摘要:Metal halide perovskite light-emitting diodes (PeLEDs) have wide color gamut and high color purity, with broad application prospects in lighting and displays. A groundbreaking study by a research team at the University of London published in Scientific Reports found that exposure to red light for just 3 minutes a day could significantly alleviate vision decline. The tunability of perovskite’s spectrum and its high color purity provide assurance for the realization of eye-protective red-emitted PeLEDs. Unlike previous interface engineering or ligand engineering methods, this paper proposes a new approach to enhance the external quantum efficiency (EQE) of quasi-two-dimensional perovskite red PeLEDs by combining them with microcavity structures to achieve narrower linewidths in electroluminescent devices. The results show that by integrating distributed Bragg reflectors (DBRs) with PeLEDs, narrow linewidth high-performance PeLEDs based on microcavity structures were designed and fabricated, achieving a doubling of EQE on top of narrowing the electroluminescence (EL) full width at half maximum for microcavity PeLEDs, with a maximum EQE reaching 11.26%. Compared to reference devices prepared under the same conditions, PeLED devices with microcavity structures narrowed their EL linewidth to one-third that of reference devices, only 11 nm.
关键词:quasi-two-dimensional perovskite;distributed bragg mirror;red emitted;electroluminescence;half-height full width
摘要:Artificial intelligence has been bringing a great of convenience for human in manufacture, life, science and technology, for its abilities of efficient data analyses, accurate prediction, automatic task executing, and personalized service. Machine learning and high-throughput computing have extensively permeated and successfully applied in the field of materials, opening up new horizons for innovative research and design methods in luminescent materials. By employing efficient algorithms for mining and processing large-scale data, the screening and design process of new materials is accelerated, thereby driving the discovery and application progress of novel materials. This article provides an overview of the recent advances in data-driven research on luminescent materials. Based on relevant research cases, it outlines the entire process of data-driven material research and elaborates on the importance and implementation strategies of data acquisition in the development of luminescent materials. It also conducts a thorough analysis of how to accurately extract core features that characterize material performance, while exploring algorithm selection strategies applicable to the field of luminescent materials. Finally, the bottleneck of the current research on data-driven luminescent materials is pointed out, such as a lack of high-quality data and difficulties in constructing complex structure-performance correlation models. It also provides an outlook on future development directions, with a particular emphasis on the construction of luminescent material database platforms, implementation of high-throughput experiments, and establishment of corresponding data production standards.
关键词:data-driven;luminescent materials;machine learning;high-throughput computing;Luminescent Materials Data Fab
摘要:The coherent acoustic phonons generated by femtosecond laser pulse excitation of thin-film materials can obtain non-destructive interface structure characteristics of light-emitting materials and devices. It is important for non-destructive testing and imaging of functional interfaces of opto-electronic devices. Compared with traditional metal thin-film photoacoustic transducers with thermoelastic mechanisms, two-dimensional semiconductor films own the advantages of broad spectrum absorption, atomic-level surface flatness, and robust control of the layer number. During the interaction of femtosecond laser pulse and two-dimensional semiconductor, coherent acoustic phonon oscillation can be generated, which set a foundation for further launching ultrafast acoustic pulses to extract interface information. This should be widely applicable for nondestructive evaluation of defect distribution, mechanical properties, and interface quality of light-emitting devices. In this paper, we introduce the research progress of coherent acoustic phonons in two-dimensional semiconductors and overlook the scientific significance of ultrafast opto-acoustic measurement technique.
摘要:Fluorescent carbon dots (CDs) have excellent characteristics such as wide range of raw materials, non-toxic and non-polluting, adjustable luminescence color, low cost and biocompatibility, and have broad application prospects in the field of luminescence. In recent years, CDs-based electro-luminescent devices have a great achievements. In this paper, we mainly summarize the latest progress of CDs-based electroluminescent devices, even focus on the feasibility of synthesizing high-efficiency CDs and manipulating the device structure to obtain high-performance devices. In addition, combined with the analysis of the development status and future needs of CDs in the application of electroluminescent devices, this paper looks forward to the realization of high-performance CDs-based electroluminescent devices.
