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Latest Issue
Issue 4 ， 2021
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Dynamic Limb-pressure Visualization and Measurement Based on Mechanoluminescent Materials
Abstract：Mechanoluminescence(ML) is the light-emitting phenomenon of materials excited by external mechanical forces. ML materials, especially elastic-mechanoluminescent(EML) ones, have important applications for visualization sensing of stress/strain. Based on the reproducible properties of EML materials and the liner relationship between luminescent intensity and stress value, it can be used to make an intelligent stress distribution image sensor that detects the stress intensity and the location of structure, so as to realize the non-destructive detection and stress visualization of dynamic force of movement of human body. The dynamic pressure distribution of the human body can reflect the condition of the body, the force and movement state of the body posture, and even the health of the human body. Through the test and analysis of limb pressure, it can obtain the physiological and functional parameters of the human body under various postures and exercises, which are of great significance for clinical medical diagnosis, biomechanics and sports. In this article, the solid-state reaction method is applied to prepare the SrAl2O4∶Eu2+(SAO-E) EML material with green light emission, and then the SAO-E and silicone rubber(Ecoflex composite) are prepared to design a flexible membrane. The membrane is used to collect limb pressure images, which can not only achieve the visualization purpose of dynamic pressure, but also analyze the distribution of pressure at different positions of the limb. Compared with traditional measurement methods, the limb pressure measurement method based on EML materials can be directly visualized, which not only improves the recognition, but also obtains the detailed characteristics of the pressure, and also provides a new way of thinking for foot health monitoring.Keywords：mechanoluminescence;luminescence;pressure monitoring;SrAl2O4- 1396
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Published：2021-04-23
Cover Story
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Advances in Recoverable Mechanoluminescence in Inorganic Materials
Abstract：Mechanoluminescence(ML) is generated during exposures of certain materials to mechanical stimuli. Many solid materials produce ML during their fracturing, however, the irreversibility of fracto-induced ML limits the practical applications of these materials. The discovery of recoverable mechanoluminescence(RML) creates opportunities for ML materials to solve practical problems, such as stress probes for structural health diagnosis, stress-driven advanced light sources and display devices, and biomechanical stress sensors. This review summarizes the research advances of inorganic RML materials in the past two decades. It focuses on the classification, characterization, mechanism and application of RML materials, and concludes with discussions on future directions of ML research and specific challenges to realize real-world applications, with a view to benefitting the development and application of such materials.Keywords：stress;sensor;mechanoluminescence;stress distribution;stress imaging- 1385
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Published：2021-04-23 -
Progress of Quantum Dots and Perovskite as Color Conversion Materials for Full-color Display
Abstract：Quantum dots(QDs) have many excellent optoelectronic characteristics, such as high color purity, tunable emission color, high photoluminescence quantum yield and so on. At present, the display applications of quantum dots are mainly based on their photoluminescence characteristics, or color conversion characteristics, to enhance the color gamut of liquid crystal display panels or to achieve full-color display combining with blue light-emitting devices. In this paper, we will first review the progress of conventional quantum dots(CdSe, InP) in liquid crystal display(LCD) application. Special focus would be laid on the panel architecture, optical properties, reliability and process technologies which are significant as incorporating QDs into LCD panels. In the next, we will analyze the application of color conversion potentials of QDs for active light-emitting displays. Finally, the progress of perovskite materials in color conversion applications for full-color display will be discussed.Keywords：quantum dots;perovskite;color conversion;photoluminescence;full-color display- 1023
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Published：2021-04-23
Invited Review
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Growth of InGaAs/GaAsP Strain-compensated Multiple Quantum Wells
