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Latest Issue
Issue 7 ， 2021
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Impact of Auger Recombination, Electron Leakage and Hole Injection on Efficiency Droop for DUV LEDs Enhanced Publication
Abstract：We reveal the impact of the Auger recombination, electron leakage and hole injection on the efficiency droop for deep-ultraviolet light-emitting diodes(DUV LEDs). According to our results, the minor change of the efficiency droop is caused by the Auger recombination when the Auger recombination coefficients range from 10-32 cm6·s-1 to 10-30 cm6·s-1. The Auger recombination induces notable role on the efficiency droop by defining the Auger recombination coefficient of 10-29 cm6·s-1. However, the large Auger recombination coefficient is not realistic for AlGaN materials. Besides, we find that the efficiency droop becomes significant with the increased electron leakage, even when the adopted Auger recombination coefficient is as small as 10-32 cm6·s-1. Thus, we can prove electron leakage is a major factor causing the severe efficiency droop for DUV LEDs. We then prove that increasing hole injection can suppress efficiency droop because more electrons can recombine with holes instead of escaping from multiple quantum wells(MQWs).Keywords：DUV LED;Auger recombination;electron leakage;hole injection;efficiency droop- 534
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Published：2021-07-22
Cover Story
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Recent Advances on Thermally Activated Delayed Fluorescence Dendrimers Enhanced Publication
Abstract：Dendritic luminescent materials are a kind of three-dimensional(3D) organic optoelectrical functional materials composed of the central core and the dendrons. They are regarded as an important category of organic luminescent materials for the development of cost-effective and high-efficiency organic light emitting devices(OLEDs) because they possess well-defined molecular structure like small molecules and excellent solubility like polymers. Thermally activated delayed fluorescence(TADF) dendrimers-based OLEDs can realize 100% internal quantum efficiency by utilizing triplet excitons through enhanced reverse intersystem crossing process from the lowest triplet state to singlet state. Thus, TADF dendrimers represent a promising approach towards highly efficient dendritic luminescent materials. During these years, significant progress has been made on the molecular design and device performance of TADF dendrimers. In this review, we classify the TADF dendrimers according to their core structure and summarize their research progress with the emphasis on molecular structure, photophysical properties and device performances. Finally, the perspectives and the key challenges on developing TADF dendrimers are discussed.Keywords：thermally activated delayed fluorescence;dendritic luminescent materials;solution processible;organic light-emitting diodes- 525
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Research Progress of Lu3Al5O12-based Scintillation Ceramics
Abstract：Recent research progress of lutetium aluminum garnet(Lu3Al5O12, LuAG) based scintillation ceramics is introduced. The crystal structure, physical and chemical properties, fabrication methods and structural defects of LuAG-based scintillation ceramics, as well as the novel results in the design of LuAG-based scintillation materials through composition engineering and theory calculation, are summarized in detail. Among those, fruitful progress have been made in Ce3+ and Pr3+ doped LuAG scintillation ceramics, better scintillation properties than their single crystal analogous have been achieved in some ceramic components. The devices assembling were developed correspondingly. Herein, Ce∶LuAG ceramics are considered as the candidate materials for the new generation of electromagnetic calorimeters in high energy physics field due to their high luminescence efficiency and excellent radiation hardness performance. Pr∶LuAG has fast decay time and high temperature luminescence thermal stability, showing potential applications in nuclear medicine PET imaging and well-logging. Based on the idea of defect engineering and band gap engineering, breakthrough has been achieved on their scintillation properties improvement through Mg2+ and Y3+ co-doping. Based on transparent ceramic technology, LuAG-based scintillation ceramics with high optical quality show important application prospect and development potential.Keywords：Lu3Al5O12(LuAG);scintillation ceramics;defects;Ce∶LuAG ceramics;Pr∶LuAG ceramics- 502
