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- light-emitting diode
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- Technical University of Gabrovo
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Piezo-phototronic effect on optoelectronic nanodevices
摘要： Optoelectronic nanoscale devices have wide applications in chemical, biological, and medical technologies. Improving the performance efficiency of these devices remains a challenge. Performance is mainly dictated by the structure and characteristics of the semiconductor materials. Once a nanodevice is fabricated, its efficiency is determined. The key to improving efficiency is to control the interfaces in the device. In this article, we describe how the piezo-phototronic effect can be effectively utilized to modulate the band at the interface of a metal/semiconductor contact or a p–n junction to enhance the external efficiency of many optoelectronic nanoscale devices such as photodetectors, solar cells, and light-emitting diodes (LEDs). The piezo-phototronic effect can be highly effective at enhancing the efficiency of energy conversion in today’s green and renewable energy technology without using the sophisticated nanofabrication procedures that have high cost and complexity.
关键词： photodetectors,light-emitting diodes,optoelectronic nanodevices,solar cells,piezo-phototronic effect
更新于2025-09-04 15:30:14
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Influence of Light Emitting Diode on Bone Marrow and Healing of Dermatome Wounds
摘要： The irradiation of large surfaces or whole body with light emitting diode LED λ-470 nm and λ-940 nm (LED shower) causes structural changes in bone marrow and stimulates healing of experimental dermatome wounds. The increase of migration of the bone marrow cells in derma and epithelial layers of skin indicates that LED-shower intensifies intercellular interactions and cells migration between tissues.
关键词： Bone marrow,Dermatome wounds,Light emitting diode irradiation,Morphology
更新于2025-09-04 15:30:14
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Light Emitting Diodes Based on Inorganic Composite Halide Perovskites
摘要： CsPbBr3 is a promising type of light-emitting halide perovskite with inorganic composition and desirable thermal stability. The luminescence efficiency of pristine CsPbBr3 thin films, however, appears to be limited. In this work, light emitting diodes based on CsPbBr3|Cs4PbBr6 composites are demonstrated. Both quantum efficiency and emission brightness are improved significantly compared with similar devices constructed using pure CsPbBr3. The high brightness can be attributed to the enhanced radiative recombination from CsPbBr3 crystallites confined in the Cs4PbBr6 host matrix. The unfavorable charge transport property of Cs4PbBr6 can be circumvented by optimizing the ratio between the host and the guest components and the total thickness of the composite thin films. The inorganic composition of the emitting layer also leads to improved device stability under the condition of continuous operation.
关键词： stability,conductivity,composite perovskite,light emitting diode,Cs4PbBr6
更新于2025-09-04 15:30:14
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[IEEE 2018 1st International Cognitive Cities Conference (IC3) - Okinawa, Japan (2018.8.7-2018.8.9)] 2018 1st International Cognitive Cities Conference (IC3) - A Novel Image Analysis of Light Emitting Diode Array Biostimulation Applied on Microcirculation
摘要： A novel development platform of the specific microcirculation analysis was proposed in this study. This study was to observe the effect of the blood microcirculation with LED stimulation. The experiment involved the light emitting diode array (LEDA), the designed control board and the image processing algorithm on the platform. LEDA (six LEDs, wavelength 660 nm, operating frequency 8 - 15 Hz) was used to stimulate the palm of the subject, and then, the microcirculation images were analyzed by the image processing algorithm. The blood velocity on the ring finger was increased after LEDA stimulation, and it was approximately 1.7 times compared with and without the light stimulation. Thus, LEDA stimulation on the palm enhanced the microcirculation. Also, a specific platform of LEDA system with microcirculation measurement was developed in this study.
关键词： image processing algorithm,microcirculation,light emitting diode array
更新于2025-09-04 15:30:14
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Design and energy transfer mechanism for single-phased Gd2MgTiO6: Bi3+, Eu3+ tunable white light-emitting phosphors
摘要： In recent years, numerous efforts have been made to develop single-phased white light-emitting phosphors for the near-UV region to solve problems of color reabsorption and ratio regulation between different phosphors. In this work, we have designed Bi3+- and Eu3+-codoped single-phased Gd2MgTiO6 phosphors to achieve tunable white light emission based on multi-luminescence center energy transfer. The structural analysis showed that all the samples were crystallized as a monoclinic double perovskite with the P21/n symmetry space group (No. 14), with HRTEM images showing clear lattice fringes between the lattice planes. The single Bi3+-doped Gd2MgTiO6 sample exhibits two obvious emission peaks at 417 and 508 nm, which correspond to a characteristic 3P1 → 1S0 transition for the Bi3+ ions under near-UV excitation due to two types of Bi3+ emission centers, with their relative emission intensity depending closely on the value of the excitation wavelength. In this case, a suitable choice of excitation wavelength can achieve tunable emission for Gd2MgTiO6: Bi3+ between blue and green. Eu3+ is codoped into Gd2MgTiO6 as a red emission component and shows sharp emission lines that correspond to the characteristic 5D0 → 7FJ (J = 1, 2, 3, and 4) transitions of Eu3+ ions. Energy transfer in Gd2MgTiO6: Bi3+, Eu3+ has been confirmed by the electric dipole–dipole (d–d) interaction from Bi3+ to Eu3+. Our experiments show that it is straightforward to create tunable white light emission by adjusting the excitation scheme and Eu3+ concentration. Moreover, a schematic for the energy transfer mechanism and simplified spectral levels based on Bi3+ and Eu3+ ions has also been established.
