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Property of the nanocrystals’ surface structure plays a key role in developing novel nanomaterials with high performance and new functionalities. Conventional methods of nanocrystal surface enginee...

Interface engineering is an effective way to improve the performance of heterojunction photodetectors (PDs). We have constructed p-Si/n-ZnGa2O4 heterojunction solar-blind ultraviolet (UV) PDs with and without an SiO2 interfacial layer and studied the effect of the SiO2 interfacial layer on device performance in detail. At −1 V bias, the dark current of the device from 3.8 × 10−8 A to 5.7 × 10−12 A was greatly reduced, specifically 6.7 × 103 fold, attributed to the high barrier induced by the insertion of the SiO2 interfacial layer. With the introduction of the SiO2 interfacial layer, the photo-to-dark current ratio and the detectivity of the device were greatly improved due to the substantial reduction of dark current. Owing to the insertion of the SiO2 layer reducing the carrier trapping at the interface defects, the rise and decay times of the device were significantly reduced from 0.96 s/0.88 s to 0.12 s/0.08 s, i.e. 8 fold and 11 fold, respectively. Moreover, the large conduction band offset of Si/SiO2 could effectively block visible-light-generated electrons in Si, thereby suppressing the visible-light response and enhancing the UV-visible rejection ratio of the Si/SiO2/ZnGa2O4 PD. Our work has provided a feasible approach for enhancing the performance of Si/wide-bandgap semiconductor heterojunction solar-blind UV PDs.

The sensitivity to weak light signals is a key parameter for UV photodetectors. However, a highly sensitive device has to suffer slow response speed (with photoconductive gain) or large noise current (with avalanche gain). In this work, a new type of photoconductive gain with controllable response speed is discovered in the Ga2O3 photodetector. The persistent photocurrent can be quenched by a 500 μs zero-voltage pulse. The photoconductive gain and the quenching of persistent photocurrent are respectively attributed to the forming and breaking of conductive filaments composed of oxygen vacancies. UV illumination has been demonstrated to accelerate the formation of the filament. This work provides a direction for the combination of speed-control and high sensitivity for photodiodes.

Excitons in van der Waals (vdW) stacking interfaces can be trapped in ordered moire potential arrays giving rise to attractive phenomenons of quantum optics and bosonic many-body effects. Compare to the prevalent transition metal dichalcogenides (TMDs) systems, due to the wide bandgap and low dielectric constant, excitons in twist-stacked hexagonal boron nitride (hBN) are anticipated trapped in deeper moire potential, which enhances the strength of interactions. However, constrained by the common low detectivity of weak light-emitting in the deep-ultraviolet (DUV) bands, the moire excitons in twisthBN remain elusive. Here, we report that a remarkable DUV emitting band (peak located at ~260 nm) only emerges at the twisted stacking area of hBN, which is performed by a high collection efficiency and spatially-resolved cathodoluminescence (CL) at room temperature. Significant peak redshifting contrast to defect-bound excitons of bulk hBN indicates the giant trapping effects of moir\'e potential for excitons. The observation of deeply trapped excitons motivates further studies of bosonic strongly correlation physics based on the twist-hBN system., Comment: 20 pages, 9 pictures

In this work, individual ZnO via Ga-doped (ZnO:Ga) microbelts with excellent crystallinity and smooth facets can enable the realization of lateral microresonator Fabry-Perot (F-P) microlasers, and the F-P lasing action originates from excitonic state. Interestingly, introducing Ag nanoparticles (AgNPs) deposited on the microbelt can increase F-P lasing characteristics containing a lower threshold and enhanced lasing output. Especially for the large size AgNPs (the diameter d is approximately 200 nm), the lasing features also exhibit a significant redshift of each lasing peak and an observable broadening of the spectral line width with an increase of the excitation fluence. And the remarkable lasing characteristics are belonging to the electron-hole plasma (EHP) luminescence. The behavior and dynamics of the stimulated radiation in an AgNPs@ZnO:Ga microbelt are studied, suggesting the Mott-transition from the excitonic state to EHP state that is responsible for the F-P lasing. These features can be attributed to the working mechanism that the hot electrons created by the large size AgNPs through nonradiative decay can fill the conduction band of nearby ZnO:Ga, leading to a downward shift of the conduction band edge. This novel filling influence can facilitate bandgap renormalization and result in EHP emission. The results provide a comprehensive understanding of the transition between excitonic and EHP states in the stimulated emission process. More importantly, it also can provide new scheme to developing high efficiency and ultra-low threshold microlasing diodes.