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Published：2021-09-22 -
Research Progress of Fluorescent Probes for Monoamine Oxidases Enhanced Publication
Abstract：Monoamine oxidases(MAOs) are a family of membrane-bound mitochondrial enzymes that play important roles in maintaining the homeostasis of neurotransmitters and other bioamines in the biological system through catalytic oxidation and deamination. The dysfunction of MAOs is closely related to many neurological and psychiatric disorders. Thus, monitoring the activity/level of MAOs is of great significance for deeply understanding their physiological functions and for clinical diagnosis of MAOs-related diseases. Fluorescent probes with the ability of in situ, noninvasive and real-time imaging provide an effective method to accurately detect MAOs activity. In this review, the research progress of fluorescent probes for MAOs in recent years and their applications for the diagnosis and therapy of MAOs-related diseases are reviewed.Keywords：monoamine oxidase;fluorescent probes;disease diagnosis;inhibitor;bioimaging- 259
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Luminescence of Mn2+ in Metal Chalcogenide Cluster-based Semiconductors
Abstract：The relatively stable luminescence properties of manganese ions and the success of manganese doped phosphors benefit the continuous study on the luminescence properties of manganese ions. In this paper, cluster structures and component-related luminescence properties of Mn2+ ions in the Mn2+ doped metal chalcogenide cluster-based semiconductors are reviewed. Metal chalcogenide cluster-based semiconductors with precisely structure in atomic level, provide an ideal model for exploring the precise "structure-property relationship" corresponding to the luminescence of Mn2+ ions. In the Mn2+ doped metal chalcogenide cluster-based semiconductors, the difference of bond length near Mn2+ ions and the assembly mode of clusters determine the change of Mn2+ coordination field intensity, further affect the change of Mn2+ ion emission wavelength. In the Mn2+ doped metal chalcogenide nanoclusters, the aggregation form of Mn2+ ions and the number of Mn2+ ions in the aggregate determine the magnitude of Mn-Mn coupling interactions, which directly affect the luminescence efficiency, lifetime, and excitation characteristics of Mn2+ ions.Keywords：metal chalcogenides;manganese doping;semiconductor- 294
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Published：2021-07-22
Invited Review
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Synthesis and Mechanofluorochromic Property of Dicyanodistyrylbenzene Derivative Enhanced Publication
Abstract：Mechanochromic luminescent materials have potential applications in pressure sensitive sensing due to their mechanical response properties. In this paper, a dicyanodistyrylbenzene(DCS) derivative(DCS-Bn) with aggregation-induced emission(AIE) property was synthesized, and its molecular structure was characterized by high-resolution mass spectra. The photophysical properties of DCS-Bn were studied by absorption spectra and fluorescence emission spectra. Furthermore, the aggregation structures of DCS-Bn were measured by differential scanning calorimetry and X-ray diffraction experiment. The results revealed that DCS-Bn has high efficiency luminescence both in solution and solid state. DCS-Bn has the mechanofluorochromic property due to its unique rod molecular structure and the changes of aggregated structures(crystalline or amorphous state). The fluorescence emission color can recover to pristine state through solvent fuming or heating treatment, thus, DCS-Bn has potential application value in the fields of rewritable fluorescent materials.Keywords：aggregation-induced emission;dicyanodistyrylbenzene;high fluorescence quantum yield;aggregation structures;mechanofluorochromic- 297
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Preparation of Controllable Luminescence CDs@MOFs Fluorescent Composites and Their Application in High Color Rendering White LED Enhanced Publication