摘要:X-ray imaging has widespread demands in the fields of nuclear radiation safety, nondestructive testing, security inspection, and medical diagnosis. However, traditional scintillation single crystals have been impeded by high cost and time-consuming process, limited size, and intrinsic brittleness, which leads to extreme difficulty in achieving efficient and flexible X-ray imaging. In contrast, scintillator films based on metal halide nanocrystals/microcrystals have significant advantages such as simple fabrication, large area, flexible deformation, and efficient luminescence, providing a huge potential for X-ray imaging applications. In this work, the X-ray imaging research progress of metal halide scintillator films has been reviewed in detail in recent years. Firstly, according to whether the metal halide nanocrystal/microcrystal is synthesized individually or not, the preparation strategies of scintillator films have been generalized into two categories: crystal composite strategy and in-situ crystallization strategy, the advantages and disadvantages of which have been further analyzed in comparison. Secondly, the luminescence mechanism of metal halide crystals has been investigated, which has been utilized to improve the luminescence performances of scintillator films, gathering the effective methods for increasing the luminescence efficiency of scintillator films. Furthermore, various performances related to X-ray imaging of metal halide scintillator films have been further summarized, mainly including spatial resolution, flexibility, stability, and self-healing. Finally, the summarization and prospect have been put forward according to the current performances of scintillator films.
“Researchers have made significant progress in the field of optoelectronics, synthesizing formamidinium lead bromide (FAPbBr3) nanocrystals with different sizes using ligand-assisted precipitation technology at room temperature. The study revealed their two-photon pumped amplified spontaneous emission and nonlinear optical properties, with a large two-photon absorption coefficient and high non-linear absorption cross-section. These findings indicate that FAPbBr3 nanocrystals could be a promising green-emitting frequency-upconversion material for the development of high-performance two-photon pump lasers.”
WANG Yajuan,TAY Yong Kang Eugene,WANG Fang,YU Sheng,SUM Tze Chien,LIU Wei
摘要:Formamidinium lead bromide (FAPbBr3) nanocrystals (NCs) have been considered to be a good optoelectronic material due to their pure green emission, excellent stability and superior carrier transport characteristics. However, two-photon pumped amplified spontaneous emission (ASE) and the corresponding nonlinear optical properties of FAPbBr3 NCs are scarcely revealed. Herein, we synthesized colloidal FAPbBr3 NCs with different sizes by changing the molar ratio of FABr/PbBr2 in the precursor solution, using ligand assisted precipitation (LARP) technology at room temperature. Photoluminescence (PL) and time resolved photoluminescence (TRPL) spectroscopy were measured to characterize their ASE properties. And their nonlinear optical properties were studied through the Z-scan technique and the two-photon excited fluorescence method. The stimulated emission properties including one- and two-photon pumped ASE have been realized from FAPbBr3 NCs. With large two-photon absorption coefficient (0.27 cm/GW) and high non-linear absorption cross-section (7.52×105 GM), ASE with threshold as low as 9.8 μJ/cm2 and 487 μJ/cm2 have been obtained from colloidal FAPbBr3 NCs using one- and two-photon excitations. These results indicate that as a new possible green-emitting frequency-upconversion material with low thresholds, FAPbBr3 NCs hold great potential in the development of high-performance two-photon pump lasers.
