Commercial Diode Research Articles

A speed-amplified tri-stable piezoelectric-electromagnetic-triboelectric hybrid energy harvester for low-frequency applications

This work proposes a new speed-amplified multi-stable tri-hybrid energy harvesting technique via the multi-stable nonlinearity enhanced frequency up-conversion and rack-pinion mechanisms to efficiently harness structural and biomechanical vibration energy. In the present design, two frequency up-conversion piezoelectric generators, an array-type electromagnetic generator and a sliding-mode triboelectric nanogenerator are integrated together to form a compact and interactive system. By utilizing the rack-pinion mechanism, the relative speed between the stators and the translators of the electromagnetic and triboelectric generators are both doubled. Meanwhile, the process of frequency up-conversion in the piezoelectric generators is also doubled per each cycle. This results in better performance under wideband and low-frequency vibration sources. For verification, a prototype of this design is tested by mechanical excitations and body-induced motions. In the shaker test, the prototype can generate a peak output power of 446.16 mW under an optimal resistance load, resulting in a normalized power density of 4.20 mW cm–3 g–2 at 5 Hz under 1 g. The prototype also exhibits exceptional performance under various human motion tests, it can drive 600 commercial light-emitting diodes simultaneously. Using a commercial DC/DC voltage regulator circuit, the proposed harvester can serve as a universal power source to charge commercial electronic devices, including smartphones and GPS sensors. The present design shows great potential as a sustainable power source for wearable/portable electronics as well as wireless monitoring systems.

Experimental study of spatial and temporal coherence in a laser diode with optical feedback.

Optical feedback can reduce the linewidth of a semiconductor laser by several orders of magnitude, but it can also cause line broadening. Although these effects on the temporal coherence of the laser are well known, a good understanding of the effects of feedback on the spatial coherence is still lacking. Here we present an experimental technique that allows discriminating the effects of feedback on temporal and spatial coherence of the laser beam. We analyze the output of a commercial edge-emitting laser diode, comparing the contrast of speckle images recorded using a multimode (MM) or single mode (SM) fiber and an optical diffuser, and also, comparing the optical spectra at the end of the MM or SM fiber. Optical spectra reveal feedback-induced line broadening, while speckle analyses reveal reduced spatial coherence due to feedback-excited spatial modes. These modes reduce the speckle contrast (SC) up to 50% when speckle images are recorded using the MM fiber, but do not affect the SC when the images are recorded using the SM fiber and diffuser, because the spatial modes that are excited by the feedback are filtered out by the SM fiber. This technique is generic and can be used to discriminate spatial and temporal coherence of other types of lasers and under other operating conditions that can induce a chaotic output.

Growth and spectroscopic properties of a novel Tm3+-doped YSr3(PO4)3 disordered crystal

A novel Tm3+-doped YSr3(PO4)3 (Tm:YSP) crystal with a disordered crystal structure was grown by using the Czochralski pulling method. The single crystal growth, structure, absorption and emission spectra were systematically analyzed. The absorption bandwidth at ∼792 nm was found to be 21 nm, showing that the Tm:YSP crystal was very suitable for commercial laser diodes pumping of AlGaAs. Furthermore, the maximum emission cross section centering at 1835 nm was determined to be 0.86 × 10−20 cm2 with an emission bandwidth of 202 nm, which indicates the promising applications in the fields of ultrafast and tunable lasers. In addition, Spectroscopic parameters, containing Judd – Ofelt intensity, line strengths, radiative transition probabilities, fluorescence branching ratio and radiative lifetime, were analyzed by using the Judd – Ofelt theory. All above results showed that the Tm:YSP crystal with a disordered structure was a potential laser medium in the ⁓ 2 μm region.

