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High production-yield solid-state carbon dots with tunable photoluminescence for white/multi-color light-emitting diodes
摘要： Plastic waste is generally resistant to natural degradation and has become a major environmental pollution problem globally. The pollution of ecosystems seriously affects the health and survival of organisms, including humans. Much attention has been paid to finding suitable ways to convert plastic waste into high-value-added carbon materials. To this end, we report the high production yield (60%–85%) of carbon dots (CDs) for solid-state fluorescence (SSF) obtained by a one-step solvothermal method using waste expanded polystyrene as the precursor. The SSF mechanism of the CDs was also explored. Their emission wavelength, with a large full width at half maximum of 150–200 nm, exhibited tunable photoluminescence from white to yellow and orange. CDs powder was used to fabricate single-component white and multi-colour light-emitting diodes on UV chips. Overall, plastic waste was converted into tunable solid-state fluorescent CDs powder, which has promising applications in carbon-based lighting, by a simple solvothermal method that provides a viable method for recycling plastic waste.
关键词： High production yield,Light-emitting dots,Solid-state fluorescence,Carbon dots
更新于2025-09-19 17:13:59
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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) - Gravitational Physics with Atomic Quantum Sensors
摘要： This paper proposes a practical solution of high-frequency-link dc transformer based on switched capacitor (SCDCT) for medium-voltage dc (MVDC) power distribution application. Compared to the traditional dc transformer scheme, the proposed SCDCT can disconnect from MVDC distribution grid effectively as a dc breaker when a short fault occurs in the distribution, can enhance power transfer capacity, and always ensures high-frequency-link voltage match to improve current impact and ef?ciency performances, and the redundancy design can be achieved when some submodules fail to improve the reliability. In the paper, the topology, voltage and power characterization, control strategy, startup, and fault solution of SCDCT are presented and analyzed comprehensively. At last, an SCDCT prototype is built and the experimental results verify the correctness and effectively of the proposed solution.
关键词： switched capacitor,dc transformer,dc–dc converter,solid-state transformer (SST),DC distribution,high-frequency-link,dual active bridge (DAB)
更新于2025-09-19 17:13:59
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In Depth Analysis of Photovoltaic Performance of Chlorophyll Derivative-Based a??All Solid-Statea?? Dye-Sensitized Solar Cells
摘要： “all solid-state” dye-sensitized solar cells (DSSCs) with chlorophyll derivatives were integrated into a mesoporous TiO2 electrode and 2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene as the hole-transport material. Despite modest power conversion efficiencies (PCEs) between 0.26% and 0.55% achieved for these chlorin dyes, a systematic investigation was carried out in order to elucidate their main limitations. To provide a comprehensive understanding of the parameters (structure, nature of the anchoring group, adsorption . . . ) and their relationship with the PCEs, density functional theory (DFT) calculations, optical and photovoltaic studies and electron paramagnetic resonance analysis exploiting the 4-carboxy-TEMPO spin probe were combined. The recombination kinetics, the frontier molecular orbitals of these DSSCs and the adsorption efficiency onto the TiO2 surface were found to be the key parameters that govern their photovoltaic response.
关键词： EPR,chlorophyll,spirulina,solid state dye sensitized solar cells,anchoring groups
更新于2025-09-19 17:13:59
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Efficient Tm:LiYF4 Lasers at ～2.3 lm: Effect of Energy-Transfer Upconversion
摘要： The 3H4 → 3H5 transition of Thulium ions (Tm3+), which features laser emission at ~2.3 μm is studied in details. We revise the conditions for efficient laser operation using a rate- equation model accounting for the ground-state bleaching, cross- relaxation and energy-transfer upconversion (ETU). We show that ETU has a crucial role in reaching more than unity pump quantum efficiency (QE) for ~2.3 μm Tm lasers based on highly- doped crystals. A Ti:Sapphire pumped quasi-continuous-wave 3.5 at.% Tm:LiYF4 laser generated 0.73 W at 2306 nm with a record-high slope efficiency of 47.3% (versus the absorbed pump power, for double-pass pumping) featuring a QE of 1.27. Diode- pumping of this crystal yielded a peak output power of >2 W. The first 2.3 μm Tm waveguide laser is also reported based on Tm:LiYF4 epitaxial layers with even higher doping of 6.2 at.% generating 0.23 W with a slope efficiency of 19.8%. The spectroscopic properties of Tm:LiYF4 relevant for the ~2.3 μm laser operation are revised as well.