Recently, heterojunctions consisting of hybrid organic-inorganic lead (Pb) halide perovskites and other semiconductors have drawn increasing attention for the potential application in photodetectors due to their exceptional performance. However, their performance is usually limited by the relatively low crystalline quality of perovskites, and the response spectra of the devices are difficult to adjust according to the practical requirement. Here, high quality CH3NH3PbCl3 micro-sized crystals have been successfully fabricated on one side of individual ZnO microwire to form heterojunction photodetector by a two-step crystallization method. The heterojunction device presents a low dark current (60 nA at −6 V) along with a rapid response speed (rise time of μs and fall time of ∼500 μs). More interestingly, the modulation of the response spectra and the responsivity can be realized by operating the device under front or back illumination due to the self-filtering properties. Our findings provide a promising method for combining perovskites with other inorganic materials to form high-performance heterojunction photodetectors.

Packaging is one of the most important procedures of the fabrication of photoelectric devices, such as ZnMgO solar blind ultraviolet (UV) photodetectors. The roles of packaging are: electrically interconnecting an unpackaged photodetector and pin as well as fixing it, and protecting the unpackaged photodetector from external dirt, humidity and atmosphere. Nowadays, the research on the ZnMgO solar-blind UV photodetectors has well developed. However, the research on the packaging of these photodetectors are rare. In this study, we have focused on the packaging of ZnMgO solar blind UV photodetectors. After a direct wire bonding method between steel wires and unpackaged photodetectors by conductive silver adhesives and a sealing treatment by silica gel, the ZnMgO photodetector was packaged, and the responsivity of the device was found to increase after the packaging. A −3 dB cutoff wavelength of 295 nm and a responsivity of 191 A W−1 were achieved under a bias of 10 V. The 90–10% decay time of the device was 280 ms, and the dark current of the device was 115 pA under a bias of 10 V. Moreover, the stability of the ZnMgO-based solar blind photodetector obviously improved due to the well-sealed packaged structure.

A high performance p-GaN/n-ZnMgO heterojunction photodiode was demonstrated and investigated. A high quality p-GaN film was grown on GaN/sapphire templates by plasma-assisted molecular beam epitaxy and subsequently an n-ZnMgO layer was deposited on p-GaN by a metal organic chemical vapor deposition technique. The p-GaN/n-ZnMgO heterojunction photodetector shows a clear rectifying I–V characteristic with a turn-on voltage of 2.5 V. At zero-bias voltage, the device shows a high peak responsivity of 196 mA W−1 at 362 nm. The 10–90% rise time and 90–10% decay time of the device can be as short as 1.7 ms and 3.3 ms, respectively. The excellent crystal quality and electrical properties of p-GaN play an important role in the high performance of the photodiode. This work provides a feasible way for the development of high-performance heterojunction self-powered UV detectors.

A hybrid perovskite MAPbCl3 (MA = CH3NH3+) single crystal is considered to be one of the most viable candidates for the development of photodetectors because of its outstanding optoelectronic properties. However, the relatively lower crystalline quality of the reported MAPbCl3 single crystals fabricated by the traditional one-step inverse temperature crystallization results in momentous degradation in the performance of their photodetectors. Here, we present a novel two-step temperature process to fabricate high-quality MAPbCl3 single crystals, namely, lower temperature nucleation and higher temperature crystallization. These MAPbCl3 single crystals present low defect density (∼7.9 × 109 cm-3) commensurate with the best-quality crystals of hybrid organic-inorganic lead halide perovskites reported so far. Moreover, a high-performance ultraviolet photodetector was demonstrated on MAPbCl3 single crystals. At 30 V, the peak responsivity at 415 nm of the photodetector is as high as 3.73 A W-1 (light intensity = 1 mW cm-2), ∼2-3 orders of magnitude higher than that of the previously reported MAPbCl3 photodetectors. Meanwhile, the device has an ultrafast response speed with a rise time of 130 ns, which is one of the shortest values of MAPbX3-based photodetectors. Our findings open a new way to obtain high-quality perovskite single crystals and their high-performance photodetectors.

