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van der Waals heterostructures combining perovskites of strong light absorption with atomically thin two-dimensional (2D) transition-metal dichalcogenides (TMDs) hold great potential for light-harvesting and optoelectronic applications. However, current research studies integrating TMDs with low-dimensional perovskite nanomaterials generally suffer from poor carrier/energy transport and harnessing, stemming from poor interfacial interaction due to the nanostructured nature and ligands on surface/interface. To overcome the limitations, here, we report prototypical three-dimensional (3D)/2D perovskite/TMD heterostructures by combing highly smooth and ligand-free CsPbBr3 film with a WSe2 monolayer. We show that the energy transfer at interface occurs through asymmetric two-step charge-transfer process, with ultrafast hole transfer in ∼200 fs and subsequent electron transfer in ∼10 ps, driven by the asymmetric type I band alignment. The energy migration and transfer from CsPbBr3 film to WSe2 can be well described by a one-dimensional diffusion model with a carrier diffusion length of ∼500 nm in CsPbBr3 film. Thanks to the long-range carrier migration and ultrafast interfacial transfer, highly efficient (>90%) energy transfer to WSe2 can be achieved with CsPbBr3 film as thick as ∼180 nm, which can capture most of the light above its band gap. The efficient light and energy harvesting in perovskite/TMD 3D/2D heterostructures suggest great promise in optoelectronic and photonic devices.

Two-dimensional silicon-based materials have unique physical and chemical properties due to high surface area and quantum confinement effects. Herein, a topochemical reaction method is used for preparing silicene quantum dots confined in few layer siloxene nanosheets with FeCl3·6H2O as oxidant, which shows a thickness less than 2 nm. The experimentally prepared siloxene nanosheets are dispersible, with silicene quantum dots having an average diameter less than 5 nm. The silicene quantum dots are self-organized through the oxidation of FeCl3, showing unique optical properties of blue emission. The UV–visible absorption and PL emission spectra indicate the quasi-direct band gap transition to the emission. Besides, the few-layer siloxene nanosheets with silicene quantum dots have a radiative lifetime of 1.098 ns at an emission wavelength of 435 nm, which derives from the quasi-direct band transition of silicene quantum dots. Such two-dimensional nanosheets of silicon possess potential applications for the em...

Vacuum vapor deposition (VVD) is a promising way to advancing the commercialization of perovskite light sources owing to its convenience for wafer-scale mass production and compatibility with silicon photonics manufacturing infrastructure. However, the light emission performance of VVD-grown perovskites still lags far behind that of the conventional solution-processed counterparts due to their inferior luminescence properties. Here, a 0D/3D cesium-lead-bromide perovskite composite film is prepared on Si/SiO

Solution-processed all-inorganic CsPbX3 perovskites exhibit outstanding optoelectronic properties and are being considered as a promising optical gain medium, with impressive performance in the green and red region. However, the development of CsPbX3 for blue emission is still lagging far behind, owing to difficulties in thin films synthesis and spectral instability subject to light irradiation. Here, a facile vapor anion exchange (VAE) method that enables preparation of blue-emitting perovskite films with both excellent surface morphology and good photo-stability is reported. The mixed-Br/Cl quasi-2D perovskite films show spectrally stable pure blue emission (471 nm) under continuous-wave laser irradiation with power density as high as 81 W cm-2 . Furthermore, optically pumped blue amplified spontaneous emission (ASE) is realized based on the mixed-Br/Cl perovskite films. By changing the duration of VAE treatment, the ASE peak can be tuned from 537 nm down to 475 nm. This work not only presents a facile method to prepare high quality mixed halide Cs-based perovskite films, but also pave the way for further exploration of stable blue perovskite lasing.

Colloidal all-inorganic perovskite CsPbBr3 nanocrystals present versatile outstanding optoelectronic properties as well as greatly improved stability when compared with their hybrid analogues. Howe...

