Abstract：Phosphorescent metal complexes tend to be quenched at high concentration. The host-guest strategy is usually employed to improve the electroluminescent efficiency. Due to the reverse intersystem crossing， thermally activated delayed fluorescence （TADF） materials could potentially achieve 100% internal quantum efficiency. To explore the influence of the host on the electroluminescence of the solution-processed organic light-emitting devices， the ternary-blend emitting layers were constructed with a TADF polymer as the sensitizer and a phosphorescent emitter which were hosted by a conventional fluorescent material and a TADF material， respectively. For the phosphorescent emitter with the concentration of 1%， 5% and 50%， the external quantum efficiencies of the devices based on the sky-blue TADF host were respectively higher than those of the devices based on the conventional fluorescent host. With 1 % phosphorescent emitter PO-01-TB doped in the ternary-blend emitting layer， the peak external quantum efficiency of the solution-processed device hosted by the TADF material DMAC-DPS was up to 12.2%， which was 14% higher than that of the device with the fluorescent host （10.7%）. This is attributed to efficient cascade energy transfer in the presence of the TADF host with the bipolar property and reverse intersystem crossing， which alleviates the triplet annihilation and quenching effects under high driving current.
Keywords：organic light-emitting diode;ternary blend;thermally activated delayed fluorescence;phosphorescence;energy transfer
Abstract：With the rapid development of smart materials， photoresponsive metal-organic frameworks （MOFs） has attracted extensive attention of researchers. Under the alternating irradiation of ultraviolet and visible light， photoresponsive MOFs can be reversibly switched between different morphologies， accompanied by changes in physical and chemical properties， which have broad development prospect in the fields of drug transport， gas separation， photo-controlled catalysis and smart sensing. Most of the photoresponsive MOFs are formed by the coordination of photoresponsive ligands and metal ions. Different photoresponsive ligands make the systems have unique properties and application scenarios. In this article， the recent research progress of photoresponsive MOFs is reviewed， including the main types of photoresponsive MOFs and their applications in different fields such as gas separation， material transport， dynamic anti-counterfeiting， and optoelectronic devices. Finally， the future development of photoresponsive MOFs is prospected.
Abstract：As an excellent crystal growth method， the EFG （Edge-defined film-fed growth） method is excepted to grow Er∶Lu2O3 crystal with high quality， large size and high doping concentrations. In this letter， the fluorescence spectrum and continuous-wave （CW） laser performances of Er∶Lu2O3 crystal grown by EFG method have been characterized. A 2.85 μm CW laser with a slope efficiency of 23.1% was realized at room temperature， and the maximum output power was 5.24 W. The RMS （Root mean square） power stability is better than 1.4% during 80 min， and the M2 factor of laser beam quality at different power levels is better than 2.17. The experimental results demonstrate that Er∶Lu2O3 laser gain medium grown by EFG method has the ability to generate high output power and high efficiency mid-infrared laser.
Abstract：Near-infrared （NIR） spectral modification is crucial for the development of NIR phosphors. With 3d3 configuration， the Cr3+ ion shows wavelength-controllable wide-band NIR emissions， which is an ideal NIR activator ion. Due to the sensitivity of d orbitals to crystal field， the emission wavelength of Cr3+ strongly depends on its coordination structure. Clarifying the structure-function relationship between its coordination structure and luminescence properties is the theoretical basis to guide the rational design of NIR phosphors. In fact， limited by the complexity of the crystal structure， there are too many factors affecting the local coordination structure properties. A clarified structure-function relationship is still a serious challenge. A series of pyrophosphate crystals AMP2O7（A=Li， K； M=Ga， Sc， In） contain isolated ［MO6］ octahedron feature， which provides isolated coordination environment for Cr3+. The isolated coordination greatly suppresses the effect of the next-closed coordination structures and guarantees the reasonability of the related structure-function relationship. This paper studies the series of AMP2O7∶Cr3+ phosphors. The Cr3+ ions are introduced into the central site of the isolated ［MO6］ octahedra， which show wavelength-tunable NIR emissions depending on the composed M3+ and A+. We build a preliminary structure-function relationship of ［MO6］—NIR wavelength of Cr3+ based on the correlation of Cr3+ emissions and the isolated coordination structure features， which provides theoretical basis and ideas for rational design of Cr3+ NIR emitting materials.