We have demonstrated a self-powered solar-blind ultraviolet (UV) photodetector based on the Au/ZnMgO/ZnO:Al vertical structure. The comb-shaped Au was selected as the Schottky electrode due to its high transmittance (more than 60%) in the wavelength region from 200 nm to 300 nm. At 0 V bias, the detector showed a responsivity of 55 mA/W under 265 nm light illumination with the intensity of 80 nW/cm2, which is larger than that of any other previously reported ZnO-based self-powered UV photodetectors. And a fast response speed can be also clearly observed with 10%–90% rise and 90%-10% decay times of 20 μs and 300 μs, respectively. The excellent self-powered solar-blind UV detection of our Au/ZnMgO/ZnO:Al device should be associated with the high external quantum efficiency, especially for the weak signal detection. Our findings offered new chances in high-performance self-powered photodetectors fabrication.

Metal–semiconductor–metal structured photodetectors based on β-Ga2O3 thin films were fabricated. Because of the high dark-resistance and considerable photoconduction, extremely uneven distribution ...

One-dimensional (1D) micro/nanowires of wide band gap semiconductors have become one of the most promising blocks of high-performance photodetectors. However, in the axial direction of micro/nanowires, the carriers can transport freely driven by an external electric field, which usually produces large dark current and low detectivity. Here, an UV photodetector built from three cross-intersecting ZnO microwires with double homo-interfaces is demonstrated by the chemical vapor deposition and physical transfer techniques. Compared with the reference device without interface, the dark current of this ZnO double-interface photodetector is significantly reduced by nearly 5 orders of magnitude, while the responsivity decreases slightly, thereby greatly improving the normalized photocurrent-to-dark current ratio. In addition, ZnO double-interface photodetector exhibits a much faster response speed (∼ 0.65 s) than the no-interface device (∼ 95 s). The improved performance is attributed to the potential barriers at the microwire–microwire homo-interfaces, which can regulate the carrier transport. Our findings in this work provide a promising approach for the design and development of high-performance photodetectors.

An ideal solar-blind photodetector should possess high responsivity, low dark current, high speed, high spectral selectivity, high stability and a facile fabrication method. In this work, a high-quality single β-Ga2O3 microbelt photodetector is fabricated through low-pressure chemical vapor deposition and in situ atmospheric pressure annealing techniques. Due to the high quality and low defect density, this device shows a peak responsivity of 9.47 A W−1 at 256 nm, a dark current of 1 pA and an ultrashort fall time of 1.37 μs under 20 V bias. Moreover, an ultrahigh specific detectivity of ∼1014 Jones and an extremely large solar-blind/ultraviolet A rejection ratio of nearly 105 have also been achieved, suggesting the excellent sensitivity and wavelength selectivity of our single β-Ga2O3 microbelt photodetector. Besides that, the β-Ga2O3 microbelt photodetector exhibits excellent mechanical and long-term stabilities. Our findings provide a facile and promising route to develop high performance solar-blind UV photodetectors.

Two-dimensional van der Waals crystals arise limitless scope for designing novel combinations of physical properties via controlling the stacking order or twist angle of individual layers. Lattice orientation between stacked monolayers is significant not only for the engineering symmetry breaking but also for the study of many-body quantum phases and band topology. So far the state-of-art exfoliation approaches focusing on achievements of quality, size, yield, and scalability while lacking sufficient information on lattice orientation. Consequently, interlayer alignment is usually determined by later experiments, such as second harmonic generation spectroscopy, which increased the number of trials and errors for a designed artificial ordering and hampered the efficiency of systematic study. Herein, we report a lattice orientation distinguishable exfoliation method via gold favor epitaxy along the specific atomic step edges, meanwhile, fulfill requirements of high-quality, large-size, and high-yield of monolayers. Hexagonal- and rhombohedral-stacking configurations of bilayer transition metal dichalcogenides are built directly at once result of foreseeing the lattice orientation. Optical spectroscopy, electron diffraction, and angle-resolved photoemission spectroscopy are used to study crystals quality, symmetric breaking, and band tuning, which supports the exfoliating mechanism we proposed. This strategy shows the ability for facilitates the development of ordering stacking especially for multilayers assembling in the future., Comment: 29 pages, 7 figures

