Increase In Doping Concentration Research Articles

Improved luminescence and photocatalytic properties of Sm3+-doped ZnO nanoparticles via modified sol–gel route: A unified experimental and DFT+U approach

In the current study, a modified sol-gel route was used to produce undoped and Sm3+ doped (1 mol%, 3 mol% and 5 mol%) ZnO nanoparticles (NPs). The study of opto-structural properties of Sm3+ doped NPs was carried out both experimentally and theoretically. Complete dissolution of Sm3+ ions into the ZnO lattice is obviously seen from X-ray diffraction (XRD) analysis. Morphological evolution with doping was studied using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) was carried out to confirm the presence of Sm3+ on the doped NPs. Increasing dopant quantity results in a redshift of the NPs along with a reduction in bandgap with increasing absorption in the visible range, and a minimum of 3.18 eV of optical bandgap for Zn0.97Sm0.03O is found. Photoluminescence spectroscopy reveals a drop in the recombination rate of electron–hole with increasing doping content till 3 mol%, followed by an increase of Zn0.95Sm0.05O. Photogenerated electron–hole pair recombination is revealed by the orange band in the luminescence spectra. Theoretical analysis was also carried out with density functional theory (DFT). This work also unfolds the fundamental understanding of the structural properties of the synthesized NPs to enhance photocatalytic activity successfully. Later, photocatalytic activity for the optimum composition, i.e., 3 mol%, was assessed experimentally.

Toughness enhancement mechanism of Ni-doped Cr2N

In this paper, experiments combined with density functional theory (DFT) are used to investigate the toughness enhancement mechanism of Ni-doped Cr2N coatings. The deposited Cr2-xNixN (x = 0–4.5 at%) coating exhibits a single trigonal structure identified as a Cr2N-Ni solid solution. The columnar structure of the Cr2N coating, with a width of approximately 80 nm, does not change with the doping of Ni. With 2.0 at% Ni alloyed, the hardness increases from 27 GPa for Cr2N to the maximum of 34 GPa. which is mainly due to an increase in residual compressive stress and dislocation density resulting from Ni doping. Interestingly, the elastic modulus shows a linearly decreasing trend as the Ni doping content increases, which indicates that Ni alloying improves the ductility of the Cr2N coating. The sand erosion test shows that the erosion rate of the Cr2N coating is significantly reduced when the Ni doping content is 2.0 at%, decreasing from 0.42 µm·min−1 to 0.15 µm·min−1. DFT results reveal that the metallic d-d state density increases with increased d-electron concentration contributed by Ni atoms, enhancing metallic interaction along the Ni-Cr stacking plane under shear loading, which leads to the improved ductility of the Cr2-xNixN coating.

Electronic, Optical, Thermoelectric and Elastic Properties of RbxCs1-xPbBr3 Perovskite.

Inorganic halide perovskites of the type AMX3, where A is an inorganic cation, M is a metal cation, and X is a halide anion, have attracted attention for optoelectronics applications due to their better optical and electronic properties, and stability, under a moist and elevated temperature environment. In this contribution, the electronic, optical, thermoelectric, and elastic properties of cesium lead bromide, CsPbBr3, and Rb-doped CsPbBr3, were evaluated using the density functional theory (DFT). The generalized gradient approximation (GGA) in the scheme of Perdew, Burke, and Ernzerhof (PBE) was employed for the exchange-correlation potential. The calculated value of the lattice parameter is in agreement with the available experimental and theoretical results. According to the electronic property results, as the doping content increases, so does the energy bandgap, which decreases after doping 0.75. These compounds undergo a direct band gap and present an energies gap values of about 1.70 eV (x = 0), 3.76 eV (x = 0.75), and 1.71 eV (x = 1). The optical properties, such as the real and imaginary parts of the dielectric function, the absorption coefficient, optical conductivity, refractive index, and extinction coefficient, were studied. The thermoelectric results show that after raising the temperature to 800 K, the thermal and electrical conductivities of the compound RbxCs1-xPbBr3 increases (x = 0, 0.25, 0.50 and 1). Rb0.75Cs0.25PbBr3 (x = 0.75), which has a large band gap, can work well for applications in the ultraviolet region of the spectrum, such as UV detectors, are potential candidates for solar cells; whereas, CsPbBr3 (x = 0) and RbPbBr3 (x = 1), have a narrow and direct band gap and outstanding absorption power in the visible ultraviolet energy range.