Abstract：In this paper, neutral red and thiourea were chosen as the raw materials to prepare a novel yellow light carbon dots(CDs) aqueous solution emitting at 540 nm with excitation-dependent fluorescence property. CDs@Al-MOFs and CDs@Zn-MOFs composite fluorescent materials were prepared by Al-MOFs and Zn-MOFs as the support matrices for CDs, respectively, and both of them shown excitation-independent fluorescence property. The optimal emission peaks of CDs@Al-MOFs and CDs@Zn-MOFs were at 555 nm and 612 nm, respectively. Both composites appeared red-shifted to different degrees compared to the emission wavelength at 540 nm of CDs aqueous solution. Through a series of characterizations including TEM, XRD, FT-IR, XPS, UV-Vis and FL on yellow light CDs and their composite fluorescent materials, it was proven that the luminescence mechanism was dominated by the transition of the surface state luminescence of CDs to molecular state luminescence. White light LED devices with different luminescent properties can be obtained by adjusting the ratio of two kinds of composite fluorescent materials. When the mass ratio of CDs@Al-MOFs and CDs@Zn-MOFs is 1∶0.65, the color temperature of the white light LED is 3 968 K and the color rendering index is as high as 82.4, indicating that the CDs@MOFs composite fluorescent material has broad development prospects and application value in the field of white LED.Keywords：yellow emissive carbon dots;metal-organic framework;solid lighting;white light-emitting diodes- 179
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Y2O3-MgO Composite Nano-ceramics Prepared from Core-shell Nano-powders Enhanced Publication
Abstract：Y2O3-MgO composite nano-ceramics are regarded as a significant candidate of infrared transparent ceramics on account of excellent optical and mechanical properties. Nevertheless, a huge challenge remains regarding the critical optical scattering and needless absorption in the near- and mid-infrared bands, which hinders its applications in extreme harsh environments. In present work, Y2O3-MgO core-shell structure nano-powders were prepared via urea precipitation method before that Y2O3-MgO composite nano-ceramics were prepared under spark plasma sintering. Thermogravimetric and differential scanning calorimetry(TG/DSC), X-ray diffraction and scanning electron microscope were performed to analyze as prepared core-shell structure nano-powders and composite nano-ceramics. The size of Y2O3-MgO core-shell structure nano-powders is about 250 nm, and average grain size of the prepared ceramics is approximately 360 nm. The transmittance is 57% at 6 μm, and the Vickers hardness is 820 HV. The powder synthesis method accomplished in present work offers a novel solution for composite nano-ceramics, which easily regulate particle size and proportion of different components.Keywords：Y2O3-MgO composite nano-ceramics;Core-shell structure nano-powder;Urea precipitation method;Spark plasma sintering- 196
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Published：2021-07-22 -
Optical Characterization of Free-space Coupled Microsphere Resonators Enhanced Publication
Abstract：Most current microsphere resonators rely on the evanescent field of micro/nano fiber tapers to provide pump energy. The mode coupling efficiency of this method is high, but it lacks some flexibility in practical application, and needs to be equipped with precise coupling device. In this work, we study the feasibility of pumping microsphere resonators using truncated optical fibers from free space. An Nd3+-doped tellurite glass microsphere/fiber taper coupling system is used as the experimental setup. We demonstrate that when the microsphere is directly illuminated by a free-space truncated optical fiber, additional pump energy can be introduced into the microsphere and output powers of microsphere laser modes can be increased. We also demonstrate that the free-space coupling method can excite a single longitudinal mode laser independently, without the assistance of the pump energy provided by the fiber taper. In this paper, the simulation models of finite-difference time-domain(FDTD) and geometric ray-tracing are used to restore the whole process of the free-space coupling method. Simulation and experimental results show that this free-space coupling method can potentially be used as a supportive pumping method for the classic fiber taper coupling method and can be helpful in experimental settings when additional pump powers or wavelength selections are needed.Keywords：free-space coupling;microsphere laser;rare earth ions doping;whispering gallery mode- 161
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Published：2021-07-22
Synthesis and Properties of Materials
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Research Progress in Surface Plasmon Enhanced Photodetectors