A simple and efficient method to grow continuous large-area ZnO/MoS2 heterostructures is demonstrated by pulsed laser deposition. The layer number of MoS2 films is controlled by the number of laser pulses. The MoS2 film acts as a closely lattice-matched buffer layer for the subsequent ZnO growth, which improves the structural and optical quality of the ZnO film. ZnO film and multilayer MoS2 forms a type-II heterostructure, and the band offsets between them are quantitatively determined.

ZnO is one of the most important functional materials with a wide direct band gap, large exciton binding energy, and facile growth of high quality nanostructures, which make it very promising for various optoelectronic applications, especially in light-emitting diodes, piezotronics and nanoelectronics. However, ZnO suffers from the doping asymmetry problem, and p-type doping is not stable, which is major hurdle for its application in optoelectronics. Co-doping, which is defined as doping acceptor with other impurities simultaneously, was proposed and attempted to address the p-type doping problem by enhancing the solubility and reducing the ionization energy of acceptor dopants. During the past two decades, extensive studies on co-doping have shown positive effects on improving the p-type conductivity of ZnO. The success was made mainly in ZnO films and nanowires. In this article, we provide an overview of the experimental efforts for growing p-type ZnO nanocrystalline films by the co-doping method, which are mainly classified as acceptor-donor co-doping, dual-acceptor co-doping, acceptor-hydrogen co-doping, and acceptor-isovalence co-doping. In addition, a few works on co-doped p-type ZnO nanowires are also summarized. Finally, we discuss the remaining problems of p-type ZnO by co-doping.

A facile and scalable in situ microelectrolysis nanofabrication technique is developed for preparing cross-linked Ni(OH)2 nanosheets on a novel three-dimensional porous nickel template (Ni(OH)2@3DPN). For the constructed template, the porogen of NaCl particles not only induces a self-limiting surficial hot corrosion to claim the “start engine stop” mechanism but also serves as the primary battery electrolyte to greatly accelerate the growth of Ni(OH)2. As far as we know, the microelectrolysis nanofabrication is superior to the other reported Ni(OH)2 synthesis methods due to the mild condition (60 °C, 6 h, NaCl solution, ambient environment) and without any post-treatment. The integrated Ni(OH)2@3DPN electrode with a highly suitable microstructure and a porous architecture implies a potential application in electrochemistry. As a proof-of-concept demonstration, the electrode was employed for nonenzymatic glucose sensing, which exhibits an outstanding sensitivity of 2761.6 μA mM–1 cm–2 ranging from 0.46 to ...

We report a facile solution-based approach to the in situ growth of perovskite films consisting of monolayers of CsPbBr3 nanoplates passivated by bulky phenylbutylammonium (PBA) cations, that is, two-dimensional layered PBA2(CsPbBr3)n−1PbBr4 perovskites. Optimizing film formation processes leads to layered perovskites with controlled n values in the range of 12–16. The layered perovskite emitters show quantum-confined band gap energies with a narrow distribution, suggesting the formation of thickness-controlled quantum-well (TCQW) structures. The TCQW CsPbBr3 films exhibit smooth surface features, narrow emission line widths, low trap densities, and high room-temperature photoluminance quantum yields, resulting in high-color-purity green light-emitting diodes (LEDs) with remarkably high external quantum efficiencies (EQEs) of up to 10.4%. The solution-based approach is extended to the preparation of TCQW CsPbI3 films for high-color-purity red perovskite LEDs with high EQEs of up to 7.3%.

Zinc vacancy (V Zn ) plays key roles in the optical and electrical properties of ZnO, but its behaviors are not fully understood. Here we report the formation and abnormal photoluminescence (PL) of V Zn -related complex in Zn + -implanted ZnO single crystals. With increasing excitation density, we observed a new and gradually increased broad emission around 550 nm. The 550 nm emission is unexpectedly invisible under low power level excitation, indicating the lower priority of recombination of the related defect centers. Electron paramagnetic resonance (EPR) results suggest the formation of V Zn -Zn i complex after implantation, which is responsible for the abnormal PL properties.

