Abstract：The quasi-2D Ruddlesden-Popper（R-P） halide perovskite has been widely used in solar cells， light-emitting diodes， lasers and other optoelectronic devices due to its excellent photoelectric properties. However， the exciton-phonon interaction， which seriously affects the relaxation and transport characteristics of carriers， has not been fully revealed. Compared with the widely studied 3D perovskite structure， quasi 2D perovskite has a naturally formed quantum well structure with greater exciton binding energy and more obvious exciton effect. However， the exciton-phonon interaction of quasi 2D perovskite is still less studied. Therefore， a quasi-2D R-P perovskite film （PEA）2Csn-1PbnBr3n+1 has been prepared by solution method with a gain coefficient of ~1 090.62 cm-1 and an amplified spontaneous emission of low threshold （~12.48 μJ/cm2）. Based on this， we studied the luminescence properties of （PEA）2Csn-1PbnBr3n+1 film with temperature variation by using variable temperature fluorescence spectroscopy（77-300 K） and transient absorption spectroscopy， in order to elaborate the influence of exciton-phonon interaction on its luminescence properties. It was found that in the low temperature domain （77-120 K）， The bandgap change caused by exciton-phonon interaction is relatively weak， and the lattice thermal expansion is dominant. With the increase of temperature， the exciton-phonon interaction has a great influence on the change of bandgap. On the other hand， the exciton-phonon interaction causes the line width of the luminescence spectrum to widen， but we observed the abnormal line width narrowing in the temperature range of 77-120 K， which is attributed to an energy transfer mechanism in the multi-quantum well caused by the localization effect. Until above 120 K， the line widening caused by the exciton-phonon interaction is sufficient to reverse this trend. In this paper， the exciton-phonon interaction of quasi 2D perovskite is of guiding value for improving the optical properties and luminescence applications of quasi 2D perovskite.
Abstract：Metal halide perovskite solar cells have been able to achieve certified photovoltaic conversion efficiencies of 25.7%， approaching the maximum certified efficiency of 26.7% for crystalline silicon solar cells. It is well known that the component engineering of the crystal structure of ABX3 perovskite materials plays a key role in achieving efficient and stable devices， especially the component engineering of the X-site halide anion， which has received much attention from researchers in recent years. Recently， researchers have carried out several studies on the introduction of pseudo-halide anions as doping components， precursor additives， thin film post-treatment materials， charge transport materials， interfacial passivation， and modifiers for perovskite crystals， and the results demonstrate that pseudo-halide ion modification is an important strategy to improve device efficiency and stability. This review provides a detailed comparison and summary of the various types of pseudo-halide ions currently available for use in perovskite solar cells and provides an in-depth summary of the mechanisms and nature of their effects on perovskite crystal film morphology， photovoltaic properties， carrier migration properties， and device photovoltaic characteristics and stability. At the same time， this paper also provides an outlook and analysis of the currently unexplored pseudo-halide ions to effectively contribute to the enhancement of the photovoltaic properties of perovskite solar cells in future research.
Keywords：Pseudo-halide ions;Component engineering;perovskite solar cells;Defect passivation
Abstract：A series of Na3Sc2（1-x）（BO3）3∶xTb3+ phosphors were prepared by high-temperature solid-state method. We investigated the crystal structure， surface morphology， elemental composition， and luminescence properties through X-Ray diffraction（XRD）， scanning electron microscope（SEM）， photoluminescence（PL） spectrum， vacuum ultra violet（VUV） fluorescence spectrum， high temperature fluorescence spectrum and fluorescence decay lifetime. The results indicate that the Na3Sc2（1-x）（BO3）3∶xTb3+ phosphors can emit bright green light（~553 nm） under 242 nm UV excitation. The PL intensity of Na3Sc2（1-x）（BO3）3∶xTb3+ reaches the maximum when x=0.025. Vacuum UV fluorescence spectra show that these phosphors could be also excited by 187 nm deep ultraviolet light. And when the ambient temperature starts to rise from room temperature， the Na3Sc1.95（BO3）3∶0.025Tb3+ exhibits an anti-thermal-quenching phenomenon. When the temperature reaches 473 K， the luminescence intensity of the sample reached the highest， 109.3% of that at room temperature （298 K）. The strong emission and high thermal stability of these new green phosphors indicate the certain potential application in lighting and display fields.