Comparison of the effects of continuous and intermittent electron irradiation on commercial 4H-SiC Schottky barrier diodes

The radiation hardness of commercial 4H-SiC Schottky barrier diodes (STPSC1006D) has been investigated in this study. Primarily, intermittent irradiation at 0.5 Hz and continuous irradiation were analyzed and compared. Current–voltage (I–V), capacitance–voltage transform deep-level transient spectroscopy (FT-DLTS) were used to characterize the devices before and after irradiation. The devices show stability in their I–V characteristics upon irradiation. The free carrier concentration of the devices obtained from the C–V results decreased with the increasing of electron fluence. Additionally, new defects were observed after irradiation, which was the reason for the degradation in the electrical properties of the devices. The comparison of the devices irradiated intermittently and those irradiated continuous reveals that intermittent irradiation causes greater changes in electrical properties than continuous irradiation. These characteristics show the impact of STPSC1006D in space applications.

Polarization Entanglement from Parametric Down-conversion with an LED Pump

Spontaneous parametric down-conversion (SPDC) is a reliable platform for entanglement generation. Routinely, a coherent laser beam is an essential prerequisite for pumping the nonlinear crystal. Here we break this barrier to generate polarization-entangled photon pairs by using a commercial light-emitting diode (LED) source to serve as the pump beam. This effect is counterintuitive, as the LED source is of extremely low spatial coherence, which is transferred during the down-conversion process to the biphoton wave function. However, the type-II phase matching condition naturally filters the specific frequency and wavelength of LED light exclusively to participate in SPDC such that localized polarization Bell states can be generated, regardless of the global incoherence over the full transverse plane. In our experiment, we characterize the degree of LED light-induced polarization entanglement in the standard framework of the violation of Bell's inequality. We achieve the Bell value $S=2.33\ifmmode\pm\else\textpm\fi{}0.097$, obviously surpassing the classical bound $S=2$ and thus witnessing the quantum entanglement. Our work can be extended to prepare polarization entanglement by using other natural light sources, such as sunlight and biolight, which holds promise for electricity-free quantum communications in outer space.

Flexible, stripe-patterned organic solar cells and modules based on multilayer-printed Ag fibers for smart textile applications

Rapid advancement in the fabrication technologies of stripe/fiber-shaped optoelectronic devices has driven the performance of smart textile electronics to a new height. In the development of high-performance smart textile electronics, indium tin oxide (ITO)-free flexible transparent conductive electrodes (TCEs) are particularly desirable because they offer superior flexibility and lower manufacturing cost than the brittle ITO-based counterparts. Herein, we innovatively combine spin-coating and three-dimensional direct-ink writing (three-dimensional-DIW) techniques to develop large-area (5 × 5 cm2) PEDOT:PSS/Ag-fibers hybrid TCEs (denoted as DIW-TCEs) for application in flexible organic solar cells (OSCs). Through a multilayer printing strategy, high aspect-ratio Ag-fibers are successfully deposited on top of the planar PEDOT:PSS film. The resulting DIW-TCEs, when fully embedded in a colorless polyimide substrate, exhibit excellent electrical conductivity (sheet resistance ∼ 4 Ω/□), superior optical transmittance, and mechanical flexibility. One-dimensional stripe-patterned OSCs (stripe-OSCs) based on DIW-TCEs achieved power conversion efficiency of 9.3% and 8.2% at an active area of 0.11 cm2 and 0.31 cm2, respectively. For real-life application, a flexible power module was constructed using eight stripe-OSCs. When attached on textile, the module successfully lit up a commercial light-emitting diode upon photocharging. The unique DIW-TCE fabricated herein can be the ITO-free alternative for the production of smart textile electronics.

Spectroscopic characterization of Tm:CaYAlO4 shaped crystal fibers grown by the micro-pulling-down method

Tm3+-doped CaYAlO4 (Tm:CALYO) shaped crystals fibers with various doping concentration of 2 at.%, 3 at.%, 5 at.% and 7 at.% have been successfully grown by the micro-pulling-down (μ-PD) method. The polarized absorption spectra, polarized fluorescence spectra and fluorescence decay curves were analyzed at room temperature. The absorption bands of 3H6→3H4 transition centered at around 800 nm match well with commercial AlGaAs laser diode pumping sources. For 7 at.% Tm:CALYO crystal fiber, the full width at half maximum (FWHM) of the emission band for π polarization at 1806 nm was 225.4 nm. The fluorescence of 3F4 level decreased strongly as the thulium concentration increased. All the results indicate that Tm:CALYO crystal fibers are promising for ultrashort and tunable laser operation.

