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The electronic structures and optical properties of pure, Cr, S single- and Cr/S co-doped rutile TiO2 were calculated by the first-principle plane wave pseudopotential method based on density functional theory. The calculated results indicate that the three different doping ways can lead to lattice distortion in the rutile TiO2 and introduce local electronic states in the forbidden band of TiO2. The local energy levels in the forbidden band of TiO2 are mainly contributed by Cr-3d and S-3p orbital. Compared with pure TiO2, the absorption edges (i.e. the edge of the main peak) of the doped TiO2 have different blue shifts; however, the light response ranges of the doped systems are extended, especially in the case of Cr single- and Cr/S co-doped TiO2. The extension of the visible light response range of the doped TiO2 may enhance its visible light photocatalytic performance. In addition, the co-doped TiO2 has a stronger oxidation ability, which may increase the catalytic efficiency of TiO2.

An electrochemical metallization memristor based on Zr0.5Hf0.5O2 film and an active Cu electrode with quantum conductance and neuromorphic behavior has been reported in this work. After electroforming in the Cu/Zr0.5Hf0.5O2/Pt device, linear conductance characteristics in low resistance states were found and the stepwise changes of conductance with the order of G0 ((=2e2)/h) multilevel states were obtained by varying pulse amplitude, width and adjacent-pulse time interval, which is beneficial for backpropagation learning algorithms belonging to deep neural networks, essentially using memristors as vector–matrix multiplication accelerators in image processing. The gradual resistance tuning served as the basis of memory and learning. Under the coactivity of pre- and post-synaptic spikes, bidirectional long-term Hebbian plasticity modulation was realized. The temporal difference, spike rate and size of the top and bottom electrode pulse voltage can strongly affect the sign and degree of Hebbian plasticity. Moreover, the quantum conductance phenomenon was ascribed to interstitial Cu in the dielectric layer forming single- and multi-atom chains. The results can provide multilevel storage and next-generation parallel neuromorphic computing architecture, promoting the development of functional plastic electronic synapses.

Upon 300 nm excitation, monoclinic Lu2–xYbxWO6 (0 ≤ x ≤ 0.3) phosphors displayed concentration-dependent visible (vis) and near-infrared (NIR) luminescence with the strongest peak centers at about 450 and 970 nm. Rietveld refinement indicated that Yb occupancy numbers in three Lu sites depended closely on the impurity concentration. The scanning electron microscopy and transmission electron microscopy characterizations showed that all of the samples were aggregates of particles with different shapes and sizes. Through hybridized density functional theory calculation, this NIR emission was proposed to originate from electron transition in three unoccupied spin down 4f state of Yb3+ with different energy positions in the forbidden band. Energy transfer from WO66– to Yb3+ was only a single-step transfer process according to a lifetime spectra and theoretical result. Therefore, Lu2–xYbxWO6 can be used as light–light conversion layer in solar cell, and the first-principles calculation successfully explained th...

Through ground state and constrained density function calculations, Sm3+ ions luminescence in self-activated monoclinic Lu2WO6 was originated from intra 4f → 4f transitions, not inter 5d → 4f transitions. Theoretically the white luminescence was obtained by combining red and blue-green emissions of 4f energy levels and W–O charge transfer transitions. Experimentally, pure and Sm3+ doping Lu2WO6 powders were synthesized using solid phase reaction calcined in air atmosphere. By the analysis of X-ray photoelectron spectroscopy and Rietveld refinement, element Sm charge state was trivalent, and Sm3+ doping was concentration-dependent selectively doping in three Lu sites. With the increase of Sm3+ concentrations, the color coordinates changed gradually from blue (0.17, 0.17) through white light (0.33, 0.25) toward orange (0.44, 0.32) in the visible spectral under 325 nm excitation. On the basis of the theoretical prediction and experimental preparation, a white emission LED lamp was produced using a 365 nm ult...

