First-principles study of La and Sb-doping effects onelectronic structure and optical properties of SrTiO3

The effects of La and Sb doping on the electronic structure and optical properties of SrTiO 3 are investigated by first-principles calculation of the plane wave ultra-soft pseudo-potential based on density functional theory. The calculated results reveal that corner-shared TiO 6 octahedra dominate the main electronic properties of SrTiO 3 , and its structural stability can be improved by La doping. The La 3+ ion fully acts as an electron donor in Sr 0.875 La 0.125 TiO 3 and the Fermi level shifts into the conduction bands (CBs) after La doping. As for SrSb 0.125 Ti 0.875 O 3 , there is a distortion near the bottom of the CBs for SrSb 0.125 Ti 0.875 O 3 after Sb doping and an incipient localization of some of the doped electrons trapped in the Ti site, making it impossible to describe the evolution of the density of states (DOS) within the rigid band model. At the same time, the DOSs of the two electron-doped systems shift towards low energies and the optical band gaps are broadened by about 0.4 and 0.6 eV for Sr0.875La0.125TiO3 and SrSb0.125Ti0.875O3 , respectively. Moreover, the transmittance of SrSb0.125Ti0.875O3 is as high as 95% in most of the visible region, which is higher than that of Sr0.875La0.125TiO3 (85%). The wide band gap, the small transition probability and the weak absorption due to the low partial density of states (PDOS) of impurity in the Fermi level result in the significant optical transparency of SrSb0.125 Ti0.875 O3 .     

ZnO高掺杂Ga的浓度对导电性能和红移效应影响的第一性原理研究

采用基于密度泛函理论框架下的第一性原理平面波超软赝势方法,在相同环境条件下建立了浓度不同的由Ga原子取代Zn原子的Zn_1-xGa_xO模型.对低温高掺杂Ga原子的Zn_1-xGa_xO半导体的能带结构、态密度和吸收光谱进行了计算.结果表明:Ga原子浓度越大,进入导带的相对电子数越多,但是电子迁移率反而减小.通过对掺杂和未掺杂ZnO的电导率以及最小间隙带宽度分别进行了比较 关键词： ZnO高掺杂Ga 电导率 红移 第一性原理     

Titanium atoms dimerization phenomenon and magnetic properties of titanium-antisite (TiO) and chromium doped rutile TiO2, ab-initio calculation

The ab-initio calculations based on the Korringa Kohn Rostoker approximation approach combined with coherent potential approximation (KKR-CPA), were used to study the magnetic properties of the titanium anti-site (Ti_O) and chromium (Cr) doped TiO₂. In the considered systems, we used different concentrations for Ti_O defect and Cr doping. In TiO_2(0.98)(Ti_O)_0.02, the obtained results indicate that Ti_O is a donor having half-metal behavior. Ti_O[3d] band is located at the Fermi level, although isn’t 100% polarized, the ferromagnetic (FM) state is verified as being more stable than disordered local moment (DLM) state. For Ti_0.98Cr_0.02O₂ the Cr doping introduced new states which give the material half-metallic feature. The majority spin of Cr impurities are located at the Fermi level and the conduction electrons around the Fermi level are 100% spin polarized. This indicates the stability of (FM) state. Moreover, in Ti_0.98Cr_0.02O_2(0.98)(Ti_O)_0.02, the top of the valence band is shifted to lower energy compared to pure TiO₂, and the n-type of TiO₂ is verified. The majority spin of Cr[3d] are located at 0.025 Ry close to the Fermi level. The predicted Curie temperatures (Tc) were calculated using the mean field approximation (MFA) and we predicted that Ti_O defect in Cr doped TiO₂ makes Tc higher. This kind of defect makes the material useful for spinotronics's applications and devices.     

过渡金属Fe或Ag掺杂K2Ti6O13的电子结构和光学性质

本文利用基于密度泛函理论（DFT）的第一性原理计算研究了它们的电子结构和光学性质.光学性质的计算结果和实验相一致.结果表明,Fe或Ag掺杂后,K₂Ti₆O₁₃的带隙中出现了杂质带且其带隙值变小,因而使掺杂后的K₂Ti₆O₁₃的吸收边发生红移并实现了其对可见光吸收.其中杂质带主要由Fe 3d态或Ag 4d态与Ti 3d态和O 2p态杂化而成.对于Fe掺杂的K₂Ti₆O₁₃,杂质带位于带隙中间,因此可以作为电子从价带跃迁到导带的桥梁.对于Ag掺杂的K₂Ti₆O₁₃,杂质带位于价带顶附近为受主能级,可以降低光生载流子的复合概率.实验和计算研究表明,通过Fe或Ag的掺杂可以实现了K₂Ti₆O₁₃对可见光的吸收,这对进一步研究K₂Ti₆O₁₃的光学性质具有重要意义.     