Abstract：Photodetectors can realize the conversion of optical signal to electrical signal, and have shown great application value in the fields of industry, military, medical treatment and so on. However, the traditional flat photodetector has a weak ability to capture line light, which limits the further improvement of responsiveness and other performance indicators to a certain extent. Surface plasmon resonance effect based on noble metal nanostructure can dramatically enhance the electric field intensity in the near field region and strengthen the ability of the photodetector to capture the line light, thus greatly improve the performance of photodetector. In this paper, the basic principle of surface plasmons is introduced at first. Then, the research progress of surface plasmon enhanced photodetectors with different structures, such as metal nanoparticles and metal gratings, is introduced in detail. Finally, the thesis is summarized and the development prospect of surface plasmon enhanced photodetectors is put forward.Keywords：Propagating surface plasmon polaritons;localized surface plasmon polaritons;photodetector;metal nanoparticles;metal grating- 196
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Published：2021-07-22 -
Effect of Passivation Layer on Trap Assisted Recombination in Inverted Perovskite Solar Cells Enhanced Publication
Abstract：Organic-inorganic lead halide perovskite polycrystalline thin film solar cells have achieved rapid growth in photoelectric conversion efficiency in recent years of research. However, the active layer of its polycrystalline structure causes the device to still suffer performance degradation caused by defects in the surface and grain boundary positions. In this study, two organic salts, namely, phenethylammonium iodide(PEAI) and 2-fluorophenylethylammonium iodide(o-F-PEAI), were used to form a passivation layer on the surface of perovskite film. Scanning electron microscopy(SEM) and atomic force microscopy(AFM) analysis results show that the grain boundaries of the perovskite film treated with PEAI and o-F-PEAI are obviously filled with passivation layer, and the surface roughness is also significantly reduced. In addition, the fluorescence lifetime imaging(FLIM) analysis results show that the passivated perovskite film has more photons and longer fluorescence lifetime. The above results indicate that the passivation layer induced by PEAI and o-F-PEAI can effectively inhibit the composite behavior of defects on the surface and grain boundary of the polycrystalline film. Therefore, the power conversion efficiency(PCE) of the inverted structure perovskite solar cell device after passivation can reach 21%. In addition, the devices after o-F-PEAI passivation show better device stability due to the effect of fluoride ions.Keywords：Fluorescence-lifetime imaging microscopy;Inverted perovskite solar cell;surface passivation;PEAI;o-F-PEAI- 234
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Published：2021-07-22 -
Waveguide Optimization and Efficiency Characteristic Analysis of 808 nm Laser Diodes Enhanced Publication
Abstract：The waveguide thickness of 808 nm InAlGaAs/AlGaAs laser diode chip was optimized in this paper. The study found that when the thickness ratio of the N-waveguide to the P-waveguide was 1.8, the chip had the highest power conversion efficiency. Chip-on-submount(COS) packaged single emitters and fiber-coupled modules@core diameter 62.5 μm, numerical aperture(NA) 0.22 were presented based on this conclusion, and the efficiency characteristic of the devices in the range of -10-90 ℃ was analyzed. The results showed that when the temperature increased from -10 to 90 ℃, the carrier leakage ratio of COS single emitter increased from 1.18% to 16.67%, and the carrier leakage ratio of fiber-coupled module increased from 1.99% to 17.73%, indicating that the increase of carrier leakage caused by temperature rise was the main factor leading to the decrease of power conversion efficiency. Moreover, the effects of high-temperature aging, thermal vacuum conditions and space radiation on the power conversion efficiency of fiber-coupled module were studied and the internal factors that lead to the reduction of the device's power conversion efficiency were revealed.Keywords：diode lasers;fiber-coupled module;optical power;power conversion efficiency- 167
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Published：2021-07-22 -
Characteristics of Passively