关键词： Eu3+,Bi3+,Gd2MgTiO6,white light-emitting phosphors,energy transfer,tunable emission,near-UV
更新于2025-09-04 15:30:14
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Synthesis, Photophysical, Electrochemical and Thermal Study of Biphenyl Luminophors: Green Light Emitting Materials
摘要： Novel luminophors of anthracene (AN) and tetracene (TN) doped biphenyl were prepared using Conventional Solid State reaction technique. Fluorescence spectroscopy, XRD, SEM, TGA-DSC and Cyclic Voltammetry techniques have been employed for photophysical, electrochemical and thermal study. The X-ray diffraction study revealed the formation of homogeneous biphenyl solid solutions with the added guests AN and TN. Fluorescent biphenyl absorbing short wave UV radiation and emitting at long wave UV radiation has been used as a solid matrix. From the fluorescence spectra it is seen that the added guests shifts the UV fluorescence of biphenyl emitting in green region of visible spectrum at 532 nm. SEM images of the prepared luminophors showed the crystallites of average size 140 nm which makes them suitable candidates for their use in Optoelectronic devices. HOMO and LUMO energy levels of the synthesized luminophors from electrochemical data observed in 5.50–5.64 eV and 3.09–3.13 eV with band gap 2.37–2.55 eV, respectively. TGA-DSC study revealed the thermal stability of prepared luminophors.
关键词： Green light emitting novel luminophors,EET process,Optoelectronic devices
更新于2025-09-04 15:30:14
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Charge transport layers manage mobility and Carrier density balance in light-emitting layers influencing the operational stability of organic light emitting diodes
摘要： Organic light emitting diodes (OLEDs) consist of several organic layers, including the charge injection layer, charge transport layer, and light emitting layer (EML). Of these layers, the charge transport layer is crucial for ensuring device longevity, but its overall effects on charge transport and corresponding device stability are poorly understood. Herein we report the factors influencing differences in lifetime between two OLEDs with different hole transporting layers (HTLs). Comprehensive electrical analysis of the materials and the devices reveals that the mobility, accumulation, trapping, and the transport path of holes in the EML are totally changed by the HTLs. The charge transport layers affect mobility and carrier density balance in the EML through the modification of the charge transport path and the energetic barrier. This results in a reduction of overbalanced polaron density, which is critical for bond dissociation in excitonic interactions. Consequently, device lifetime is increased sevenfold through modification of the HTL structure without any alteration of the EML. These results imply that the analysis of polaronic transport through impedance spectroscopy is a crucial step in determining the requisite electrical properties for charge transport layers, with a view to maximizing the operational stability of OLEDs.
关键词： charge transport,Organic light-emitting diodes,device stability,impedance spectroscopy
更新于2025-09-04 15:30:14
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Experimental Evidence for “Hot Exciton” Thermally Activated Delayed Fluorescence Emitters
摘要： Contradiction between no effective photophysical experiments and high device results causes the “hot exciton” thermally activated delayed fluorescence (TADF) mechanism to be still a controversial question. Here, the steady and transient photophysical characterization combined with theoretical calculation based on 4,7-bis(9,9-dimethyl-9H-fluoren-2-yl)-5,6-difluorobenzo[c][1,2,5]thiadiazole (2F-BTH-DMF), 4,7-bis(9,9-dimethyl-9H-fluoren-2-yl)benzo[c][1,2,5]thiadiazole (BTH-DMF), and 5,6-bis(9,9-dimethyl-9H-fluoren-2-yl)benzo[c][1,2,5] thiadiazole (o-BTH-DMF) demonstrate that all the emitters exhibit TADF via reverse intersystem crossing (RISC) from “hot exciton” triplet excited state. The fast RISC process “hot exciton” mechanism affords a very short delayed lifetime (1 μs). Organic light-emitting diodes (OLEDs) based on these emitters exhibit high exciton utilization over 25% and the best device shows a maximum current efficiency of 31.02 cd A?1, maximum power efficiency of 27.85 lm W?1, and external quantum efficiency of 9.13%, which are the highest performances for reported OLEDs with “hot exciton” mechanism. The experimental evidence for fast RISC process via “hot exciton” triplet state and short delayed lifetime highlights the TADF emitters with “hot exciton” mechanism for high-performance OLEDs with very low efficiency roll-off.
关键词： hot excitons,reverse intersystem crossing,thermally activated delayed fluorescence,organic light-emitting devices
更新于2025-09-04 15:30:14
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Highly Efficient Fluorescent Organic Light-Emitting Devices Using a Luminescent Radical as the Sensitizer
摘要： In traditional fluorescent organic light-emitting diodes (OLEDs), the upper limit of internal quantum efficiency (IQE) is only 25% because 75 % triplet excitons created on the fluorescent dyes are non-luminous. Here, luminescent radicals are proposed as the sensitizer. Under ideal conditions, electrons and holes firstly recombine on the sensitizer molecule to create doublet excitons, then through energy transfer to generate singlet excitons on the fluorescent dye, finally via radiative decay to emit light. The upper limit of IQE can theoretically reach 100%. As an example, the maximum external quantum efficiency (EQE) of a fluorescent OLED sensitized by a luminescent radical, TTM-1Cz, has reached 8.1%, which is much higher than the upper limit of EQE of traditional fluorensenct OLEDs. Our results suggest a new route to realize highly efficient fluorescent OLEDs.
关键词： organic light-emitting device,doublet,luminescent radical,sensitize,deep-red
更新于2025-09-04 15:30:14