High-Performance Stretchable Thermoelectric Generator for Self-Powered Wearable Electronics.

Wearable thermoelectric generators (TEGs), which can convert human body heat to electricity, provide a promising solution for self-powered wearable electronics. However, their power densities still need to be improved aiming at broad practical applications. Here, a stretchable TEG that achieves comfortable wearability and outstanding output performance simultaneously is reported. When worn on the forehead at an ambient temperature of 15°C, the stretchable TEG exhibits excellent power densities with a maximum value of 13.8 µW cm-2 under the breezeless condition, and even as high as 71.8 µW cm-2 at an air speed of 2 m s-1 , being one of the highest values for wearable TEGs. Furthermore, this study demonstrates that this stretchable TEG can effectively power a commercial light-emitting diode and stably drive an electrocardiogram module in real-time without the assistance of any additional power supply. These results highlight the great potential of these stretchable TEGs for power generation applications.

Effect of Electrolytic Cations on a 3D Cd-MOF for Supercapacitive Electrodes

A cadmium-based metal-organic framework (Cd-MOF) is synthesized in a facile manner at ambient temperature by an easy slow diffusion process. The three-dimensional (3D) structure of Cd-MOF is authenticated by single-crystal X-ray diffraction studies and exhibits a cuboid-shaped morphology with an average edge length of ∼1.13 μm. The prepared Cd-MOF was found to be electroactive in nature, which resulted in a specific capacitance of 647 F g-1 at 4 A g-1 by maintaining a retention of ∼78% over 10,000 successive cycles in the absence of any binder. Further, to distinguish the efficiency of Cd-MOF electrodes, different electrolytes (NaOH, KOH, and LiOH) were explored, wherein NaOH revealed a higher capacitive response due to its combined effect of ionic and hydrated ionic radii. To investigate the practical applicability, an asymmetric supercapacitor (ASC) device is fabricated by employing Cd-MOF as the positive electrode and activated carbon (AC) as the negative electrode, enabling it to light a commercial light-emitting diode (LED) bulb (∼1.8 V). The as-fabricated ASC device delivers comparable energy density and power density.

Green means go: Green light promotes hypocotyl elongation via brassinosteroid signaling.

Although many studies have elucidated the mechanisms by which different wavelengths of light (blue, red, far-red, or ultraviolet-B [UV-B]) regulate plant development, whether and how green light regulates plant development remains largely unknown. Previous studies reported that green light participates in regulating growth and development in land plants, but these studies have reported conflicting results, likely due to technical problems. For example, commercial green light-emitting diode light sources emit a little blue or red light. Here, using a pure green light source, we determined that unlike blue, red, far-red, or UV-B light, which inhibits hypocotyl elongation, green light promotes hypocotyl elongation in Arabidopsis thaliana and several other plants during the first 2-3 d after planting. Phytochromes, cryptochromes, and other known photoreceptors do not mediate green-light-promoted hypocotyl elongation, but the brassinosteroid (BR) signaling pathway is involved in this process. Green light promotes the DNA binding activity of BRI1-EMS-SUPPRESSOR 1 (BES1), a master transcription factor of the BR pathway, thus regulating gene transcription to promote hypocotyl elongation. Our results indicate that pure green light promotes elongation via BR signaling and acts as a shade signal to enable plants to adapt their development to a green-light-dominant environment under a canopy.

