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Systematic investigations on the effect of prolong UV illumination on optoelectronic properties of ZnO honeycomb nanostructures
摘要： Herein, the effect of prolong UV illumination over ZnO optoelectronic characteristics has been investigated. The photoluminescence analysis has shown significant enhancement in deep level emission (DLE) after sample being exposed to UV radiations. The formation of photo-induced oxygen vacancies (VO) over the ZnO surface was found to be responsible for such noteworthy enhancement in DLE. The observed phenomenon was further utilized for controlled incorporation of VO in ZnO via UV illumination, towards obtaining optimal device performance. The UV treated photo-detector has shown significantly high photo-responsivity and photo-sensitivity in the deep UV region.
关键词： Zinc oxide,Honeycomb structure,Deep UV photodetector,XRD,Lattice defects
更新于2025-09-23 15:23:52
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Largea??Scale Ultrathin 2D Widea??Bandgap BiOBr Nanoflakes for Gatea??Controlled Deepa??Ultraviolet Phototransistors
摘要： Ternary two-dimensional (2D) semiconductors with controllable wide bandgap, high ultraviolet (UV) absorption coefficient, and critical tuning freedom degree of stoichiometry variation have a great application prospect for UV detection. However, as-reported ternary 2D semiconductors often possess a bandgap below 3.0 eV, which must be further enlarged to achieve comprehensively improved UV, especially deep-UV (DUV), detection capacity. Herein, sub-one-unit-cell 2D monolayer BiOBr nanoflakes (≈0.57 nm) with a large size of 70 μm are synthesized for high-performance DUV detection due to the large bandgap of 3.69 eV. Phototransistors based on the 2D ultrathin BiOBr nanoflakes deliver remarkable DUV detection performance including ultrahigh photoresponsivity (Rλ, 12739.13 A W?1), ultrahigh external quantum efficiency (EQE, 6.46 × 106%), and excellent detectivity (D*, 8.37 × 1012 Jones) at 245 nm with a gate voltage (Vg) of 35 V attributed to the photogating effects. The ultrafast response (τrise = 102 μs) can be achieved by utilizing photoconduction effects at Vg of ?40 V. The combination of photocurrent generation mechanisms for BiOBr-based phototransistors controlled by Vg can pave a way for designing novel 2D optoelectronic materials to achieve optimal device performance.
关键词： monolayer BiOBr,deep UV phototransistors,wide-bandgap semiconductors,high gain
更新于2025-09-23 15:19:57
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Noise and spectral stability of deep-UV gas-filled fiber-based supercontinuum sources driven by ultrafast mid-IR pulses
摘要： Deep-UV (DUV) supercontinuum (SC) sources based on gas-filled hollow-core fibers constitute perhaps the most viable solution towards ultrafast, compact, and tunable lasers in the UV spectral region, which can even also extend into the mid-infrared (iR). noise and spectral stability of such broadband sources are key parameters that define their true potential and suitability towards real-world applications. In order to investigate the spectral stability and noise levels in these fiber-based DUV sources, we generate an SC spectrum that extends from 180 nm (through phase-matched dispersive waves - DWs) to 4 μm by pumping an argon-filled hollow-core anti-resonant fiber at a mid-IR wavelength of 2.45 μm. We characterize the long-term stability of the source over several days and the pulse-to-pulse relative intensity noise (RIN) of the DW at 275 nm. The results indicate no sign of spectral degradation over 110 hours, but the RIN of the DW pulses at 275 nm is found to be as high as 33.3%. Numerical simulations were carried out to investigate the spectral distribution of the RIN and the results confirm the experimental measurements and that the poor noise performance is due to the high Rin of the mid-IR pump laser, which was hitherto not considered in numerical modelling of these sources. The results presented herein provide an important step towards an understanding of the noise mechanism underlying such complex light-gas nonlinear interactions and demonstrate the need for pump laser stabilization.
关键词： Deep-UV,supercontinuum sources,spectral stability,ultrafast mid-IR pulses,gas-filled fiber,noise
更新于2025-09-23 15:19:57
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A novel multi-center activated single-component white light-emitting phosphor for deep UV chip-based high color-rendering WLEDs
摘要： Single-component white light-emitting phosphors for phosphors-converted WLEDs are a hot spot of solid-state lighting field. Dy3+ is a promising candidate for white light generation in single-component hosts; however, the inappropriate ratio of yellow light to blue and the lack of red light restrict its applications in full-color display and indoor lighting. Here, a novel multi-center activated single-component white light-emitting phosphor, Sr2LaGaO5:Dy3+,Sm3+, has been designed and synthesized. It is surprisingly found that there is no evident energy transfer between the host and the dopants even though they satisfy the rule of spectral overlap, which can be explained from the special structure of the phosphor. The co-excitation of the host and the dopants would be a facile strategy to finely tune the luminescent spectra of phosphors. By adjusting the doping concentrations of Dy3+ and Sm3+, we can control the relative intensities of the emissions peaked at 493 nm and 574 nm from Dy3+, 604 nm from Sm3+ and the broadband within the range of 400 - 500 nm from the host. Therefore, the emission color of the co-doped phosphors can be tuned from white light to orangish red region with correlated color temperature decreasing from 5708 K to 1971 K. A WLED device with extremely high color-rendering index (Ra) up to 91.4 was fabricated by coating the synthesized phosphor with a deep UV LED chip. And it is the first time to use a single-component white light-emitting phosphor co-activated with Dy3+ and Sm3+ in deep UV chip excited WLEDs with high Ra.
