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Issue 1 ， 2022
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Effect of Barrier Height on Modulation Characteristics of AlGaN-based Deep Ultraviolet Light-emitting Diodes Enhanced Publication
Abstract：AlGaN-based deep ultraviolet LED has attracted more and more attention in ultraviolet communication due to its high modulation bandwidth and small chip size. In this study,AlGaN-based deep ultraviolet LEDs with varied Al composition of 50%, 55%, 60% in quantum barriers are fabricated. The effect of barrier height on the photoelectric and modulation characteristics of deep ultraviolet LEDs is studied. It is found that the optical power and external quantum efficiency (EQE) of the deep ultraviolet LED increase first and then decreased, and carrier lifetime decreases first and then increases as the quantum barrier height increases. The peak wavelength of the spectra shows a blue-shift. APSYS simulation revealed that the spacial overlap between the wave function of electron and hole is enhanced as Al composition increases. But further increase on barrier height will lead to current leakage which reduces the radiation recombination rate and carrier density in multi-quantum well layer. The -3 dB bandwidth of deep ultraviolet LED with 55% Al composition in quantum barrier is measured to be 94.4 MHz, higher than those with 50% and 60% Al composition in quantum barrier.Keywords：ultraviolet communication;deep ultraviolet light-emitting diodes;multiple-quantum-well layer;modulation bandwidth;optical power- 528
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Published：2022-01-14
Cover Story
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Rare Earth Ion Doped Perovskite Nanocrystals Enhanced Publication
Abstract：In recent years, due to their excellent photoelectric properties, perovskite nanocrystals have been extensively studied in the fields of luminescence and photoelectric conversion, and they have become "star materials" in scientific research circles. However, perovskite nanocrystals have some shortcomings(such as poor stability, the spectrum is limited to the visible light region, etc.), which limit their application. Rare earth ions have abundant 4f energy levels and special electronic configurations. Therefore, doping rare earth ions into perovskite nanocrystals can significantly improve the photoelectric properties of the material, improve the stability, and solve the key problem of the perovskite nanocrystals for practical application requirements. We introduce the properties of rare earth-doped perovskite nanocrystals, and focus on the application of materials in light-emitting diodes, solar cells, and photodetectors, respectively.Keywords：perovskite;nanocrystals;rare earth;doping;luminescence- 1322
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Analysis of Site-occupation of Activator in Phosphors Enhanced Publication
Abstract：Besides the electron configuration of the activator, the luminescent properties of a phosphor are also influenced by the nephelauxetic effect and crystal field splitting effect that the activator experiences in a matrix. The degree of the nephelauxetic effect depends on the bonding features between the activator and the ligands(the ratio between the ionic bonding content and the covalent bonding content) as well as the polarizability of the anions, while the degree of the crystal field splitting effect depends on the coordination number, the average bond length, the distortion, and the point group symmetry of the coordination polyhedron composed by the nearest coordinating anions around the activator. Identification of the doping site, which helps analyze the coordination polyhedron, is of great significance in understanding the luminescence properties of the phosphor and developing new phosphors. This mini-review summarizes the eight methods used to identify the site-occupancy of an activator in a phosphor matrix, which can be classified into three categories, i.e., the spectroscopy methods, the structural analysis method, and the theoretical calculation method. Among them, the spectroscopy methods include five different measurements:(1)excitation wavelength dependent emission spectra and emission wavelength dependent excitation spectra, (2)emission wavelength dependent luminescence decay curves, (3)time-resolved emission spectra, (4)temperature-dependent emission spectra and/or luminescence decay curves, (5)activator-concentration-dependent emission spectra. For clarifying the features of the above methods, some related researches were introduced as examples, which refer to some Ce3+, Eu2+, or Mn4+ activated phosphors for application in white light emitting diodes. The pros and cons of each method were also analyzed.Keywords：luminescent materials;Activator;Site occupancy- 2053