The realization of electrically pumped lasers at deep sub-micro and nanometer scale operating far beyond the diffraction limit is still a crucial goal in nanophotonics and plasmonics for prospective fundamental research and application. Herein, electrically pumped spasing action was captured from a cross-stacked architecture composed of a single Ga-doped ZnO microwire (ZnO:Ga MW) crossed with another ZnO:Ga MW covered by Au nanoparticles. To exploit the spasing feature, a plasmonic nanocavity could be constructed based on the sandwiched structures, with isolated Au nanoparticles filling the spacer between the crossed MWs. When both emission regions from the crossed MWs overlapped with each other, the cross-stacked architecture exhibited quasi-Schottky junction behavior, resulting in the formation of a tunneling junction. When the injection current exceeded certain values, bright and localizing emissions were observed at the crossed regions, with a sharp peak emerging in the emission spectra. The dominant emission wavelengths centered at 550 nm were accompanied by the spectral linewidth rapidly narrowing to 2 nm, suggesting a transition from spontaneous to stimulated emission. The electrically pumped lasing characteristics can be attributed to efficient metal plasmons amplification by the stimulated emission of radiation from Au nanoparticles, which filled the nanocavities. Therefore, this cross-stacked architecture provides a natural route towards electrical injection schemes that can be employed to construct electrical-pumping spasers. This technology also provides a candidate to investigate the fabrication of tunneling diodes.

There has been a long standing debate on the luminescence origination from carbon nanodots (CDs). Herein, we report the solvent dependent piezochromism of CDs by diamond anvil cells experiment. Red- and blue-shift piezochromism were observed in CDs with N,N-dimethylformamide and water as pressure transmitting medium (PTM) with increasing pressure from atmospheric pressure to 25 GPa, which were related to increased π-π stacking and protic-solvent-induced surface chemical structural changes, respectively. Based on theoretical modeling and structural analysis of hydrothermally treated CDs (h-CDs), the reversible and irreversible piezochromism from green emission to blue emission with water as PTM was attributed to pressure induced enhanced intermolecular hydrogen bonding and addition reaction between water molecules and surface electron withdrawing groups on the CDs, respectively. The decreased electron withdrawing ability of the surface chemical structures of CDs further affects their intrinsic luminescence. This work provides a new understanding of the piezochromic luminescence origination from CDs, which is related to the surface related intrinsic luminescence.

Carbon dots that exhibit near-infrared fluorescence (NIR CDs) are considered emerging nanomaterials for advanced biomedical applications with low toxicity and superior photostability and targeting compared to currently used photoluminescence agents. Despite progress in the synthesis of NIR CDs, there remains a key obstacle to using them as an in vivo theranostic agent. This work demonstrates that the newly developed sulfur and nitrogen codoped NIR CDs are highly efficient in photothermal therapy (PTT) in mouse models (conversion efficiency of 59%) and can be readily visualized by photoluminescence and photoacoustic imaging. The real theranostic potential of NIR CDs is enhanced by their unique biodistribution and targeting. Contrary to all other nanomaterials that have been tested in biomedicine, they are excreted through the body’s renal filtration system. Moreover, after intravenous injection, NIR CDs are accumulated in tumor tissue via passive targeting, without any active species such as antibodies. Due to their accumulation in tumor tissue without the need for intratumor injection, high photothermal conversion, excellent optical and photoacoustic imaging performance, and renal excretion, the developed CDs are suitable for transfer to clinical biomedical practice., Carbon dots: Lighting up for cancer therapy and diagnosis ‘Carbon dot’ nanoparticles composed largely of carbon, but doped with sulfur and nitrogen, accumulate within cancer cells and absorb near-infrared laser light to generate cell-killing heat. The procedure was developed and tested by researchers in China and the Czech Republic, led by Songnan Qu at the Changchung Institute of Optics, Fine Mechanics and Physics. The nanoparticles accumulated passively in tumors after intravenous injection into mice, with no specific targeting methods required. Tumors were effectively eradicated by the highly efficient conversion of the light energy into heat. The nanoparticles are biocompatible and are eventually excreted harmlessly in urine. In addition to the potential for treating cancer, diagnosis can also be assisted using the particles’ fluorescent properties. This combination of therapy and diagnosis – ‘theranostics’ – can now be further developed and explored for use in patients.