过渡金属(Fe,Co,Ni,Zn)掺杂金红石TiO2的电子结构和光学性质

采用基于密度泛函理论的第一性原理方法对未掺杂以及不同浓度过渡金属Fe,Co,Ni,Zn掺杂金红石TiO₂的超晶胞体系进行了几何优化,并讨论了其晶格常数,电子能带结构和光学性质.研究结果表明:掺杂前后的晶格参数与实验值偏差在3.6%以下;适量的过渡金属掺杂不但影响体系能带结构,拓宽光吸收范围,而且扮演着俘获电子的重要角色,有利于光生电子-空穴对的有效分离以及增强光吸收能力;Fe,Co,Ni,Zn最佳理论掺杂体系分别为Ti_0.75Fe_0.25O₂,Ti_0.75Co_0.25O₂,Ti_0.75Ni_0.25O₂,Ti_0.83Zn_0.17O₂;Fe,Co,Ni3d态分裂为t_2g和e_g态,分别贡献于价带高能级和导带低能级部分,促进了电子-空穴对的生成,从而可提高TiO₂的光催化性能;Zn3d态电子成对填满轨道,不易被激发,故光催化活性无明显提高.     

Nb高掺杂量对锐钛矿TiO2导电和光学性能影响

目前, 在Nb高掺杂量摩尔数分别为0.050和0.0625的条件下, 对掺杂体系锐钛矿TiO₂电阻最低存在相反的两种实验结果都有文献报道. 为解决这个矛盾, 本文采用基于密度泛函理论的平面波超软赝势方法, 计算了纯的单胞和三种不同Nb高掺杂量对锐钛矿Ti_1-xNb_xO₂ (x=0.03125, 0.050, 0.0625)超胞的能带结构分布、态密度分布和光学性质. 结果表明, 在本文限定掺杂量的条件下, Nb掺杂量越增加, 掺杂体系的体积越增加, 总能量越升高, 稳定性越下降, 形成能越升高, 掺杂越难, 相对自由电子浓度越增加, 电子有效质量越增加, 电子迁移率越减小, 电子电导率越减小, 最小光学带隙越变宽, 吸收光谱和反射率向低能方向移动越显著, 透射率越增加. 计算结果与实验结果相吻合.     

Electronic and optical properties of pure and Mo doped anatase TiO2 using GGA and GGA+U calculations

Comparative GGA and GGA+U calculations for pure and Mo doped anatase TiO₂ are performed based on first principle theory, whose results show that GGA+U calculation provide more reliable results as compared to the experimental findings. The direct band gap nature of the anatase TiO₂ is confirmed, both by using GGA and GGA+U calculations. Mo doping in anatase TiO₂ narrows the band gap of TiO₂ by introducing Mo 4d states below the conduction band minimum. Significant reduction of the band gap of anatase TiO₂ is found with increasing Mo doping concentration due to the introduction of widely distributed Mo 4d states below the conduction band minimum. The increase in the width of the conduction band with increasing doping concentration shows enhancement in the conductivity which may be helpful in increasing electron–hole pairs separation and consequently decreases the carrier recombination. The Mo doped anatase TiO₂ exhibits the n-type characteristic due to the shifting of Fermi level from the top of the valence band to the bottom of the conduction band. Furthermore, a shift in the absorption edge towards visible light region is apparent from the absorption spectrum which will enhance its photocatalytic activity. All the doped models have depicted visible light absorption and the absorption peaks shift towards higher energies in the visible region with increasing doping concentration. Our results describe the way to tailor the band gap of anatase TiO₂ by changing Mo doping concentration. The Mo doped anatase TiO₂ will be a very useful photocatalyst with enhanced visible light photocatalytic activity.     

