Infrared radiation performance and calculation of B-site doped lanthanum aluminate from first principles

Pure LaAlO₃ and LaAl_1-xNi_xO₃ samples (x?=?0.05, 0.1, 0.15, 0.2, 0.25, 0.3) were prepared using a sol-gel technique. The samples were analyzed and characterized using XRD, SEM, FT-IR and XPS. The results showed that the infrared emissivity of LaAl_1-xNi_xO₃ powder prepared at 1500?℃ for 2?h increases with Ni²⁺ doping content. For x?=?0.25, the mean emissivity in the 3–5?µm infrared spectral region was 0.835. This was a 142% increase compared with that of pure LaAlO₃ (0.345). The doped Ni ions mainly exist with valences of +?2 and +?3 in the LaAlO₃ lattice. After doping, the concentration of electron holes and oxygen vacancies increased, leading to an enhancement of free carrier absorption in the system. It indicated that the Ni²⁺ doping would introduce an impurity energy level in the forbidden band of LaAlO₃ by first principles calculation, forming primarily by the hybridization of the 3d orbital electrons of the Ni ions and the 2p orbital electrons of the oxygen atoms. When x?=?0.25, the band gap decreased from 3.50?eV to 0.77?eV. The impurity energy level allows for a reduction in the energy required for the electrons transferring from the valence band to the conduction band, causing increased numbers of electron transitions between the band gaps, thus enhancing free carrier absorption and increasing the infrared emissivity of the material. The LaAl_1-xNi_xO₃ oxide materials prepared in this work had excellent infrared radiation properties. As a lining material at high temperature reacting furnace, the energy loss could be reduced, the heat utilization efficiency would be greatly improved, and the utility model could be used in the field of high-temperature thermal energy saving.     

Influence of N2/Ar gas mixture ratio and annealing on optical properties of SiCBN thin films prepared by rf sputtering

Optical properties of amorphous thin films of silicon carbon boron nitride (Si–C–B–N) obtained by reactive sputtering has been studied. Compositional variations were obtained by changing the nitrogen and argon gas mixture ratio in the sputtering ambient. The effect of gas ratios and annealing on the optical properties was investigated. It was found that the transmittance of the films increases with nitrogen incorporation. Annealing at higher temperatures leads to considerable increase in transmittance. Optical energy gap (Tauc gap) calculated from absorption data is influenced by annealing temperatures and reactive process gas mixture. Changes in optical properties were correlated to the chemical modifications in the films due to annealing, through X-ray photoelectron spectroscopy. Studies reveal that the carbon and nitrogen concentrations in the films are highly sensitive to temperature. Annealing at higher temperatures leads to broken C–N bonds which results in the loss of C and N in the films. This is believed to be the primary cause for variations in optical properties of the films.     

Effect of Mn-doping on optical properties of lead-free (K0.4Na0.6)NbO3 ferroelectric single crystals

Optical properties of <001>-oriented pure (K_0.4Na_0.6)NbO₃ (KNN) and 0.5 wt% Mn-doped KNN (Mn-KNN) single crystals were studied. The refractive indices (n) of both crystals exhibited a normal dispersion behavior in the wavelength range of 300−1100 nm. The modified Sellmeier dispersion equations for n were obtained by least-squares fit. In addition, Sellmeier coefficients were determined by single-oscillator dispersion relation, which related to energy band structures of crystals. Compared with KNN, a decrease about 10 % in transmittance (over 350 nm) was observed in Mn-KNN due to the losses resulting from the increase of domain wall density. Furthermore, a 20 nm blue-shift in the absorption edge was observed for Mn-KNN. Based on Tauc equation, the band gap energies of 3.26 and 3.42 eV were obtained for KNN and Mn-KNN, respectively. The increase of band gap energy in Mn-KNN was attributed to the distortion of BO₆ octahedron building block caused by Mn²⁺ occupying the B-site.     