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Published：2022-01-14
Invited Review
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Continuous-wave and Pulsed Laser Performance of Yb∶LuAG Single Crystal Fiber Enhanced Publication
Abstract：Single crystal fiber is a kind of functional crystal material with quasi-one-dimensional structure, combining the excellent physical and chemical properties of bulk crystal with the structural advantages of large specific surface area of traditional optical fiber materials, which makes it a potential laser gain medium. At present, the research on single crystal fiber laser mainly focuses on continuous-wave laser output, while the research on its pulsed laser performance is relatively few. With Yb∶LuAG single crystal fiber (SCF) prepared by micro-pull-down method(μ-PD) as the gain medium, a continuous-wave laser output of more than 4 W with a slope efficiency of 21.66% was obtained. The beam quality factor M2 is close to 1. On this basis, the linear optical properties of saturable absorber(SA) MoTe2 were tested, and the nonlinear saturable absorption characteristics at 532 nm and 1 064 nm were verified. Finally, a passive Q-switched Yb∶LuAG single crystal fiber pulsed laser output with the highest single pulse energy of 3.39 μJ was realized. This work provides a reference for the application of Yb∶LuAG SCF in all-solid-state high-power continuous-wave and pulsed lasers.Keywords：single crystal fiber;Yb∶LuAG;pulsed laser;MoTe2;passive Q-switched- 314
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Published：2022-01-14 -
Broadband Near-infrared Luminescence and Regulation Mechanism of Tellurium-doped Calcium-Aluminum-germanate Glass Enhanced Publication
Abstract：Tunable broadband near-infrared(NIR)-emitting materials play a crucial role as NIR light sources and tunable fiber lasers in modern technologies such as high-capacity telecommunication, imaging, and remote sensing. In this work, we report the control scheme and mechanism of the broadband near-infrared luminescence properties in the tellurium-doped calcium-aluminum-germanate glass. By introducing carbon to construct a reducing atmosphere, the raw material TeO2 is reduced to tellurium element. Through optimizing CaO and Al2O3 content, the configurations and size of topological cages in tellurium doped calcium-aluminum-germanate glass were adjusted to stabilize and tailor tellurium clusters, enabling tunable NIR emission. Furthermore, adjusting the content of TeO2 provides optimal tellurium source to form clusters, and thus enhancing tellurium NIR luminescence. The regulation mechanism of tellurium NIR luminescence performance in the calcium-aluminum-germanate glass is clarified. This work provides important guidance for the design of broadband, efficient and tunable NIR luminescent materials, promoting their practical application in broadband optical amplifiers and tunable lasers.Keywords：tellurium clusters;near-infrared luminescence;tunable broadband;regulation mechanism- 224
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Novel Far-red Phosphors (La,Gd,Y)2MgTiO6∶Cr3+ with Tunable Luminescence Spectra for Grow Light Enhanced Publication
Abstract：Cr3+-activated double perovskite structure phosphor has drawn wide attention due to its far-red and near-infrared emission. In this work, we synthesized a series of (La,Gd,Y)2MgTiO6∶Cr3+ phosphors which can be excited by ultraviolet light of about 345 nm, and the emission bands are in the range of 700-900 nm. The spectra were tuned by ions substitution strategy. The main emission peaks were blue shifted from 766 nm to 737 nm and 757 nm by substituting the La site with Gd and Y, respectively. Meanwhile, the thermal stability at 150 ℃ increased from 41.7% to 69.1% and 67%, respectively. The crystal structure, microstructure, decay time, thermal stability and band gap were investigated systematically. The substitution of Gd/Y ions causes the lattice contraction, which results in the change of the nephelauxetic effect, and eventually leads to the blue shift of the spectra. The emission spectra of these phosphors have good matching with the 730 nm absorption peak of phytochrome FR(PFR), indicating their application prospect in plant growth lighting. Cationic substitution strategy can regulate the luminescence properties of Cr3+, which provides ideas for the development of phosphors for plant growth lamps in the future.Keywords：phosphor;double perovskite structure;luminescence tuning performance;far-red light;Cr3+- 355