Preparation of novel KAlSiO4: Ce3+ broadband cyan-emitting phosphors via partial cation substitution for applications in white-light LEDs

Broadband cyan-emitting phosphors with strong absorption between 300 and 400 nm are ideal replacements for traditional blue and green phosphors used in commercial light-emitting diodes (LEDs). In this paper, a series of K1-xAlSiO4: xCe3+(x = 0.02–0.06) broadband cyan phosphors were prepared using the traditional high-temperature solid state method and the cation un-equivalent substitution strategy. It was found that the KAlSiO4 matrix has a monoclinic structure with high symmetry. The experimental and theoretical optical band gaps of the host were 5.6 eV and 4.86 eV, respectively. After doping with Ce3+, strong absorption was observed in the near ultraviolet region. The optimum Ce3+ doping concentration in the host was 0.04 as indicated by the strongest observed emission intensity. The full width at half maximum of the emission spectra of the series of samples are all greater than 120 nm and covered the blue and green wavelength ranges (370–600 nm). The luminous intensity of the K0·96AlSiO4: 0.04Ce3+phosphor at 150 °C was 91.1% of that at room temperature, and the Gaussian peak of the emission spectrum slightly broadened. These results were also combination with theoretical DFT calculations. It was found that the phosphor had very good thermal stability and rigidity. The phosphor was also mixed with a commercial red phosphor, interfaced with a UV chip and packaged into an LED. This LED was characterized and had a color rendering index greater than 90 across a broad range of drive currents. This work highlights the utility of the fabricated phosphor as means of simplifying white-light LED fabrication.

Defect engineering on VO2(B) nanoleaves/graphene oxide for the high performance of cathodes of zinc-ion batteries with a wide temperature range

Designing cathodes with long service life, remarkable rate capability and all-climate workable is crucial to improve the performance of aqueous zinc-ion batteries (AZIBs). Herein, we constructed a vanadium dioxide/graphene oxide (VO2(B)/GO) sample that combines VO2 with GO through hydrothermal route and can simultaneously provide rate capability. VO2(B)/GO is rich in oxygen vacancies, which weakens the electrostatic force, and GO prevents vanadium oxidation. Density functional theory (DFT) calculations elucidate oxygen vacancies can offer more storage sites with increased reaction kinetics. The electrode exhibited a high reversible capacity of 423 mAh g−1 at 0.5 A g−1 and preserved long-life cycling properties at 15 A g−1. The presence of oxygen vacancies and GO can contribute to the excellent performance and prevent the structure of VO2 from collapsing during cycling. We successfully lit up commercial light-emitting diode (LED) lights with a VO2(B)/GO electrode. In addition, VO2(B)/GO exhibits excellent performance in all-climate conditions (-15-60 °C). This combinatorial design strategy provides a broadly applicable approach for durability and all-climate workable batteries.

An efficient blue-excitable broadband Y3ScAl4O12:Ce3+ garnet phosphor for WLEDs.

Most commercial phosphor-converted white light-emitting diodes (pc-WLEDs) are manufactured with blue LED chips and yellow-emitting Y3Al5O12:Ce3+ (YAG:Ce3+) garnet phosphor, but the lack of blue-green light in the spectrum results in a low color rendering index (CRI). In this paper, we synthesized Y3ScAl4O12:Ce3+ (YSAG:Ce3+) by replacing Al3+ in YAG:Ce3+ with Sc3+. The introduction of Sc3+ with a larger ionic radius through a cation substitution strategy causes lattice expansion, elongation of the Y-O bond, and ultimately a decrease in Ce3+ 5d level crystal field splitting. As a consequence, the emission spectrum undergoes a blue-shift of 10 nm. Furthermore, the YSAG:Ce3+ phosphor exhibits good thermal stability, and its emission intensity at 423 K is about 58% of that at 303 K. Moreover, the analysis of Eu3+ emission spectra demonstrates that the introduction of Sc3+ resulted in a slight reduction of the dodecahedral lattice symmetry. YSAG:Ce3+ effectively compensates for the lack of the blue-green region, and WLEDs with high color rendering index (90.1), low color temperature (4566 K) and high luminous efficiency (133.59 lm W-1) were prepared using the combination of YSAG:0.08Ce3+, CaAlSiN3:Eu2+ and 450 nm blue chips. These findings indicate that YSAG:Ce3+ garnet phosphor has potential to be used in high quality WLEDs.