Dopants induced structural and optical anomalies of anisotropic edges of black phosphorous thin films and crystals

A detailed experimental investigation of dopants modified black-phosphorus and methodology to deposit film on glass substrate have been conducted in order to improve the optical properties and wider utility. It was observed that Raman peaks were less intense for film, compared to separately grown black-P crystals. It was also observed that when synthesis duration was reduced to four hours, all Raman peaks became broader. A non-uniform material luminescence with dominance of green luminescence was observed when black-P crystals were irradiated with light of wavelength ~565–575 nm. The sulfur doped black-P illustrated fascinating rod-and-globule like deposits on the parent nano-coral black phosphorous substrate, whereas selenium doped black-P exhibits a localized concentration of Se in the near homogeneous phosphorous coverage. The boron and sulfur doping increased the band gap. In contrast, Se, In, and Ga doping resulted in a significant decrease in band gap energy. Frequency dependent dielectric functions of the anisotropic zig-zag and armchair edges of phosphorene suggest that doping of black –P causes a diminution in the first peak position for the zigzag electric field polarization demonstrating a gradual red shift. The red shift in the first peak position was perceived to be greatest for doping with boron exhibiting a band edge at 0.65 eV and least in the case of doping with sulfur, resulting in a band edge at 1.09 eV.     

Heat treatment effects on the structural and optical properties of thin Bi2(Se1-xTex)3 films

Thin layers of Bi₂-chalcogenides, in the form of Bi₂(Se_1-xTe_x)₃ films, were evaporated on glass substrates by means of the vacuum thermal evaporation. Microstructure of the as prepared layers was investigated by x-ray diffraction (XRD) analysis. Identifications of the surface morphology and roughness were determined via scanning electron microscope (SEM). Optical transmissivity spectra proved that the as prepared films have low transparency with growing trend upon increasing the wavelength beyond the infra-red region. Low transmittance was observed for the as prepared films. Heat treatment, in the form of temperature annealing, was carried out aiming at boosting the structural features and the materials transmissivity. Structural properties and surface features of the annealed films were probed also via XRD and SEM analyses. It was found that the crystal size increases while the micro-strain and the dislocation density decrease obviously due to annealing. It was also observed that the annealing process significantly enhances the materials transmission especially in the range of higher wavelengths. Optical band gap was studied after annealing at various temperatures. Notable change in the band gap value was observed as a result of annealing. The band gap of the undoped (Bi₂Se₃) materials showed significant rise from 0.14 to 1.79 eV due to annealing. Similarly, the Te-doped samples exhibited notable increase in their band gap values after annealing. For example, the optical band gap of the sample doped at x = 0.20 increased from 0.03 to 0.41 eV by annealing. On the other hand, transmittance was also enhanced by annealing. For samples treated at 250 °C for 3 h, their optical transmissivity is enhanced to over 99% at the visible near-IR range. Such significant enhancement can be ascribed to structural enhancements. With such enhancement in the optical transmissivity, optoelectronic applications including transparent electrode can be met.     

Effect of amount of doping agent on sintering,microstructure and optical properties of Zr- and La-doped alumina sintered by SPS

SPS-produced α-alumina samples are prepared from powders doped with different amounts of Zr⁴⁺ and La³⁺ cations. Zr⁴⁺ cations segregate at grain boundaries. m-ZrO₂ particles are formed at 570 but not at 280 cat ppm. A β-alumina LaAl₁₁O₁₈ structure is found at 310 cat ppm when the lanthanum grain boundary solubility limit is exceeded (∼200 cat ppm). 100 cat ppm La is sufficient to block the diffusion path across grain boundaries and inhibit grain growth. Both doping cations disturb the grain boundary diffusion whatever their amount. They delay the densification at higher temperatures while limiting grain growth. The real in-line transmittance (RIT) of α-alumina is improved due to the reduced grain size. Nevertheless, increasing the cation amount leads to an increase in porosity or even the formation of secondary phase particles, both detrimental for optical properties. Finally, optimised amounts of cation of 200 and 150 cat ppm are found for La- and Zr-doped alumina, respectively.     

Variation of the key morphological,structural, optical and electrical properties of SILAR CdO with alkaline earth Ca2+ ions doping