Abstract：Herein， a new Mn4+-doped hydrate calcium hexafluorotitanic CaTiF6·2H2O∶Mn4+ red phosphor is reported. Physical properties of host， luminescence properties and warm white LED application of this phosphor are studied carefully. CaTiF6·2H2O∶Mn4+ removes H2O to be CaTiF6∶Mn4+ with changed emission spectrum. CaTiF6∶Mn4+ could adsorb H2O and recover to CaTiF6·2H2O∶Mn4+ except emission intensity. Importantly， it emits extremely strong zero phonon line（ZPL） and ν6 vibration peaking at longer wavelength of 626 nm and 635 nm in sequence. This unique emission gives color coordinates of （0.701， 0.299）， more closing to the red-light boundary of human eyes sensibility（650 nm， chromaticity coordinate x~0.72， y~0.28）， which could enhance the color rendering index（Ra） of WLED and widen the color gamut of backlight display. The combination of crystal structure and crystal field strength calculation demonstrates that Mn4+ ion locates at a highly unsymmetric lattice and experiences weak crystal field strength with strongly covalent Mn—F bond in CaTiF6·2H2O∶Mn4+. Moreover， coating with hydrophobic layer enhances the moisture resistant of CaTiF6·2H2O∶Mn4+. Codoping small ionic radius Si4+ improves its thermal stability. Using CaTiF6·2H2O∶Mn4+ as red-light component， a warm white LED with high Ra ~90 and R9 ~ 68 was achieved， showing potential in high color quality warm white lighting applications.
Keywords：Mn4+-doped fluorides;CaTiF6·2H2O∶Mn4+;strong zero-phonon line;high color rendering index;warm WLED
Abstract：Tm3+/Yb3+ co-doped germanate glass ceramics containing LaF3 nanocrystals were prepared by traditional melt quenching technique and subsequent heat treatment. The thermal properties and the controllable precipitation of LaF3 nanocrystals were studied by DTA and XRD. The optical properties of the glasses were studied by transmission spectra and upconversion luminescence spectra. The temperature dependence of upconversion luminescence spectra of glass ceramics excited by 980 nm laser was studied by fluorescence intensity ratio （FIR） technique. It is found that the maximum absolute sensitivity （Sa） and the maximum relative sensitivity （Sr） of the glass ceramics are 2.6×10-4 K-1 （573 K） and 2.3×10-2 K-1（313 K） at the temperature range of 313-573 K， respectively. The results show that Tm3+/Yb3+ co-doped germanate glass ceramics containing LaF3 nanocrystals have potential application prospects in the field of temperature sensing.
Abstract：Y7O6F9∶Er，Yb orthorhombic crystals were synthesized by hydrothermal method and high-temperature calcination， which achieves efficient up-conversion luminescence and has satisfactory polymer affinity. Y7O6F9∶Er， Yb/PAN composite fibers with high temperature sensing properties， and commendable flexibility were prepared by high voltage electrospinning technology. Under the excitation of 977 nm laser， the composite fibers show efficient up-conversion luminescence and better temperature sensing performance than crystals in the temperature range of 303 K to 433 K. Within the temperature range of measurement， the maximum value of SA and SR of Y7O6F9∶Er，Yb crystals is 0.720%·K‒1 and 1.142%·K‒1， and the minimum temperature resolution was 0.37 K. The maximum value of SA and SR of Y7O6F9∶Er，Yb/PAN composite fibers is 0.811%·K‒1 and 1.143%·K‒1， and the minimum temperature resolution was 0.15 K. The sensitivities and temperature resolution of composite fibers with flexibility are higher than those of crystals. Therefore， the flexible Y7O6F9∶Er，Yb/PAN composite fibers not only have admirable temperature sensing characteristics but also can adapt to complex and diverse application environments， which is a viable candidate material for realizing temperature sensing performance in the field of intelligent wearable.
