Abstract：Due to low-dimensional semiconductor micro/nano-structures， visible light-emitting devices， especially for green/yellow light sources locating in the wavelengths of 500-600 nm， have reached a broad audience in ultrahigh resolution display and lighting， single-photon source， single-molecule sensing and imaging in life science and other fields. In developing high-performance green/yellow light-emitting devices， the preparation of light-emitting materials and device structures is highly restricted by the “green/yellow gap” and “efficiency droop”. In the present research， a new generation of yellow light-emitting diode， which is composed of a single Ga-doped ZnO microwire（ZnO∶Ga MW） and p-type InGaN substrate， is demonstrated at a wavelength of 580 nm together with a linewidth of about 50 nm. With increasing the drive current at high injection levels， hardly little variation in the spectral profiles， such as the main emission wavelengths and the linewidth， could be distinctly noticed， as well as the quantum Stark effect that has been normally observed in InGaN-based light sources. The color coordinate is well matched with the yellow of the REC.2020 standard. Interestingly， the external quantum efficiency of the device is relatively stable even at high current injection. By comparing with the photoluminescence properties of a ZnO∶Ga MW and p-InGaN film， the energy band structure of the as-fabricated n-ZnO∶Ga/p-InGaN heterojunction emission device was constructed. It is clearly inferred that the electroluminescence is derived from the generation of electron-hole recombination， which occurring close to the ZnO∶Ga/InGaN heterointerface， instead of the p-InGaN side. The experimental results show that the as-designed n-ZnO∶Ga MW/p-InGaN heterojunction can be used to fabricate high-performance low-dimensional yellow light-emitting diodes.
Abstract：By introducing the related basic knowledge， this paper provided a tutorial for understanding the optical property of Mn4+ ion， including how to determine the LS term of a free Mn4+ ion， and how to determine the splitting of these LS terms in an Oh point group， etc. Finally， this paper discussed how to analyze the photoluminescence spectra of Mn4+-doped phosphors， including how to determine the zero phonon line energy of each involved transitions， how to adjust the energy of the emitting photons， etc.
DAI Ke-cheng,ZHAI Yue,WU Na,MEI Hang,ZHANG Hong,ZHU Qiang-qiang,WANG Le
Abstract：All-inorganic cesium lead halide perovskite film has received extensive attention due to their excellent photoelectric properties. However， the poor stability of the perovskite film and the use of numerous expensive as well as toxic organic solvents during the preparation process severely hinder its commercial application process. In this work， aqueous solution is used as the solvent to prepare a perovskite precursor solution containing with sodium chloride（NaCl）. The in-situ NaCl/CsPbBr3 cesium lead bromide perovskite composite film is obtained by a one-step solution method， and dimethyl sulfoxide（DMSO） solution is introduced to optimize the crystal structure and optical properties of the composite film. It is found that the synergistic effect of NaCl and DMSO can change the morphology of the crystal grains， improve the phase purity and enhance the fluorescence emission of the composite film. The composite film exhibits the optimal green light emission with the 48.2% photoluminescence quantum yield when the volume ratio of DMSO and the precursor solution reaches to 1∶2. In addition， benefiting from the effective combination of NaCl and the optimized crystal structure， the prepared composite film has the enhanced stability. The design is beneficial to the preparation of flexible， large-area and high-stability display fluorescence conversion films.
Abstract：Inorganic lead halide perovskite has broad application prospects in light-emitting devices and photovoltaic devices due to its advantages， such as high fluorescence quantum yield， adjustable band gap， and high absorption coefficient. Due to the toxic lead ions which is harmful to the environment and organisms， the development of lead-free perovskite materials and their derived materials has become a research hotspot. Among many materials， compared with perovskite materials， perovskite-derived materials-metal halides have the advantages of many types， many structural types， and excellent luminescent properties. In this paper， the perovskite-derived material Cs3MnBr5 was prepared by the oleic acid reduction method， which has the advantages of environmental friendliness， low energy consumption， high product purity， and mass production. The Cs3MnBr5 material shows bright green luminescence under near-ultraviolet excitation， the emission peak locates at 528 nm， the full width at half maximum is 43 nm， the color coordinates are （0.25， 0.69）， PLQY is 64.96％ and the color purity is as high as 92%. These indicate that Cs3MnBr5 material has potential applications in commercial LED lighting and displays.