关键词:perovskites;Formamidinium lead bromide nanocrystals;nonlinear;optical gain;amplified spontaneous emission
摘要:In recent years, the demand for white LED lighting with high color rendering index has posed new challenges to the LED industry. Carbon dots, as a new type of nanomaterial in the 21st century, is expected to become an ideal single component phosphor for white LED devices with high color rendering index, because of its advantages of simple preparation process, high stability, optical tunability and wide emission. However, aggregation-caused quenching (ACQ) of carbon dots greatly limits its application in solid-state lighting. In this paper, high-efficiency fluorescent carbon dots were synthesized by microwave method under mild preparation process with phenphenolline as raw material, and the surface functional group tuning of the carbon dots was realized by doping technique. One-component solid carbon dots phosphors with anti-ACQ were successfully prepared by one-step method, which can be applied to white LED devices with high color rendering index. Its solid quantum yield is as high as 37%, and the white LED prepared with it as phosphor shows excellent photoelectric performance.
摘要:Most luminescent materials are greatly limited in their applications due to strong fluorescence quenching in solid state or high doping concentration. Therefore, it is particularly important to research and develop new materials that can exhibit excellent luminescent properties in aggregated states. Four compounds based on the thiophene ethylene skeleton structure, Br-thph, Br-2thph, Thph-czm, and 2Thph-czm were synthesized in this paper. The photophysical properties of this type of compound have been studied in detail in low concentration solutions, aggregates, and solid films. The results showed that all four compounds exhibited significant aggregation induced luminescence properties, with weak luminescence in low concentration solutions, but exhibited strong luminescence with increasing concentration or in aggregated states. Among them, compounds Br-thph and Br-2thph exhibit 410 and 180 times enhanced luminescence compared to low concentration solutions, while Thph-czm and 2Thh-czm exhibit 78 and 40 times enhanced luminescence, respectively. Moreover, all four compounds exhibited significant mechanofluorochromic effects and exhibited a certain spectral blue shift. Through preliminary exploration of the photophysical properties of these compounds, it is indicated that these novel thiophene ethylene derivatives have potential application value in anti-counterfeiting and display fields.
摘要:Herein, a series of ZnxMg0.993-xGa2O4∶0.7%Ni2+(x=0-0.5)(ZMGO∶Ni2+) phosphors with inverse spinel structure were successfully prepared through a hydrothermal method followed by a vacuum heat treatment, emitting within the 2nd near-infrared transmittance window(NIR-Ⅱ: 1 000-1 700 nm). The particle size of ZMGO∶Ni2+ phosphors exhibited a gradual increase with increasing Zn2+ doping content. Upon excitation by a 635 nm laser, ZMGO∶Ni2+ phosphors exhibited a broad emission band centered at approximately 1 279 nm, which can be attributed to the characteristic emission of Ni2+. Their thermal activation energy is decreased from 244 meV to 224 meV after Zn2+ doping. A NIR-Ⅱ phosphor-converted light-emitting diode (NIR-Ⅱ pc-LED) was fabricated by employing ZMGO∶Ni2+ phosphors with the strongest luminescence intensity, in conjunction with a 620 nm red LED chip. Based on high penetration ability, minimal scattering property and auto-fluorescence-free background of NIR-Ⅱ light, night vision imaging with occlusion and tissue imaging were performed using the NIR-Ⅱ pc-LED, respectively.
关键词:photoluminescence;transition metal ion;NIR-Ⅱ;phosphors
摘要:The effect of a novel post-growth process, i.e. high-temperature thermal annealing process in NH3, on the crystal quality, luminescence property, and electrical conductivity of the heavily Mg-doped GaN was studied. The experimental results showed that, compared with the traditional high-temperature annealing process in N2, the high-temperature thermal annealing process in NH3 can improve crystal quality in the heavily Mg-doped GaN, while promote the further effective doping of Mg acceptors, resulting in an enhancement of the intensity of the blue luminescence band in its photoluminescence spectra. The heavily Mg-doped GaN with significantly lower background electron concentration was obtained by combining high-temperature thermal annealing process in NH3 with low-temperature thermal annealing process in N2. This is because that the thermal decomposition products of NH3 in the post-growth process can effectively reduce the concentration of shallow donor-type defects such as N vacancies and interstitial Ga atoms in the material, ultimately improving electrical conductivity of the heavily Mg-doped GaN.