via MOCVD TechnologyAbstract：The large mismatched InGaAs multiple quantum wells on GaAs substrates were prepared by metal-organic chemical vapor deposition(MOCVD) technology. In order to solve the large lattice mismatch between InGaAs and GaAs, the GaAsP strain compensation layer structure was designed. And our systematically theoretical and experimental studies were performed upon the composition adjustment of P in the GaAsP materials. The three-periods InxGa1-xAs/GaAs1-yPy multi-quantum wells structures with the P component of 0, 0.128, 0.184, and 0.257 were prepared. Compared with PL, XRD, AFM testing results of the samples with and without GaAsP layer, it is found that tensile strain compensation of higher barrier GaAsP material could improve the crystal quality. When the content of P was 0.184, the PL wavelength of InGaAs/GaAsP MWQs was 1 043.6 nm, the FWHM was 29.9 nm. The XRD peaks had multi-level satellite peaks, and the FWHM of the satellite peaks was small. The AFM roughness was 0.130 nm, and the surface morphology showed a step flow growth mode.Keywords：metal-organic chemical vapour deposition(MOCVD);InGaAs/GaAsP;strain compensation;multiple quantum wells;lattice mismatch- 465
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Published：2021-04-23 -
Preparation and Luminescence Properties of Red Sr3LiSbO6∶Eu3+ Phosphor
Abstract：Sr3LiSbO6∶Eu3+ red phosphors were synthesized by high temperature state reaction. The influence of Eu3+ concentration on the luminous intensity was systematically studied, and the samples were analyzed by XRD, fluorescence spectroscopy(PL), fluorescence lifetime, thermal stability and color coordinates. The results show that the prepared phosphor Sr3LiSbO6∶Eu3+ can be excited by ultraviolet light and exhibits a strong red light emission band at 612 nm. The concentration quenching effect of the sample was studied, and the best doping concentration of the sample was 0.04%, which was mainly caused by the dipole-dipole interaction. In addition, the thermal stability of the sample was also discussed. The luminous intensity at 423 K was 43.1% of that at room temperature. Finally, the fluorescence lifetime and CIE of the samples were tested. The above results indicate that the prepared phosphor Sr3LiSbO6∶Eu3+ has great prospects in the synthesis of LEDs.Keywords：Sr3LiSbO6;Eu3+ doped;phosphors;WLED- 395
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Published：2021-04-23 -
Synthesis and Properties of A Mitochondria-targeted Coumarin-based pH Fluorescent Probe
Abstract：Mitochondrion is an important organelle whose functions include energy supply, signal transduction, cell differentiation, cell death, and the control of cell physiological cycle and cell growth. Any damage to mitochondria and subsequent dysfunction could lead to a range of human diseases. Mitochondrial pH directly affects its biochemical process, and the normal pH level is the basis for the normal operation of mitochondrial function. In this paper, a mitochondria-targeted pH fluorescent probe(CMPH) was synthesized by choosing 7-hydroxycoumarin as the raw material. Its optical properties, cytotoxicity and mitochondria-targeted ability were studied. The results showed that probe CMPH had a large Stokes shift, can specifically give a fluorescent response to pH, and its fluorescent intensities had a good linear relationship to pH values in the range of pH=6.5-8.2. Cytotoxicity testing indicated that probe CMPH had low cytotoxicity. Confocal fluorescence imaging demonstrated that CMPH can efficiently target mitochondria and monitor the change of mitochondrial pH. Our purpose is to provide a new imaging tool for monitoring the change of mitochondrial pH.Keywords：fluorescent probe;coumarin;pH;Mitochondria- 235
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Published：2021-04-23 -
Synthesis and Luminescence Properties of Sr3(BN2)2 Phosphor
Abstract：A new type of phosphor Sr3(BN2)2 (hereinafter abbreviated as SBN) was synthesized by high temperature solid phase one-step method. The phase composition, morphology and luminescent properties of the phosphor were characterized by X-ray diffraction, scanning electron microscopy and fluorescence spectrophotometer. The defect luminescence mechanism and long afterglow characteristics of SBN phosphors were discussed. The results show that the prepared sample SBN crystals is cubic crystal system Im-3m. The results show that there is a wide excitation band in the ultraviolet region, and the emission spectrum peak is at 525 nm, and the half peak width is 3 334 cm-1. The SBN phosphor material has inherent defects. Sr vacancies are formed in the matrix, and the luminous center is formed under light excitation. Further decay curve and thermoluminescence curve also confirm that the material has inherent defects, and the afterglow time is about 10 s. The variable temperature spectrum shows that when the temperature reaches 150 ℃, the fluorescence intensity is 43% of the initial intensity at room temperature, which is better than the 10% attenuation result of rare earth doped boron nitride. The SBN phosphor has a simple synthesis process, a stable structure, and excellent performance such as long afterglow green light emission obtained by ultraviolet wavelength excitation, and has potential application prospects in white light LED lighting and indication.Keywords：Sr3(BN2)2;Defective luminescent material;long afterglow;luminescence mechanism- 183
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Published：2021-04-23 -
Preparation and Properties of GGAG∶Ce Composite Fluorescent Film for White LED