Abstract：The nonlinear optical effect of all-inorganic metal halide perovskite materials is important for the design of novel micro- and nano-photonic devices. In this paper， the two-photon luminescence of micro-scale CsPbBr3 perovskite single crystal particles is investigated. In the experiment， CsPbBr3 microcrystals with different sizes were prepared based on the sonochemistry synthesis method， and the variations of the two-photon luminescence were studied by adjusting the energy density， wavelength and polarization of the pump laser beam. The experimental results demonstrate that the CsPbBr3 microcrystals possess strong two-photon luminescence at room temperature. The wavelength-dependent two-photon luminescence spectrum shows that under the same absorption band gap， the luminescence peak position does not change much compared with the single-photon emission， and the two-photon emission intensity gradually decreases with the increase of excitation wavelength. In addition， the two-photon emission of CsPbBr3 microcrystals reveals polarization-dependent behavior and the polarization angle presents quadruple symmetry in the range of 0°-360°. The two-photon luminescence responses of the CsPbBr3 microcrystals make them promising for nonlinear integrated devices.
Abstract：In this paper， a novel auxiliary ligand functionalized donor-acceptor（D-A） type near infrared-emitting iridium（Ⅲ） complex （CH3OTPA-BTz-Iq）2Ir（pic-FL） was synthesized by connecting alkylfluorene（FL） to picolinic acid（pic）. Through the study of UV-Vis absorption and photoluminescence spectrum， the complex has a strong intramolecular charge transfer transition （ICT） absorption peak and a photoluminescence peak about 720 nm due to the strong D-A effect of the CH3OTPA-BTz-Iq ligand. Furthermore， the photoluminescence and electroluminescent properties of （CH3OTPA-BTz-Iq）2Ir（pic-FL） were improved by introducing alkyl chains and FL group with high fluorescence quantum efficiency， good solubility and film forming performance. In （CH3OTPA-BTz-Iq）2Ir‐（pic-FL）-based OLEDs， a maximum external quantum efficiency （EQEmax） of 0.92% at 722 nm was obtained， which is much superior than that of the （CH3OTPA-BTz-Iq）2Irpic-based OLEDs （0.41% at 723 nm）.
WANG Xin-ran,WANG Feng-xiang,LIAO Yu,MA Yi-zhi,ZHANG Yu,WANG Kai-xuan,ZHOU Xue-lian,CHAO Ke-fu,NA Ri-su
Abstract：Self-activated phosphors have received a lot of attention from researchers， among which nitridoborate defect phosphors have the potential to become a new generation of phosphors for LEDs due to low toxicity， simple synthesis， and structural diversity， but low thermal stability limits their practical applications. In this paper， a new LiSr2Ca2（BN2）3（LSCBN） phosphor was synthesized by partially replacing Sr in LiSr4（BN2）3（LSBN） using a high-temperature solid-phase one-step method. The phase composition， morphology， and optical properties of the phosphor were characterized by X-ray diffraction， scanning electron microscopy， and fluorescence spectrometry. The results show that the prepared sample LSBN is a cubic crystal system with the space group Im‐3m. It has a wide excitation band in the UV region， the peak of the emission spectrum is located at 561 nm， and the full width at half maximum（FWHM） is about 4 504 cm-1. The luminescence intensity of a LSCBN is twice that of a LSBN. In LSCBN， the partial replacement of Sr by Ca introduces substitutional defects that form new luminescence centers. In the temperature dependence PL spectra， the intensity of LSBN at 150 ℃ is 17% of the initial value， and LSCBN can maintain 57% of the initial intensity at 150 ℃， which exceeds other nitridoborate phosphors that have been reported. This ion-substitution method can effectively regulate the luminescence wavelength and enhance the luminous intensity， improve the thermal stability， and provide a new idea and application prospect for the improvement of the luminescence performance of defect-related nitridoborate phosphors.