Keywords：Y7O6F9∶Er，Yb/PAN composite fibers;high voltage electrospinning;up-conversion luminescence;temperature sensing
Abstract：A series of CaSc2O4∶Er3+，Nd3+ nanocrystals were synthesized by the hydrothermal method. The luminescence properties of the CaSc2O4∶Er3+，Nd3+ oxide crystals in the visible-light and near infrared （NIR） regions were investigated in detail as the Nd3+ concentrations and excited wavelengths vary. Under 808 nm excitation， the luminescence intensity of Er3+ ions appears to be enhanced as the concentration of Nd3+ ions increase. The relative red intensity also has the slight enhancement. Under 980 nm excitation， Nd3+ ions hardly absorb 980 nm photons， only the absorption and emission of Er3+ ions are found. The relative red intensity has no change. Furthermore， only the emission of Er3+ ion was observed in NIR spectrum， which is consist as the visible spectrum. The detailed study reveals the possible upconversion luminescence （UCL） mechanism involved in a novel CaSc2O4∶Er3+，Nd3+ nanocrystals under 808 nm and 980 nm NIR excitation.
Abstract：A method to one-pot synthesize solid fluorescent materials by coating carbon dots via the crystallization of phthalic acid precursor as matrix is reported. The crystalline CDs， emitting blue and green fluorescence respectively， are synthesized by changing the solvent in microwave method. After detailed structural and spectral characterizations， it is found that a crystalline matrix is grown around the CDs by the phthalic acid precursor when the CDs is formed， and the dispersion effect of the matrix on the CDs effectively blocked the aggregation of the CDs， thus preventing the occurrence of fluorescence quenching of the CDs. Furthermore， the change of crystalline matrix structure in G-CDs leads to the increase of pyridine nitrogenous groups at the interface between core and matrix in the CDs， resulting in a change of fluorescent color of the CDs with different crystalline structures. The resultant crystalline CDs are also used to fabricate white-light emitting diode devices （WLED） in view of its excellent luminescence performance， which achieves a warm-white light with the correlated color temperature （CCT） of 4 061 K， color rendering index （CRI） of 88.4 at the chromaticity coordinates of （0.37， 0.36） using B-CDs combined with the commercial phosphors and another warm-white light with the CCT of 4 478 K， CRI of 85 at the chromaticity coordinates of （0.36， 0.34） using G-CDs combined with the commercial phosphors. The excellent photometric parameters give these fluorescent nanomaterials potential application value in optoelectronic field.
Abstract：The effect of pump focusing characteristic on output laser characteristics of passively Q-switched solid-state（PQS） laser is studied. Using a 10 W laser diode（LD） and a coupling focusing lens with focal length of 4 mm， without changing the cavity structure and the distance between LD and resonator（15 mm）， five coupling focusing lens positions were selected to research the effect of pump focusing characteristic on output laser characteristics， especially on the stability of the output pulse. When the distance between LD and the coupling focusing lens is 7.50 mm， at a continuous-wave pump power of 3.550 W， a passively Q-switched laser with higher repetition rate（160 kHz）， higher average output power（360 mW）， higher single-pulse energy（2.250 μJ） and lower time jitter（120 ns） was obtained. The experimental results indicate that the match degree between pump focusing spot and fundamental mode spot is good when the distance between LD and the coupling focusing lens is 7.50 mm. The theoretical calculation results indicate that the ratio of the fundamental mode spot size to the focusing spot size is 0.854 when the distance between LD and the coupling focusing lens is 7.50 mm. The ratio can be used as a reference for the research of high repetition-frequency PQS laser.