Portable Frequency Stabilized Lasers for Quantum Technologies Using Digital Techniques

Quantum atomic technologies such as optical clocks and atom interferometers have demonstrated their potential in laboratory settings, however their widespread deployment for real-world applications requires significant improvement in their Size, Weight, Power and Cost (SWaP-C). We have fabricated compact laser avionics suitable for laser cooling and spectroscopy applications. The system employs a commercial laser diode, fibre-coupled optics, current and temperature controllers, analogue-to-digital converters, all-digital signal processing, and operates on a single 5V power supply. Using these components, a 780nm laser has been stabilised to the Rb D2 transition via FM spectroscopy, with a SWaP budget of 1 L, 300 g, less than 10W. Due to its modular design and digital re-programmability, the low-SWaP-C system developed here can be applied to devices across the quantum technology sector.

Continuous-wave three-wavelength operation of a diode-pumped Tm:YVO4 laser on the 3H4→3H5 and 3F4→3H6 transitions

A diode-pumped continuous-wave Tm:YVO4 laser operating on the H34→H35 and F43→H36 transitions was demonstrated for the first time, to the best of our knowledge. An a-cut Tm:YVO4 crystal with 1.5% (atomic fraction) Tm3+ ion concentration was used to characterize the laser behavior. A common commercial laser diode with a central wavelength of 790 nm and a bandwidth of 3.2 nm was utilized as a pump source. With an output coupler for the H34→H35 and F34→H36 transitions, simultaneous three-wavelength laser operation was achieved. The laser emissions at 2292 and 2363 nm in π-polarization and at 2108 nm in σ-polarization were realized. With an incident pump power of 22 W, the total output power of 1.17 W at 2292, 2363, and 2108 nm was obtained. The output power at 2292 and 2363 nm was measured to be 750 mW, and the output power at 2108 nm was measured to be 420 mW.

Self-Trapped Excitons Mediated Energy Transfer to Sm3+ in Cs2AgIn(1–x)SmxCl6:Bi Double Perovskite Nanocrystals

Lanthanide ions (Ln3+) are well-known dopants for controlling the optoelectronic properties of double perovskites (DPs). However, the excitation energy of Ln3+-doped Cs2AgInCl6 being too high (∼250–290 nm) limits its direct excitation by commercial UV light-emitting diodes (≥365 nm). To overcome this challenge, we employed Bi3+ as a sensitizer to induce the emission of Sm3+ at much lower excitation energy in Sm3+–Bi3+ codoped Cs2AgInCl6 DP nanocrystals (NCs). Spectral analysis shows that a trace amount of Bi3+ (∼1%) doping provides dual emission of self-trapped excitons (STEs) and characteristic emissions of Sm3+ assigned to 4G5/2 to 6HJ (J = 5/2, 7/2, 9/2, and 11/2) transitions with 368 nm excitation energy. Transient absorption spectroscopic results revealed the existence of nonradiative energy transfer from STE states. Subsequently, we propose a mechanism to explain the formation of energy-transfer channels from STEs to excited states of Sm3+. Our study demonstrates that Bi3+ can efficiently sensitize Sm3+ to modify the optical properties of lead-free DP NCs to expand their luminescence application.