Pristine and alkaline earth Ca²⁺ ions doped (Ca_xCd_1-xO (0 ≤ x ≤ 0.025)) CdO films were fabricated by SILAR technique on the soda lime glass substrates. The influence of increasing Ca content on the morphological, structural, optical and electrical properties of deposited films was analyzed. Metallurgical Microscope (MM), Scanning Electron Microscope (SEM) and Atomic Force Microscopy (AFM) images of the samples exhibited that the morphology was dramatically changed with the addition of Ca to the synthesis solution when compared to the pristine CdO film. Energy Dispersive Spectrometry (EDS) analyses confirmed the presence of Ca in the doped films. X-ray diffraction (XRD) analysis of the pristine and Ca-doped CdO films exhibited cubic crystalline structure with preferred orientation of (111) and (200) direction. The existence of chemical bonding was confirmed by Fourier Transform Infrared Spectroscopy (FTIR) study. Optical studies revealed that the energy band gap were dependent on Ca-doping content in accordance with both Vegard's relation and Tauc's law calculations. The impedance analysis and four-point probe measurement results of CdO thin films were studied. Sheet resistances of the thin films were increased by Ca doping up to doping level of 1.5%. Further doping level causes degradation in sheet resistance.     

聚苯胺能带结构和激发能与导电性能的理论分析

用PM3和UPM3-BS方法分别优化了二聚到十聚苯胺掺杂前(全还原型、全氧化型)及其电荷掺杂体的几何结构,同时获得了其HOMO-LUMO能隙;用ZINDO//PM3和UZINDO//UPM3-BS方法分别计算了它们的S0→S1光谱激发能;分别结合周期性边界条件方法和齐聚物外推法,系统地计算了几种形态聚苯胺的能带结构和H...     

An experimental and theoretical study on the photocatalytic antibacterial activity of boron-doped TiO2 nanoparticles

Boron-doped titanium dioxide nanoparticles (B–TiO₂ NPs) were prepared by a sol-gel method. The physicochemical properties of B–TiO₂ NPs were characterized by X-ray diffraction, transmission electron microscopy, ultraviolet–visible diffuse reflectance spectroscopy and photoluminescence spectroscopy. The band structure and electrical properties of B–TiO₂ NPs were investigated using the first-principle. The effects of the concentration gradient of doping B ions on the photocatalytic antibacterial activity of B–TiO₂ NPs under visible-light irradiation were investigated by the inhibition zone method and the shaking flask method. The experimental results show that B–TiO₂ NPs are mainly composed of the anatase phase, but no B-related phase was observed. With the increase of the doping amount of boron ions, the particle size decreases and the specific surface area increases. B atoms mainly exist in the form of substitutional dopant and interstitial dopant. Theoretical calculations reveal that B atoms in the TiO₂ matrix exist much more easily as interstitial dopant, but B–TiO₂ NPs composed of B substituted dopant have better photocatalytic performance. The results of the antibacterial assays show that B–TiO₂ NPs have strong antibacterial activities and some bactericidal activities. Finally, the mechanism of the antibacterial activity of B–TiO₂ NPs are examined.     

Influence of silicon carbide on structural,optical and magnetic properties of Wollastonite/Fe2O3 nanocomposites

The influence of adding 10, 20 and 30% molar ratio of silicon carbide (SiC) separately to a composite of wollastonite (W) with a fixed content of 10%Fe₂O₃ prepared by wet precipitation method was studied. The crystal structure of the annealed composite powders was inspected by X-ray diffraction (XRD); revealing multi-phase structure. The highest estimated crystallite size investigated by Scherrer equation of W, SiC, WFe:SiC₁₀, WFe:SiC₂₀ and WFe:SiC₃₀ were 53.89, 54.6, 56.3, 48.5 and 54.6 nm respectively; demonstrating the formation of nanocomposites. Particles shape, size and crystallinity of the samples were studied using high resolution transmission electron microscope (HR-TEM). The band gap E_g values of the nanocomposites increased with SiC content having an intermediate value that lies between that of γ-Fe₂O₃ (maghemite) and SiC. Ferromagnetic and paramagnetic contributions were observed in the magnetic hysteresis loops for the composites. This study highlighted that the coercive field (H_ci) of the composites improved with increasing the SiC content. The innovative wollastonite/Fe₂O₃/SiC with amended magnetic properties elicited attention due to their promising application in bone filler and industrial purposes.     

Impacts of thickness reduction and heat treatment on the optical properties of thin chalcogenide films

Bi-based chalcogenides, in the form of thin crystalline films, were deposited at different thicknesses onto highly cleaned glass slides with the aid of vacuum thermal evaporation technique. The influence of thermal annealing on the optical properties of Bi₂Te₃-Bi₂Se₃ films at different thicknesses is investigated in this work. Wavelength dependence of the optical transmittance and reflectance was recorded, for the as-prepared and the annealed films, in the wavelength range from 350 to 2700 nm using a double beam spectrophotometer. Fundamental optical properties such as absorption coefficient and energy band gap were derived based on the measured spectra and film's thickness. We demonstrate in the present work that the synergy of annealing and thickness reduction can be exploited for light transmittance enhancements, and consequently for optoelectronic applications including transparent conductive electrodes.     