Structural, magnetic and electrical transport properties of the sol-gel derived La1-xCaxMnO3 (0≤x≤0.3) nanoparticles

Sol-gel (SG) prepared calcium doped La1-xCaxMnO3 (0 ≤ x ≤ 0.3) nanoparticles (>35 nm) show a phase transformation from rhombohedral-R3c to orthorhombic-Pnma. The dopant concentration influences the bond length and lattice parameters and their variations as observed from the rietveld refinement. The phase stability and chemical compositions are confirmed using the Thermogravimetric and differential thermal analysis (TG-DTA) and Fourier transform infrared (FTIR) spectroscopy measurements. The latter confirms the presence of dangling bonds from the changes in the characteristic vibrational frequencies and intensities. Field emission scanning electron microscope-energy dispersive X-ray analysis (FESEM-EDAX) confirms the nano-dimension of the particles and good chemical homogeneity of the samples. The Curie temperature Tc, estimated from the field cooled magnetization curve, shifts towards room temperature (Tc = 160–270 K) with the increase of dopant concentration. The samples exhibit a clear metal to insulator transition, the temperature of which shifts to higher values (169–267 K) with increase in dopant content. With the application of an external magnetic field, local ordering of magnetic moments occurs and the evolution of a ferromagnetic metallic phase suppresses the existing paramagnetic insulating phase, decreasing the value of resistivity. Three different temperature ranges demarked in the resistivity curves are studied using different theoretical models. The observed low temperature resistivity upturn is explained on the basis of the Kondo-like model while the ferromagnetic metallic region is studied using different scattering processes like electron – electron, electron – magnon etc. The variable range and small polaron hopping (VRH and SPH) models are used in the high-temperature region data and with the aid of Holstein's relation the non-adiabatic SPH model it is found to be most suitable to understand the conductivity behavior. The temperature dependent evolution of the Griffith's like phase can explain and correlate the electric transport and magnetic properties exhibited by the samples. This highlights the evolution of Mn3+-O2--Mn4+ FM oriented networks, which form conduction channels with the lowering of temperatures. These channels mediate the enhanced conduction and helps set in long-range FM ordering in the samples/

First-principles study on p-type transformation of ZnO doped by Ag element

The optical properties of intrinsic ZnO and Ag-doped ZnO for p-type transformation with different concentrations is studied using the first principles. The results show that the lattice constant and cell volume increase after Ag doping, and the total energy of the system gradually decreases, and the structure becomes more stable with the increase of Ag doping concentration. In supercell of Zn13Ag3O16, the impurity level is reduced, so the required ionization energy is reduced, which contributing to the ionization of impurity, leading to the significant improvement of charge transfer, hence, the conductivity is enhanced. Both absorption and reflection spectra appear red shift with the increase of Ag doping concentration, and the peak intensity is significantly increased with a higher Ag doping concentration. High Ag concentration is beneficial to the stability of p-type ZnO and the enhancement of photoelectric characteristics, which provides a basis for the application of ZnO in optoelectronic devices.

Growth of Zn1−xNixO Thin Films and Their Structural, Optical and Magneto-Optical Properties