Magnéli相亚氧化钛Ti8O15的电子结构和光学性能的第一性原理研究

采用基于密度泛函理论的平面波超软赝势法研究了Magnéli相亚氧化钛Ti₈O₁₅的电子结构和光学性能. 计算出的能带结构显示Ti₈O₁₅相比锐钛型TiO₂禁带宽度大幅度降低. 态密度分析表明, 其原因在于Ti₈O₁₅的O原子的2p轨道以及Ti原子的3p, 3d轨道相对于TiO₂的相应轨道向左产生了偏移, 同时由于O原子的缺失使得Ti原子的3d, 3p轨道多余电子在Fermi能级附近聚集形成新的电子能级. 态密度分析结果还显示, 相对于TiO₂, Ti₈O₁₅ Fermi能级附近电子格局发生了如下变化: O原子的2p轨道电子贡献减少, Ti原子的3d轨道的电子对Fermi能级贡献增大. 光吸收计算图谱表明, TiO₂仅在紫外光区有较高的光吸收能力, 而Ti₈O₁₅由于禁带宽度变窄引起光吸收范围红移到可见光区, 从而在紫外光区和可见光区都有较高的光吸收能力, 计算结果与实验得到的紫外-可见漫反射吸收光谱结果一致. 关键词： 第一性原理 8O₁₅')" href="#">Magnéli相亚氧化钛Ti₈O₁₅ 电子结构 光学性能     

Optical properties of transparent cobalt-containing magnesium aluminosilicate glass-ceramics doped with gallium oxide for saturable absorbers

Transparent glass-ceramic materials based on glasses of the MgO–Al₂O₃–SiO₂–TiO₂ system doped with CoO and Ga₂O₃ are synthesized. The secondary heat treatment of the initial glasses at temperatures of 800–950°C leads to precipitation of nanosized (6–7 nm) crystals of magnesium aluminogallium spinel doped with cobalt ions and magnesium aluminotitanate solid solutions. The optical absorption spectra of the initial glass and glass-ceramic materials are studied. It is shown that the absorption band caused by the ⁴A₂(⁴F)→ ⁴T₁(⁴F) transitions of tetrahedrally coordinated Co²⁺ ions in glass-ceramics with nanosized Co:Mg(Al,Ga)₂O₄ crystals is shifted to longer wavelengths (up to ~1.67 µm) compared to the position of this band in materials with Co:MgAl₂O₄ crystals. The synthesized glass-ceramics are characterized by a relatively low saturation fluence FS ~ 0.5 ± 0.1 J/cm² at a wavelength of 1.54 µm, as well as by a high radiation resistance to nanosecond laser pulses, which is no lower than ~15 ± 2 J/cm². This explains their attractiveness as materials for saturable absorbers for erbium lasers emitting in the spectral range 1.5–1.7 µm.     

Ga/N高共掺浓度对ZnO导电性能和红移影响的第一性原理研究

采用密度泛函理论框架下的第一性原理平面波超软赝势方法, 建立了未掺杂ZnO单胞和两种不同浓度的Ga/N高共掺ZnO超胞模型, 分别进行了几何结构优化、总态密度分布和能带分布的计算. 研究表明, ZnO高共掺Ga/N的条件下, Ga/N高共掺浓度越大, 导电性能越弱, 并且高掺杂后高能区红移效应显著, 计算得到的结果与实验结果的变化趋势一致. 关键词： Ga/N高共掺ZnO 电导率 红移 第一性原理     

Theoretical study on electronic and optical properties of Zn-doped In<Subscript>0.25</Subscript>Ga<Subscript>0.75</Subscript>As photocathodes

First-principles calculations for intrinsic and Zn-doped In_0.25Ga_0.75As are performed based on density functional theory to study the influence of Zn doping on electronic and optical properties. The band structure, density of state, Mulliken population, dielectric function, complex refractive index, absorption coefficient and reflectivity of In_0.25Ga_0.75As are calculated. Results show that the Fermi levels of two Zn-doped models enter into the valence bands and Zn atom is more easily to replace In atom than Ga atom. The lattice constant of In_0.2344Ga_0.75Zn_0.0156As reduced after optimization, while that of In_0.25Ga_0.7344Zn_0.0156As increased to the contrary. The Mulliken bond population shows that the doping Zn atoms can enlarge the strength of In–As and Ga–As polar covalent bonds. Furthermore, the calculated absorption coefficient and reflectivity are used to characterize the performance of photoemission, indicates that the photoresponses of Zn-doped models are better than that of the intrinsic.     