摘要:Infrared thermal radiation modulators based on mechanically responsive materials offer advantages such as low cost, simple structure, and easy operation. Traditional infrared thermal radiation modulators based on mechanical responses typically involve constructing metal films (such as gold, aluminum, copper, etc.) on an elastic substrate, which modulate infrared thermal radiation dynamically through the cracking and closing of the film layers. However, traditional dynamic infrared modulators are generally opaque in the visible light spectrum, which greatly limits their applications in fields like visible-infrared dual-band camouflage. In this study, ITO films were deposited on transparent elastic polymers that are transparent across a wide visible-infrared spectrum using a magnetron sputtering technique, creating thermal radiation modulators that are transparent in the visible light spectrum and highly reflective in the infrared spectrum. Under mechanical stretching, the device exhibits an infrared reflectance range of 40%-77% at the 10 µm and a visible light transmittance of over 82% at 550 nm.
摘要:Inkjet printing technology of perovskite quantum dots(PQD) hold great potential in full-color display applications, but several key issues still affect their efficiency, such as unbalanced charge carrier injection, low-quality perovskite films, and non-radiative recombination pathways of PQDs themselves. To address these issues, we introduce an interface improvement layer of Phenethylammonium bromide(PEABr) to balance the charge carrier transport in devices. PEABr has a similar structure to the binary solvent of perovskite(toluene, naphthalene), which can improve the printing characteristics and film-forming ability of PQDs and effectively passivate the Br- vacancies and interface defects of PQD films. Based on this strategy, we successfully achieved inkjet-printed perovskite quantum dot light-emitting diodes(PeLEDs) with a maximum external quantum efficiency(EQE) of 8.82% and a current efficiency(CE) of 29.15 cd/A at a brightness of 414 cd/m², providing beneficial insights for inkjet printing technology in future display applications.
摘要:Graphene and transition metal sulfide WS2 have stable chemical properties and broadband absorption spectra, which can realize the pulse operation of laser in the mid-infrared band. This paper reports the application of graphene and WS2 as saturable absorbers in mode-locked lasers in mid-infrared band. Experiments show that graphene/WS2 composites have better nonlinear absorption characteristics, and exhibit low mode-locked threshold and high material damage threshold during mode-locked modulation. When the pump power is 5 W, The mode-locked pulse with pulse width of 24.04 ps was obtained at 2 781.7 nm. The maximum average output power of the laser was 237.7 mW and the peak power was 395.5 W. Finally, the wavelength tunable output of the laser is realized by grating, and the output wavelength of the graphene/WS2 mode-locked laser is widened to 2 730-2 810 nm.
关键词:mid-infrared laser;mode locking;the wavelength is tunable;graphene;WS2
摘要:It is great significance for the preparation of perovskite solar cells (PSCs) in the ambient air for its commercialization process. However, there are a lot of anion and cation defects appeared in perovskite film during the air environment prepare procedure, which seriously affects the device performance. Hence, orotic acid (OA) was used as additive to regulate the defects in mixed cation perovskite layer through additive engineering. The carboxyl group in OA can bond with the uncoordinated Pb2+ in the perovskite, and the nitrogen-containing group on the pyridine ring forms a hydrogen bond with the uncoordinated I-, which can reduce the defect density and increase the grain size of the perovskite film, and inhibiting the non-radiative recombination of carriers. The photoelectric conversion efficiency (PCE) of PSCs passivated by OA increased from 19.89% to 22.09%, and which can keep 93.85% the initial PCE after 1 000 hours in the ambient air.