The Role of Intrinsic and Surface States on the Emission Properties of Colloidal CdSe and CdSe/ZnS Quantum Dots

Time Resolved Photoluminescence (TRPL) measurements on the picosecond time scale (temporal resolution of 17 ps) on colloidal CdSe and CdSe/ZnS Quantum Dots (QDs) were performed. Transient PL spectra reveal three emission peaks with different lifetimes (60 ps, 460 ps and 9–10 ns, from the bluest to the reddest peak). By considering the characteristic decay times and by comparing the energetic separations among the states with those theoretically expected, we attribute the two higher energy peaks to ± 1 ^U and ± 1 ^L bright states of the fine structure picture of spherical CdSe QDs, and the third one to surface states emission. We show that the contribution of surface emission to the PL results to be different for the two samples studied (67% in the CdSe QDs and 32% in CdSe/ZnS QDs), confirming the decisive role of the ZnS shell in the improvement of the surface passivation.     

Effect of Fe2O3 doping on colour and mechanical properties of Y-TZP ceramics

Yttria-stabilized zirconia (Y-TZP) samples with different Fe concentrations were prepared aiming to study the effects of Fe₂O₃ doping on colour and mechanical properties. Since colour is an important optical property for jewellery and watchmaking, the investigation of colour in zirconia ceramics has a great scientific and technological interest. An investigation of the mechanical and optical properties, specifically the colour, was developed starting from commercial partially yttria-stabilized zirconia (Y-TZP) powders produced by Emulsion Detonation Synthesis (EDS). Within the strategies to get colours, the use of colouring oxides such as iron oxide (Fe₂O₃) was the chosen approach. The addition of specific ions into the ZrO₂ matrix can be used to tune zirconia colour without compromising its outstanding mechanical properties. Doping with iron oxide has proved to be a suitable, reproducible and irreversible colouring mechanism, allowing the development of a chromatically beige stable material with respect to its use in different processing conditions such as different atmospheres and temperature ranges. XRD results suggested that iron ions dissolved into tetragonal zirconia phase are at interstitial positions since the unit-cell volume of the tetragonal zirconia increases with increasing iron content. The effect of dopant addition on the mechanical properties of Y-TZP ceramics was also assessed. Compared to the undoped samples, doped ones exhibit a similar Vickers hardness (>1200?MPa) and biaxial flexural strength (>1000?MPa). However, it was observed that Fe₂O₃ doping slightly decreased the fracture toughness of Y-TZP ceramics.     

The effects of Se/S ratio on the photoelectric properties of nitrogen -doped graphene quantum dots decorated CdSxSe1-x composites

In the work, CdS_xSe_1-x/N-GQDs composites were fabricated via a simple one-step hydrothermal process and their tunable composition, structure and photoelectric properties were characterized by various techniques. The photoelectric properties of CdS_xSe_1-x/N-GQDs could be adjusted by different Se/S ratios and tunable band-gaps. CdS_xSe_1-x/N-GQDs composites reached the optimal photocurrent response and the lowest interfacial impedance at the Se/S ratio of 0.75:0.25. Mott-Schottky plots and LSV spectra showed that the n-type CdS_0.25Se_0.75/N-GQDs presented a higher carrier density under light illumination. The excellent properties of the composites could be attributed to the mechanism involved in the excitation and electron-transfer process. On one hand, the band-gap of CdS_0.25Se_0.75/N-GQDs was narrowed, and more electrons were excited by the lower band-gap energy to promote a superior electron separation and transportation. On the other hand, N-GQDs acted as charge carriers and conductive way providers for electron-transfer instead of electron-hole recombination in the composites.     