We report the formation of high-quality Cs0.4MA0.6PbBr3 thin films with nearly full surface coverage and good emission properties upon the introduction of Cs+ into perovskite crystals. The Cs0.4MA0.6PbBr3 thin films were applied as emissive layers in light-emitting diodes. A maximum external quantum efficiency of ~2.0% was achieved for these green-emitting devices.

We report a room-temperature colloidal synthesis of few-unit-cell-thick CsPbBr3 QWs with lengths over a hundred nanometers. The surfactant-directed oriented attachment growth mechanism was proposed to explain the formation of such CsPbBr3 QWs. Owing to the strong quantum confinement effect, the photoluminescence (PL) emission peak of few-unit-cell-thick CsPbBr3 QWs blue-shifted to 430 nm. The ensemble PL quantum yield (PLQY) of the few-unit-cell-thick CsPbBr3 QWs increased to 21.13% through a simple heat-treatment process. The improvement of PLQY was ascribed to the reduction of the density of surface trap states and defect states induced by the heat-treatment process. Notably, the dependence of the bandgap on the diameter with different numbers of unit cells was presented for the first time in 1-D CsPbBr3 QWs on the basis of the produced few-unit-cell-thick CsPbBr3 QWs.

Achieving a high internal quantum efficiency (IQE) of luminescence is critical to the optoelectronic applications but still a challenge for ZnO materials. In this work, we demonstrate that the IQE of bulk ZnO crystals can be greatly increased by Zn+ ion implantation and subsequent annealing. The implantation dose, energy, and annealing temperature are found to affect the IQE significantly. A highest IQE of 30.8% can be achieved when the ZnO crystal is implanted with dose of 1 × 1015cm−2 and rapidly annealed at 700 °C. The improving of IQE is interpreted as a combination result of suppressed formation of vacancy defects and enhanced exciton–phonon coupling.

Two-dimensional (2D) perovskites represent a class of promising nanostructures for optoelectronic applications owing to their giant oscillator strength transition of excitons and high luminescence. However, major challenges lie in the surface ligand engineering and ambient stability. Here, we show that air-stable quasi-2D CsPbBr3 nanoplatelets can be formed in the matrix of Cs4PbBr6 nanosheets by reducing the thickness of Cs4PbBr6 to ∼7.6 nm, the scale comparable to the exciton Bohr radius of CsPbBr3. The 2D behavior of excitons is evidenced by the linear increase of the radiative lifetime with increasing temperature. Moreover, the wide-bandgap Cs4PbBr6 plays roles of surface passivation and protection, which leads to good photoluminescence properties without the photobleaching effect and with ambient stability for over 1 month. Our work demonstrates a unique quasi-2D heterostructure of perovskite nanomaterials, which may either serve as a workbench for studying the exciton recombination dynamics or find application in high-performance optoelectronic devices.

ZnO/ZnMgO multiple quantum wells (MQWs) were grown on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy. Optical properties of the MQWs under high excitation were investigated by temperature- and excitation intensity-dependent photoluminescence spectroscopy. For weak confinement, increasing the excitation intensity leads to escape of excitons from the MQWs and appearance of ZnMgO barrier emission. While for better confinement, the ZnMgO barrier emission is almost independent on temperature and excitation intensity. The internal quantum efficiency of the MQWs increases monotonously with excitation intensity, reaching a highest value of 47% at room temperature, which suggests high quality of the MQWs.