Exploration of solid-state efficient red emissive carbon dots (CDs) phosphors is strongly desired for the development of high performance CDs-based white light-emitting diodes (WLEDs). In this work, enhanced red emissive CDs-based phosphors with photoluminescence quantum yields (PLQYs) of 25% were prepared by embedding red emissive CDs (PLQYs of 23%) into polyvinyl pyrrolidone (PVP). Because of the protection of PVP, the phosphors could preserve strong luminescence under long-term UV excitation or being mixed with conventional packaging materials. By applying the red emissive phosphors as the color conversion layer, WLEDs with high color rendering index of 92 and color coordinate of (0.33, 0.33) are fabricated.

Recent investigations indicate that the performance of organic–inorganic perovskite optoelectronic devices can be improved by combining the perovskites and the inorganic materials. However, very few studies have focused on the investigation of perovskites/inorganic semiconductor hybrid UV photodetectors and their detailed performance-enhancement mechanism is still not very clear. In this work, a CH3NH3PbCl3/ZnO UV photodetector has been first demonstrated and investigated. Both the photoresponsivity and response speed of the hybrid device are higher than those of pure CH3NH3PbCl3 and ZnO devices. The photoluminescence and transient absorption spectra indicate that the photoinduced electron transfer between CH3NH3PbCl3 and ZnO should be responsible for the performance enhancement of the hybrid device. In addition, the high crystal quality of CH3NH3PbCl3 on ZnO film is another important reason for the excellent UV detection performance. Our findings in this work provide new insights into the intrinsic photo...

We investigated the spatial cathodoluminescence (CL) quenching of Si doped AlN/Al shell/core particles along the radial direction. The quenching characteristic position gradually shifts to a more central location with emission wavelength increasing. This effect is due to the transport process of hot electrons, which produced by Al-plasmon decay via Landau damping. In this transport process, donor levels (Di) in AlN were partly occupied by hot electrons from Al core, which will reduce the quantum efficiency of recombination channel i (Di to Ai). A phenomenological theory has been used to discuss carriers recombination dynamics processes.

Widely studied as a photocatalytic material for many environmental and clean energy applications, and as an electrode material for solar cells and rechargeable batteries, titanium dioxide (TiO2) has been recently demonstrated as a new microwave absorbing material after hydrogenation. Herein, we report that hydrogenated TiO2 nanoparticles have an efficient terahertz (THz) absorption in a wide THz frequency range between 0.6 and 2.5 THz. With competitive performances over other THz absorbing materials or structures, hydrogenated TiO2 nanomaterials have therefore displayed a bright future for broadband THz absorption and opened a new application for TiO2 nanomaterials.

The generation of hot electrons from metal nanostructures through plasmon decay provided a direct interfacial charge transfer mechanism, which no longer suffers from the barrier height restrictions observed for metal/semiconductor interfaces. Metal plasmon-mediated energy conversion with higher efficiency has been proposed as a promising alternative to construct novel optoelectronic devices, such as photodetectors, photovoltaic and photocatalytic devices, etc. However, the realization of the electrically-driven generation of hot electrons, and the application in light-emitting devices remain big challenges. Here, hybrid architectures comprising individual Ga-doped ZnO (ZnO:Ga) microwires via metal quasiparticle film decoration were fabricated. The hottest spots could be formed towards the center of the wires, and the quasiparticle films were converted into physically isolated nanoparticles by applying a bias onto the wires. Thus, the hot electrons became spatially localized towards the hottest regions, leading to a release of energy in the form of emitting photons. By adjusting the sputtering times and appropriate alloys, such as Au and Ag, wavelength-tunable emissions could be achieved. To exploit the EL emission characteristics, metal plasmons could be used as active elements to mediate the generation of hot electrons from metal nanostructures, which are located in the light-emitting regions, followed by injection into ZnO:Ga microwire-channels; thus, the production of plasmon decay-induced hot-electrons could function as an efficient approach to dominate emission wavelengths. Therefore, by introducing metal nanostructure decoration, individual ZnO:Ga microwires can be used to construct wavelength-tunable fluorescent emitters. The hybrid architectures of metal-ZnO micro/nanostructures offer a fantastic candidate to broaden the potential applications of semiconducting optoelectronic devices, such as photovoltaic devices, photodetectors, optoelectronic sensors, etc.