Synthesis and investigation of environmental protection and earth-abundant kesterite Cu2MgxZn1-xSn(S,Se)4 thin films for solar cells

We have synthesized Cu₂Mg_xZn_1–xSn(S,Se)₄ (0?≤?x?≤?0.6) thin films by a facile sol-gel method, and studied the influence of Mg concentration on the crystal structure, surface morphology and photoelectric performance of Cu₂Mg_xZn_1–xSn(S,Se)₄ thin films systematically. It was shown that the smaller Zn²⁺ in Kesterite phase Cu₂ZnSn(S,Se)₄ will be replaced by larger Mg²⁺, forming uniform pure phase Cu₂Mg_xZn_1–xSn(S,Se)₄. The band gap of Cu₂Mg_xZn_1–xSn(S,Se)₄ films can be adjusted from 1.12 to 0.88?eV as the x value changes from 0 to 0.6. Furthermore, the Cu₂Mg_xZn_1–xSn(S,Se)₄ thin films with large grain size, smooth surface and less grain boundaries was obtained at an optimized condition of x?=?0.2. The carrier concentration of Cu₂Mg_xZn_1–xSn(S,Se)₄ thin film reaches the maximum 6.47?×?10¹⁸ cm^?3 at x?=?0.2, which is a potential material to be the absorption layer of high efficiency solar cells.     

Growth and optical properties of cerium dioxide nanocrystallites prepared by coprecipitation routes

Nanosized cerium dioxide (CeO₂) powders have been synthesized using coprecipitation methods and cerium nitrate hexahydrate (Ce(NO₃)₃·6H₂O) as the starting material. The growth and optical properties of nanosized CeO₂ powders were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), nano-beam electron diffraction (NBED), high resolution TEM (HRTEM), and ultraviolet–visible (UV–vis) absorption spectrophotometry. The XRD result shows that the dried CeO₂ precursor powders (both before and after calcination at various temperatures and times) contained a single crystalline phase of CeO₂. In the dried precursor powders, the crystallites of CeO₂ measured 10.4 nm and 66.8 nm before and after calcination at 1273 K for 240 min, respectively. The indirect band gap energy (_Ei$E_i$) of CeO₂ decreased from 3.03 eV to 2.68 eV as the crystallite size increased from 10.4 nm to 66.8 nm, whereas the direct band gap energy (_Ed$E_d$) of CeO₂ also decreased from 3.79 eV to 3.38 eV.     

Antibacterial efficiency of alkali-free bio-glasses incorporating ZnO and/or SrO as therapeutic agents

A series of seven alkali-free silica-based bioactive glasses (SBG) with ZnO and/or SrO additives (in concentrations of 0–12?mol%) were synthesized by melt-quenching, aiming to delineate a candidate formulation possessing (i) a coefficient of thermal expansion (CTE) similar to the one of titanium (Ti) and its medical grade super-alloys (crucial for the future development of mechanically adherent implant-type SBG coatings) and (ii) antibacterial efficiency, while (iii) conserving a good cytocompatibility. The SBGs powders were multi-parametrically evaluated by X-ray diffraction, Fourier transform infrared and micro-Raman spectroscopy, dilatometry, inductively coupled plasma mass spectrometry, antibacterial (against Staphylococcus aureus and Escherichia coli strains) suspension inhibition and agar diffusion tests, and human mesenchymal stem cells cytocompatibility assays. The results showed that the coupled incorporation of zinc and strontium ions into the parent glass composition has a combinatorial and additive benefit. In particular, the “Z6S4” formulation (mol%: SiO₂—38.49, CaO—32.07, P₂O₅—5.61, MgO—13.24, CaF₂—0.59, ZnO—6.0, SrO—4.0) conferred strong antimicrobial activity against both types of strains, minimal cytotoxicity combined with good stem cells viability and proliferation, and a CTE (~?8.7?×?10^?6 ×?°C^?1) matching well those of the Ti-based implant materials.     

Effects of Ga substitution for Al on the fabrication and optical properties of transparent Ce:GAGG-based ceramics

Ce³⁺-doped Gd₃(Al_1-xGa_x)₅O₁₂ (Ce:GAGG) transparent ceramics were successfully prepared via a solid state reaction/oxygen sintering method. The effects of Ga substitution on the structure and optical properties of the ceramics were investigated. The highest quantum yield and relatively high scintillation light yield were achieved in the Gd₃(Al_0.6Ga_0.4)₅O₁₂. The investigated processing technique demonstrated advantages such as increased flexibility and short processing time, thus being very cost effective. The investigated approach provides a much more economical alternative to the conventional melt growth processes used to fabricate single crystals.