The radio frequency (RF) reactive sputtering technique has been used to prepare Zn1−xNixO thin films with 0 ≤ x ≤ 0.08. Composite targets were obtained by mixing and pressing NiO and ZnO powders. Sapphire, quartz and glass were used as substrates. X-ray diffraction analysis of Ni-doped ZnO films indicates that all samples are crystalised in a hexagonal wurtzite structure with a preferred orientation along the (002) plane. Any secondary phase, corresponding to metallic nickel clusters or nickel oxides was not observed. High-resolution transmission electron microscopy (HR-TEM) image observed for Zn1−xNixO thin film shows a strong preferred orientation (texture) of crystalline columns in the direction perpendicular to the substrate surface. Different surface morphology was revealed in AFM images depending on the film composition and growth condition. Optical absorption spectra suggest the substitution of Zn2+ ions in the ZnO lattice by Ni2+ ions. The energy bandgap value was also found a complex dependence with an increase in Ni dopant concentration. In photoluminescence spectra, two main peaks were revealed, which are ascribed to near band gap emission and vacancy or defect states. Faraday rotation demonstrates its enhancement and growth of ferromagnetism with the increase in Ni content of Zn1−xNixO thin films at room temperature.

Effect of silver-doping on the structural, topography and optical CdSe thin films

Using thermal evaporation, thin films of silver-doped CdSe were synthesized on glass bases. A hexagonal structure with a preference orientation along (100) plane according to the X-ray diffraction pattern. The surface topography was determined using Atomic Force Microscopy (AFM). AFM detects spherical nature nanoparticles and roughness rate of the CdSe thin film decreases and the root mean square decreases with (2 and 4) % doping in silver. As the doping content increase, the optical energy bandgap decrease from 1.85 eV to 1.75 eV. Optical analysis indicates that Ag doping in CdSe results in a redshift in band edge.

Sharp MIR plasmonic modes in gratings made of heavily doped pulsed laser-melted Ge1-xSnx

Plasmonic structures made out of highly doped group-IV semiconductor materials are of large interest for the realization of fully integrated mid-infrared (MIR) devices. Utilizing highly doped Ge1-xSnx alloys grown on Si substrates is one promising route to enable device operation at near-infrared (NIR) wavelengths. Due to the lower effective mass of electrons in Sn compared to Ge, the incorporation of Sn can potentially lower the plasma wavelength of Ge1-xSnx alloys compared to that of pure Ge. However, defects introduced by the large lattice mismatch to Si substrates as well as the introduction of alloy scattering limit device applications in practice. Here, we investigate pulsed laser melting as one strategy to increase material quality in highly doped Ge1-xSnx alloys. We show that a pulsed laser melting treatment of our Ge1-xSnx films not only serves to lower the material’s plasma frequency but also leads to an increase in active dopant concentration. We demonstrate the application of this material in plasmonic gratings with sharp optical extinction peaks at MIR wavelengths.

Modulation of optical and photoluminescence properties of ZnO thin films by Mg dopant

Nanostructured Zn1−xMgxO (x = 0–0.04) thin films were deposited on a glass substrate through the sol–gel dip coating. X-ray diffraction indicates the films exhibited a hexagonal wurtzite structure with maximum intensity at (1 0 1) plane. The intensity of the diffraction peak decreased with increasing the Mg doping concentration. The crystallite size varied as a function of the increase in Mg doping concentration. The deposits showed a nanograin structure for pure ZnO, which changes in the presence of Mg content, and elemental composition was confirmed by using energy-dispersive spectra. Optical analysis showed a significant increase in transmittance from 80 to 90% in the visible range and a decrement in the optical bandgap energy from 3.305 to 3.261 eV with an increase in Mg doping. Photoluminescence spectra showed there was a quenching of near band edge emission with doping concentration and a red emission for Zn0.96Mg0.04O film. The color coordinates of the deposits were in the nearly white light region, showing the maximal white light emission.

Insights into the role of Nb segregation on grain boundary structural transition and mechanical response in a Ni–Nb system