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Synthesis and Optical Properties of Barium Doped CsPbBr3 Blue Luminescence Quantum Dots Enhanced Publication
Abstract：In recent years, all-inorganic halide perovskite CsPbX3(X=Cl, Br, I) has attracted tremendous attention owning to its narrow emission full width at half maximum, tunable bandgap, low production cost, and high photoluminescence quantum yield (PLQY). However, the blue luminescence perovskite quantum dots(QDs) is still lag behind their red and green luminescence counterparts. Herein, the Ba2+ ion doped CsPbBr3 QDs was obtained by adjusting the molar ratio of BaBr2 and PbBr2 in precursor solution. The crystal structure, morphology, and optical property of as-prepared QDs were studied. The results exhibited that the decrease of particle size and blue shift in absorption and photoluminescence spectra as the increase of the Ba/Pb molar ratio. It is mainly contributed that the ionic radius of Ba2+ is smaller than Pb2+ ion, and the bandgap of as-prepared quantum dots is enlarged by partially replacement Pb2+ ion with Ba2+ ion. The particle size is decreases from 11.37 nm(undoped) to 10.36 nm(Ba/Pb molar ratio of 1.0). The photoluminescence is blue shift from 510 nm(undoped) to 461 nm(Ba2+ ion doped). Most interesting, the Ba2+ doped CsPbBr3 quantum dot with the Ba/Pb molar ratio of 0.5 demonstrated the super blue luminescence at 461 nm with PLQY of 39%. It is certified that the optical property could be effectively improved by introducing appropriate amount Ba2+ ion to partially replacement of Pb2+ ion.Keywords：Ba2+ ion doped CsPbBr3;blue luminescence quantum dots;synthesis;optical property- 251
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Published：2022-01-14
Synthesis and Properties of Materials
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Ultra-low Efficiency Roll-off Top-emitting White Organic Light-emitting Diodes Enhanced Publication
Abstract：White top-emitting organic light-emitting devices(TEOLEDs) with very low efficiency roll-off are obtained by utilizing Ag/Alq3/Ag/Alq3/Ag as an anode. A neat bipolar transport 4, 4'-bis(9-carbazolyl)-2, 2'-biphenyl(CBP) layer is introduced between the blue fluorescent and the orange phosphorescent emission layers in order to reduce the Dexter energy transfer between the two emissive units, which can improve the emission spectrum and device efficiency. The yellow emission from bis(2-(2-fluorphenyl)-1, 3-benzothiozolato-N, C2') iridium(acetylacetonate) is manipulated by optimizing the microcavity effect of the TEOLED. As a result, we demonstrate that a very low roll-off of 17% for the current efficiency can be obtained at a super high luminance of 60 000 cd/m2. The efficiencies of the white TEOLEDs are comparable to those of the corresponding conventional bottom-emitting OLED. In comparison, the efficiency roll-off of the TEOLEDs is much lower than that of the corresponding conventional bottom-emitting device due to the microcavity effects.Keywords：organic light-emitting devices;top-emitting;microcavity effect;efficiency roll-off- 206
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Published：2022-01-14 -
High Efficiency Doping-free White Organic Light Emitting Diodes by Combining Exciplex and Phosphorescent Ultrathin Layer Enhanced Publication
Abstract：In this work, we prepared doping-free white organic light emitting diodes(WOLED) by combining exciplex and phosphorescent ultrathin layer. As results, high efficiency WOLED based two complementary color structure of Ir(pq)2acac(~0.5 nm)/mCP∶PO-T2T/Ir(pq)2acac(~0.5 nm) and red-green-blue(RGB) color structure of Ir(ppy)3(~0.5 nm)/mCP∶PO-T2T/Ir(pq)2acac(~0.5 nm) are achieved by setting different colors phosphorescent ultrathin layer on the two sides of blue exciplex emitting layer of mCP∶PO-T2T, respectively. The maximum current efficiency, power efficiency and external quantum efficiency of two complementary color WOLED are 46.1 cd/A, 43.9 lm/W and 22.2%, respectively; and the RGB WOLED are 66.8 cd/A, 63.5 lm/W and 24.2%, respectively. The discussions demonstrated the efficient energy transfer from high energy blue exciplex to low energy red and green phosphorescent ultrathin layer is responsible for the high efficiency of doping-free WOLED.Keywords：white organic light emitting diodes;exciplex;ultrathin layer;doping-free- 174
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Self-trapped Exciton Luminescence and Light-emitting-diodes Based on Zero-dimensional Organic-inorganic Hybrid Antimony Chloride Enhanced Publication
