–spin interactions reveals that doping (about 2%) of Ti, V, Cr, Mn and Fe at the Pb site of MAPbCl3 shows stable ferromagnetic ordering along with the half-metallic behaviour. 3d orbital electrons of the dopants are primarily responsible for the origin of the magnetic moment and the remaining part comes from the p-d exchange interaction between the 3d orbital electrons of the dopants and the 6p orbital electrons of Pb in the vicinity of the doping position. Additionally, the band structure calculations suggest that the doped system shows n/p-type semiconducting behaviour. Ferromagnetism, along with semiconducting behaviour in transition metal ion-doped MAPbCl3, will be suitable for spintronic applications.

First-principles study of the electronic and optical properties of Nb-doped MoSe2 by tensile strain

A first-principles method was used to explore the influence of tensile strain on the electrical and optical characteristics of Nb-doped MoSe2. The tensile strain has been discovered to have a higher influence on the electrical structure of the Nb-doped MoSe2 system than pure monolayer MoSe2. According to the energy band structure study, the pure monolayer MoSe2 is a direct bandgap semiconductor, but the system doped with Nb instead of Mo atoms is a p-type-doped semiconductor. The bandgap of the Nb-doped MoSe2 system decreases gradually with the increase of tensile strain, but still maintains the p-type semiconductor properties, and the bandgap of the pure monolayer MoSe2 also decreases gradually with the increase of tensile strain. From the density of states analysis, it is found that for the total density of states of the doped system at different tensile strains, it is mainly contributed by the Mo-4d and Se-4p orbitals. The optical properties analysis showed that the doped system under tensile strain had higher absorption coefficient and reflectance peak than the Nb-doped MoSe2 system without tensile strain. Additionally, the doped system showed redshift phenomenon in both the absorption and reflection peaks as the tensile strain increased.

Metal-Free organic polymeric room temperature phosphorescence system with Multi-Colour and ultralong lifetime

Room-temperature-phosphorescent (RTP) metal-free organic polymer materials with long-lasting luminescence properties have received considerable attention in the field of optical materials. Herein, we report unique RTP polymeric materials with ultralong-lasting multicolor luminescence prepared using a series of organic phosphorescent guest molecules and melamine formaldehyde resins. Because of facile thermal cross-linking, these materials exhibit a stable multicolor long-lasting afterglow with a maximum phosphorescence lifetime of > 1 s and a maximum phosphorescence emission efficiency of up to 3.4 %. In addition, polymer doping systems with flexible processability were easily printed on 2D substrates and further used as patterned security labels with full-color dynamic phosphorescence. Further, different materials were combined to form a ternary digital encryption system. In addition, although reports on 3D-printed phosphorescent materials are scarce, by using a similar thermoforming method, we successfully prepared a 3D-molding phosphorescent material that can exhibit a satisfactory long-lasting afterglow even after it is kept underwater for 30 days. In conclusion, this work will usher in advancements in the development and application of metal-free polymer-based RTP materials with long-lasting luminescence and 3D printing potential.

A novel preparation of trace iron-doped 3D urchin-like TiO2 for efficient degradation and mineralization of trimethoprim under simulated sunlight

In this study, trace iron-doped 3D urchin-like titanium dioxide (Fe–TiO2) were prepared via a straightforward water bath process. The successful incorporation of trace iron into the TiO2 structure was confirmed through detailed EDX, EPR, and XPS analyses. Moreover, the Fe–TiO2 photocatalyst exhibited remarkable efficacy in degrading the targeted compound, trimethoprim (TMP), achieving an impressive degradation rate of 95.6 % within a concise 60-min timeframe and a captivating mineralization rate of 32.1 % within 120 min. These performance metrics outshone those of pristine TiO2 by substantial factors of 1.9 and 1.2, respectively. Photoelectric characterization results also confirmed that Fe doping significantly enhanced the efficiency of charge carrier separation of TiO2. Furthermore, the catalytic performance of Fe–TiO2 remains essentially unchanged after a tenfold expansion in equal proportion using the water bath doping system. This confirms the practicality of the batch preparation approach for Fe-doped TiO2. The Fe–TiO2 catalyst consistently demonstrated efficient degradation capabilities across various water sources, ranging from natural river water to treated secondary effluents from sewage plants and tap water, further emphasizing its significant potential for practical applications. This comprehensive study provides fresh insights into the batch preparation of doped catalysts and their utility in mitigating water pollution.