Abstract：White LED has gradually become a mainstream product in the lighting industry due to its high luminous efficiency, long life, energy saving and environmental protection. Generally, white light LEDs for lighting are required to have high color rendering index and low color temperature. In this paper, the GGAG∶Ce nano-powder was synthesized by chemical co-precipitation method. And the translucent Gd3(Al,Ga)5O12∶Ce (GGAG∶Ce) flexible composite fluorescent film was prepared successfully by uniformly dispersing the GGAG∶Ce nano-powder into the silica gel matrix, which can be used for white light LEDs. The phase construct, morphology and luminescence properties of the composite fluorescent film were discussed by X-ray diffraction(XRD), fluorescence spectroscopy, scanning electron microscope(SEM), and variable temperature fluorescence spectroscopy. The results show that the main crystal phase of composite fluorescent film is GGAG∶Ce crystal phase. The main excitation peak and emission wavelength of the GGAG∶Ce composite fluorescent film are located at 450 nm and 540 nm, respectively, which belong to the 5d → 4f electronic transition of Ce3+, and the decay time is about 40 ns. Fluorescence performance shows that the optimal composite concentration of the composite fluorescent film is about 20%, its color rendering index reaches 85.1, and its color temperature is 6 295 K. The variable temperature emission spectra present the composite fluorescent film has a good thermostability, which has potential application prospects in white LEDs.Keywords：GGAG∶Ce;composite fluorescent film;white LED;color rendering index- 215
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Published：2021-04-23
Synthesis and Properties of Materials
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Research Progress in Humidity Stability and Light-thermal Stability of All-inorganic Perovskite Solar Cells
Abstract：In recent years, perovskite solar cells have received continuous attention due to their high efficiency and low cost, but there are problems in the stability of organic components. Compared with organic-inorganic hybrid perovskite solar cells, all-inorganic perovskite materials can avoid the influence of the external environment, with low requirements for oxygen environment and relatively high tolerance for humidity environment. Due to its own structure, it is also superior to organic-inorganic hybrid perovskite in terms of photothermal stability. Therefore, the development of perovskite solar cells is one of the directions to effectively improve the stability of perovskite solar cells. In this paper, the latest progress in the study of all-inorganic perovskite solar cells is systematically introduced from the aspect of stability. Combined with the influencing factors of the stability of all-inorganic perovskite solar cells, the main solutions to the current stability problems of all-inorganic perovskite solar cells are summarized, and the prospects for the stability of all-inorganic perovskite solar cells are given.Keywords：all-inorganic perovskite;solar cells;stability- 376
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Published：2021-04-23 -
Development of 808 nm High-power Distributed Feedback Laser Array
Abstract：In order to improve the pumping efficiency of high-power semiconductor lasers, the drift coefficient of the output wavelength of the semiconductor laser with temperature must be reduced. The high-power distributed feedback laser array is fabricated using MOCVD epitaxial technology, nano-imprinting, dry etching and wet etching. The cavity length of this laser array is 1 mm, and the wavelength is 808 nm at 25 ℃. By testing the P-V-I curve and spectrogram at different heat sink temperatures, it is shown that when the pulse working current is 148 A, the output power of the laser array can reach 100 W. The slope efficiency is 0.9 W/A. The FWHM of the spectrum is 0.5 nm. The side mode suppression ratio can reach 40 dB. The thermal drift coefficient of the emission wavelength is 0.056 nm/℃. Single-array wavelength lock ranges up to 50 ℃ and total lock ranges 100 ℃. In addition, the influence of the cavity surface coating on the wavelength locking effect is also analyzed.Keywords：lasers;distributed feedback laser diode array;inner Bragg grating;wavelength stabilization- 151
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Published：2021-04-23 -
On the Characteristics of Pulsed Laser Driver Based on RLC Oscillation
Abstract：The laser driver circuit is very important in time-of-flight lidar. Its performance directly affects many key system parameters such as detection range, signal-to-noise ratio and false alarm rate. This article innovatively introduces appropriate inductance in charging circuit, forming resistance, inductance and capacitance(RLC) second-order differential oscillation circuit, which can greatly increase the driving voltage of the pulse laser and thereby increasing the driving current that drives the laser to produce high-power, narrow-pulsewidth laser. Theoretical calculations, numerical simulations and experimental verification show that driving current of pulse laser can be increased for over 85%, and the output power is increased for over 114% as an appropriate inductor is introduced into the system.Keywords：lidar;high power;narrow pulse width;differential oscillator circuit- 194
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Published：2021-04-23 -
Output Characteristics of Broad-area Stripe Semiconductor Lasers with Microthermal Channel Anode Structure