Effects of H2 ambient annealing in fully 0 0 2-textured ZnO:Ga thin films grown on glass substrates using RF magnetron co-sputter deposition

Gallium doped zinc oxide (ZnO:Ga) thin films were grown on glass substrates using RF magnetron co-sputtering, followed by H₂ ambient annealing at 623 K to explore a possibility of steady and low-cost process for fabricating transparent electrodes. While it was observed that the ZnO:Ga thin films were densely packed c-axis oriented self-textured structures, in the as-deposited state, the films contained Ga₂O₃ and ZnGa₂O₄ which had adverse effect on the electrical properties. On the other hand, post-annealing in H₂ ambient improved the electrical properties significantly via reduction of Ga₂O₃ and ZnGa₂O₄ to release elemental Ga which subsequently acted as substitutional dopant increasing the carrier concentration by two orders of magnitude. Transmittance of the ZnO:Ga thin films were all over 90% that of glass while the optical band gap varied in accordance with the carrier concentrations due to changes in Fermi level. Experimental observation in this study suggests that transparent conductive oxide (TCO) films based on Ga doped ZnO with good electrical and optical properties can be realized via simple low-cost process.     

Optical properties of in situ doped and undoped titania nanocatalysts and doped titania sol-gel nanofilms

In this paper we present spectroscopic properties of doped and undoped titanium dioxide (TiO₂) as nanofilms prepared by the sol-gel process with rhodamine 6G doping and studied by photoacoustic absorption, excitation and emission spectroscopy. The absorption spectra of TiO₂ thin films doped with rhodamine 6G at very low concentration during their preparation show two absorption bands, one at 2.3 eV attributed to molecular dimmer formation, which is responsible for the fluorescence quenching of the sample and the other at 3.0 eV attributed to TiO₂ absorption, which subsequently yields a strong emission band at 600 nm. The electronic band structure and optical properties of the rutile phase of TiO₂ are calculated employing a fully relativistic, full-potential, linearized, augmented plane-wave (FPLAPW) method within the local density approximation (LDA). Comparison of this calculation with experimental data for TiO₂ films prepared for undoped sol-gels and by sputtering is performed.     

共轭低聚物中光生分子间电荷转移态的第一性原理研究

本文基于第一性原理中的Heyd-Scuseria-Ernzerh方法研究了单层In_1-xGa_xN的电子结构和光学性质.计算得到单层In_1-xGa_xN的能带结构和态密度（DOS）,发现随着掺杂比例的变化,体系带隙的变化范围是1.8~3.8 eV,表明通过Ga的掺杂可以实现体系带隙值的调节.并且还研究了单层In_1-xGa_xN的介电函数,折射率和吸收系数等光学性质,结果表明随着Ga掺杂浓度的增加,介电函数谱的主峰和吸收谱发生了显著的蓝移.此外,基于能带结构和态密度图谱,对单层In_1-xGa_xN的光学性质进行分析,预测这种材料独特的光学性质在纳米电子学和光学器件中会有广泛的应用.     

Mössbauer study of nano-TiO2 doped with Fe

A Mössbauer study of nano-TiO₂ doped with Fe is presented. The samples are prepared by sol-gel method, doping Fe by 5, 10 and 15 wt.%, respectively, which are measured with XRD, TEM and Raman spectra. Especially, Mössbauer spectra are emphasized in this study. The anatase phase is major in both doped and no-doped sample. The α-Fe₂O₃ phase is also in the doped samples. The grain size of doped sample is in 5–20 nm range, the major grains are about 13 nm. And the grain size of no-doped sample is about 8 nm. Studying Mössbauer spectra and Raman spectra, we concluded that in the doping process the Fe³⁺ ions entered anatase lattice and substituted Ti⁴⁺ ions. However, the amount of Fe ions in the site is limited to about 1.5 wt.%. It does not increase as the doping Fe increase. The more Fe doped, the more α-Fe₂O₃ formed. For comparing conveniently, it also can be described as (Ti_0.98Fe_0.02)O₂ by atomic percent.     