In this paper, all-inorganic CsPbIBr2 thin films were annealed by a two-step temperature-control process. All-inorganic, hole-transporting-layer-free, carbon-based planar perovskite solar cells (PSCs) with these CsPbIBr2 thin films (FTO/c-TiO2/CsPbIBr2/C) were fabricated. The effect of different first-step annealing temperatures during the two-step temperature-control process (50 °C/280 °C, 80 °C/280 °C, 100 °C/280 °C, 150 °C/280 °C, 180 °C/280 °C) on the photovoltaic conversion efficiency (PCE) of PSCs was investigated for the first time. When the first-step annealing temperature was 150 °C and the second-step annealing temperature was 280 °C, the highest efficiency of 8.31% was obtained. Without encapsulation, the solar cell could retain 97% of the initial PCE, when it was stored at 80 °C and zero humidity for 8 days. For comparison, solar cells with CsPbIBr2 films annealed by a one-step temperature-control process were fabricated. The highest PCE was 4.98%. From this, we could see that there is an increase of 66.9% in PCE, through using a two-step temperature-control annealing process. And also, in order to investigate why the PSCs by a two-step temperature-control annealing process has a higher PCE, all kinds of measurements were done for the first time. According to the results of the measurements, the perovskite film annealed by a two-step temperature-control process has a bigger crystal size, fewer grain boundaries, stronger PL and UV–vis absorption intensities, longer lifetime of minority carriers, less energy loss for hole transporting.

All-inorganic lead halide perovskite quantum dots (CsPbBr3 QDs) are attracting significant research interests because of their highly efficient light-emitting performance combined with tunable emission wavelength facilely realized by ion exchange. However, blue emission from perovskite QDs with strong quantum confinement is rarely reported and suffers from lower luminescence efficiency. Here we report blue-emitting ultrasmall (∼3 nm) CsPbBr3 QDs with photoluminescence (PL) quantum yield as high as 68%. Using time-resolved and steady-state PL spectroscopy, we elucidate the mechanism of the highly efficient PL as recombination of excitons localized in radiative band tail states. Through analyzing the spectral-dependent PL lifetime and the PL line shape, we obtain a large band tail width of ∼80 meV and a high density of state of ∼1020 cm–3. The relaxation of photocarriers into the radiative tail states suppresses the capture by nonradiative centers. Our results provide solid evidence for the positive role of...

Cu-doped ZnO nano-films were synthesized by a hydrothermal method combined with post-annealing process. The mechanism for the formation of the nano-films can be explained by a Cu-adsorbed face-selective crystal growth inhibition mechanism. The 2 at.% Cu-doped sample behaved p-type conductivity, which can be verified by a p–n homojunction with well-defined rectifying characteristic. The origin of p-type conduction of the Cu-doped sample was studied by XPS and PL analyses. The Cu Zn +1 acceptor with the ionization energy of 326 meV should be the main reason for the p-type conductivity.

We have investigated metal-enhanced excitonic emission from ZnO/ZnMgO multiple quantum wells (MQWs) grown by molecular beam epitaxy. Capping of Al nanoparticles results in ~1.5-fold enhancement of photoluminescence (PL) at room temperature. Temperature-dependent PL analysis suggests that exciton dissociation acts as an additional non-radiative recombination channel when the MQWs are capped with metal. The non-radiative recombination rate is found to be larger than the radiative one by ~21-fold. This explains the relatively low enhancement ratio of PL although significant surface plasmon coupling is present.

A unique all-wurtzite ZnO/ZnSe hetero-nanohelix is formed via growing wurtzite ZnSe nanoteeth on ZnO nanobelts through a one step thermal evaporation method. The microstructure and growth mechanism of the hetero-nanohelix are investigated in detail. The formation of metastable wurtzite ZnSe is attributed to the wurtzite ZnO template. Mechanical forces, thermal expansion and polar plane in hexagonal crystals are suggested to contribute to the bending of the nanohelix. A boomerang-like structural block is proposed to assemble the zigzag ZnO nanobelts. The incorporation of Se into ZnO results in a strong orange emission. The heterostructure of the ZnO/ZnSe nanohelix is confirmed by elemental mapping and luminescence imaging. The fabrication of such a hetero-nanohelix may provide insights into the growth mechanism of the rich family of ZnO-based nanostructures.

We carry out photoluminescence (PL) study on Na-doped ZnO nanorods to provide insights into the behavior of Na acceptor. We demonstrate the successful growth of Na-doped ZnO nanorods array by metalorganic chemical vapor deposition. PL analysis reveals the very low concentration of deep level defects such as oxygen vacancy. Unlike most ZnO materials, the low temperature PL of Na-doped ZnO nanorods is dominated by excitons bound to ionized donors (D+X), suggesting the formation of Na acceptors and high compensation between the donors and acceptors. The formation of Na acceptors is supported by the shift of Fermi level toward the valence band.