Low-loss ferroelectricity in (Bi, Sn)-modified Na1−xBaxNb1−xTixO3 (x = 12.5%)

Na0.875Ba0.125Nb0.875Ti0.125O3 (NNBT) and Na0.875Ba0.11Bi0.01Nb0.875Ti0.11Sn0.0112O3 synthesized by solid-state technique exhibit P4bm symmetry. Dielectric-relaxations for NNBT show a transition to an antiferroelectric state below 449 °C (TC) with a prominent fall in the dielectric constant and the dielectric loss, like parent NaNbO3. Below 175 °C (TF) Ba, Ti-doping induced frequency-independent dielectric peak marks the ferroelectric phase. With 1.5% Bi, Sn-doping in NNBT, the grain size and the density of the ceramic increase. Bi, Sn-doped NNBT exhibits dielectric transitions at TC and a diffused TF but with reduced conductivity. The doped NNBT system presents a high electrostrictive coefficient of ∼0.06 m4/C2.

Ni-doping effects on formation and migration of oxygen vacancies in SrFe1-xNixO3-δ oxygen carriers.

Ni is a promising B-site doping element capable of improving the oxygen carrier performance of SrFeO3 perovskite. In this work, the effect of Ni doping on the formation and migration of oxygen vacancies in SrFe1-xNixO3-δ (x = 0, 0.0625, 0.125, 0.1875, and 0.25) is investigated using density functional theory calculations. Our results show that the oxygen vacancies formed from Ni-O-Fe chains exhibit lower formation energy (Ef) compared to those from Fe-O-Fe chains in each doping system. Additionally, Ef generally decreases with an increase of Ni content. This Ni-promoted formation of VO is attributed to three factors: weakened Ni-O bonding, the closure of O-2p states to the Fermi level by Ni-O hybridization, and Ni3+ decreasing the positive charges to be compensated by VO formation. Due to these multiple advantages, a modest Ni doping of x = 0.25 can induce a higher PO2 and a lower T comparted to the relatively larger Co doping of x = 0.5, thermodynamically. Kinetically, Ni-doping appears to be a disadvantage as it hinders oxygen migration, due to a higher oxygen migration barrier through SrSrNi compared to the SrSrFe pathway. However, the overall oxygen ion conduction would not be significantly influenced by hopping through a nearby pathway of SrSrFe with a low migration barrier in a system doped with a small amount of Ni. In a word, a small amount of Ni doping has an advantage over Co doping in terms of enhancing the oxygen carrier performance of the parent SrFeO3 system.

Tracking of structural defects induced by Eu-doping in β-Ag2MoO4: their influences on electrical properties.

In this study, several methods were employed to investigate the electrical characteristics of β-Ag2MoO4 systems, both Eu-doped and undoped, synthesized using the microwave-assisted hydrothermal method. The focus extended to understanding how synthesis time influences material defects, with doping fixed at 1%. A systematic shift in the silver vacancy (VAg) concentration was observed within the doped β-Ag2MoO4 system. Specifically, this study demonstrated that the incorporation of Eu3+ into polycrystalline β-Ag2MoO4 initially increases the VAg concentration. However, as the synthesis time progresses, the VAg concentration decreases, resulting in alterations in the resulting electrical properties, arising from the intricate interplay between the number of grain boundaries and carrier density. By combining information obtained from photoluminescence, positron annihilation lifetime spectroscopy, and impedance spectroscopy, a comprehensive conduction mechanism was formulated, shedding light on both doped and undoped β-Ag2MoO4 systems.

Growth regulation of an easily crystallized organic long-persistent luminescence system with in situ anti-counterfeiting applications

A new method to regulate the growth of OLPL-doped materials, focusing on easily crystallizable doping systems for in situ anti-counterfeiting ‘paper-ink’ strategy applications.