Abstract：Gallium oxide（β-Ga2O3） was deposited on silicon （111） substrate by RF magnetron sputtering， and the effect of substrate temperature on the microstructure and optical property of the Ga2O3 was studied. The crystal structure， surface morphology and optical propery of as-deposited Ga2O3 were characterized by X-ray diffraction， scanning electron microscopy， fluorescence spectrometer， etc. The experimental results show that in a high-purity Ar atmosphere， the surface morphology of as-deposited Ga2O3 is related to its growth mechanism at different sputtering temperatures. When the sputtering temperature is 300 ℃， Ga2O3 undergoes thermal decomposition to form clusters of metal Ga； when the sputtering temperature reaches 400 ℃， the metal Ga clusters act as the catalyst to trigger the self-catalytic growth of Ga2O3 nanowires. According to the photoluminescence（PL） spectra， the Ga2O3 samples show four emission peaks located in the ultraviolet， blue and green light regions in the spectral range of 300 nm to 700 nm. The emission peaks of the Ga2O3 nanowires obtained at the sputtering temperature of 400 ℃ are significantly enhanced and exhibit slight blueshifts. It is revealed that the larger specific surface area and the quantum size effects of nanowires have important effects on the PL performance of Ga2O3. Raman spectroscopy（Raman） characterizations suggest that the crystalline quality of as-grown Ga2O3 is improved with the increasing sputtering temperature. New Raman vibration modes appear in the spectra detected from the Ga2O3 nanowires grown at 400 ℃， and the Raman peak shows a blueshift of 18 cm-1.
YE Zi-qing,ZHANG Deng-liang,DUAN Xing-xing,YU Bu-fan,XING Zhao-hui,CHEN Jiang-shan
Abstract：During the past few years， the performance of perovskite light-emitting diodes（PeLEDs） has been greatly improved. Constructing quasi-2D perovskites with quantum wells is an effective approach to develop high performance PeLEDs. And the organic cations with large size are crucial to quasi-2D perovskites， which play an important role in regulating the film structures and optoelectronic properties of quasi-2D perovskites. Here we incorporated 2-fluorophenethylammonium bromide （ortho-substituted o-FPEABr） and 4-fluorophenethylammonium bromide（para-substituted p-FPEABr） into cesium lead halides to prepare quasi-2D perovskite films by one-step method without antisolvent for PeLEDs， and studied the effect of the fluorine substituted organic cations on the phase distribution and device performance. It was found that p-FPEABr allowed the quasi-2D perovskites to form abundant low-n phases， especially the 2D phases（n=1） with strong exciton-phonon coupling， and a few high-n phases. On the contrary， the incorporation of o-FPEABr suppressed the formation of low-n phases and promoted the formation of high-n phases， which is conducive to reduce non-radiative recombination and improve radiative recombination. The determined formation energies indicated that the low-n phases based on p-FPEABr show higher thermodynamic stability than those based on o-FPEABr， leading to the difference of phase distribution in the quasi-2D perovskite films. This demonstrated that changing the fluorine substituted position in organic cations can regulate the crystallization kinetic of quasi-2D perovskites， and then affect the device performance. Based on o-FPEABr， efficient green and blue PeLEDs were fabricated， a green device with emission peak at 521 nm achieved the maximum external quantum efficiency（EQE） of 10.27%， and a blue device with emission peak at 488 nm showed the maximum EQE of 8.88%.