In recent years, 2D layered organic–inorganic lead halide perovskites have attracted considerable attention due to the distinctive quantum confinement effects as well as prominent excitonic luminescence. Herein, we show that the recombination dynamics and photoluminescence (PL) of the 2D layered perovskites can be tuned by the organic cation length. 2D lead iodide perovskite crystals with increased length of the organic chains reveal blue-shifted PL as well as enhanced relative internal quantum efficiency. Furthermore, we provide experimental evidence that the formation of face-sharing [PbI6]4– octahedron in perovskites with long alkyls induces additional confinement for the excitons, leading to 1D-like recombination. As a result, the PL spectra show enhanced inhomogeneous broadening at low temperature. Our work provides physical understanding of the role of organic cation in the optical properties of 2D layered perovskites, and would benefit the improvement of luminescence efficiency of such materials.

Monolayer ZnO represents a class of new two-dimensional (2D) materials that are expected to exhibit unique optoelectronic properties and applications. Here we report a novel strategy to synthesize free-standing atomically thin ZnO layers via the oxidation of hydrothermally grown ultrathin zinc chalcogenide nanosheets. With micrometer-scaled lateral size, the obtained ultrathin ZnO layer has a thickness of ∼2 nm, and the layered structure still maintained well after high temperature oxidation. The thermal treatment strongly improves the crystal quality as well without inducing cracks or pinholes in the ultrathin layers. The atomically thin ZnO layers are highly luminescent with dominant green emission. High quality white light is obtained from the mixed phosphors containing the ZnO layers, exhibiting their potential as compelling ultraviolet-excited phosphors.

Fundamental to understanding and predicting the optoelectronic properties of semiconductors is the basic parameters of excitons such as oscillator strength and exciton binding energy. However, such knowledge of CsPbBr3 perovskite, a promising optoelectronic material, is still unexplored. Here we demonstrate that quasi-two-dimensional (quasi-2D) CsPbBr3 nanoplatelets (NPLs) with 2D exciton behaviors serve as an ideal system for the determination of these parameters. It is found that the oscillator strength of CsPbBr3 NPLs is up to 1.18 × 104, higher than that of colloidal II–VI NPLs and epitaxial quantum wells. Furthermore, the exciton binding energy is determined to be of ∼120 meV from either the optical absorption or the photoluminescence analysis, comparable to that reported in colloidal II–VI quantum wells. Our work provides physical understanding of the observed excellent optical properties of CsPbBr3 nanocrystals and would benefit the prediction of high-performance excitonic devices based on such mat...

Ion implantation was used to dope Na acceptor into ZnO single crystals. With three mixed implantation energies, uniform depth distribution of Na ion in the surface region (~300 nm) of ZnO bulk crystals is achieved. Via post-implantation annealing, a donor–acceptor pair recombination band is identified in the low-temperature photoluminescence spectra, from which the energy level of Na-related acceptor in single crystalline ZnO is estimated to be 300 meV. A p–n junction based on this ZnO–Na layer shows rectifying characteristics, confirming the p-type conductivity.

Micro-pattern of Ag nanoparticles and Ag film is inserted between ZnCdO film and the substrate to enhance the photoluminescence (PL) of ZnCdO films, achieving enhancement ratio of 21.2 and 7.1, respectively. Time-resolved photoluminescence shows that the PL lifetime of Ag/ZnCdO films is longer than that of bare ZnCdO, which is attributed to surface modification and surface plasmons coupling. The improved enhancement in the sample with Ag pattern is attributed to the fact that periodic Ag structure offers additional scattering mediums and thus increases the light extraction efficiency.