ZnO film was fabricated on p-GaN film using the molecular beam epitaxy technique to form heterojunction light emitting diodes (LEDs). The devices exhibited strong light emission under both forward and reverse bias. The origin of different luminescence peaks has been investigated by comparing electroluminescence (EL) and photoluminescence spectra. When a forward bias is applied to the device, intense ultraviolet emission at ∼376 nm originating from ZnO rather than GaN can be observed, which is associated with the larger hole mobility of p-GaN than the electron mobility of n-ZnO. Under the reverse bias, the device shows broad emission at 520 nm originating from deep level-related recombination in ZnO, emission at 430 nm from GaN, 376 nm from ZnO and weak emission at 408 nm from the interface with a lower injection current of 10 mA. As the injection reverse current increases to 20 mA, the EL emission at 376 nm exhibits a dramatic increase in intensity without a peak shift. The emission mechanism of the heterojunction LED is discussed in terms of interface states and energy band theory. Our findings in this work provide an innovative path for the design and development of ZnO-based ultraviolet diodes.

Aggregation-induced quenching (ACQ) in carbon nanodots (CNDs) impede their applications in solid devices. Herein, the concept of alternating quantum dot (QD) chains was proposed to overcome the common issue of fluorescence quenching in CNDs; in this study, CNDs and ZnO QDs were interlinked to form carbon-ZnO alternating quantum dot chains (CZA-QDCs), which overcame the ACQ of CNDs and hence ensured efficient full-spectrum fluorescence for white light-emitting devices (WLEDs) without excessive blue emission. Under the excitation of 365 nm lines, white emission resulting from the combination of blue emission from the CNDs and yellow emission from the ZnO QDs has been achieved from these powders. The quantum efficiency of the CZA-QDC powders can reach 49% and remain stable for two months. By coating the powders onto an ultraviolet chip as phosphors, WLEDs with a luminous efficiency of 20.1 lm W-1, color coordinate of (0.30, 0.35), correlated color temperature of 5205 K, and a color rendering index of 84 have been fabricated. Due to the relatively high abundance and eco-friendly characteristics of both carbon and ZnO, the results reported herein may provide a promising alternative to fluorescent phosphors that are widely used in WLEDs.

We demonstrate for the first time that multilevel resistive random access memories (RRAMs) can be utilized to modulate the luminescence of light-emitting devices (LEDs) in Au/GaOx/p-GaN/n-ZnO structures. In these structures, Au/GaOx/p-GaN multilevel RRAMs are integrated with p-GaN/n-ZnO LEDs. The injection current of the LEDs can be controlled by the resistance states of the multilevel RRAMs, thus modulating the luminous intensity. The results reported in this paper may offer a route to more integrated and low-cost LED displays. Moreover, our approach may provide a clue for the diversified applications by integrating RRAMs with other functional electronics.

A hybrid perovskite MAPbCl

Self-supporting ZnO nano-networks have been demonstrated by a substrate-free chemical vapor deposition process for the application as flexible ultraviolet (UV) photodetector. The device shows a responsivity of ∼300 mA W-1over a wide wavelength range from 254 to 365 nm and a high UV/visible rejection ratio of more than 104. More interestingly, a short 90%-10% decay time of

The slower response speed is the main problem in the application of ZnO quantum dots (QDs) photodetector, which has been commonly attributed to the presence of excess oxygen vacancy defects and oxygen adsorption/desorption processes. However, the detailed mechanism is still not very clear. Herein, the properties of ZnO QDs and their photodetectors with different amounts of oxygen vacancy (VO) defects controlled by hydrogen peroxide (H2O2) solution treatment have been investigated. After H2O2 solution treatment, VO concentration of ZnO QDs decreased. The H2O2 solution-treated device has a higher photocurrent and a lower dark current. Meanwhile, with the increase in VO concentration of ZnO QDs, the response speed of the device has been improved due to the increase of oxygen adsorption/desorption rate. More interestingly, the response speed of the device became less sensitive to temperature and oxygen concentration with the increase of VO defects. The findings in this work clarify that the surface VO defects of ZnO QDs could enhance the photoresponse speed, which is helpful for sensor designing.