Abstract：Lead halide perovskite is a popular research field in photodetectors（PDs） due to its excellent photoelectric characteristics such as high light absorption coefficient， long carrier diffusion length and high fluorescence quantum efficiency. However， heavy biological toxicity and low environmental stability restrict the development and application of this kind of devices. So far， Sn， Ge， Sb， Bi and other materials have been studied， in which bismuth-based perovskites have become one of the candidate materials due to stability， non-toxicity and wide band gap. The performance of PDs is limited by many factors， and dark current suppression is one of the important means to improve device performance. Based on the traditional hole transport layer（HTL） of PEDOT∶PSS replaced by the inorganic compound CuSCN through spin-coating， the p-i-n type photodetectors with an architecture of ITO/CuSCN/Cs3Bi2I6Br3/ZnO/Ag were fabricated. CuSCN can effectively block electron injecting through the interface between the hole transport layer and the perovskite absorption layer， because the lowest unoccupied molecular orbital（LUMO） energy level of CuSCN is -1.5 eV， the electron injection barrier with ITO is as high as 3.3 eV， which is much higher than that of PEDOT∶PSS and ITO（1.8 eV）. Under self-powered condition， the dark current of the device was as low as 3.52×10-11 A. Its on/off ratio reaches 105， which is two orders of magnitude higher than the detector of PEDOT∶PSS. In addition， the rise and fall time of the detector are less than 0.1 s and 0.12 s， which are better than the detector of PEDOT∶PSS. This result can be attributed to the higher carrier transport mobility of CuSCN higher than PEDOT∶PSS. The results show that the structure of ITO/CuSCN/Cs3Bi2I6Br3/ZnO/Ag photodetector posseses many characteristics， such as self-driven， high on/off ratio， non-toxic and stable. It provides a feasible strategy for realizing commercialization.
Keywords：lead-free perovskite;photodetector;hole transport layer;dark current
Abstract：The dual-wavelength lasing from vertical external cavity surface emitting laser（VECSEL） is realized by the large gain spectra and cavity mode detuning， and the stable external cavity is designed. The emission wavelength can be switched between single-wavelength lasing and dual-wavelength lasing according to our simulation results， and three operation modes are proposed and proved by our experiments. The side-mode of VECSEL with side-mode wavelength appears when the pump power exceeds the threshold power. As the pump power is increased， the rollover of output power can be observed on the power curve. However， when the pump power is further increased， the output power can be increased again， which we called the second-threshold phenomenon. And the dual-wavelength lasing can be observed. The output power can reach 359 mW during the dual-wavelength lasing with the lasing wavelengths located at 954.2 nm and 1 001.2 nm. When the pump power exceeds the second threshold， only one lasing wavelength of 1 002.4 nm can be observed， and this wavelength is the cavity-mode wavelength. The laser spot behaves the circular symmetrical shape with Gaussian morphology at both the single-wavelength and dual-wavelength lasing. The divergence angle of VECSEL is increased from 5.9° to 7.9°， which might be caused by the mode competition between the two modes. The dual-wavelength lasing of VECSEL from single gain chip proposed by us has great potential in the LiDAR and terahertz applications in the future.
Abstract：Self-powered photodetectors can meet the demands of modern optoelectronic devices for energy conservation and lightweight， but the complex process and high cost limit their further development. In this work， Se-MT/PEDOT heterojunction has been prepared by spin-coating with selenium microtube（Se-MT） and polythiophene（PEDOT）， which shows a good photoresponse at 350-700 nm and a responsivity of 8 mA/W at 500 nm without bias voltage. To enhance the responsivity， Se-MT/PEDOT/Ag-NW was prepared by adding silver nanowires（Ag-NW） on the surface of Se-MT/PEDOT heterojunction， enhancing the UV-Vis absorption to improve the photoelectric performance of the device. Compared to the Se-MT/PEDOT， the Se-MT/PEDOT/Ag-NW device shows enhanced photocurrent at the wavelength of 350-700 nm， especially under 500 nm illumination at zero bias， 800% improvement in responsivity of 65 mA/W， the on-off ratio up to 552 with 400% enhancement， obvious reduction in response time（rise/decay time of 15/28 ms）. This result indicates that the Ag-NWs modification of organic/inorganic heterojunction can be applied to the preparation of high-performance photodetectors.