关键词： Co-excitation,Sr2LaGaO5:Dy3+,Sm3+,Deep UV-LED chip,White light-emitting phosphor,High color-rendering index
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Harmonic Concatenation of 1.5-Femtosecond-Pulses in the Deep UV
摘要： Waveforms with durations short enough to probe the electronic timescale can be generated both in the extreme UV and in the IR-VIS region of the electromagnetic spectrum. In the deep UV (DUV), where for example many basic aromatic molecules absorb radiation and undergo photochemical reactions, pulses with such extremely short durations have not yet been demonstrated. A fundamental difficulty is rooted in the large group velocity dispersion of any optical component in the DUV, causing a DUV pulse to be readily broadened and distorted before it reaches the sample. The present record for the shortest DUV pulses is 2.8 fs. Here, a scheme for the coherent synthesis of DUV waveforms is presented. The principle is the concatenation of spatial and temporal harmonics that are created by two noncollinear IR-VIS pulses. Cascaded processes of frequency conversion and self-diffraction in a thin MgF2 plate yield a multifaceted emission pattern of temporal and spatial harmonics. The emission angle Φ of the harmonic orders depends on the frequency. Broadband waveforms arise, of which the lower frequency bands belong to one spatial harmonic, and the higher frequency bands belong to the other spatial harmonic. In order to synthesize ultrashort waveforms from these frequency bands, their phases must be adjusted. This is accomplished by controlling the groove-envelope phase (φGEP) of the fundamental pulses, which is determined by their delay on the subcycle timescale. Using temporal harmonics of third order, the concatenation of two spatial harmonics synthesizes DUV pulses of 1.5 fs. A generic feature is that these waveforms are spatially separated from the fundamental pulses and are therefore available for immediate spectroscopy usage without any subsequent optical elements.
关键词： Harmonic concatenation,femtosecond-pulses,spatial harmonics,deep UV,temporal harmonics,coherent synthesis
更新于2025-09-12 10:27:22
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Deep UV laser at 249 nm based on GaN quantum wells
摘要： In this letter, we report on deep UV laser emitting at 249 nm based on thin GaN quantum wells (QWs) by optical pumping at room temperature. The laser threshold was 190 kW/cm2 that is comparable to state-of-the-art AlGaN QW lasers at similar wavelengths. The laser structure was pseudomorphically grown on a c-plane sapphire substrate by metalorganic chemical vapor deposition, comprising 40 pairs of 4 monolayer (ML) GaN QWs sandwiched by 6 ML AlN quantum barriers (QBs). The low threshold at the wavelength was attributed to large optical and quantum confinement, and high quality of the material, interface, and Fabry-P?rot facet. The emissions below and above the threshold were both dominated by transverse electric polarizations thanks to the valence band characteristics of GaN. This work unambiguously demonstrates the potentials of the binary AlN/GaN heterojunctions for high-performance UV emitters.
关键词： GaN quantum wells,deep UV laser,UV emitters,AlN/GaN heterojunctions,optical pumping
更新于2025-09-12 10:27:22
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Ultra-Robust Deep-UV Photovoltaic Detector Based on Graphene/(AlGa) <sub/>2</sub> O <sub/>3</sub> /GaN with High-Performance in Temperature Fluctuations
摘要： A strategy of adopting Ga2O3 alloyed with Al element to reduce the oxygen vacancy defect density and to enhance the interface barrier height of Ga2O3 heterojunction is proposed to fabricate deep-UV photovoltaic detectors with high thermal stability, high photoresponsivity and fast response speed. Here, a graphene/(AlGa)2O3/GaN device with a photoresponsivity of ~20 mA/W, a rise time of ~2 μs and a decay time of ~10 ms is presented at 0 V bias. At the working temperature of 453 K, the device still exhibits a photo-to-dark current ratio (PDCR) of ~1.8×103, which is 1-2 orders of magnitude higher than that of reported high temperature deep-UV film detectors. By comparing the formation energy of oxygen vacancy defects and the interface barrier height of heterojunction at different temperatures in graphene/Ga2O3/GaN and graphene/(AlGa)2O3/GaN systems respectively, the strategy of synthesizing (AlGa)2O3 ternary composite alloy is proved reliable for fabricating high performance deep-UV photovoltaic detectors. The method proposed in this paper can provide reference for the preparation of deep-UV photovoltaic detectors with high photoresponsivity and thermal stability in the future.