Q -switched Mode Locked Tm∶LuScO3 Ceramic Laser Enhanced PublicationAbstract：The stable Q-switched mode-locked operation of Tm∶LuScO3 mixed trioxide ceramics prepared by solid-state reaction sintering method is demonstrated in an all solid-state laser. The maximum continuous wave output power is 257 mW with 3% output mirror. The central wavelength is 1 993 nm and the slope efficiency is 14.06%. The narrowest mode-locked pulse width is 749-891 ps, the repetition rate is 121.9 MHz, the corresponding Q-switched envelope pulse width is 50 μs, the repetition rate is 45.45 kHz, the maximum output power is 167 mW, the center wavelength is 1 987 nm, and the corresponding maximum single pulse energy is 1.37 nJ.Keywords：Q-switched mode-locked;2 μm laser;Tm∶LuScO3 ceramic laser;semiconductor saturable absorber mirror(SESAM)- 114
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Published：2021-07-22 -
High Performance Broadband Photomultiplication-type Quaternary Organic Photodetectors Enhanced Publication
Abstract：Quaternary photomultiplication(PM)-type organic photodetectors(OPDs) with a structure of ITO/PEDOT∶PSS/active layer/Al were fabricated by a solution-processing method. The bulk-heterojunction active layer of devices was composed of P3HT∶PTB7-Th∶IEICO∶PC71BM with a weight ratio of 90∶10∶0.5∶0.5. As the bias voltage increases, the external quantum efficiencies(EQEs) of the devices are much larger than 100% and exhibit a wide spectral response range of 300-850 nm. At 330 nm and 780 nm, the highest EQE and responsivity of the devices are 773000% and 2 057 A·W-1, and 311000% and 1 956 A·W-1, respectively, which are one of the highest EQEs and responsivity values in ultraviolet and near-infrared areas for the OPDs. Under -25 V bias, compared to the ternary devices with a structure of ITO/PEDOT∶PSS/P3HT∶PTB7-Th∶IEICO(90∶10∶1)/Al, the average EQE(388167%), responsivity(1 604 A·W-1) and detectivity(3.6×1013 Jones) of quaternary devices are more than 0.5, 0.5, 0.4 times larger, respectively, effectively improving the detecting capacity of devices on weak light. The above results provide an effective strategy for preparing multi-element broadband PM-type OPDs to improve the detecting ability of the devices on weak light, especially improving the response and detecting ability of the devices in ultraviolet and near-infrared regions.Keywords：solution processing method;quaternary;photomultiplication-type organic photodetectors;ultraviolet;near infrared- 152
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Published：2021-07-22
Device Fabrication and Physics
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Degradation Mechanism of Pd/p-GaN Ohmic Contacts
Abstract：GaN-based wide bandgap semiconductors and devices have been quickly emerging as a new frontier and cutting-edge technique. It is necessary to fabricate Ohmic contact for GaN device application. Pd is one of candidate metals for fabricating metal/p-GaN Ohmic contacts. Under the identical preparation conditions, different thickness Pd films were sputtered on p-GaN epilayers in sputtering chamber directly connected with MOCVD growth system. After the metal deposition, the samples were then annealed at 300 ℃ and 600 ℃ in ambient atmosphere of N2∶O2=4∶1 or under vacuum conditions for 90 s. They were measured and characterized by four-probe Van de Pauw, X-ray photoelectron spectroscopy(XPS), and atomic force microscopy(AFM). It is found that the electrical properties and surface morphologies of samples were dependent on annealing ambient atmosphere and heat treatment temperature conditions. When the samples were annealed at 600 ℃ under high vacuum conditions, Ga can be diffused out from Pd/p-GaN interface. It would be helpful to make Ga and Pd reactive to become alloy as well as to produce Ga vacancy for Ohmic contact. While the samples were annealed in N2∶O2=4∶1 environment, however, oxidation of metal Pd and Ga becomes a dominant factor resulting in degradation of the Ohmic contacts.The higher the annealing temperature in oxygen environment, the worse the electrical properties. Surface morphologies of the annealed samples were completely changed from a smooth atomic step morphology to a dendritic polycrystal grain state if oxygen was participated into the interface during the annealing process. Therefore, avoiding oxygen incorporation at Pd/p-GaN interface shall be a key role in forming alloy and Ohmic contact, which favors the stability and reliability of device performance.Keywords：p-GaN;ohmic contact;XPS;interface- 196
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Published：2021-07-22
Luminescence Industry and Technology Frontier
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