Keywords：LD-pumped;passively Q-switched;coupling focusing lens position
Abstract：The lateral lasing of vertical external cavity surface emitting laser（VECSEL） is the key to restrict its high performance. We designed a gain chip structure with a large mismatch（30 nm） between the quantum well gain peak and the surface cavity mode at room temperature， and confirmed that this structure can effectively suppress the lateral lasing enhancement of VECSEL when the pump power increases. When the substrate temperature of the gain chip is 20 ℃， the longitudinal lasing wavelength of VECSEL is 980 nm and the lateral lasing wavelength is 950 nm. As the pump power increases gradually， the lateral lasing intensity decreases rapidly with the emergence of longitudinal lasing. This is because the stimulated radiation level of the quantum well matches the longitudinal lasing laser mode when the laser is longitudinal lasing. The longitudinal lasing laser mode can obtain higher mode gain and have an advantage in the competition with the lateral mode. When the substrate temperature is controlled at 0 ℃ and 10 ℃， the mismatch between the quantum well intrinsic gain peak and the surface cavity mode increases. At this time， VECSEL still shows a stable lateral lasing suppression effect.
Abstract：AlGaN-based deep ultraviolet（DUV） light-emitting diodes（LEDs） are deemed as the alternative of traditional mercury lamp used for sterilization， water purification， phototherapy， polymer curing， sensing， and non-line-of-sight communication， which own broad application prospects in biological， environmental， industrial， medical， and military fields. To improve the low external quantum efficiency of DUV LEDs， this work proposes a DUV LED scheme with ultra-thin vertical structure. Based on the sapphire-silicon wafer bonding and physical thinning processes， high-quality DUV LED epitaxial layers are transferred from sapphire substrate to high thermal conductivity silicon substrate. Subsequently the fabrication of DUV LED is successfully realized using the ultra-thin epitaxial layers. The light-emitting surface of the device can be roughened at the nanometer level without special chemical treatment after the thinning process. The combination of rough surface and ultra-thin epitaxial layers have serious detuned micro-cavity effect， which helps to destroy the high-order waveguide mode， thereby increasing the light extraction efficiency. The measured thickness of the epitaxial layers after transfer is about 710 nm. The peak wavelength of the fabricated DUV LED electroluminescent spectrum is about 271 nm. The vertical DUV LED fabrication scheme provides a feasible path for realizing a high-efficiency DUV light source.
Keywords：DUV LED;epilayer transfer;wafer bonding;thinning process
Abstract：Metal-halide perovskite light-emitting diodes have become a research hotspot in recent years， for they have the advantages of tunable emission color， high color purity and excellent spectral stability. Solution processed polycrystalline thin film perovskite light-emitting diodes have simple and low-cost preparation process， but it is easy to form defects in the crystallization process， which will affect the performance of the device. In this work， low-cost glucose is used as passivation agent to prepare polycrystalline thin film perovskite light-emitting diodes. The addition of glucose can effectively inhibit the trap-assisted nonradiative recombination loss in the devices. When the glucose concentration was 0.2 mol·L-1， the maximum brightness of the device reached 11 840 cd·m-2， the maximum current efficiency was 7.89 cd·A-1. Our devices have excellent spectral stability， color purity and repeatability. This work provides a simple and effective method for the passivation of defects in polycrystalline thin film perovskite light-emitting diodes.