Previous studies have shown that hydrogen treatment leads to the formation of blue to black TiO_2, which exhibits photocatalytic activity different from that of white pristine TiO_2. However, the underlying mechanism remains poorly understood. Herein, density functional theory is combined with comprehensive analytical approaches such as X-ray absorption near edge structure spectroscopy and transient absorption spectroscopy to gain fundamental understanding of the correlation among the oxygen vacancy, electronic band structure, charge separation, charge carrier lifetime, reactive oxygen species (ROS) generation, and photocatalytic activity. The present work reveals that hydrogen treatment results in chemical reduction of TiO_2, inducing surface and subsurface oxygen vacancies, which create shallow and deep sub-band gap Ti(III) states below the conduction band. This leads to a blue color but limited enhancement of visible light photocatalytic activity up to 440 nm at the cost of reduced ultraviolet photocatalytic activity. The extended light absorption spectral range for reduced TiO_2 is ascribed to both the defect-to-conduction band transitions and the valence band-to-defect transitions. The photogenerated charge carriers from the defect states to the conduction band have lifetimes too short to drive photocatalysis. The Ti(III) deep and shallow trap states below the conduction band are also found to reduce the lifetime of photogenerated charge carriers under ultraviolet light irradiation. The ROS generated by the reduced TiO_2 are less than those generated by pristine TiO_2. Consequently, the reduced TiO_2 exhibits ultraviolet-responsive photocatalytic activity worse than that of pristine TiO_2. This report shows that increasing the light absorption spectral range of a semiconductor by doping or introduction of defects does not necessarily guarantee an increase in photocatalytic activity.

A photocatalyst which consists of zero-dimension (0D) ZnFe2O4 (ZFO) and two-dimension (2D) Fe-doped g-C3N4 (Fe-CN) has been prepared successfully through a facile solvothermal method. The Fe doping into g-C3N4 lattice has been identified by both the infrared (IR) and X-ray photoelectron spectra (XPS), respectively. Introducing Fe into CN extends the spectral response to 700 nm while ZFO serves as a near infrared (NIR) photosensitizer of the Fe-CN component. The formation of Fe-CN heterostructure not only contributes to visible light absorption but also promotes the separation of photo-generated electron-hole pairs. Furthermore, the density functional theory (DFT) calculation indicated that the N2 molecules prefer to be adsorbed onto the Fe sites with a reduced potential barrier for N2 fixation. More importantly, the Fe atoms doped into the CN lattice acted as the reaction sites for accelerating photocatalytic N2 fixation reaction, which was also demonstrated by DFT. These factors lead to a high photocatalytic NH4+ generation rate of 25.3 mg g−1 h−1 under a full-spectrum irradiation, which is much higher than the value (4.4 mg g−1 h−1) of pure CN catalysts. This research might provide a novel approach for rationally designing full-spectrum-response N2 fixation photocatalyst.

Heterojunction composite plays an important role in enhancing photocatalysis activity through inhibit electron-hole recombination. In this paper, biphasic heterojunction BiVO4 and HoVO4 is insitu-grown and characterized through XRD, TEM, Raman, SEM, EDS, and XPS. These two structures form n type staggered band configuration using Mott-Schottky and DRS. Rhodamine B (RhB) photodegradation efficiency of the optimal sample is 90.7% after 90 min, higher than single BiVO4 54% and HoVO4 34.5%. The main reason is ascribed to fast photogenerated charge separation via O O bond connection according to photoluminescence, photocurrent response, and theory calculation. The RhB degradation path is revealed from intermediate products identification. Therefore this study unveils photodegradation dyes application of BiVO4/HoVO4 samples.

