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- light-emitting diode
- light distribution
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- Technical University of Gabrovo
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Ultrathin, Core–Shell Structured SiO <sub/>2</sub> Coated Mn <sup>2+</sup> ‐Doped Perovskite Quantum Dots for Bright White Light‐Emitting Diodes
摘要： All-inorganic semiconductor perovskite quantum dots (QDs) with outstanding optoelectronic properties have already been extensively investigated and implemented in various applications. However, great challenges exist for the fabrication of nanodevices including toxicity, fast anion-exchange reactions, and unsatisfactory stability. Here, the ultrathin, core–shell structured SiO2 coated Mn2+ doped CsPbX3 (X = Br, Cl) QDs are prepared via one facile reverse microemulsion method at room temperature. By incorporation of a multibranched capping ligand of trioctylphosphine oxide, it is found that the breakage of the CsPbMnX3 core QDs contributed from the hydrolysis of silane could be effectively blocked. The thickness of silica shell can be well-controlled within 2 nm, which gives the CsPbMnX3@SiO2 QDs a high quantum yield of 50.5% and improves thermostability and water resistance. Moreover, the mixture of CsPbBr3 QDs with green emission and CsPbMnX3@SiO2 QDs with yellow emission presents no ion exchange effect and provides white light emission. As a result, a white light-emitting diode (LED) is successfully prepared by the combination of a blue on-chip LED device and the above perovskite mixture. The as-prepared white LED displays a high luminous efficiency of 68.4 lm W?1 and a high color-rendering index of Ra = 91, demonstrating their broad future applications in solid-state lighting fields.
关键词： quantum dots,white light-emitting diodes,core–shells,Mn2+-doping,SiO2-coating
更新于2025-11-14 15:32:45
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Optical Characterization of Doped Thermoplastic and Thermosetting Polymer-Optical-Fibers
摘要： The emission properties of a graded-index thermoplastic polymer optical fiber and a step-index thermosetting one, both doped with rhodamine 6G, have been studied. The work includes a detailed analysis of the amplified spontaneous emission together with a study of the optical gains and losses of the fibers. The photostability of the emission of both types of fibers has also been investigated. Comparisons between the results of both doped polymer optical fibers are presented and discussed.
关键词： polymer optical fibers,thermoplastic fibers,rhodamine 6G,light-emitting polymers,optical gain,amplified spontaneous emission,thermosetting fibers
更新于2025-11-14 15:30:11
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Tricolor- and White Light–Emitting Ce <sup>3+</sup> /Tb <sup>3+</sup> /Mn <sup>2+</sup> -Coactivated Li <sub/>2</sub> Ca <sub/>4</sub> Si <sub/>4</sub> O <sub/>13</sub> Phosphor via Energy Transfer
摘要： Single-component tunable Li2Ca4Si4O13:Ce3+,Tb3+,Mn2+ phosphors were successfully synthesized at 950 °C. Li2Ca4Si4O13:Ce3+,Tb3+ exhibits two luminescence peaking at 430 and 550 nm, which originated from the allowed 5d → 4f transition of the Ce3+ ion and the 5D4 → 7FJ (J = 6, 5, 4, 3) transition of the Tb3+ ion, respectively. Moreover, by codoping Ce3+ ions in the Li2Ca4Si4O13:Mn2+ system, yellow-red emission from the forbidden transition of Mn2+ could be enhanced. Under UV excitation, dual energy transfers (ETs), namely, Ce3+ → Mn2+ and Ce3+ → Tb3+, are present in the Li2Ca4Si4O13:Ce3+,Tb3+,Mn2+ system. The ET process was confirmed by the overlap of the excitation spectra, variations in the emission spectra, ET efficiency, and decay times of phosphors. In addition, quantum yields and CIE chromatic coordinates are presented. The emission color of these phosphors can be tuned precisely from blue to green via ET of Ce3+ → Tb3+ and from blue to yellow via ET of Ce3+ → Mn2+. White light can also be achieved upon excitation of UV light by properly tuning the relative composition of Tb3+/Mn2+. This result indicates that the developed phosphor may be regarded as a good tunable emitting phosphor for UV light-emitting diodes.
关键词： phosphor,energy transfer,Mn2+,Tb3+,Li2Ca4Si4O13,Ce3+,white light-emitting diodes
更新于2025-11-14 15:29:11
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Eu and Dy doped borophosphosilicate glass-ceramics for near ultraviolet based light-emitting diode applications
摘要： The Eu and Dy doped borophosphosilicate glass-ceramics prepared using melt quenching technique are investigated for light-emitting diode applications. The X-ray diffraction results show that the precipitation of AlPO4 crystals in glass matrix occurred during the melt quenching process, leading to the formation of glass-ceramics. The content of AlPO4 crystals depends on the B2O3/P2O5 relative content in glass matrix composition. The spontaneous conversion of Eu3+ to Eu2+ takes place in the as-obtained glass-ceramics without using reducing atmosphere during the preparation process. The conversion extent of Eu3+ to Eu2+, optical properties and structure of the as-obtained materials are related to the B2O3/P2O5 relative content. The Eu/Dy co-doped borophosphosilicate glass-ceramics display the emission bands in the blue, yellow, and red light regions and their combinations generate near white light-emission. In addition, the tunable light emission can be realized by changing the concentration of Eu and B2O3/P2O5 relative content. The as-developed Eu and Dy doped borophosphosilicate glass-ceramics show promising prospects in light-emitting diode applications.