Abstract：SnOx deposited by atomic layer deposition exhibits uniform and dense nature， which is commonly used to improve the stability of inverted planar perovskite solar cells. Meanwhile， the characteristics of SnOx films have an essential impact on power conversion efficiency（PCE） of devices. In this paper， the characteristics of atomic-layer-deposited SnOx are adjusted by the oxygen sources（H2O， O3）， including energy level and conductivity， so as to achieve the improvement of PCE of devices. The results show that the SnOx film with O3 as a single oxygen source has good energy level alignment. SnOx， which only has water as an oxygen source （denoted H2O-SnOx）， performs higher electrical conductivity. While， taking advantage of mentioned sources， the SnOx （denoted as MIX-SnOx） not only obtains good energy level alignment， but also excellent conductivity， which effectively improves the PCE of the devices， reaching 20.9%. Moreover， thanks to the denseness of SnOx film， it can largely prevent the ingress of moisture into devices， and also inhibit the decomposition of perovskite， dramatically enhancing the stability of perovskite solar cells， which can retain 86% of initial PCE after aging at 85 ℃ （nitrogen atmosphere） for more than 646 h.
Keywords：perovskite solar cells;atomic layer deposition;oxygen resources adjustment;SnOx
Abstract：Image quality has always been a hot topic in LED display field， one of momentous contributing factors is white balance parameter， which directly determines the luminance and chroma fidelity. Generally， white balance is adjusted by fixed ratio of luminance of the primaries. Furthermore， balance ratio is relatively stable. But for each primary of the LED， changes in environmental factors will cause changes in the primary parameters. As a result， the white balance of the display panel drifts， which seriously affects the image display quality. Based on the theory of chromaticity and characteristics of LED， this paper builds a gamut model of a specific LED display to discuss the effect of each primary on white balance parameters in different temperature environments only when the brightness changes. The variation of white balance parameters and hue distortion under temperature fluctuation are mainly quantitative analyzed. In that， this paper provides a valuable theoretical basis for the revision of the high-definition LED display control system， which helps to enhance the qualities of high-end LED display products.
Abstract：The biomedical application of aggregation-induced emission（AIE） nanoprobes that emit fluorescence in the second near-infrared（NIR-Ⅱ） optical window is an emerging research area. In comparison with traditional fluorescent materials， NIR-Ⅱ AIE nanoprobes have been established to show superiority in deeper tissue penetration ability， minimized light damage， and good quantum yield in aggregated state. It has been proven that rational molecular engineering could realize the controllable regulation between the radiative and nonradiative dispersion of the excited state energy of the NIR-Ⅱ AIE chromophores. The unique propeller-like conformation of AIE luminogens determines its easily modulable attribute between radiative decay which can be used for fluorescence imaging（FLI） and nonradiative decay which can be harnessed to conduct photothermal imaging（PTI）/photoacoustic imaging（PAI）/photothermal therapy（PTT）/photodynamic therapy（PDT）. At present， AIE luminogens have developed into an alternative candidate to build integrated “one-for-all” theranostic platform. Herein， this review systematically summarizes the latest research advancements of NIR-Ⅱ AIE probes， on the aspects of molecular design and biomedical applications. Besides， the current challenges and future research directions of NIR-Ⅱ AIE nanoprobes are briefly discussed in the end.
Abstract：In this paper， a water-soluble Sm∶ZnO-NH2 QDs fluorescent probe with stable fluorescence performance was prepared by means of 3-aminopropyltriethoxysilane（APTEs） terminated zinc oxide quantum dots（ZnO QDs）. Materials were characterized by transmission electron microscopy（TEM）， X-ray diffraction（XRD）， X-ray photoelectron spectroscopy（XPS）， Fourier transform infrared spectrometer（FT-IR）， nanoparticles size and Zeta potentiometers（DLS）， steady transient fluorescence spectrometer（PL）， etc. The probe prepared under optimal conditions has good fluorescence performance in water， and its fluorescence intensity remains 92% after 10 d of storage at 4 ℃. Based on the probe fluorescence can be directly quenched by dopamine（DA）， a new method for fluorescence analysis for selective detection of DA content was established， and the probe showed a good linear relationship（y=0.46393x+0.008530， R2=0.996 3） and a detection limit of 1.08 ng/mL within a concentration of 50-1 600 ng/mL， which had good stability and reproducibility. It was successfully applied to the detection of human urine samples， and the recovery rate was 98.18% to 107.84%.