In this study, a simple TiN/SiO2/p-Si tunneling junction structure was fabricated via thermal oxidation growth on a Si substrate annealed at 600 °C. After electroforming, the number of cycle times for the SiO2-based tunneling junction device can reach an order of magnitude of greater than 105. The resistances at low and high resistance states and the threshold voltage of the device fluctuated in a very narrow range. More interestingly, excitatory and inhibitory postsynaptic current phenomena (EPSC and IPSC) were observed during the pulse mode measurements, indicating that the device can be used in biological synapse applications. At different measurement temperatures and electric fields, direct, Fowler–Nordheim, and trap-assisted tunneling were responsible for the intrinsic conductance mechanism of the device before and after electroforming. This study provides a convenient approach to prepare simple tunneling junction structures for resistive random access memory applications with superior properties.

Molecular orbital theory predicts that interactions between lone-pair electrons give rise to van der Waals forces between layers due to the nonequivalent hybridization in bulk black phosphorus. First-principles calculations show that phosphorene nanoribbons (PNRs) have a high activity and can be bonded easily with oxygen atoms and hydroxyl groups, indicating that the PNRs can be oxidized easily. The cliff PNR configuration can be maintained when it is passivated with hydroxyl groups, indicating that it could be stable in a strong alkaline environment. Upon oxidation of their zigzag, armchair, and cliff edges, phosphorene nanoribbons can be changed from semimetallic to semiconducting, and the band gap can be changed from direct to indirect. OHO- [(OH + O)-] and OH- [(O + H)-] passivated PNRs have intrinsic spin magnetic moments of approximately 2.00 μB, which originate from the edge unsaturation electrons and the symmetry reduction. Therefore, oxidized PNRs might have potential applications in photoelectro...

Since the establishment of the well-known Kohn‒Sham equation on the basis of the density functional theory (DFT), the DFT has been the most powerful tool of electronic-structure calculation in the field of condensed-matter physics. In luminous research regions, the DFT calculation finds wide application in revealing the luminescence mechanism and designing luminous materials. In this chapter, we first introduce the first-principles calculation foundation theory, related software, and the luminescence physics processes. Then various materials properties obtained using DFT are reviewed. Application of the first-principles calculation in exploring the intrinsic, native defect and dopant, as well as the doping-induced defect of photoluminescence origin, is illustrated by providing several examples. In addition, the excited-state calculation and band-gap correction approaches are presented. The calculation method and computation procedures must be improved and optimized in the future to make first-principles calculation play a more important role in luminescence-materials investigation.

In this work, graphene oxide quantum dots (GOQDs) are introduced as an electron-trapped layer in Pd/Zr[Formula: see text]Hf[Formula: see text]O2 (ZHO)/SiO2/Si memory device. This structure possessed longer than 104 s retention capability, a low operation voltage around [Formula: see text][Formula: see text]V and 2.61[Formula: see text]V storage windows. GOQDs contained carbon–carbon and carbon–oxygen single/double bonds based on the analysis of C-1[Formula: see text] and O-1[Formula: see text] X-ray photoelectron spectra. It is proposed that the GOQDs’ wide bandgap with many oxygen-containing functional groups favors charge capture to a greater extent. This new type of charge-trapping memory can be a promising candidate for wide application to storing information with non-volatility in the big data era.

In this study, we present a metal/Ba0.6Sr0.4TiO3/SiO2/Si (MBOS) structure for charge trapping memory, where the single Ba0.6Sr0.4TiO3 film acts as the blocking layer and charge trapping layer. This MBOS device structure demonstrates excellent charge trapping characteristics, a large memory window up to 8.4 V under an applied voltage of ±12 V, robust charge retention of only 4% charge loss after 1.08 × 104 s, fast switching rate, and great program/erase endurance. These attractive features are attributed to the high density of defect states in the Ba0.6Sr0.4TiO3 film and its inter-diffusion interface with SiO2. The properties of defect states in the Ba0.6Sr0.4TiO3 film are investigated through measurements of photoluminescence and photoluminescence excitation spectroscopy. The energy levels of these defect states are found to be distributed between 2.66 eV and 4.05 eV above the valence band. The inter-diffusion at the Ba0.6Sr0.4TiO3/SiO2 interface is observed by high-resolution transmission electron micros...