The role of Nb segregation on the grain boundary (GB) structural transformation and mechanical response has been studied in a binary Ni–Nb system through atomistic simulation. To investigate the effect of dopant concentration on the GB structural transitions, a Σ5 (310) GB has been created with the help of molecular statics simulation. Thereafter, hybrid Monte Carlo and Molecular dynamics (MD) simulations have been performed to segregate Nb atoms at the Σ5 (310) GB. At lower dopant concentrations, the Nb atoms preferably segregated at the tip of the kite structure. With an increase in dopant concentration and temperature, the Nb atoms segregated at other sites in the GB as well as in the matrix and the GB structure becomes disordered. The effect of doping on the mechanical behavior has been investigated by applying constant strain rate along X-direction through MD. The stress-strain curve of the Ni–Nb system at 300 K revealed an increase in the strength and ductility with the dopant concentration up to a certain limit (0.4 at. % Nb) and decreased thereafter. The superior mechanical response of the Ni-0.4Nb system is attributed to the formation of stacking faults and sessile dislocations during deformation. Stacking faults delay the formation of cracks while sessile dislocations impede the dislocation motion, resulting in higher ductility and strength. Contrarily, nucleation of voids and cracks takes place at a lower extent of strain, resulting in an early fracture in the pure Ni. However, the strength of the doped specimen is found to be lower than the undoped one at 700 K due to the early initiation of cracks in the disordered GB region of the former specimen. The comprehensive understanding of the effect of interfacial segregation on the structural and mechanical behaviour would open up new avenues for alloy design and the development of advanced materials.

Study of epsilon-near-zero response in Al substituted titanium oxynitride thin films using computational and experimental investigations

Titanium oxide (TiO2) is considered as an important semiconductor material due to having promising tuneable optoelectronic, thermoelectric, and photovoltaic applications. First-principles calculations based on the density functional theory were used to elucidate the effect of dopant on various properties. Thin films have been fabricated using a reactive magnetron sputtering. X-ray diffraction analysis displayed the formation of the rutile phase of Titania in thin films. Atomic force and scanning electron microscopy revealed the growth of uniform, smooth, and well distributed granular thin films. Photoluminescence intensity was observed to decrease with an increase in dopant concentration. Experimentally obtained energy bandgap of the un-doped and doped TiO2 thin film samples was found to decrease and observed as 2.90 eV for pure Titania and 0.85 eV for maximum dopant contents. The present study exhibited that prepared oxynitrides thin films with epsilon near zero response are suitable candidate for enhanced optoelectronic and thermoelectric applications.

Phonon dynamics in lead free perovskite (1-x)KNN-xBAN (x = 0.0–0.1): a temperature dependent raman study

K0.5Na0.5NbO3 (KNN) has been under extensive focus in recent times due to it being an alternative to lead-free multifunctional materials and properties like room temperature ferroelectricity, stability in air and technology friendly applications. In this work, we report a comprehensive temperature dependent, compositional change induced structural variation and polarization dependent Raman spectroscopy on BaAl0.5Nb0.5O3 (BAN) doped KNN in the spectral range of 10–1000 cm−1. Multiple phase transitions are marked by the strong renormalization of the phonon self-energy parameters, i.e. mode frequencies and linewidths, in the temperature range of 83 K to 623 K. Change in the phase transition temperature is tracked via phonon anomalies with varying doping concentration, x = 0.0, 0.02, 0.05, 0.07 and 0.1, and is found to be as large as ∼100 K for orthorhombic to tetragonal phase transition for x = 0.1. Raman extracted phase diagram shows that the stability of the ferroelectric orthorhombic phase in the vicinity of room temperature increases with the increasing doping concentration. Also, from our polarization-dependent measurements we could decipher the symmetry of the observed phonon modes for KNN system.

Sensitive Detection of Doped Polymer Thin Films Using Terahertz Metamaterial Based on Analog of Electromagnetically Induced Transparency

We propose a novel terahertz (THz) metamaterial (MM)-based sensor for the sensitive detection of doped polymer thin films. The MM constructed by periodic quasi-ring resonators can generate the analog of electromagnetically induced transparency (EIT) at the THz region and work in a wide range of incident angles. The simulated results show that the frequency and magnitude of the EIT-like resonance can be, respectively, affected by the refractive index and dielectric loss of the analyte, which is further explained by a coupled harmonic oscillator model. The theoretical sensitivity of the proposed sensor is calculated as 185 GHz/RIU [refractive index unit (RIU)], showing a good sensing capability. In experiments, the dispersed red 1 (DR1)-doped polymethylmethacrylate (PMMA) thin films with a subwavelength thickness of 600 nm were covered on the MM surface. The measured results show that the EIT-like resonance experiences frequency redshift and magnitude attenuation as the doping concentration increases, indicating the addition of DR1 can lead to the increase in both refractive index and dielectric loss of the PMMA thin film. The proposed MM-based sensor can successfully identify the dielectric change of extremely thin polymer films caused by doping, offering a novel way to achieve high-sensitivity thin-film sensing.