Keywords：phosphor;Tb3+ doped;anti-thermal-quenching;lighting and display
Abstract：A series of Tb3+/Eu3+ single-doped， co-doped Ca0.3Sr0.7（MoO4）2 phosphors with a tunable color were synthesized by the conventional co-precipitation method. The crystal structure and morphology of phosphors were characterized by X-ray diffraction and field emission scanning electron microscopy. The results showed that a small amount of Tb3+ and Eu3+ doped into the sample has no effect on the crystal structure of the sample， and there are no impurity peaks. We researched the luminescence properties and temperature sensing properties. The energy transfer from Tb3+ to Eu3+ in Sr0.3Ca0.7（MoO4）2∶Tb3+，Eu3+ phosphors was confirmed in the luminescence characteristics of the samples. The temperature-dependent emission spectra suggested that the as-prepared samples possessed good thermal stability. The absolute sensitivity and relative sensitivity of samples were calculated， and the maximum relativity sensitivity of Sr0.3Ca0.625（MoO4）2∶0.05Tb3+，0.025 Eu3+ sample was 0.861%·K-1 at 514 K. In addition， under near-ultraviolet light by adjusting the doping concentration of Eu3+， the Sr0.3Ca0.7（MoO4）2∶Tb3+，Eu3+ phosphors realized tunability of emission color.
Keywords：Photoluminescence properties;energy transfer;phosphors;Optical temperature sensing
Abstract：A series of Gd2 （1-x-y）ZnTiO6∶xBi3+，yEu3+ phosphors with dual emission centers were prepared by high-temperature solid phase method. The structure， luminescence properties and temperature sensing characteristics of the material were systematically studied by X-ray diffraction， scanning electron microscopy， fluorescence spectroscopy， lifetime decay curve and variable temperature emission spectroscopy， respectively. In Gd2ZnTiO6∶Bi3+，Eu3+ phosphor， Bi3+ and Eu3+ ions occupy Gd3+ ion position. Under UV excitation， the excitation spectra of Eu3+ and emission spectra of Bi3+ overlap， indicating that there may be energy transfer from Bi3+ to Eu3+ . The fluorescence intensity ratio technique was used to explore the different temperature response characteristics of Bi3+ blue light emission and Eu3+ red light emission. In the temperature range of 293-473 K， the maximum relative temperature sensitivity of Gd2ZnTiO6∶Bi3+，Eu3+ phosphors was 1.133%·K-1， and the maximum absolute sensitivity value was 0.73%·K-1 ， respectively. Therefore， Gd2ZnTiO6∶Bi3+，Eu3+ phosphor is a potential non-contact optical temperature measurement material.
Keywords：Gd2ZnTiO6∶Bi3+，Eu3+;double perovskite;fluorescence energy transfer;optical thermometry;fluorescence intensity ratio
Abstract：In order to study the localized states in high-strain InGaAs/GaAs multiple quantum wells （MQWs）， a five-period In0.3Ga0.7As/GaAs MQWs structure was designed and grown by metal-organic chemical vapor deposition （MOCVD） technique in this paper. By means of AFM and temperature-dependent PL， the material disorders in MQWs such as defects and component fluctuation were found， and the existence and origin of localized states in MQWs were verified. The influence of the localized states on the spectra at low temperature was different for different measurement positions， exhibiting a bimodal distribution and an “S”-shaped change in peak position， respectively. This further indicated that different disorder within the material led to different depths of localized states. Based on the fitting of the temperature-bandgap relationship， the potential distribution of the MQWs structure containing localized states was proposed， and the recombination mechanism of the localized state carriers and free carriers was revealed. The optical properties of localized states at different depths under different excitation power densities were studied with the help of excitation power-dependent PL measurement.
Keywords：InGaAs/GaAs MQWs;localized states;high strain;metal⁃organic chemical vapor deposition（MOCVD）
Abstract：The cesium lead bromide perovskite thin films prepared by chemical vapor deposition （CVD） have excellent optoelectronic properties， but the thin films generally have two different phase structures， CsPbBr3 and CsPb2Br5. In our work， CVD method is considered to prepare cesium lead bromide perovskite thin films， and the effects of reaction pressure and N2 flow on CsPb2Br5 in the thin films were studied by X-ray diffraction （XRD）， scanning electron microscopy（SEM）， energy dispersive spectroscopy（EDS） and fluorescence spectrometer. The results show that the change of the reaction pressure has no effect on the CsPb2Br5 phase. However， with the decrease of the N2 flow， part of the CsPb2Br5 phase in the film gradually transforms into the CsPbBr3 phase， and its luminescence also converts from a broadband emission dominated by ~630 nm to a narrowband emission dominated by ~530 nm. Experimental results reveal that N2 flow is an effective means to control the phase structure and luminescence properties of CsPb2Br5.
Keywords：chemical vapor deposition（CVD）;cesium lead bromide perovskite film;CsPb2Br5 phase
Abstract：In recent years， flexible display technologies have attracted widespread attention in the field of folding mobile phones and wearable electronics. Especially， flexible displays are indispensable in these flexible electronics. Among them， quantum dot light emitting diodes （QLEDs） have great advantages due to their high color purity， high efficiency and good stability. In this paper， we first give a brief introduction of flexible QLEDs （flex-QLEDs） and summarize the recent development of flex-QLEDs. Then we discussed the device structure and the interface regulation of flex-QLEDs. For flex-QLEDs with multilayer heterostructures， the strategies are categorized into three： anode interface regulation， cathode interface regulation， and light-emitting layer regulation. The regulation focuses on reducing the surface roughness， enhancing the interfacial force， and optimizing the energy level. Finally， the performances of advanced flex-QLEDs are compared and summarized， and the future challenges and opportunities are prospected.