关键词： deep-UV,high temperature,photovoltaic,(AlGa)2O3,high photo-to-dark current ratio
更新于2025-09-11 14:15:04
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Synthesis of Mesoporous TiO2/Boron-Doped Diamond Photocatalyst and Its Photocatalytic Activity under Deep UV Light (λ = 222 nm) Irradiation
摘要： There is a need for highly efficient photocatalysts, particularly for water purification. In this study, we fabricated a mesoporous TiO2 thin film on a boron-doped diamond (BDD) layer by a surfactant-assisted sol-gel method, in which self-assembled amphiphilic surfactant micelles were used as an organic template. Scanning electron microscopy revealed uniform mesopores, approximately 20 nm in diameter, that were hexagonally packed in the TiO2 thin film. Wide-angle X-ray diffraction and Raman spectroscopy clarified that the framework crystallized in the anatase phase. Current–voltage (I–V) measurements showed rectification features at the TiO2/BDD heterojunction, confirming that a p–n hetero-interface formed. The as-synthesized mesoporous TiO2/BDD worked well as a photocatalyst, even with a small volume of TiO2 (15 mm × 15 mm × c.a. 1.5 μm in thickness). The use of deep UV light (λ = 222 nm) as a light source was necessary to enhance photocatalytic activity, due to photo-excitation occurring in both BDD and TiO2.
关键词： photocatalyst,water purification,thin film,surfactant-assisted sol-gel method,p-n heterojunction,deep UV light,mesoporous metal oxide
更新于2025-09-10 09:29:36
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Triaxially uniform high-quality Al<sub>x</sub>Ga<sub>(1-x)</sub>N (x∽50%) nanowires on template free sapphire substrate
摘要： We have demonstrated the growth of high-quality AlxGa(1-x)N (x~50%) nanowires(NWs) for the first time on the sapphire substrate without using GaN NWs as the template by Plasma-Assisted Molecular Beam Epitaxy. Our newly developed process elucidates that depending on the substrate temperature and V/III ratio an AlGaN network is formed on sapphire substrate prior to the NWs growth. We find that the ledges of this kinked shaped network act as nucleation sites for the NW growth. The present observations suggest that availability of nucleation sites and higher substrate temperature during growth are the key parameters for the growth of homogeneous AlGaN NWs on the sapphire substrates. Energy Dispersive X-ray Spectroscopy, High-Resolution Transmission Electron Microscopy, Raman Spectroscopy, X–ray diffraction, Photoluminescence spectroscopy, and Scanning Electron Microscopy analysis show that AlGaN NWs exhibit near-atomic scale compositional uniformity along the length as well as across the diameter.
关键词： AlGaN NW,Deep UV light,PAMBE
更新于2025-09-10 09:29:36
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Y2(CO3)3?H2O and (NH4)2Ca2Y4(CO3)9?H2O: Partial Aliovalent Cation Substitution Enabling Evolution from Centrosymmetry to Noncentrosymmetry for Nonlinear Optical Response
摘要： An effective approach, the partial aliovalent cation substitution (PACS), was successfully employed to develop nonlinear optical (NLO) material. Two novel rare earth carbonates, Y2(CO3)3·H2O (YC) and (NH4)2Ca2Y4(CO3)9·H2O (CYC), were synthesized, which feature the same honeycomb-like framework structure. From YC to CYC, the partial substitution of Y3+ with Ca2+ led to the evolution of space group from centrosymmetric P63/mcm to noncentrosymmetric P63mc. The CYC exhibited a second harmonic generation (SHG) effect of 2.1 × KH2PO4 (KDP) and a deep-UV cut-off edge (<200 nm). It was concluded that the SHG effect originates from the ordered arrangement of (CO3)2- groups and the dipole polarization enhancement of [Ca0.33Y0.67O9] polyhedra. Specifically, the long-range ordered electric field of channels induced the ordered arrangement of (CO3)2- groups. This synthetic approach and SHG-activated induction mechanism may afford new strategies for the design and synthesis of NLO materials.
关键词： nonlinear optical materials,partial aliovalent cation substitution,rare earth carbonates,deep-UV cut-off edge,second harmonic generation
更新于2025-09-04 15:30:14