关键词:perovskite solar cells;oroic acid;Defect passivation;additive engineering
摘要:Vertical-cavity surface-emitting laser (VCSEL) is easily integrated on-chip and is a key optoelectronic device in systems such as laser radar and security lighting. However, the severe self-heating phenomenon can affect the output power, high-speed characteristics, and stability of the devices. Therefore, thermal management technology is extremely important, and adopting an optimized packaging approach can effectively increase the heat dissipation of VCSELs, which is an important method to improve VCSELs’ thermal performance. This article is based on a finite element method (FEM) computational model to numerically analyze the thermal characteristics of VCSELs with different packaging methods and a thin copper layer covering the devices’ surface. The simulation results indicate that compared to the top-emitting packaging method, the flip-chip packaging with substrate-emitting (fully etched top and bottom DBR) can effectively reduce the active region temperature, with a reduction rate exceeding 56%. As the device mesa diameter gradually increases, devices using the top-emitting packaging method show a decreasing trend in temperature and thermal resistance, with a temperature reduction 50 ℃ and the thermal resistance reduction of over 3.25 K/mW. However, devices with a fully etched top and bottom DBR structure using flip-chip packaging and devices with only etched P-DBR structure using flip-chip packaging both exhibit a slowly increasing trend in temperature and thermal resistance, with temperature increases of 2 ℃ and thermal resistance increases of 0.15 K/mW. Covering the device mesa, sidewalls, and substrate surfaces with a layer of copper can effectively reduce the temperature of the active region. When the thickness of the copper layer is 3 μm, the temperature reduction of the active region is 43% and thermal resisitance reduction is 1.9 K/mW. This article analyzes the impact of packaging methods on the thermal characteristics of VCSELs and proposes optimization solutions, which have guiding significance for the effective thermal packaging of VCSELs.
摘要:In this work, the geometric structures, electronic structures, and absorption spectra of various neutral and positively charged ultrasmall size silver clusters([Agm]n+, m=2-8, n=0-2), have been investigated using density functional theory and time-dependent density functional theory. The simulation results demonstrate that the electronic energy level structures and absorption spectra of the ultrasmall size silver clusters are influenced by multiple factors, including size, symmetry, open-shell and closed-shell systems, and electric charges of clusters. Furthermore, average binding energy calculations indicate that an increase in the size of neutral ultrasmall size silver clusters results in a gradual enhancement in their stability. However, positively charged ultrasmall size silver clusters are subject to the parity oscillations phenomenon, which means that the dominant configuration in the anionic polyhedral network is not necessarily the lowest-energy configuration. This study has led to the construction of a database of the geometrical structures, electronic structures, and absorption spectra of ultrasmall size silver clusters. This dataset has been created to identify the characteristic luminescence of ultrasmall size silver clusters in specific configurations in fluorescent glasses. Furthermore, the database will provide theoretical support data for expanding the structural and spectroscopic studies of ultrasmall size silver clusters in other types of inorganic as well as organic ligands.
关键词:silver clusters;density functional theory;time-dependent density functional theory;absorption spectra
摘要:To explore the virus inactivation efficiency of AlGaN based LED with different light emission wavelengths fabricated on high-temperature annealed (HTA) AlN templates, 7 groups of AlGaN based LEDs were fabricated with emission wavelengths varied from 257 nm to 294 nm, and the inactivation efficiency for Coxsackie virus was explored. The experimental results show that the threading dislocation density of HTA AlN templates can be decreased to 1.33×107 cm-2, which is beneficial for fabricating AlGaN based LED. The Coxsackie virus inactivation rate is more than 99.90% for the AlGaN based LED with central emission wavelength between 257 nm and 278 nm under the experimental conditions (inactivation distance of 2 cm, UV irradiation time of 30 s), while the Coxsackie virus inactivation rate only reaches 99.47% and 96.15% for the LED with central emitting wavelength of 288 nm and 294 nm, respectively. According to the above results, AlGaN based LEDs with emission wavelength between 257 nm and 278 nm are suitable for application in virus sterilization field, while the LED with wavelength longer than 288 nm has poor efficacy in virus sterilization under the experimental conditions.
关键词:High temperature anneal;AlN template;AlGaN;LED;Virus inactivation