Applications of ZnO quantum dots (QDs) in photodetectors are generally limited by a slower response speed and a higher dark current. The corresponding mechanism is not very clear, and how to resolve these problems is still in big challenge. Herein, we have demonstrated a photodetector on 700 nm-thick ZnO QDs film with a large number of oxygen vacancy defects by adjusting the ratio of the reactants and the reaction time. The device exhibits a quick response speed with a rise time of ~1.00 s and a recovery time of ~0.19 s. Meanwhile, the dark current and the responsivity under 730 μW/cm2 UV light illumination were found to be 20 pA and 260 mA/W under 10 V bias, respectively. The mechanism of these phenomena has been investigated, and the fast response speed of ZnO QDs photodetector in the air should originate from the adsorption/desorption of oxygen on the surface oxygen vacancy defects of ZnO QDs. The findings in this work can be used to guide design of high-performance photodetectors based on ZnO QDs and other nanomaterials with large surface to volume ratio.

The photodetectors based on the wide bandgap semiconductor (WBS)/Si heterojunction have attracted more and more attention in recent years due to their excellent photoelectric characteristics and easy integration capabilities. In this work, we have demonstrated a self-powered solar-blind ultraviolet (UV) photodetector based on the ZnGa2O4/Si heterojunction. A typical rectification characteristic with a rectification ratio exceeding 103 within ±5 V can be obtained. At 0 V bias, the −3 dB cutoff wavelength of ∼255 nm and the UV-visible rejection ratio of ∼3 × 102 show that the device has excellent self-powered solar-blind UV detection performance. In addition, the responsivity and the response speed of ZnGa2O4/Si heterojunction can be efficiently enhanced by a transient spike current at 0 V bias when turning on and off the 254 nm UV light. The interface pyroelectric effect of the ZnGa2O4 film should be responsible for this transient spike photocurrent phenomenon. Our findings in this work pave a feasible way to realize high-performance WBS/Si heterojunction self-powered solar-blind photodetectors.

Aggregation-induced luminescence quenching of carbon dots (CDots) is the main obstacle for their applications in the solid state. Herein, we report a method to produce strongly luminescent CDots@silica composite gels with highly concentrated emitting centers, where the gelation of tetraethyl orthosilicate is initiated by the surface hydroxyl groups of CDots. The key feature of this approach is to prevent both the collision between high concentrated CDots in gelating solution and their aggregation upon drying. The resultant CDots@silica composite xerogel exhibits both high CDots loading fraction (19.2 wt %) and photoluminescence quantum yields (>40%).

Individual Sb-doped ZnO (ZnO:Sb) microwires with durable and reproducible p-type conduction have been synthesized, and by increasing the Sb2O3 weight ratios in the precursor mixtures, tunable p-type conduction characteristics can be obtained. Meanwhile, wavelength-tuning electroluminescence (EL) has been observed by applying bias onto individual ZnO:Sb microwires, in which the ZnO:Sb microwires act as emitting filaments. The as-synthesized p-type ZnO:Sb microwires are applied to fabricate homojunction light-emitting devices. The corresponding p–n junction demonstrates excellent diode characteristics, and strong near band edge emissions can be observed with the dominant EL emission wavelengths centered at 400 nm. The results demonstrated the emitting filament characteristics of ZnO:Sb microwires for the first time, and also demonstrated their applicability in homojunction light-emitting diodes, and thus may offer alluring prospects as compact, efficient, reliable building blocks for microscale light sources.

Herein, ZnMgO thin film ultraviolet (UV) photodetectors based on metal-semiconductor-metal structure were fabricated on a-plane sapphire substrates by plasma-assisted molecular beam epitaxy. The effect of H2O2 solution treatment on the properties of the ZnMgO thin film and its UV photodetectors was investigated. After immersing the ZnMgO UV photodetector in a H2O2 solution at 100 degrees C for 3 min, the dark current of the device was reduced by more than one order of magnitude under 1 V bias, whereas the responsivity was slightly decreased. More interestingly, the response speed became much quicker and insensitive to the atmosphere after the treatment of the photodetector with H2O2 solution, which can be attributed to the reduction in the oxygen vacancy defects. Our findings may provide a promising approach for improving the performance of photodetectors.