关键词： mid-infrared,spectroscopy,laser transitions,Solid-state lasers
更新于2025-09-19 17:13:59
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Control of the photoluminescence properties of Nd:YAG crystals by laser irradiation
摘要： This paper presents luminescence properties of Nd:YAG crystal defects including oxygen vacancy, O-hole center, F and F+ centers. The Nd:YAG crystal defects have photoluminescence emission peaks in the ~ 350-500 nm range of UV-Vis spectral region. The results show that laser irradiation can control photoluminescence properties of the Nd:YAG crystal samples. Our results can be very important in solid state laser and surface engineering.
关键词： solid state laser,laser irradiation,crystal defects,photoluminescence,Nd:YAG
更新于2025-09-19 17:13:59
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Rich reddish-orange emitting PBTNAPr glasses for laser applications
摘要： Lead borate oxyfluoride glasses containing different amounts of PrF3 with composition PbO–B2O3–TeO2–NaF–AlF3-PrF3 were prepared and characterized for visible and fiber lasers. The amorphous phase and compositional analysis were carried out through powder X-ray diffraction and Fourier transform infrared spectra, respectively. Using the room temperature optical absorption spectra, the spectroscopic properties were determined applying the modified Judd-Ofelt theory. The photoluminescence excitation spectral studies obtained by controlling the emission through Pr3+: 1D2 → 3H4 (604 nm) transition shows prominent excitation band positioned at ~448 nm (3H4 → 3P2). Upon 448 nm excitation, the studied glasses exhibit an intense emission through 1D2 → 3H4 (604 nm) transition along with feeble emissions from 3P1 and 3P0 metastable levels to the inner energy levels. The emission spectra show a shift towards longer wavelengths (called the red-shift) with increase of PrF3 content. The luminescence decay time of 1D2 emission level was found decreased with increase of PrF3 content. The quenching of decay time was assigned to the transfer of energy among the excited Pr3+ ions at relatively higher PrF3 contents. The experimental results show that the studied glasses with 0.1 mol% of PrF3 could be the suitable candidate to design rich reddish-orange emitting lasers.
关键词： Solid state lasers,Photoluminescence,Judd-Ofelt analysis,Lead borate glasses
更新于2025-09-19 17:13:59
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Facile synthesis of ZnO microrod photodetectors by solid-state reaction
摘要： In this study, ZnO microrods were directly synthesized via a single-step solid-state reaction using ZnO powders mixed with graphite without a catalyst under an air atmosphere, instead of using vacuum systems and flowing gases. The structure, growth mechanism, and electrical and optical properties of the microrods were investigated under varying growth conditions. The high-resolution transmission electron microscopy images confirmed the formation of single-crystal ZnO microrods. The photoluminescence spectra of the microrods showed green emission, suggesting the formation of non-stoichiometric ZnO microrods due to the formation of oxygen vacancies during sintering. The length and width of the ZnO microrods could be modulated by controlling the graphite content, sintering temperature, and residual time. A simple photodetector consisting of a single-crystal ZnO microrod on a SiO2-coated Si substrate was fabricated. The photodetector exhibited a linear current–voltage curve in visible light. The slope of the curve increased under ultraviolet (UV) irradiation, maintaining a linear shape of the curve. The curve reversibly returned to the initial shape in the absence of UV illumination. The UV on-off current ratio increased because of the decrease in the off-current by compensating for the oxygen vacancies through annealing in an oxygen atmosphere. Thus, in this study, we proposed a simple and efficient approach to fabricate single-crystal ZnO microrods for application in low-cost photodetectors.