Tuning the magnetic properties of van der Waals Fe3GaTe2 crystals by Co doping.

Tuning the magnetic properties of two-dimensional van der Waals ferromagnets has special importance for their practical applications. Using first-principles calculations, we investigate the magnetic properties of Co-doped Fe3GaTe2 with different Co concentrations and different Co atomic sites. Calculation results show that Fe or Co atoms with relatively lower atomic concentrations preferentially occupy Fe1 sites with interlayer coupling, which is more energetically favorable. As the doping concentration of Co atoms increases, the total magnetic moment of the doped system decreases, while the average atomic magnetic moments of Fe1 and Fe2 increase and decrease, respectively, with Fe1 reaching ∼2.08μB. The spin polarization of the doped model 2Co-2 near the Fermi energy level is significantly reduced, while 4Co-3 exhibits an enhanced trend. At some doping level, a phase change from ferromagnetism to antiferromagnetism appears at high Co concentration. These results provide a theoretical basis for experimental studies and valuable information for the development of Fe3GaTe2-based spintronic devices.

First principles study of Be-doped graphdiyne as anode material for lithium-ion batteries

The performances of beryllium-doped graphdiyne (GDY), which is used as an anode material for lithium-ion batteries at various doping sites, are investigated by first-principles methods based on density functional theory. Calculations of the formation energy and cohesive energy of GDY at different doping concentrations indicate that beryllium-doped GDY has excellent prospects for experimental synthesis. More importantly, the beryllium-doped GDY exhibits good electrical conductivity. The adsorption energy for a single lithium atom on beryllium-doped GDY is –4.22 eV, which is significantly higher than that for boron, nitrogen-doped GDY, and intrinsic GDY. As the number of stored lithium atoms increases, the adsorption energy remains greater than the cohesive energy of solid lithium, and the average open-circuit voltage stays between 0 and 1 V, ensuring the safety of the battery. Additionally, the lithium storage capacity is increased to 881 mAh/g, which is 1.14 times that of undoped GDY and 2.36 times that of graphite. Meanwhile, the diffusion performance of lithium on beryllium-doped GDY is also enhanced. For the C<sub>III</sub> site doping system, by studying the ion transports at low, medium, and high lithium concentrations, we find that as the lithium concentration increases, the diffusion barriers are 0.38, 0.44, and 0.77 eV, respectively, making lithium ion movement more difficult, but still superior to those of other element-doped GDY. In summary, beryllium-doped GDY has great potential as an excellent anode material for lithium-ion batteries.

Study of the magnetism of C-doped MgO based on first-principles calculations and the Ising model.

The electronic and magnetic properties of d0 dilute magnetic semiconductors formed by rock-salt structured magnesium oxide (MgO) doped with C are systematically studied based on first-principles calculations and the Ising model. It is shown that the electronic holes of p states are generated due to the impurity carbon replacing oxygen in MgO, and the magnetic moment of 2μB is introduced by each C impurity. The polarization energy and formation energy of C-doped MgO are calculated, and the magnetization energy of C-doped MgO is also calculated which is used to obtain the exchange constant between C impurities. By means of the Ising model, we simulated the magnetization and the susceptibility of the doped system with increasing temperature and obtained the Curie temperature of C-doped MgO.

Structural confinement helps achieve more accurate energy transfer: studies on garnet structural NYGlG:Tb3+,Eu3+ phosphors

Structural confinement in sodium-rich garnets enables more accurate Tb3+–Eu3+ energy transfer, enhancing luminescence performance. The Na+-doped system shows an energy transfer efficiency of 95% and stable emission for WLED applications.