Abstract：The emerging of the zero-dimensional metal halide materials has attracted great attention of researchers due to their excellent photoelectric properties. Herein, the luminescent material and device based on zero-dimensional metal halide tetraphenylphosphonium antimony chloride [(C6H5)4P] 2SbCl5 were prepared by anti-solvent method and spin-coating method, respectively. The optoelectronic properties of [(C6H5)4P] 2SbCl5 were investigated by excitation spectra, emission spectra, and time-resolved spectra. The results show that [(C6H5)4P] 2SbCl5 can emit bright orange-red emission under the ultraviolet excitation. This orange-red emission originates from the triplet self-trapped exciton induced by the zero-dimensional spatial confinement. Temperature dependent PL and decay lifetime studies reveal that the material has a thermal activation energy with the value of ~600 meV, thus it has favorable anti-thermal quenching effect. By optimizing the device structure and introducing poly [bis(4-phenyl)(4-butylphenyl)amine] (Poly-TPD) as a hole transport layer, the warm white emission by mixing the fluorescence emission of Poly-TPD and the self-trapped exciton emission of [(C6H5)4P] 2SbCl5 was obtained with a brightness of 126 cd/m2 under a bias of 6 V. This work provides an alternative approach for the development of the manufacture of lead-free metal halide electroluminescent devices by solution method.Keywords：zero-dimensional luminescent material;self-trapped exciton;electroluminescence- 652
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Published：2022-01-14 -
High-performance Ultraviolet Inorganic-organic Composite Structure Photodetectors Based on Electric Field Control Enhanced Publication
Abstract：The ultraviolet inorganic-organic composite structure photodetectors with an architecture of ITO/ZnO/P3HT∶ITIC/Ag were fabricated by a solution spin-coating method. In the blended film, the weight ratio of polymer donor(P3HT) to non-fullerene small molecule acceptor(ITIC) is 100∶1. Due to the discontinuity of carrier transport-channel, the dark current density of devices under zero bias voltage is very small(5.8×10-10 A·cm-2), which provides the condition for devices to realize the external electric-field adjustable and photocurrent multiplied. Under forward bias voltages, the free electrons and holes generated by the zinc oxide(ZnO) interfacial layer through absorbing ultraviolet light can participate in carrier transport(reducing the probability of carrier recombination), thereby improving the external quantum efficiency(EQE) of devices. With the increase of forward bias voltages, ZnO interfacial layer can work together with active layer(P3HT∶ITIC) to multiply the photocurrent of devices. Under 45 V bias, the EQE spectral response-peak with a minimum half height width of about 49 nm can be obtained by devices at 350 nm, with the highest EQE, responsivity and detectivity of 420000%, 1 185 A·W-1 and 1.8×1013 Jones, respectively. The above content provides an effective strategy to fabricate high-performance ultraviolet narrowband inorganic-organic composite structure photodetectors based on electric-field adjustment.Keywords：solution spin-coating;ultraviolet;inorganic-organic composite;photodetector;zinc oxide- 160
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Published：2022-01-14 -
High Performance InGaAs/AlGaAs Quantum Well Semiconductor Laser Diode with Non-absorption Window Enhanced Publication
Abstract：In order to solve catastrophic optical mirror damage(COMD), the problem of limiting the output power of near-infrared single-emitting InGaAs/AlGaAs quantum well semiconductor laser diodes(LD), a new-typed LD with a non-absorption window(NAW) based on Si impurity induced quantum well intermixing(QWI) technology was designed and fabricated, and its performance is tested and analyzed. Firstly, for the diode with NAW, a 50 nm Si/100 nm SiO2 composite dielectric layer is covered in the window region near the front and rear cavity surfaces above the cavity, and a 50 nm Si/100 nm TiO2 composite dielectric layer is covered in the gain region far away from the cavity surface. A rapid thermal annealing(RTA) process of 875 ℃/90 s is used to promote Si impurity diffusion induces QWI and remove non-radiation recombination centers. Then, based on the same epitaxial structure and preparation process, the traditional LD without NAW is prepared as the control group. Finally, the test results show that the catastrophic failure threshold power and the catastrophic failure threshold current of the new LD with NAW increase about 33.6% and 50.4%, respectively, and the occurrence probability and damage degree of COMD of the new LD are significantly reduced. Moreover, there is no degradation of the characteristics of threshold current, slope efficiency and full width half maximum of the new LD. This study proves that the NAW prepared by Si impurity induced QWI technology has a significant suppression effect on the COMD of near-infrared single-emitting InGaAs/AlGaAs quantum well semiconductor LD.Keywords：semiconductor lasers;catastrophic optical mirror damage;quantum well intermixing;non-absorption window- 186