关键词： oxygen vacancies,solid-state reaction,single-crystal,ZnO microrods,photodetector
更新于2025-09-19 17:13:59
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Fabrication of Er:Y2O3 transparent ceramics for 2.7?μm mid-infrared solid-state lasers
摘要： Laser grade 7 at.% Er:Y2O3 transparent ceramics with submicron grain size were fabricated by using one-step vacuum sintering followed by hot isostatic pressing (HIPing) technique. Through studying the sintering trajectory of Er:Y2O3 ceramics, the sintering temperature zone where sufficient relative density (> 96%), no pore-boundary separation, and sub-micron grain size (< 1 μm) ceramic samples could be identified. The samples pre-sintered in this zone were readily densified by HIPing. To maximum the densification and achieve high transparency, it is critical to suppress the final-stage grain growth. After HIPing at 1520 °C, the Er:Y2O3 ceramics were fully densified without further grain growth, and exhibited in-line transmission of about 81.6% at 2000 nm. Continuous wave (CW) room temperature laser operation of the Er:Y2O3 transparent ceramic at 2.7 μm was demonstrated.
关键词： Transparent ceramics,Microstructure,Mid-infrared,Solid-state lasers
更新于2025-09-19 17:13:59
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Epitaxial n++-InGaAs ultra-shallow junctions for highly scaled n-MOS devices
摘要： High electron mobility III-V semiconductors like InGaAs are excellent candidates for sub-10 nm n-metal-oxide-semiconductor (nMOS) devices. One of the critical challenges in downscaling III-V devices is achieving low-resistance contacts by forming low-defect, ultra-shallow junctions < 9 nm in depth, with n-type dopant concentrations above 1019 cm?3. In the current study, we combine time-of-flight secondary ion mass spectrometry (ToF-SIMS) depth profile analysis, atomic force microscopy (AFM) imaging, and high-resolution transmission electron microscopy (HR-TEM) to determine the optimal doping strategy for growing Si-doped n++-In0.25Ga0.75As ultra-shallow junctions by molecular beam epitaxy. We test three different approaches to doping: homogeneous co-deposition, single δ-layer (continuous) doping, and triple δ-layer (pulsed) doping. We demonstrate the formation of technologically suitable n++-In0.25Ga0.75As junctions 5–7 nm deep, grown under As-rich conditions with a single δ-layer at temperatures as low as 400 °C. These junctions have peak Si concentrations between 6 × 1019 and 1 × 1020 cm?3 and high crystal quality. The surface self-organizes into smooth ripples or mounds, up to a peak dopant concentration of ~2 × 1020 cm-3. Above this value, enhanced diffusion of Si and In due to a large population of Ga vacancies increases lattice strain in the semiconductor epilayer, triggering a transition from 2D growth to 3D growth and the formation of In0.85Ga0.15As clusters on the surface.
关键词： Time-of-flight secondary ion mass spectrometry,Indium gallium arsenide,Semiconductor growth,Ultra-shallow junctions,Self-organization,Solid-state diffusion
更新于2025-09-19 17:13:59
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Temperature dependent linewidth rebroadening in quantum dot semiconductor lasers
摘要： We experimentally and analytically investigate the influence of temperature on the linewidth of an InP quantum dot (QD) laser. The full width half maximum (FWHM) of the peak in the optical spectrum strongly depends on the pump current and rebroadens at high injection levels. We show that with increasing temperature these effects are amplified. Applying a QD laser model including the excited (ES) and ground state (GS) with detailed balance scattering rates, we are capable of reproducing the experimentally observed data qualitatively and thus show that a relatively simple QD-laser model is capable of capturing this complex behavior. Additionally, we include a temperature dependent energy band gap reduction needed to fit the data and show that this effect enhances the rebroadening effect for higher temperatures.
关键词： Solid State Physics,Linewidth,Quantum Dot Lasers
更新于2025-09-19 17:13:59