Gamma Ray Effects on Multi-Colored Commercial Light-Emitting Diodes at MGy Level

Light-emitting diodes (LEDs) are of interest for implementation in radiation environments, such as part of illumination systems of radiation-tolerant cameras able to provide images at high doses (>MGy). It is then mandatory to characterize the radiation effects on all of the LED key properties exploited for such applications. To this aim, the evolution of the optical properties of commercial LEDs after they have been exposed to γ-rays, up to total ionizing dose (TID) levels of 2 MGy(air) at room temperature, is discussed. The devices under test include four LEDs of different colors (red, green, blue and white) in the same package. This allows a direct comparison between the responses of the different structures and technologies, as the proximity between the diodes ensures the uniformity of their irradiation conditions. The radiation effect on the electron–photon conversion mechanisms inside these LEDs is investigated through the evolution of their external quantum efficiency (EQE) vs. current characteristics. The spectral emission pattern of LEDs after irradiation at different dose levels is then characterized to estimate the TID effects on the lens which surrounds the LED package. The presented results show a monotone radiation-induced EQE decrease as a function of the TID, especially in the red LEDs. For the tested red LEDs, the EQE decreased up to 78% after a TID of 1 MGy when they were OFF during irradiation, and up to 8% when they were ON during irradiation. A visual inspection of the devices after irradiation shows a mechanical degradation of the lens shared among the four diodes. However, the emission pattern analysis does not show any significant radiation-induced changes in the optical properties of the lens. Based on these results, it appears possible to design LED-based illumination systems able to survive to MGy dose levels that can be integrated as subsystems of radiation-hardened cameras.

Design of ultracompact broadband focusing spectrometers based on diffractive optical networks.

We propose the inverse design of ultracompact, broadband focusing spectrometers based on adaptive diffractive optical networks (a-DONs). Specifically, we introduce and characterize two-layer diffractive devices with engineered angular dispersion that focus and steer broadband incident radiation along predefined focal trajectories with the desired bandwidth and nanometer spectral resolution. Moreover, we systematically study the focusing efficiency of two-layer devices with side length L=100μ m and focal length f=300μ m across the visible spectrum and demonstrate accurate reconstruction of the emission spectrum from a commercial superluminescent diode. The proposed a-DONs design method extends the capabilities of efficient multi-focal diffractive optical devices to include single-shot focusing spectrometers with customized focal trajectories for applications to ultracompact spectroscopic imaging and lensless microscopy.

All-Optical Nanosensor for Displacement Detection in Mechanical Applications.

In this paper, we propose the design of an optical system based on two parallel suspended silicon nanowires that support a range of optical resonances that efficiently confine and scatter light in the infrared range as the base of an all-optical displacement sensor. The effects of the variation of the distance between the nanowires are analyzed. The simulation models are designed by COMSOL Multiphysics software, which is based on the finite element method. The diameter of the nanocylinders (d = 140 nm) was previously optimized to achieve resonances at the operating wavelengths (λ = 1064 nm and 1310 nm). The results pointed out that a detectable change in their resonant behavior and optical interaction was achieved. The proposed design aims to use a simple light source using a commercial diode laser and simplify the readout systems with a high sensitivity of 1.1 × 106 V/m2 and 1.14 × 106 V/m2 at 1064 nm and 1310 nm, respectively. The results may provide an opportunity to investigate alternative designs of displacement sensors from an all-optical approach and explore their potential use.

Direct growth of hierarchically SnS2 layered nanostructure on nickel foam for high-performance solid-state supercapacitors

SnS2 is a promising candidate for an electrode material in lithium-ion batteries and photocatalysts due to its high accessible surface area and significant interlayer nanostructure. Here, we have synthesized hierarchically SnS2 layered nanostructure developed on nickel foam through a facile one-step template-free solvothermal process. FESEM images show the two-dimensional (2D) layer structure of SnS2 arranged in a flower petallike configuration. Further, the electrochemical properties of hierarchically SnS2 were investigated in 1 M KOH electrolyte for supercapacitor (SC) implementation. Synthesized SnS2 electrode material shows excellent specific capacitance of 604F g−1 at 1 mVs−1 and better cyclic stability of 86.2 % over 3000 cycles because the unique layered nanostructure increases the active sites and ion/electron transfer at the electrolyte/electrode interface. The hierarchically structured SnS2 electrode and its potential practical applications were tested by fabricating an SSC device to effectively light a commercial light-emitting diode (LED). This research shows that layered 3D SnS2 electrodes are a promising technology for sustainable energy storage applications. The above results indicated that hierarchically SnS2 with a 2D layered structure has a huge capability as an electrode material for high-performance SC applications and a promising potential for future energy storage devices.