Organo-lead halide perovskite has emerged as a promising optical gain media. However, continuous efforts are needed to improve the amplified spontaneous emission (ASE) even lasing properties to evade the poor photostability and thermal instability of the perovskites. Herein, we report that simply through the coating of polymer layer, the CH3NH3PbBr3 polycrystalline films prepared by a modified sequential deposition process show remarkably enhanced photoluminescence and prolonged decay lifetime. As a result, under nanosecond pulse pumping, the ASE threshold of the perovskite films is significantly reduced from 303 to 140 μJ/cm2. Furthermore, the light exposure stability is improved greatly after the polymer coating. We confirmed that the polymer layer plays the roles of both surface passivation and symmetric waveguides. Our results may shed light upon the stable and sustained output of laser from perovskite materials.

Violet photoluminescence was observed in high-energy hydrogen-plasma-treated ZnO nanorods at 13 K. The photoluminescence spectrum is dominated by a strong violet emission and a shoulder attributed to excitonic emission. The violet emission shows normal thermal behavior with an average lifetime of about 1 μs at 13 K. According to the time-resolved and excitation density-dependent photoluminescence, it was found that the violet emission is determined by at least two emitting channels, which was confirmed by annealing experiments. Evidence was also given that the violet emission is related to hydrogen. We suggested that the hydrogen-related complex defects formed under high-energy hydrogen plasma treatment are responsible for this violet emission.

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.

The electrical and optical properties of zinc oxide (ZnO) films doped with different Na contents and grown by pulsed laser deposition were investigated. Hall measurements witnessed the conductivity conversion from n-type to p-type with targeted Na doping content increased up to more than 1%. The photoluminescence intensity first decreased as the targeted Na content increased to 1%, while non-degraded and even enhanced PL intensity was observed in p-type ZnO:Na0.02 film. This photoluminescence enhancement was ascribed to enhanced radiative recombination with more acceptor (NaZn) introduced. The band-gap shift of ZnO:Nax films was related to the variation of carrier type and concentration. Band-gap shrinkage was adopted to explain the carrier type- and concentration-dependent band-gap shift of ZnO:Nax films.

We report that oxygen plasma treatment significantly changes the surface properties of Ga-doped ZnO (GZO) thin films, leading to an increase of work function and a large reduction in contact angles. We attribute the increase of work function of the GZO thin films after oxygen plasma treatment to both the lowering of the Fermi level and the shift in ionization potential.

Electrically pumped ultraviolet random lasing was achieved in metal-insulator-semiconductor (MIS) diodes based on ZnO films at room temperature. The ZnO films were grown by plasma assisted molecular beam epitaxy. Two different kinds of insulator layers, SiO x (0

High-quality ZnO thin films were grown on a-plane sapphire substrates by plasma-assisted molecular beam epitaxy. X-ray diffraction and transmission electron microscopy reveal that the ZnO films have high structural quality and an atomically sharp ZnO/Al2O3 interface. The full width at half maximum values of the 0002 and $30\bar{3}2$ ZnO ω-rocking curves are 467.8 and 813.5 arc sec for a 600 nm thick ZnO film. A screw dislocation density of 4.35×108 cm−2 and an edge dislocation density of 3.38×109 cm−2 are estimated by X-ray diffraction. The surface of the ZnO epilayers contains hexagonal pits, which can be observed in the Zn-polar ZnO. The films have a resistivity of 0.119 Ω cm, an electron concentration of 6.85×1017 cm−3, and a mobility of 76.5 cm2 V−1 s−1 at room temperature. Low temperature photoluminescence measurements show good optical properties comparable to ZnO single crystals.

In this paper, 3D flower-like Au-ZnO microstructures with controlled morphology and dimensions were synthesized by a facile one-step aqueous solution route at room temperature, and the photocatalytic properties of these structures were investigated. The as-prepared flower-like Au-ZnO structures with a diameter of about 3 μm consisted of many ZnO nanosheets which interacted with each other. These nanosheets, which were successfully decorated by Au NPs, showed an average thickness of 10 nm and a single-crystalline structure with {2-1-10} planar surfaces. The growth process of Au-ZnO structures and the effects of trisodium citrate on the nucleation and growth of ZnO were investigated. The formation of Au NPs in this experiment was discussed too. The Au-ZnO structures showed higher photocatalytic activity than that of pure ZnO.