Synthesis and Characterization of Fe Doped Aurivillius-Phase PbBi2Nb2O9 Perovskite and Their Photocatalytic Activity on the Degradation of Methylene Blue

A simple solid-state reaction was applied to synthesize Fe-doped perovskite-type PBFNO catalysts, and methylene blue decomposition studies were performed in the form of visible light according to the changes in the Fe doping content (0.4 to 1.9 mol ratio compared with Bi mol) and the amount of catalyst used (0.05 to 0.2 g used). As the Fe doping content increases, the absorbance and bang gap energy of the PBFNOs sample rapidly increase and decrease, respectively, because the Fe dopant in the PBNO lattice acts as an intermediate band between the valence and conduction bands of the PBNO and reduces the band gap energy. As a result, it showed a performance degradation of approximately 42% compared to the maximum performance. In addition, the presence of Fe dopants in the PBNO lattice greatly reduces the intensity of the photoluminescent lines. This is because the Fe dopant can play an important role in light-induced electron transfer and as a hole trap, reducing the recombination rate. Additionally, when too much photocatalyst was used (>0.1 g used), the Fe dopant played an important role as a light-induced electron transfer and hole trap, reducing the recombination rate and lowering the overall photocatalytic activity by 51%. In particular, 0.1 g of PBNO-0.2-F showed continuous catalytic activity, even when the photocatalytic reaction proceeded for 180 min. Therefore, this study demonstrates that the Fe-doped aurivillius-phase PBFNO photocatalyst is very promising for the dye manufacturing industry.

Variation in Crystallite Size and Particle Size of Strontium Doped Bismuth Ferrite Thin Films

The pure and strontium doped bismuth ferrite thin films are fabricated using spray pyrolysis technique. The occurrence of strontium, bismuth and ferrous particles are confirmed by EDAX spectra. The crystallite size of the fabricated thin films is determined from WH plot method and it is found that crystallite size decreased with increase in dopant concentration. The particle size calculation is done for the FESEM images revealed the decrement in particle size with strontium dopant. The variation of crystallite size and particle size with strontium doping on Bismuth ferrite thin films are considered in this analysis.

Preparation and Properties of Copper-Based Composites Containing Nb1-x(Ti/Ta)xSe2

In this study, copper-based-Nb1-x(Ti/Ta)xSe2 composites were prepared by powder metallurgy, and Nb1-x(Ti/Ta)xSe2 copper-based composites with different Ti/Ta doping atomic fractions were studied. physical, electrical and tribological properties. Among them, the doping amount of Ti and Ta has an important influence on the properties of the composite material. The doping amount of Ti can improve the mechanical, electrical and tribological properties of copper matrix composites within a certain range, especially when the doping amount of Ti is At 10at.%, the copper matrix composites exhibited excellent tribological properties. The addition of Ta greatly improved the tribological properties of the composites, and with the increase of Ta doping content, the friction coefficient of the copper-based composites gradually decreased. The research shows that the copper-based Nb1-x(Ti/Ta)xSe2 composite is a very promising new composite material.

Cr dopant induced tailoring of intrinsic defects and trap distribution in MgAl2O4 nanocrystals: electron spin resonance and thermoluminescence

Thermoluminescence (TL) response of γ-irradiated Cr3+ doped MgAl2O4 nanocrystals is studied to investigate the impact of dopant ions on intrinsic defects and trap distribution. At low doping concentration, the broad TL glow curve has a dominant incomplete peak attributed to deep F+ centers around 673 K and contribution from shallow , , and trapping states in low temperature region. TL glow curve intensity and trap distribution is found to be influenced with increase in Cr doping concentration. Electron spin resonance spectra show the interaction of electron spins at paramagnetic F+/V− centers with isolated and paired Cr3+ ions with increase in Cr doping concentration. Cr3+ ions doped at octahedral sites are found to be perturbed by the presence of , , etc defect centers and may cause the formation of Cr associated defect clusters at higher doping concentration. A trapping mechanism is proposed as per the TL response obtained upon γ-irradiation to comprehend the intertrap charge transfer among various shallow and deep trapping states.