关键词： Rare earth,Luminescence,Light-emitting diode,Borophosphosilicate glass-ceramics
更新于2025-11-14 15:23:50
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Full color carbon dots through surface engineering for constructing white light-emitting diodes
摘要： White light-emitting diodes (WLEDs) devices are replacing the filament lamp and they can provide a light close to the natural sunlight, which have thus drawn considerable attention in these recent years. It remains a scientific challenge to develop WLEDs using environmentally friendly, easy-to-process and cost-effective phosphors. Here we synthesized blue-, green- and red-carbon dots (denoted as B-, G- and R-CDs) by a facile solvothermal method with high dispersity both in aqueous and organic solvent. The quantum yield (QY) of the R-CDs achieved up to 24.7%. These CDs can be easily dissolved in polyvinylpyrrolidone (PVP) colloid, leading to the production of ultraviolet (UV)-excited LED devices to avoid the retinal damage caused by blue ray excitation. The fluorescence emission of the WLED has a wide band, covering the whole visible light region. Importantly, the influence of doping that gives rise to the change of emissive colors has been elucidated by X-ray photoelectron spectroscopy (XPS) combined with a computation method in order to provide a systematic controllable tuning on the functionalization of CDs. As such, WLEDs were demonstrated with color coordinates of (0.33, 0.33), a color temperature of 5612 K in the CIE chromaticity diagram with good anti-photobleaching and a color rendering index (CRI) of 89.
关键词： polyvinylpyrrolidone,White light-emitting diodes,solvothermal method,UV-excited LED devices,density functional theory,quantum yield,X-ray photoelectron spectroscopy,carbon dots
更新于2025-11-14 15:18:02
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Study of visible-light photocatalytic degradation of 2,4-dichlorophenoxy acetic acid in batch and circulated-mode photoreactors
摘要： Purpose The consumption of pesticides and chemical fertilizers is one of the major environmental and health problems. In this report, 2,4-dichlorophenoxyacetic acid (2,4-D) was chosen to evaluate the impact of photodegradation using LED (Light-emitting diode) (400 and 365 nm) sources in batch and programmable circulated-mode photoreactors respectively. Methods A β-cyclodextrin (β-CD) grafted titanium dioxide P25 (P25/β-CD) and complexation of 2,4-D and β-CD were synthesized via photoinduced and spray-drying methods, respectively. The structures were characterized. Moreover, we investigated the effects of the amount of catalyst, the β-CD amount on bed catalyst, irradiation time, kind of photoreactor on the photocatalytic degradation efficiency. Results Based on the results of experiments in batch reactor, the optimum amount of TiO2, β-CD grafted by catalyst were 1 and 0.1 g/L, respectively. In batch-mode the photodegradation efficiency of 2,4-D after 5 h with P25, P25/β-CD as a photocatalyst and 2,4-D/β-CD complex with P25 photocatalyst were approximately 81, 85 and 95% respectively. After 8 h of irradiation in circulated-mode reactor, degradation yields with P25, P25/β-CD and 2,4-D/β-CD complex along with P25 were 89, 91 and 96% respectively. On the other hand, the circulated-mode photoreactor with high efficiency was appropriate to degradation of the high concentration of 2,4-D solution (200 mg/L). After 5 successive cycles with 25 h of irradiation, P25 and P25/β-CD maintained as high 2,4-D removal efficiency as 82.6, 84% respectively, with excellent stability and reusability. Conclusion The photodegradation method can be used as an effective and environmental friendly process in the degradation of organic compound.
关键词： 2,4-D/β-CD complex,Batch-mode photoreactor,Light-emitting diode (LED),Circulated-mode photoreactor,2,4-Dichlorophenoxyacetic acid (2,4-D)
更新于2025-11-14 15:18:02
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A novel orange–red emitting phosphor Sr2LuTaO6:Sm3+ for WLEDs
摘要： A novel double perovskite tantalite orange–red light emitting Sr2LuTaO6:Sm3+ phosphor was synthesized by the solid state reaction. The phase, crystal structure, photoluminescence properties, thermal stability and decay curves were studied. The X-ray diffraction patterns indicated that the phosphor has a pure phase of cubic phase structure. Excited by near-ultraviolet light at 407 nm, the sample exhibited three sharp emission peaks at 564 nm, 600 nm, 645 nm corresponding to the 4G5/2 → 6HJ (J = 5/2, 7/2 and 9/2) transitions, respectively. The optimum doping concentration of Sm3+ ions was determined to be 5 mol% and the concentration quenching process comes from the energy transfer among nearest-neighbor ions. The as-prepared phosphors showed excellent thermal stability, the integral intensity at 423 K is about 91.10% of the initial intensity. The CIE chromaticity coordinates of Sr2LuTaO6:Sm3+ phosphors located in orange–red region. The results suggest that Sr2LuTaO6:Sm3+ phosphors have great potential application in white light-emitting diodes.