First-principles study on anatase TiO2 codoped with nitrogen and praseodymium

The crystal structures, electronic structures and optical properties of nitrogen or/and praseodymium doped anatase TiO₂ were calculated by first principles with the plane-wave ultrasoft pseudopotential method based on density functional theory. Highly efficient visible-light-induced nitrogen or/and praseodymium doped anatase TiO₂ nanocrystal photocatalyst were synthesized by a microwave chemical method. The calculated results show that the photocatalytic activity of TiO₂ can be enhanced by N doping or Pr doping, and can be further enhanced by N+Pr codoping. The band gap change of the codoping TiO₂ is more obvious than that of the single ion doping, which results in the red shift of the optical absorption edges. The results are of great significance for the understanding and further development of visible-light response high activity modified TiO₂ photocatalyst. The photocatalytic activity of the samples for methyl blue degradation was investigated under the irradiation of fluorescent light. The experimental results show that the codoping TiO₂ photocatalytic activity is obviously higher than that of the single ion doping. The experimental results accord with the calculated results.     

EFFECT OF ZnFe22O4 DOPING ON THE OPTICAL PROPERTIES OF TiO2 THIN FILMS

Amorphous TiO₂ thin films and ZnFe₂O₄ doped TiO₂ composite films were deposited by radio frequency magnetron sputtering. The effect of ZnFe₂O₄ doping on the optical properties of TiO₂ thin films was reported. Our results show that the absorption edge of TiO₂ thin films and composite films exhibits a blue shift with decreasing annealing temperature. The absorption edge of composite films has moved to visible spectrum range, and a very large red shift occurs in comparison with TiO₂ thin film. An enhanced photoluminescence in ZnFe₂O₄ doped anatase TiO₂ thin film at room temperature.     

Tunable growth of (GaxIn1−x)2O3 nanowires by water vapor

The tunable growth of In-doped Ga₂O₃ (Ga₂O₃:In) and Ga-doped In₂O₃ (In₂O₃:Ga) nanowires (NWs) on Au-coated Si substrates was achieved by modulating the amount of water vapor in flowing Ar at 700–750 °C via carbothermal reduction of Ga₂O₃/In₂O₃ powders with a fixed weight ratio. In Ar, only the Ga₂O₃:In NWs were grown, while in wet Ar the In₂O₃:Ga NWs were synthesized instead. The Ga concentration in In₂O₃ NWs decreased with the increment of water vapor in flowing Ar. The growth of both Ga₂O₃:In and In₂O₃:Ga NWs followed the vapor–liquid–solid process. The In and Ga doping induced a redshift and a blueshift in the optical bandgaps of Ga₂O₃ NWs and In₂O₃ NWs, respectively. The growth mechanisms and optical properties of Ga₂O₃:In and In₂O₃:Ga NWs were discussed.     

Optical characterization of sol gel TiO<Subscript>2</Subscript> monoliths doped with Brilliant Green

Amorphous titanium dioxide monoliths doped with brilliant green (BG) were synthesized by the sol-gel process. The optical properties of the monoliths were characterized by Photoacoustic Spectroscopy and Photoluminescence Spectroscopy. The absorption spectra for the BG-doped TiO₂ monoliths exhibited two well defined absorption regions: a band below 400 nm corresponding to TiO₂ absorption and three absorption bands centered at 424 nm, 588 nm, and 632 nm due to brilliant green. While the undoped TiO₂ monoliths showed no luminescence, the doped samples showed a strong luminescence band at 673 nm, which increased its intensity for increasing organic dye doping.     

Influence of tungsten doping concentration on the electronic and optical properties of anatase TiO2

The structural, electronic and optical properties of tungsten-doped TiO₂ have been investigated using density functional theory with plane wave basis sets and ultrasoft pseuodopotential. Substitutional W doping at Ti sites create W 5d states just below the conduction band minimum while interstitial W doping gives isolated W 5d states in the middle of forbidden region. Averaged bond lengths show that W doping at Ti sites produce minimum structural distortion as compared to the interstitial W-doped TiO₂. Substitutional W-doped TiO₂ has better visible light absorption compared to interstitial W-doped TiO₂ and has stable configuration which provide reasonable explanation for the experimental findings. Tungsten doping in TiO₂ with different doping concentrations is investigated as an enabling concept for enhancing the visible light absorption. Optical properties show that optimal W doping concentration would improve the visible light absorption. 2.08% W doping concentration gives strong visible and ultraviolet light absorption among all doped models found consistent with experiments.