Abstract：Inverted organic light-emitting diodes （IOLEDs） consist of a bottom cathode followed by the formation of an electron injection layer （EIL）， an electron transport layer （ETL）， a light emission layer （EML）， a hole transport layer （HTL） and an anode， which have been widely investigated to match the existing n-type thin film transistor technology. In IOLEDs research， various EIL structures were studied to improve the efficiency of electron injection from the bottom cathode to ETL. In this paper， we report on high efficiency green phosphorescent IOLEDs utilizing ultra-thin Mg as EIL. The ultra-thin Mg films deposited on quartz substrates exhibited excellent light transmittance. IOLEDs based on the 2 nm Mg as EIL demonstrated the optimal device performance， with the maximum current efficiency， the maximum external quantum efficiency and turn-on voltage of 46.5 cd/A， 13.3% and 3.06 V， respectively.
Abstract：Broad-area stripe semiconductor lasers are widely used in laser pumping， laser processing and other fields. In order to solve the problems of wide output spectrum and small tuning range of broad-area stripe semiconductor lasers， reflective diffraction grating with diffraction efficiency of 28% and 55% was used as a feedback element to construct a broad-area 970 nm semiconductor laser with a grating external cavity. The effect of the parameters of semiconductor laser with a grating external cavity in Littrow configuration on its performance （tuning range， power， threshold current， linewidth） was investigated. The experimental results show that the tunable laser output with narrow linewidth can be obtained by optimizing the structure， the tuning range of the outer cavity laser can be increased by increasing the temperature appropriately， the tuning range of the outer cavity laser can be improved and the threshold current can be reduced by using a grating with higher diffraction efficiency. The maximum wavelength tuning range of semiconductor laser with a grating external cavity based on S-polarization is 27.87 nm， the spectral linewidth pressure is narrowed to 0.2 nm， and the output power can reach 1.11 W.
Keywords：semiconductor laser;diffraction grating;wavelength tuning;threshold current
Abstract：An all-solid-state quasi-continuous-wave（QCW） Nd∶YAG slab laser with a high power was demonstrated. A Nd∶YAG slab crystal is adopted for gain medium， a plane-concave cavity is set up， and the laser beam travels along a Zigzag path in the slab. An average output power of 3 420 W is obtained at a pump power of 9 kW， corresponding to a repetition rate of 1 kHz. The pulse width is 80 μs with a pulse energy of 3.42 J， and the laser beam quality with AO system β is 4.1 times of the diffraction limit.
Abstract：The nanocomposite， which is synthesized by copolymerizing erbium-doped nanocrystals and methyl methacrylate （MMA） monomer， can be used as the gain media to fabricate a polymer-based optical waveguide amplifier. The gain performance of this type device is closely related to the concentration of nanocrystals in the nanocomposite. In this paper， the uniform β-NaLu50%Y30%F4∶18%Yb3+，2%Er3+ nanocrystals were successfully synthesized by the thermal decomposition method. The nanocrystals were about 16 nm and modified with unsaturated ligands on their surfaces. Therefore， the nanocrystals could be copolymerized with MMA to form nanoparticles-polymethyl methacrylate （NPs-PMMA） nanocomposite. Three groups of nanocomposites with different bonding ratios were prepared by adjusting the doping concentrations of nanoparticles to 0.1， 0.15， 0.25 mmol， respectively. The down-conversion emission and transmission spectra showed that with the increase of the bonding nanocrystal concentration， the luminescence intensity of the nanocomposites increased gradually， but the light transmittance in the near infrared region decreased slightly. A series of embedded waveguide amplifiers were fabricated based on these three nanocomposites. At 1 550 nm， the relative gains of these devices were 3.00， 3.46， 5.61 dB， and the insertion losses were 19.20， 25.00， 26.53 dB， respectively. The results showed that even the scattering loss raised with the increase of nanocrystal concentration， the luminescence intensity of the gain media still enhanced and the relative gain improved in the series of devices in the C-band. In the experiment of this paper， increasing the concentration of the nanocrystals results in an advantage of the gain improvement over the scattering loss increase.