关键词： luminescence,thermal stability,white light-emitting diodes,Sr2LuTaO6:Sm3+,phosphor
更新于2025-11-14 15:13:28
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Microwave-assisted synthesis of FexZn1?xO nanoparticles for use in MEH-PPV nanocomposites and their application in polymer light-emitting diodes
摘要： A one-step microwave-assisted polyol method was used to fabricate FexZn1?xO (x = 0.01, 0.05, 0.10) nanoparticles. Zinc acetate dihydrate, iron (III) acetylacetonate, oleic acid and diethylene glycol were placed in a Teflon-lined reaction vessel. The reaction mixture was heated up to 250 °C for 15 min in a microwave reactor. The surface modification with oleic acid prevented agglomeration of the nanoparticles. The X-ray diffraction analysis revealed characteristics wurtzite hexagonal structure of ZnO and successful incorporation of the Fe dopant into the host crystal lattice. Doping of ZnO by Fe led to bandgap modification as estimated by Tauc plot. The as-prepared nanopowders were dispersed in toluene and mixed with a poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) polymer to make stable homogenous dispersions. Then, the FexZn1?xO/MEH-PPV nanocomposite thin films were prepared by spin coating and used as thin active layers in polymer light-emitting diodes. The thickness of deposited FexZn1?xO/MEH-PPV film was ca. 30 nm and that of reference neat MEH-PPV film was ca. 25 nm. The electroluminescent spectroscopy study showed that direct blending of MEH-PPV with Fe-doped ZnO nanoparticles is a simple and effective approach to significantly increase the luminance intensity of the diode in comparison to the diode fabricated by neat MEH-PPV.
关键词： Polymer light-emitting diodes,FexZn1?xO nanoparticles,Microwave-assisted synthesis,MEH-PPV nanocomposites
更新于2025-10-22 19:40:53
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Single crystal structure and electroluminescence efficiency of blue fluorescence OLED emitters using triple core chromophores
摘要： The relationship between the single crystal structure of materials and the EL performance of doped OLED devices was investigated. The 1,6-bis-(10-[1,1′;3′,1″]terphenyl-5′-yl-anthracen-9- yl)-pyrene (1,6 DAP-TP) has a dihedral angle (α) of 78.4 ° and a dihedral angle (β) of 81.2 °, a relatively more twisted single crystal structure compared to that of 6,12-bis-(10- [1,1′;3′,1″]terphenyl-5′-yl-anthracen-9-yl)-chrysene (DAC-TP). Such a highly twisted molecular structure can improve the electroluminescence (EL) efficiency of a material because it can inhibit rotational and vibrational motions. Also, since the doped state and single crystal structure imply, respectively, a diluted state and a molecular state, the EL efficiency of the doped OLED device is related to single crystal structure. In a 4% doped OLED device, 1,6 DAP-TP and DAC- TP showed CE of 2.10 cd A-1 and 0.93 cd A-1, respectively. With its relatively more twisted single crystal structure, 1,6 DAP-TP showed higher CE in a doped OLED device than DAC-TP. Both compounds had ultra-deep blue emission y values of 0.06 or less for the color coordinates, which satisfy high density television display requirements (y value less than 0.08).
关键词： Organic light-emitting diode,single crystal,fluorescence,dopant,blue
更新于2025-10-22 19:40:53
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Enhancing Reverse Intersystem Crossing via Secondary Acceptors: towards Sky-Blue Fluorescent Diodes with Tenfold-Improved Exter-nal Quantum Efficiency
摘要： How to simply but effectively facilitate reverse intersystem crossing (RISC) transition is always the key issue for developing high-performance thermally activated delayed fluorescence (TADF) dyes. In this work, as a proof of concept, a feasible strategy named 'acceptor enhancement' is demonstrated with a series of ternary blue emitters (xCzmPOnTPTZ) using diphenylphosphine oxide (PO) as secondary acceptors. Compared with its PO-free binary analogue, such simple introduction of PO groups in pCzPO2TPTZ dramatically enhances its RISC rate constant (kRISC) by 10 times to the level of ~105 s-1, accompanied by RISC efficiency (ηRISC) of 92%, which further improves the triplet-to-singlet upconversion for effective triplet harvesting in its devices. As the result, on the basis of a trilayer device structure, pCzPO2TPTZ realized a state-of-the-art external quantum efficiency (EQE) beyond 20% with tenfold improvement.
关键词： Organic Light-Emitting Diode,Thermally Activated Delayed Fluorescence,Excited State Transition,Blue Emission,Reverse Intersystem Crossing,Phosphine Oxide Acceptor
更新于2025-09-23 15:23:52