Mn-doped ZnO nanocrystals are synthesized by a wet chemical route and treated in H2/Ar atmosphere with different H2/Ar ratios. It is found that hydrogen annealing could change the coordination environment of Mn in ZnO lattice and manipulate the magnetic properties of Mn-doped ZnO. Mn ions initially enter into interstitial sites and a Mn3＋ 06 octahedral coordination is produced in the prepared Mn-doped ZnO sample, in which the nearest neighbor Mn3＋ and 02 ions could form a Mn3＋-O2--Mn3＋ complex. After H2 annealing, interstitial Mn ions can substitute for Zn to generate the Mn2＋O4 tetrahedral coordination in the nanocrystals, in which neighboring Mn2＋ ions and H atoms could form a Mn2＋-O2--Mn2＋ complex and Mn-H-Mn bridge structure. The magnetic measurement of the as-prepared sample shows room temperature paramagnetic behavior due to the Mn3＋-O2--Mn3＋ complex, while the annealed samples exhibit their ferromagnetism, which originates from the Mn-H-Mn bridge structure and the Mn-Mn exchange interaction in the Mn2＋-O2--Mn2＋ complex.
Zn1-xMnxO （x = 0.0005, 0.001, 0.005, 0.01, 0.02） nanocrystals are synthesized by using a wet chemical process. The coordination environment of Mn is characterized by X-ray photoelectron spectroscopy, Raman spectroscopy, and its X-ray absorption fine structure. It is found that the solubility of substitutional Mn in a ZnO lattice is very low, which is less than 0.4%. Mn ions first dissolve into the substitutional sites in the ZnO lattice, thereby forming Mn2＋O4 tetrahedral coordination when x ≤ 0.001, then entering into the interstitial sites and forming Mn3＋O6 octahedral coordination when x ≥ 0.005. All the samples exhibit paramagnetic behaviors at room temperature, and antiferromagnetic coupling can be observed below 100 K.
In recent years, some important research indicated that the visible-light activity of photocatalysts could be enhanced via incorporating p-block non-metal elements into the lattice. In this paper, we investigated the electronic structures of pure and different non-metal （C, N, S, F, Cl, and Br） doped α-Bi2O3 using first-principles calculations based on the density functional theory. The band structures, the electronic densities of states, and the effective masses of electrons and holes for doped α-Bi2O3 were obtained and analyzed. The N and S dopings narrowed the band gap and reduced the effective mass of the carriers, which are beneficial for the photocatalytic performance. The theoretical predication was further confirmed by the experimental results.
The metastable γ-Bi2O3 photocatalysts with different morphologies were fabricated by means of a chemical precipitation method. The microstructure of as-prepared samples was characterized by X-ray diffraction, transmission electron microscopy and ultraviolet-visible diffusion reflectance spectroscopy. The photocatalytic performance of Bi2O3 powder was evaluated using rhodamine B as a model pollutant under visible light irradiation. The visible light photocatalytic activity of Bi2O3 with different morphologies is as follows, nanorod 〉 nanorod/nanoflake 〉 N doped TiO2 〉 irregular particle 〉 agglomerated particle. The γ-Bi2O3 shows the best photocatalytic performance and it can effectively degrade 97% RhB within 60 min.
Weichang HaoYuan GaoXi JingWen ZouYan ChenTianmin Wang
Photocatalysis has not only invigorated the field of energy conversion materials,but also is leading to bright prospects for application in the environmental purification field[1].Akira Fujishima and Kenichi Honda[2]first reported photocatalytic water splitting on a Ti O2semiconductor electrode under ultraviolet(UV)light in1972.In semiconductor photocatalysts,electrons are excited from valence band maximum(VBM)to conduction band
Heterovalent doping represents an effective method to control the optical and electronic properties of semiconductor nanocrystals(NCs), such as the luminescence and electronic impurities(p-, n-type doping). Considering the phase structure diversity, coordination varieties of Cu atoms in Cu2 S NCs, and complexity of Cu doping in II-VI NCs, monodisperse Cu2 S NCs with pure hexagonal phase were synthesized firstly. Then through cation exchange reaction between Cd ions and well-defined Cu2 S NCs, dominant Cu(I) doped CdS NCs were produced successfully. The substitutional Cu(I) dopants with controllable concentrations were confirmed by local atom-specific fine structure from X-ray absorption near edge structure(XANES), extended X-ray absorption fine structure(EXAFS) spectroscopy, elemental analysis characterizations from X-ray photoelectron spectroscopy(XPS) and the electron spin resonance(ESR) measurement. The dominant and strong Cu(I) dopant fluorescence was verified by their absorption and photoluminescence(PL) spectra, and PL lifetime. Finally, the band positions and the p-type conductivities of the as-prepared Cu2 S and Cu(I) doped CdS NCs were identified by ultraviolet photoelectron spectroscopy(UPS) measurements. The high monodispersity of NCs enables their strong film-scale self-assembly and will hasten their subsequent applications in devices.
Bismuth-based compounds have been regarded as an important class of visible-light photocatalysts due to their special electronic structures. In this paper, iodide ions are introduced to modify bismuth-based compound, Bi（24）O（31）Br（10）, forming a Bi（24）O（31）Br（10）/BiOI heterojunction structure. A significant enhancement of photocatalytic activity compared to the parent compounds is observed in de-coloration of rhodamine B（Rh.B） solution. The improved photocatalytic property of Bi（24）O（31）Br（10）/BiOI heterojunction is ascribed to the unique electronic structure consisting of complementary band structures of BiOI and Bi（24）O（31）Br（10）.Iodide ions are regarded as an effective reagent to construct bismuth-based photocatalytic heterojunctions with improved photocatalytic activity.
Xi LouJun ShangLiang WangHaifeng FengWeichang HaoTianmin WangYi Du
We demonstrate a simple and fast post-deposition treatment with high process compatibility on the hole transport material（HTM） Spiro-MeOTAD in vapor-assisted solution processed methylammonium lead triiodide（CH3NH3PbI3）-based solar cells. The prepared Co-doped p-type Spiro-MeOTAD films are treated by O3 at room temperature for 5 min,10 min, and 20 min, respectively, prior to the deposition of the metal electrodes. Compared with the traditional oxidation of Spiro-MeOTAD films overnight in dry air, our fast O3 treatment of HTM at room temperature only needs just 10 min,and a relative 40.3% increment in the power conversion efficiency is observed with respect to the result of without-treated perovskite solar cells. This improvement of efficiency is mainly attributed to the obvious increase of the fill factor and short-circuit current density, despite a slight decrease in the open-circuit voltage. Ultraviolet photoelectron spectroscopy（UPS） and Hall effect measurement method are employed in our study to determine the changes of properties after O3 treatment in HTM. It is found that after the HTM is exposed to O3, its p-type doping level is enhanced. The enhancement of conductivity and Hall mobility of the film, resulting from the improvement in p-doping level of HTM, leads to better performances of perovskite solar cells. Best power conversion efficiencies（PCEs） of 13.05% and 16.39% are achieved with most properly optimized HTM via CH3NH3I vapor-assisted method and traditional single-step method respectively.