Improvement in hot carrier dynamics of all-inorganic halide perovskite CsPbI3 on doping Cu

Hot carrier extraction is crucial for efficient solar energy harvesting, and lead halide perovskite nanocrystals (NCs) are potential candidates for photovoltaic and light-emitting applications. Therefore, swift extraction of hot carriers is an immediate requirement to improve the energy conversion efficiency, which need longer thermalization time. To address this issue, we synthesized nominally Cu-doped CsPbI3 NCs with enhanced structural and optical characteristics compared to undoped CsPbI3 NCs. We investigated the hot carrier dynamics in both the NCs at different fluences using ultrafast transient absorption spectroscopy. Interestingly, we observed very fast thermalization at higher fluences that indicated breaking of the phonon bottleneck. On the contrary, doped NCs preserved the effects and decayed over a longer period of time possibly due to increase in size and introduction of shallow trap states of Cu 3d and Cu 4s electrons in the conduction band, as computed using density functional theory. Notably, as the carrier–carrier interaction increased, we observed a dominating bandgap renormalization in the doped system compared to the undoped system. Overall, our studies improve the understanding of Cu doping in enhancing the hot carrier dynamics in perovskites and open possibilities for further investigation in the quantum phenomenon of these materials.

Analysis of defects in <i>B</i>-vacancy compensated Sm-doped PZT(54/46) ceramics and their influences on piezoelectric properties

Rare earth dopping, especially samarium (Sm) dopping is considered as an effective way to obtain high piezoelectricity by increasing local structure heterogeneity in Pb-containing <i>AB</i>O<sub>3</sub> perovskite ceramics. Defects play an significant role in determining piezoelectric properties in aliovalent ion doping systems. In order to obtain an insight into the effect of defects, especially <i>B</i>-site vacancies on piezoelectricity, Sm-doped PZT(54/46) ceramics compensated by <i>B</i>-site vacancies are fabricated by conventional solid state reaction method. The influence of defects on piezoelectric properties is studied by positron annihilation lifetime spectroscopy (PALS), coincidence Doppler broadening spectroscopy (CDBS), and conventional methods such as X-ray diffraction (XRD), scanning electron microscope (SEM), electrical performance testing on dielectricity, ferroelectricity and pizoelectricity. The XRD results show that all ceramics crystallize in a pure perovskite phase, Sm<sup>3+</sup> doping causes a transformation from the rhombohedral to tetragonal phase and the morphotropic phase boundary (MPB) lies near Sm<sup>3+</sup> doping content <i>x</i> = 0.01–0.02. Electrical performance testing results indicate that with the increase of <i>x</i>, all of the dielectricity, ferroelectricity and pizoelectricity first increase and then decrease, the sample with <i>x</i> = 0.01 and 0.02 exhibit similar excellent dielectricity and ferroelectricity, while their pizoelectricity differs greatly, the optimal piezoelectric coefficient <i>d</i><sub>33</sub> = 572 pC/N (nearly double that of undoped sample) is obtained in the sample with <i>x</i> = 0.01. The PALS results show that Sm doping leads the defect types to change from the coexistence of <i>A</i>-site and <i>B</i>-site vacancies for <i>x</i> ≤ 0.01 to mainly <i>A</i>-site related defects for <i>x</i> ≥ 0.02. The CDBS results further verify that the concentration of <i>B</i>-site vacancies is highest for <i>x</i> = 0.01 and lowest for <i>x</i> = 0.02. It is inferred that the high pizoelectricity for <i>x</i> = 0.01 is related to its high concentration of <i>B</i>-site vacancies, which can dilute the number of <i>A</i>-site vacancies and oxygen vacancies, reducing the chance of forming defect dipoles between an <i>A</i>-site vacancy and an oxygen vacancy, facilitating domain wall motion, and enhancing piezoelectricity. This study indicates that <i>B</i>-site vacancies can enhance piezoelectricity to some extent, which will provide some guidance for defect engineering.

Characteristics and performance of layered two-dimensional materials under doping engineering.