LIU Chun-yan,WANG Yuan,YIN Cheng-yu,LI Ze,WANG Zhen-yu,FAN Si‐yu,JIANG Wen-long,DUAN Yu
Abstract：Organic light emitting diode（OLED） has the characteristics of lightness， thinness， portability， self-luminescence， low energy consumption， higher brightness， and flexible display etc.， which can increase the added value of display products， so it has been widely concerned by scientific and industrial circles. However， the key organic materials in OLED devices are very sensitive to water vapor and oxygen in the air. If the device is exposed to air for a long time without protection， it will seriously affect the long-term performance of the device and shorten the life of the OLED. In addition to selecting appropriate transmission layer material and surface layer structure， and using interface engineering to improve the water and oxygen tolerance of materials， reliable encapsulation of the device is another effective means to isolate water vapor and oxygen corrosion in the air. Atomic layer deposition（ALD） is an effective film deposition and thin film encapsulation technology that has been verified in the laboratory. Due to the self-limiting reaction characteristics of ALD， it can deposit thin films with accurate and controllable thickness， uniform and dense at low temperature. The films deposited by ALD always have good flexibility， ultra-high barrier performance and optical transmittance. In this paper， we will review the principle of atomic layer deposition technology， analyze the water vapor transmission rate， compare the advantages of ALD in single-layer and organic-inorganic laminated film encapsulation.
WAN Ping-ping,YANG Jing,LIU Hong-xiu,LIU De-quan,ZHOU Wen-li
Abstract：Poor moisture resistance is a bottleneck for the application of Mn4+-doped fluoride red phosphors in high-stability devices. This work proposes to use the passivation effect of lactobionic acid to remove Mn4+ on the surface of K2SiF6∶Mn4+， and reconstruct the Mn4+-free fluoride inert shell to improve its moisture resistance. The results show that the crystal phase， morphology and luminescence intensity of the passivated fluoride are almost unchanged. After 360 h of water immersion， the internal quantum efficiency of the passivated fluoride is 96.9%， which is much higher than that（59.8%） of the untreated fluoride. After treatment with lactobionic acid， the internal quantum yield of hydrolyzed fluoride can be recovered to 98.8%. At a driving current of 60 mA， a warm white LED with a correlated color temperature of 3 518 K， a color rendering index of 88.5， and a luminous efficiency of 130.61 lm·W-1 was encapsulated by using the passivated fluoride as the red-light component. After aging in a high temperature（85 ℃） and high humidity（85%） environment for 500 h， the LED device has high stability， and the luminous efficiency can maintain at 90.5% of the initial value， which is higher than that（82.3%） of white LED encapsulated with the untreated fluoride. Therefore， the simple lactobionic acid treatment can effectively improve the moisture resistance of Mn4+-doped fluorides. This work can provide a reference for the industrial production of highly stable fluoride red phosphors.
DING Meng-yu,ZHENG Biao,WEI Wei-ping,CHEN Lu-yao,WU Xiao-ping,HONG Jin-quan,HUANG Chun-lei,WANG Jun
Abstract：To improve the stabilities of all-inorganic perovskite nanocrystals（NCs） CsPbX3（X=Cl， Br， I） under water or thermal conditions， 3-aminopropyl-triethoxysilane（APTES） modified CsPbBr3 NCs were synthesized by a hot-injection method， and then CsPbBr3@SiO2 core-shell nanoparticles（NPs） were prepared by using tetramethyl orthosilicate（TMOS） as silicon source. The structures， morphologies， optical properties and stabilities of the CsPbBr3@SiO2 samples were characterized and analyzed by X-ray diffractions， transmission electron microscopy and fluorescence spectrometer. The results show that the SiO2 shell forms uniformly on surface of CsPbBr3 NCs， which still shows excellent optical properties. More importantly， the stabilities of CsPbBr3@SiO2 NPs are significantly improved in water or thermal atmosphere. The photoluminescence intensity of CsPbBr3@SiO2 remains 81% under heated at 60 ℃ for 30 min， and it remains 75.2% when mixed with water for 100 min. Furthermore， we fabricated CsPbBr3@SiO2-polydimethylsiloxane（PDMS） composite films to explore the applications of CsPbBr3@SiO2 in the field of flexible display and fluorescent anti-counterfeiting.