Zinc sulfide is a superior photocatalyst for H 2 evolution, whereas the wide bandgap restricts its performance to only UV region. In this work, zinc vacancy (V Zn ) defects are successfully introduced into ZnS via adding sodium sulfide as sulfur source during the hydrothermal reaction. The defective ZnS with different amount of zinc vacancies were employed as catalysts for the examination of vacancy-dependent catalytic activity toward photocatalytic hydrogen evolution under visible light irradiation. Fluorescence emission spectra and XPS results confirm that existence of abundant zinc vacancies on ZnS. These zinc vacancies exhibit remarkable effects on modifying the electronic structure of ZnS as shown in UV–visible absorption spectra and Mott–Schottky plots. Zinc vacancies can raise valence band (VB) position that weaken the oxidative capacity of the holes to protect Zn-deficient ZnS from photocorrsion. And electrochemical and photo-electrochemical experiments also demonstrate that the charge separation and the electrons transfer are more efficient with the introduction of the Zn vacancies in ZnS. The zinc-deficient ZnS-2.5 with optimum amount of Zn vacancies shows superior photocatalytic activity for H 2 evolution that reaches 337.71 ± 3.72 μmol h −1  g −1 under visible-light irradiation and also exhibits a much higher photostability. The intrinsic modify by self-defects might be a potential strategy for design novel photocatalysts with photocorrosion stability and visible-light activity in photocatalysis proton reduction.

Zinc vacancy-promoted photocatalytic activity and photostability of ZnS for efficient visible-light-driven hydrogen evolution

First‐principles electronic structure calculations on wurtzite AlN, GaN, and InN reveal crystal‐field splitting parameters ΔCF of −217, 42, and 41 meV, respectively, and spin–orbit splitting parameters Δ0 of 19, 13, and 1 meV, respectively. In the zinc blende structure ΔCF≡0 and Δ0 are 19, 15, and 6 meV, respectively. The unstrained AlN/GaN, GaN/InN, and AlN/InN valence band offsets for the wurtzite (zinc blende) materials are 0.81 (0.84), 0.48 (0.26), and 1.25 (1.04) eV, respectively. The trends in these spectroscopic quantities are discussed and recent experimental findings are analyzed in light of these predictions.

Valence band splittings and band offsets of AlN, GaN and InN.

Copper zinc tin sulfide (Cu2ZnSnS4 or CZTS) is a potential candidate for next generation thin film solar cells because it contains abundant and nontoxic elements and exhibits high light absorption. Thin films of CZTS are typically synthesized by sulfidizing a stack of zinc, copper, and tin films. In addition to CZTS, a variety of binary and ternary metal sulfides can form and distinguishing among phases with similar crystal structure can be difficult. Herein, the authors show that confocal Raman spectroscopy and imaging can distinguish between CZTS and the other binary and ternary sulfides. Specifically, Raman spectroscopy was used to detect and distinguish between CZTS (338 cm−1), Cu2SnS3 (298 cm−1), and Cu4SnS4 (318 cm−1) phases through their characteristic scattering peaks. Confocal Raman spectroscopy was then used to image the distribution of coexisting phases and is demonstrated to be a useful tool for examining the heterogeneity of CZTS films. The authors show that, during sulfidation of a zinc/copp...

Imaging and phase identification of Cu2ZnSnS4 thin films using confocal Raman spectroscopy

We have conducted an experimental and theoretical study on first- and second-order Raman scattering of zinc blende and wurtzite ZnS. Based on the calculated phonon band structure, phonon density of states, and symmetry selection rules, we have clearly identified for the first time the origins of these vibration modes in the second-order Raman spectra from these two polymorphs. For zinc blende ZnS, it is found that the previously estimated frequency of the LA mode at X point in the Brillouin-zone boundary is much smaller than the value obtained from other experiments and our calculation. Considering the involvement of LA phonon at X point, we reassign the second-order Raman active modes and some other modes which have not yet been understood so far. This work clarifies some of the controversial Raman mode assignments in zinc blende and wurtzite ZnS.