Ti, F Codoped Sodium Manganate of Layered P2-Na 0.7 MnO 2.05 Cathode for High Capacity and Long-Life Sodium-Ion Battery

Ti, F Codoped Sodium Manganate of Layered P2-Na _0.7 MnO _2.05 Cathode for High Capacity and Long-Life Sodium-Ion Battery

Influence of Y3+ and La3+ ions on the structural, magnetic, electrical, and optical properties of cobalt ferrite nanoparticles

In the current study, nanocrystalline CoY0.5xLa0.5xFe2-xO4 (where x = 0.00, 0.02, 0.04, 0.06, 0.08, and 0.10) ferrites have been synthesized via a sol-gel auto combustion process. The synthesized powders were pressed into pellet forms and sintered at 900 °C for 4 h in the air. X-ray diffractometry (XRD) confirmed the single-phase cubic spinel structure of the synthesized samples having the mean crystallite domain sizes ranging from 122 and 54 nm. FTIR spectroscopic analyses revealed two strong bands within the range of 600 to 350 cm−1, further confirming the cubic inverse spinel structure of the prepared materials. The surface morphologies and composition were investigated by Field Emission Scanning Electron Microscopy (FE-SEM) and Energy Dispersive X-ray (EDX) Spectroscopy. The magnetic hysteresis curves recorded at room temperature exhibit ferrimagnetic behavior. The highest coercivity (Hc∼1276 Oe) was found at a high doping (x = 0.10) concentration of Y3+ and La3+ in cobalt ferrite. Dielectric constant increase with increased doping concentration whereas real-impedance and dielectric loss decrease with increased in doping concentration and applied frequency. The band gap energy increased from 1.48 to 1.53 eV with increasing Y3+ and La3+concentrations in the UV–Vis region. The elevated levels of magnetic and dielectric substances in the ferrite nanoparticles suggest that the material could be used for magnetic recording media and high-frequency devices.

The effect of Er3+ concentration on the kinetics of multiband upconversion in NaYF4:Yb/Er microcrystals.

In Yb-Er co-doped upconversion (UC) nanomaterials, upconversion luminescence (UCL) can be modulated to generate multiband UCL emissions by changing the concentration of activator Er3+. Nonetheless, the effect of the Er3+ concentrations on the kinetics of these emissions is still unknown. We here study the single β-NaYF4:Yb3+/Er3+ microcrystal (MC) doped with different Er3+ concentrations by nanosecond time-resolved spectroscopy. Interestingly, different Er3+ doping concentrations exhibit different UCL emission bands and UCL response rates. At low Er3+ doping concentrations (1mol%), multiband emission in β-NaYF4:Yb3+/Er3+ (20/1mol%) MCs could not be observed and the response rate of UCL was slow (5-10μs) in β-NaYF4:Yb3+/Er3+. Increasing the Er3+ doping concentration to 10mol% can shorten the distance between Yb3+ ions and Er3+ ions, which promotes the energy transfer between them. β-NaYF4:Yb3+/Er3+ (20/10mol%) can achieve obvious multiband UCL and a quick response rate (0.3µs). However, a further increase in the Er doping concentration (80mol%) makes MCs limited by the CR process and cannot achieve the four-photon UC process (4F5/2 → 2K13/2 and 2H9/2 → 2D5/2). Therefore, the result shows that changing the Er3+ doping concentration could control the energy flow between the different energy levels in Er3+, which could affect the response time and UCL emission of the Yb/Er doped rare earth materials. Our work can facilitate the development of fast-response optoelectronics, optical-sensing, and display industries.