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Published：2022-01-14 -
Light Enhanced Absorption of Graphene Based on Parity-time Symmetry Structure Enhanced Publication
Abstract：To enhance the absorption of graphene for optical waves in near-infrared communication wavelengths, a graphene-based absorber based on a periodic parity-time(PT) symmetry structure was proposed, which consists of the top graphene layer and the underlying periodic PT-symmetry unit. The absorption properties of graphene in the wavelength range of 1 450-1 650 nm are systematically studied by the transfer matrix method(TMM). The results show that by optimizing the graphene composite PT-symmetry micronano structure parameters, a 35-fold absorptance enhancement was achieved for the normal incidence near-infrared light in the studied wavelength range as compared to the free-standing graphene absorption. Meanwhile, for the oblique incidence near-infrared light with angle ranging from 0° to 30°, the average absorptance of the TE and TM polarization light is also enhanced by 19.7 and 54 folds, respectively. The structure has high-intensity absorption characteristics for the near-infrared light, which can be widely used in the design of devices such as absorbers, photodetectors and infrared optical sensors.Keywords：parity-time symmetry;graphene;near-infrared;transfer matrix method- 259
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Published：2022-01-14 -
Bias Stress Stability of Electric-double-layer ZnO Thin-film Transistor Enhanced Publication
Abstract：The use of environmentally friendly and degradable natural biomaterials to make functional devices has attracted more and more attention. Low-operating-voltage electric-double-layer(EDL) ZnO thin-film transistor(ZnO-TFT) was prepared by radio frequency magnetron sputtering by using natural albumen as a gate dielectric layer and ZnO as an active layer. The electrical characteristics of EDL ZnO-TFT was characterized, and the stability and its physical mechanism of the device under gate-bias and drain-bias stresses were investigated. The ZnO-TFT shows good electrical properties with a saturation mobility of 5.99 cm2/(V·s), a threshold voltage of 2.18 V, a subthreshold swing of 0.57 V/dec, an on/off current ratio of 1.2×105, and an operating voltage of less than 3 V. Bias-stress stability analysis indicated that the electrical properties of the ZnO-TFT have obvious instability under the gate and drain bias stresses. We believe that the change of electrical properties caused by gate bias stress may come from the positive charge accumulation near the gate dielectric and the interface, the charge discharge effect and the composite effect of new trap states; the change of electrical properties caused by drain bias stress may come from the oxygen vacancy caused by Joule heat and the electron trap in the channel.Keywords：thin-film transistor;zinc oxide;electric double layer;bias stress;stability- 133
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Published：2022-01-14
Device Fabrication and Physics
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Fluorescence Mechanism and Biomedical Applications of pH-responsive Carbon Dots Enhanced Publication
Abstract：As a new type of zero-dimensional carbon-based nanomaterials, carbon dots(CDs) have a great application potential in the fields of fluorescence sensing and biomedicine due to their excellent fluorescence properties, good biocompatibility, low cytotoxicity, and large surface functional groups. Especially given the weakly acidic microenvironment characteristics of tumors, it is crucial to design pH-responsive carbon dots to achieve specific treatment. This article has conducted a systematic investigation on the research work based on pH-responsive carbon dots in recent years and reviewed the fluorescence mechanism of pH-responsive carbon dots and their applications in biomedical fields such as pH sensing, bioimaging, and cancer treatment. Finally, the main challenges currently faced by pH-responsive carbon dots and the future development direction have been prospected.Keywords：pH-responsive carbon dots;Fluorescence mechanism;pH sensing;bioimaging;cancer treatment- 364
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Published：2022-01-14
Luminescence Applications and Interdisciplinary Fields
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