Raman scattering study of zinc blende and wurtzite ZnS

Density functional theory can be used to interpret and predict spectroscopic properties of solid-state materials. The relevant computational solutions are usually available in disparate DFT codes, so that it is difficult to use a consistent approach for analyzing various spectroscopic features of a given material. We review the latest developments that are aimed to provide a collection of analytical tools within one DFT package, CASTEP. The applications covered include core-level EELS, solid-state NMR, optical properties, IR and Raman spectroscopy. We present also results of the EELS analysis of NbO and Nb2O5 that show the first published example of CASTEP spectra from d-states. Raman activities calculated for a test set of small molecules and the convergence requirements for such calculations are discussed.

Electron and vibrational spectroscopies using DFT, plane waves and pseudopotentials: CASTEP implementation

The optical and vibrational properties of 2H-, 4H-, and 6H-AlN are studied based on the ab initio pseudopotential density functional theory. Three polymorphs have similar electronic and optical properties implying that 4H- and 6H-AlN are also of importance to optoelectronics. Infrared spectra of the three polymorphs show two main modes at 660 and 690 cm−1 and an additional mode at 570 cm−1 can only be observed from 4H- and 6H-AlN. The Raman spectra of 4H- and 6H-AlN show more active modes than that of 2H-AlN. These infrared and Raman features can be used as the fingerprints to distinguish the three polymorphs.

Optical and vibrational properties of 2H-, 4H-, and 6H-AlN: First-principle calculations

This work presents positive experimental evidence for the hole traps in ZnO nanorods, which take part in recombination and change the thermal quenching of Cu-related green emission. The evolution of Cu impurity upon annealing, as well as the formation of Cu-related shallow donors with an energy level of ∼0.11 eV are also indicated by temperature-dependent photoluminescence.

Hole traps and Cu-related shallow donors in ZnO nanorods revealed by temperature-dependent photoluminescence

The effect of annealing on the 3.31 eV (A line) emission in ZnO nanorods is studied in detail by temperature-dependent photoluminescence (PL). Annealing results in obvious changes in peak energy and lineshape of the A line, indicating different luminescence origin in the as-grown and annealed ZnO nanorods. In the as-grown nanorods, the A line is a result of competition between free-to-neutral acceptor (FA) transition and the first longitude optical phonon replica of free exciton (FX-1LO) recombination. While for the annealed nanorods, FA transition disappears and the A line is attributed to FX-1LO only. In combination with trace impurity analysis, the results allow us to conclude that the acceptor involved in the FA transition is stacking faults rather than unintentional acceptor impurities.

Annealing-induced changes of the 3.31 eV emission in ZnO nanorods

Unusual vibronic fine structures of the ~3.0 eV violet emission from ion-implanted ZnO nanorods have been investigated by photoluminescence (PL). A set of equally separated peaks with energy spacing of 72 meV, which corresponds to the longitudinal optical (LO) phonon energy of ZnO, were well resolved in the low-temperature PL spectra. The overall emission band can be perfectly described on the basis of the LO phonon-assisted transition with the Huang–Rhys factor of 1.98, indicating intermediate electron-phonon coupling. The thermal quenching of PL gives rise to an activation energy of ~160 meV, which is attributed to the energy level of acceptor-like defects introduced by implantation.

https://iopscience.iop.org/article/10.1143/APEX.5.112102/pdf

Shuili Li

Papers

Raman scattering study of zinc blende and wurtzite ZnS

Optical and vibrational properties of 2H-, 4H-, and 6H-AlN: First-principle calculations

Hole traps and Cu-related shallow donors in ZnO nanorods revealed by temperature-dependent photoluminescence

Annealing-induced changes of the 3.31 eV emission in ZnO nanorods

Vibronic Fine Structures on the ∼3.0 eV Violet Emission in Ion-Implanted ZnO Nanorods