Time-resolved photoluminescence measurements were taken at various temperatures to investigate the behavior of excitons in ZnO/Zn0.9Mg0.1O multiple quantum wells (MQWs) grown on Si substrate using epitaxial Lu2O3 buffer layer by pulsed laser deposition. The temperature dependence of the radiative decay times of the emissions from both the ZnO wells and the Zn0.9Mg0.1O barriers is analyzed. The radiative lifetime of the well excitons exhibits linear dependence till room temperature, indicating that the excitons are effectively confined in the quantum wells and do not thermalize to 3D excitons. The short radiative lifetime of ~1.15 ns indicates high radiative recombination rate at room temperature. The radiative lifetime of the barrier excitons shows approximately T1/2 dependence on temperature. In combination with the spectral dependence of the PL lifetime, it indicates localization of excitons in the barrier due to compositional fluctuation. The short radiative lifetime at room temperature and the weak localization energy of ~9 meV suggest that our MQWs are of high optical quality.

Non-polar ZnO thin films were deposited on m-plane sapphire substrates by pulsed laser deposition at various temperatures from 300 to 700 °C. The effects of growth temperature on surface morphology, structural, electrical, and optical properties of the films were investigated. All the films exhibited unique m-plane orientation indicated by X-ray diffraction and transmission electron microscopy. Based on the scanning electron microscopy and atomic force microscopy, the obtained films had smooth and highly anisotropic surface, and the root mean square roughness was less than 10 nm above 500 °C. The maximum electron mobility was ∼18 cm2/V s, with resistivity of ∼0.26 Ω cm for the film grown at 700 °C. Room temperature photoluminescence of the m-plane films was also investigated.

Li-doped ZnCoO (ZnCoO:Li) diluted magnetic semiconductor thin films were prepared on SiO 2 substrates by pulsed laser deposition. In ZnCoO:Li films, Co 2+ substituted Zn 2+ and Li occupied the interstitial sites behaving as donors. The ZnCoO:Li films are of high electron concentration in the 10 20 cm −3 order and acceptable crystal quality with a hexagonal wurtzite structure. No cluster, precipitate, or second phase was found from the X-ray diffraction pattern and Co k -edge X-ray absorption near-edge structure measurements. The sp–d exchange interactions between the band electrons and the localized d electrons of Co ions substituting Zn ions were observed. The magnetization of ZnCoO:Li film is 0.61 μB/Co, higher than that of the ZnCoO film (0.49 μB/Co). The enhanced defect density and electron concentration due to the introduced Li donors may answer for the improvement of ferromagnetism at room temperature.

We report the growth of uncommon layer-structured ZnO nanowire arrays via metal–organic chemical vapor deposition (MOCVD). The morphology, microstructure, and photoluminescence (PL) of the nanowires are investigated. The nanowires grow along the [0001] direction, with periodic zig-zag edges formed by the {1011}-type surfaces. The nanowires exhibit unique PL features. The PL spectra at low temperature are dominated by the surface exciton recombination at 3.366 eV and the controversial 3.32 eV emission. For the 3.32 eV emission, transformation from donor–acceptor pair recombination to free electron-to-acceptor transition is observed with increasing temperature. The stacking faults formed in the interface region between the layers are likely responsible for the strong emission around 3.32 eV.

ZnO:Al thin films were prepared at a low oxygen pressure between 0.02 and 0.1 Pa by pulsed laser deposition (PLD). The structure as well as their optical and electrical properties was investigated by X-ray diffraction, optical transmittance spectroscopy, and Hall measurements. The ZnO:Al films possess resistivity of the order of 10 −4 Ω cm and the optical transmittance exceeds 80% in the visible range. The highest electron concentration (1.18×10 21 cm −3 ) is achieved at a deposition pressure of 0.02 Pa and it decreases slightly with increasing oxygen pressure. The band gap is found to depend on the electron concentration.