In recent years, doping engineering, which is widely studied in theoretical and experimental research, is an effective means to regulate the crystal structure and physical properties of two-dimensional materials and expand their application potential. Based on different types of element dopings, different 2D materials show different properties and applications. In this paper, the characteristics and performance of rich layered 2D materials under different types of doped elements are comprehensively reviewed. Firstly, 2D materials are classified according to their crystal structures. Secondly, conventional experimental methods of charge doping and heterogeneous atom substitution doping are summarized. Finally, on the basis of various theoretical research results, the properties of several typical 2D material representatives under charge doping and different kinds of atom substitution doping as well as the inspiration and expansion of doping systems for the development of related fields are discussed. Through this review, researchers can fully understand and grasp the regulation rules of different doping engineering on the properties of layered 2D materials with different crystal structures. It provides theoretical guidance for further improving and optimizing the physical properties of 2D materials, improving and enriching the relevant experimental research and device application development.

Construction and fine tuning of host-guest doping systems and the underlying mechanism of room temperature phosphorescence

To obtain ultralong and efficient pure organic room temperature phosphorescent materials, as well as explore the intrinsic mechanisms affecting the phosphorescence performance of host-guest doping systems, two carbazole derivatives with the same molecular structure, named as L-CzIPCN and CzIPCN, were prepared by using carbazole synthesized in the laboratory and commercial carbazole. By choosing L-CzIPCN/CzIPCN and polymethyl methacrylate (PMMA)/polyvinyl alcohol (PVA)/benzophenone derivatives (BP, F-BP, Br-BP, and DF-BP) as the guest and host respectively, a series of new doping systems were constructed, and optimized by tuning doping ratios between host and guest materials. Among of them, F-BP/L-CzIPCN shows the longest room temperature phosphorescence (RTP) lifetime (501.23 ms), with RTP quantum yield of 31.19 %, followed by 0.2 % L-CzIPCN@PVA film (221.66 ms, 5.86 %) and 0.2 % L-CzIPCN@PMMA film (102.73 ms, 4.28 %) respectively. Moreover, L-CzIPCN displays different RTP spectra in diverse hosts, with dual-band RTP emission at 550 nm and 600 nm in benzophenone derivatives, but single RTP emission maxima in PMMA films, as well as a main emission peak at 470–510 nm and a shoulder peak at 550–590 nm in PVA films. The UV–Vis absorption spectra, fluorescence and phosphorescence spectra, and theoretical calculations indicate that RTP comes from the guest monomers in benzophenone derivatives/L-CzIPCN doping systems, with local triple characteristics, and host materials with large dipole moment, appropriate T1 energy level, and small energy gap between S1 and T1 contribute to improving RTP performance of the doping systems. Based on the excellent luminescence and different RTP lifetimes of the doping systems, some high-level anti-counterfeiting, and information encryption patterns were successfully constructed.

Computational analysis of electronic structure and optical properties of monocrystalline silicon-vacancy defect system based on density functional theory

Monocrystalline silicon is an important substrate or base material for manufacturing integrated circuit chips, mirrors, etc. However, it is a typical hard and brittle material, which is very prone to produce defects during processing. This paper investigates the electronic structure and optical properties of sphalerite monocrystalline silicon with vacancy concentrations of 1.5625%, 3.125%, 4.6875%, and 6.25% using the first principles method based on density functional theory. The results demonstrate that the introduction of impurities results in the formation of impurity bands (IB) within the band structure, thereby facilitating electronic transitions. However, vacancy defects do not alter the properties of monocrystalline silicon as an indirect semiconductor. Regarding optical properties, an increase in defect concentration leads to a decrease in the macroscopic symmetry of the system, resulting in noticeable anisotropy in each property. Also found that the main spectral peaks of the defect system are red-shifted, and the vacancy defects introduce new peaks in the near-infrared region and the visible region with increasing intensity, but the peaks in the ultraviolet region gradually decrease with the increase of the defect concentration. The refractive index peak gradually decreases with the increase of defect concentration, and the calculated average refractive index is around 1.2. In the high-energy region, the refractive index takes a very small value, and the reflection of electromagnetic waves from the doped system is also weak at this time, which indicates that the system has a high transmittance property. Importantly, there is a higher intensity of energy loss at photon energies around 16.5 eV. Consequently, these calculations are deemed valuable for advancing research and applications involving monocrystalline silicon optical mirrors.