A self-powered solar-blind ultraviolet (UV) photodetector was realized on a Ag/ZnMgO/ZnO vertical structure. A ZnO epitaxial layer was employed to serve as both the buffer layer for the growth of ZnMgO and the bottom electrode of the device. Interestingly, the device exhibited an obvious self-powered property owing to the built-in electric fields at the Ag/ZnMgO and ZnMgO/ZnO interfaces. At 0 V, the peak responsivity at 275 nm of our device was 16 mA W−1, which is comparable to that of other ZnMgO self-powered solar-blind UV photodetectors. Moreover, the device also exhibited a very fast response speed (24 μs rise time and 300 μs decay time) at 0 V. This study could provide a much easier and more feasible way to develop ZnMgO self-powered solar-blind UV photodetectors on foreign substrates with high responsivity, fast response speed, and low cost.

One dimensional (1D) zinc oxide (ZnO) nano and microwires have been considered as one of the most promising candidates for the fabrication of novel nano and microscale electronic and optoelectronic devices. In this study, individual Ga heavily doped ZnO microwires (GZO MWs) were successfully synthesized via chemical vapor deposition methods. Bright, stable, and near-infrared light-emission from electrically biased individual GZO MWs has been achieved. Mysteriously, alternating current driven near-infrared electroluminescence (EL) devices based on individual GZO MWs can also be realized. Therefore, individual GZO MWs that can be analogous to incandescent sources, provide promising potential applications in future ultracompact near-infrared electronic and optoelectronic devices or systems.

Encryption is of vital importance in both military and civil fields. Although there have been a few attempts to encrypt information and produce anti-counterfeiting techniques employing functional materials, it is still urgently needed to develop advanced encryption routes that cannot be cracked easily. This paper presents a simple strategy for advanced encryption based on the fluorescence quenching of ZnO nanoparticles (NPs) by acid and copper ions. In this strategy, certain patterns are printed onto a ZnO NP pre-coated paper using a CuCl2 aqueous solution as an ink to produce an invisible latent image, which is only visible under ultraviolet (UV) irradiation. For encryption, the patterns can be perfectly concealed by exposure to vinegar vapour, due to the dissolution of the ZnO NPs in acidic conditions, and decryption can be performed via neutralization in an ambient soda vapour environment and subsequent uniform re-coating with ZnO NPs. An additional matrix of pixels with encoded grey levels acquired by tuning the dose of CuCl2 is demonstrated to further enhance the anti-counterfeiting capability. A 4 × 4 micron matrix with a total combination of 1.67 × 108 codes has been enciphered in the latent patterns for demonstration, and this is a huge barrier for counterfeiting. The results reported in this paper provide a simple strategy for advanced encryption, and may inspire versatile applications in the fields of information security and anti-counterfeiting.

A ZnO and carbon nanoparticle (NP) mixture has been prepared. The fluorescence color of the mixture changes from yellow to blue when the pH value of the ambient is smaller than 5.5, which accords well with the pH standard value of acid rain (

Oxygen adsorption and desorption processes can strongly slow down the response speed of ZnO-based ultraviolet photodetectors. Surface passivation of ZnO-based films is a common method to increase the response speed, but the effect of the traditional passivation technology is usually not very obvious, and often accompanies a decrease in responsivity. Herein we propose a new method to overcome this problem: treating ZnMgO UV photodetectors with HF solution. Interestingly, after treatment with HF solution, the 90–10% decay time of the device is decreased by more than one order of magnitude (from 4.6 ms to 0.34 ms), which can be attributed to the enhancement of the oxygen adsorption speed on the surface of ZnMgO due to the F-modified surface. Moreover, the dark current is decreased from 0.7 pA to 0.4 pA at a bias of 10 V and the responsivity is increased from 145 A W−1 to 326 A W−1. Thus, chemical treatment with HF solution should be a useful and effective method for improving the performance of ZnMgO UV photodetectors.

Stable p-type boron–nitrogen codoped ZnO thin films were prepared by plasma-assisted molecular beam epitaxy. The incorporations of boron and nitrogen into ZnO, identified by X-ray diffraction and X-ray photoelectron spectroscopy, led to improvement in p-type conductivity of ZnO with respect to nitrogen monodoped ZnO. It was ascribed to the marked enhancement of nitrogen doping efficiency due to the existence of two types of chemical states of nitrogen atoms: the nitrogen substituting at oxygen site with nearest neighbor of Zinc atom (N O –Zn bonding), and the nitrogen locating at the nearest neighbor of boron atom (N O –B bonding). The strong interaction between the boron and nitrogen makes the complex of B Zn - n N O ( n = 3 or 4) be a shallow acceptor, which is responsible for the observed p-type behavior.