ZnO nanorod arrays and nanowires were grown by hydrothermal and vapor phase deposition methods, respectively. At low temperature, the photoluminescence (PL) spectra of both samples are dominated by a broad peak around 3.34 eV. Combined with excitation density-dependent PL spectra and surface passivation process, it is indicated from temperature-dependent PL results that the 3.34 eV emission could be attributed to free electron-to-neutral acceptor transitions. The acceptor level is estimated to be ∼100 meV.

Adding alkali metal into lead halide perovskites has recently been demonstrated as an effective strategy for reducing nonradiative loss. However, the suggested role of the alkali metal is usually limited to surface passivation, and the semiconductor doping effect is rarely discussed. Here, the mechanism of lithium doping in the photocarrier recombination in solution‐processed methylammonium lead halide films is investigated by photoluminescence and photoelectron spectroscopies. It is demonstrated that lithium doping weakens the electron–phonon coupling and acts as donor in perovskites, which provide solid evidence that lithium enters the lattice rather than just in the surface region. The n‐type doping creates free electrons to fill the trap states in both the bulk and surface regions, leading to suppressed trapping of photocarriers and reduces nonradiative recombination.

A method for the synthesis of high quality indium-doped zinc oxide (In-doped ZnO) nanocrystals was developed using a one-step ester elimination reaction based on alcoholysis of metal carboxylate salts. The resulting nearly monodisperse nanocrystals are well-crystallized with typically crystal structure identical to that of wurtzite type of ZnO. Structural, optical, and elemental analyses on the products indicate the incorporation of indium into the host ZnO lattices. The individual nanocrystals with cubic structures were observed in the 5% In–ZnO reaction, due to the relatively high reactivity of indium precursors. Our study would provide further insights for the growth of doped oxide nanocrystals, and deepen the understanding of doping process in colloidal nanocrystal syntheses.

Quasi-aligned (Zn,Cd)O nanorods with highly faceted morphology were synthesized by a simple catalyst-free thermal evaporation method. The crystal structure and optical properties of the as-synthesized nanorods were thoroughly investigated. The results indicate that the (Zn,Cd)O nanorods are single crystals of wurtzite structure, having 12 side planes, namely, {0110} and {1120} planes. The presence of Cd is essential for obtaining these highly faceted nanorods. Room-temperature photoluminescence measurements indicated that the green emission of the products was attributed to both the surface-related defects and oxygen vacancies. These highly faceted nanorods possess significantly large surface-to-volume ratios and would be applicable in the fields of surface chemistry, photonics, and catalysis.

ZnO/MgO quasi core−shell quantum dots (QDs) were grown by a metal-organic chemical vapor deposition method on silicon substrates. The core−shell structure was well-characterized by a combination of cross-sectional transmission electron microscopy and angle-resolved X-ray photoelectron spectroscopy (XPS). Valence band XPS measurements were performed to investigate the effects of MgO shell layer on the energy band of ZnO/MgO QDs. Photoluminescence (PL) emission from the QDs showed remarkable enhancement after the growth of the MgO layer. In addition, exciton binding energy of 118 ± 5 meV in the ZnO/MgO QDs was obtained from temperature-dependent PL.

a b s t r a c t A series of ZnO/Zn1 xMgxO multi-quantum wells (MQWs) were grown on Si(111) substrates by pulsed laser deposition (PLD), with different well widths and depths. Transmission electron mi- croscopy (TEM) analysis revealed that all the samples exhib- ited a good periodic structure with clear interfaces. Moreover, temperature- dependent behavior of excitonic photoluminescence (PL) was investigated in order to investigate the mechanism of the carrier dynamics. In the temperature range studied, the lumines- cence was dominated by localized exciton (LE) emission, which was significantly blueshifted with respect to the ZnO single layer, due to the well-known quantum-size effect. The blueshift values increased with elevating Mg compositions in barrier layers or de- creasing well thickness, being consistent with the calculated re- sults. The relevant activation energies were deduced, varying in a range of 6.2 to 22 meV.