Abstract：In order to suppress the thermal lens effect of broad-area stripe semiconductor lasers, and thus improve the slow-axis beam quality of semiconductor lasers, a laser with microthermal channels anode structure is proposed and fabricated. The injection region electrode on the p-side of laser is designed as a thick electrode structure of high thermal conductivity. After packaging, an air gap is formed between the p-side of laser and the top side of AlN heat sink to suppress the transverse heat flow in the current injection region, so that the temperature distribution of the emission region is uniform and the slow-axis divergence angle is effectively reduced. The thickness and width of microthermal channels anode structure are optimized by steady-state thermal analysis of the laser packaging model. A 940 nm micro thermal channel anode structure laser is fabricated. The measurement results show that the divergence angle of the microthermal channels anode structure laser at 2 A is 24%, lower than that of the normal anode structure laser, which effectively reduces the laser slow-axis beam divergence angle.Keywords：Wide stripe semiconductor laser;thermal lens;Microthermal channel anode structure;Slow-axis divergence angle- 157
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Published：2021-04-23 -
Effect of SiO2 Patterned Sapphire Substrate on GaN Growth and LED Luminescence Performance
Abstract：To improve the luminescence performance of gallium nitride(GaN)-based light-emitting diodes(LEDs), a SiO2 film was deposited on sapphire substrates by the plasma-enhanced chemical vapor deposition(PECVD) in this study. After depositing the SiO2 film, a SiO2 patterned sapphire substrate(SPSS) was prepared through photolithography and dry etching, and a GaN-based LED device with SPSS was obtained by using epitaxial growth and micro-nano processing technology of the LED device. The effect of SPSS on the crystal quality of the GaN epitaxial layer, the light extraction efficiency, and the performance of the LED device were investigated. The experimental and simulation results show that, compared to the conventional patterned sapphire substrates(CPSS), the GaN epitaxial layer grown on SPSS had lower dislocation density and higher crystal quality, and the light extraction efficiency of SPSS-LED was increased by 26%, as well as that the light output power and brightness of SPSS-LED were both increased by about 5%.Keywords：SiO2 sapphire composite substrate;LED chip;dislocation density;GaN;light extraction efficiency- 218
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Published：2021-04-23
Device Fabrication and Physics
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Conversion Efficiency of Strained Wurtzite ZnSnN2/In
x Ga1-x N Cylindrical Quantum Dot Solar Cell Under Influence of Built-in Electric FieldAbstract：Within the effective mass approximation, the band gap of strained wurtzite ZnSnN2/InxGa1-xN cylindrical quantum dot is calculated theoretically by a variational method. Furthermore, based on the detailed balance theory, the relationship between the conversion efficiency of cylindrical quantum dot solar cell and the radius, height and In component of quantum dot under the influence of built-in electric field and multiple exciton generation are studied. The results show that the conversion efficiency of quantum dot solar cell increases monotonously with the increase of quantum dot radius, height and In component. The multiple exciton generation can obviously improve the conversion efficiency of solar cells, but the built-in electric field can reduce the conversion efficiency of solar cells significantly.Keywords：cylindrical quantum dot;solar cell;conversion efficiency;built-in electric field;multiple exciton generation- 437
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Published：2021-04-23
Theoretical Calculation and Spectral Analysis
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Status and Perspectives of Deep Ultraviolet LED Packaging Technology
Abstract：Deep ultraviolet light-emitting diode(DUV-LED) has great applications in sterilization and disinfection, biochemical detection, medical treatment, and secret communication due to its mercury-free, long life, low power consumption, high response, and compact structure. In recent years, the light efficiency and reliability of DUV-LEDs are continuously enhanced. It is attributed to the advancement of nitride material epitaxy and doping technology in chip fabrication process and the development of DUV-LED packaging technology. However, the light efficiency and reliability of DUV-LED need to enhance compared with near-ultraviolet (NUV) and blue LEDs. This review focuses on the systematic analysis of the key technologies of DUV-LED packaging, including packaging material selection, packaging structure design, packaging process optimization, reflected light loss mechanism, and junction temperature and thermal management. Meanwhile, the latest research progresses of DUV-LED packaging in light extraction efficiency and device reliability are introduced. The future technology development of DUV-LED is prospected.Keywords：DUV-LED;packaging technology;light efficiency;reliability- 550
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Published：2021-04-23
Luminescence Industry and Technology Frontier
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