Abstract：In recent years， photodetectors have been an important research subject due to their potential applications in imaging， communication， medical analysis， environmental monitoring， and biological sensing. Employing the ferroelectric materials featured with typical ferroelectric polarization as absorbers will simplify the device structure and lower the cost. In the current work， self-powered ultraviolet photodetectors have been fabricated based on ferroelectric PbZr0.52Ti0.48O3（PZT） thin films. The ferroelectric PZT thin films were prepared using a sol-gel method. Morphological， structural， electrical， and ferroelectric characterizations showed that the as-grown ferroelectric PZT thin films possessed a smooth and dense surface， low density， high remnant polarization（2Pr=35.2 μC/cm2） and coercive electric field（~105 V/cm）. On this basis， high-performance self-powered ultraviolet photodetectors with Au/PZT/FTO structure have been fabricated. Interestingly， under the bias voltage of 0 V， the responsivity and detectivity are as high as 0.072 A/W and 4.35×1011 Jones， respectively， which are higher than most of state-of-the-art reported results. The results shown in this paper highlight the superiorities of ferroelectric PZT-based self-powered ultraviolet photodetectors and provide a promising strategy for the development of high-performance self-powered photodetectors with simple device structures in future.
Abstract：Channel crosstalk is one important feature of multi-core fiber communication based on space division multiplexing technology， which could affect the signal quality and transmission distance of the broadband fiber amplification system. This paper is focused on the crosstalk problems of a 19-core weak coupling optical fiber， as that can benefit much to develop high-volume communicating fiber based on fiber extrusion technology. Then， the optical coupling theory and finite element method are adopted to complete the numerical simulation of fiber performance， here， key parameters of groove size， core refractive index distribution and their influence on the crosstalk of the fiber are optimized wholly. The simulation results show that the optimized fiber has a low crosstalk of -156 dB/100 m at 1 550 nm， which could meet the requirements of future long-distance high-capacity optical fiber communication.
Abstract：Due to the simple structure， high light-emitting efficiency， simple manufacturing process and ultra-thin thickness characteristics for organic light-emitting diode （OLED）， flexible OLED devices with bending and folding capabilities can be fabricated by combining flexible substrates. These devices play an important role in flexible display， flexible lighting and other fields. When subjected to external load mainly bending， the inorganic thin films in the flexible OLED devices are prone to failure in the form of cracks， delamination and buckling. These failures reduce the conductivity and destroy the original structure of the devices， thereby affecting their efficiency and reliability. The use of the neutral layer can effectively reduce the strain in the key parts of the devices， thereby reducing or eliminating failure， and the reliability of the devices in the bending state can also be improved. In recent years， a series of studies based on neutral layers of flexible OLED devices have been reported successively. This paper reviews the application of neutral layer technology in flexible OLED devices. Firstly， the concept of neutral layer and the method of determining the single neutral layer's position are discussed. Then， the application of single neutral layer and multiple neutral layers in practical devices is introduced. Finally， we give an outlook on the future development direction of flexible OLED devices.
Abstract：Clinical surgery is one of the main methods to treat diseases. At present， visual observation and ultrasonic technology are commonly used by surgeons to determine tumor boundaries， residual lesions and micrometastasis lesions， which probably cause cancer recurrence to a large extent. The rapid development of the second near-infrared （NIR-Ⅱ） aggregation-induced emission （AIE） materials as fluorescent surgery navigation reagents provides new avenue to solve the problem. In this review， structural design of NIR-Ⅱ AIE materials in surgical navigation is first summarized. Then the applications of NIR-Ⅱ AIE material in tumor resection surgery， in detection of lymph node resection surgery， and in other tissues are discussed. At last， the future development of NIR-Ⅱ AIE materials in surgical navigation is prospected.
Keywords：the second near-infrared;aggregation-induced emission;surgical navigation;donor;acceptor
Abstract：Dual-emission fluorescence carbon quantum dots （GP-CQDs） were synthesized by a one-step hydrothermal method using glucose and p-phenylenediamine as carbon sources. The morphology and spectral properties of GP-CQDs were studied. It was found that the GP-CQDs have dual emission fluorescence signals at 348 nm and 452 nm under a single excitation wavelength at 300 nm. When MnO4- was added to the GP-CQDs solution， the fluorescence signal of GP-CQDs at 452 nm was completely quenched； however， the signals at 348 nm kept stable. When S2- was added to the quenching system above， a new fluorescence emission peak was generated at 425 nm. Compared with the original fluorescence peak at 452 nm， the peak was blue-shifted， and the fluorescence intensity at 425 nm was linearly enhanced with the S2- concentration. With the fluorescence peak at 425 nm as the response signal and the 348 nm fluorescence peak as the reference signal， a ratiometric fluorescence sensing probe for S2- determination can be directly constructed. Under the optimal condition， this method showed a good linear relationship in the range of 3.1×10-8-8.0×10-6 mol/L and the detection limit was calculated to be 9.41×10-9 mol/L（3σ/k）. The basic mechanism of the proposed method was further discussed. Moreover， this method can be applied to detect S2- in environmental water samples with satisfactory results.