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Crystalline phase effect on the up-conversion processes and white emission of Yb3+/Er3+/Tm3+: Y2Si2O7 nanocrystals.
摘要： Yb3+, Er3+, Tm3+: Y2Si2O7 nano powders were fabricated by sol-gel method and then annealed at two different temperatures of 1050°C and 1480°C for 12 h to investigate the phase effect on the structural and optical properties. X-ray diffraction patterns (XRD) of all powders revealed that most of the peaks were in good harmony with the standard JCPDS cards of Y2Si2O7 (PDF#38-0223 and PDF#38-0440). SEM images of the powders were taken to examine the morphology and chemical analysis of the powders. Diffuse reflections spectra of Y2Si2O7 exhibited varying number of transitions depending on the dopant ion in all powders in the range of 400-1050 nm. Spectral properties of the powders were detailed to identify the possible up-conversion (UC) emission mechanism in the range between 400 - 900 nm under 975 nm excitation. The broadening white light emission was observed with increasing laser pumping power at room temperature as well. Spectral profiles of the transitions observed in both reflectance and up-conversion luminescence spectra were found to be crystalline phase depended.
关键词： Nanophosphors,Sol–gel process,Up-conversion,White emission
更新于2025-11-25 10:30:42
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Electronic structure and photoluminescence of Dy3+ single-doped and Dy3+/Tm3+ co-doped NaBi(WO4)2 phosphors
摘要： A single-phase white light emitting NaBi(WO4)2:Dy3+, Tm3+ phosphor has been successfully prepared by conventional high-temperature solid-state method. First-principles calculations were used to investigate the electronic structures of NaBi(WO4)2. The calculation results show that NaBi(WO4)2 has an indirect band gap with 3.02 eV. The crystal structure and PL properties of the obtained phosphor are characterized by SEM, powder X-ray and photoluminescence spectra, respectively. The results demonstrate that all as-prepared crystalline in a tetragonal crystal system with a space group of I4ˉ. PL results confirmed that the obtained phosphors can be efficiently excited by 365 nm and generated white light emission. Then the energy transfer between Dy3+ and Tm3+ in the host NaBi(WO4)2 was investigated. Finally, the chromaticity coordinates of preferred NaBi0.91-x(WO4)2:0.09Dy3+, 0.11 Tm3+ (0.3319, 0.3395) were close to the standard white light point (0.333, 0.333). All these results reveal that NaBi(WO4)2:Dy3+/Tm3+ was a potential single phase white light-emitting phosphor candidate for NUV-based w-LEDs.
关键词： White emission,Luminescence properties,Electronic structure,NaBi(WO4)2:Dy3+/Tm3+
更新于2025-09-23 15:22:29
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All-fluorescent white organic light-emitting diodes with EQE exceeding theoretical limit of 5% by incorporating a novel yellow fluorophor in co-doping forming blue exciplex
摘要： For all-fluorescent white organic light-emitting diodes (WOLEDs), it is a current challenge to achieve comparable device efficiency to phosphorescent devices. A novel yellow fluorophor (Y), synthesized by our group, realizes ultra-high electroluminescence performance with maximum luminance and external quantum efficiency (EQE) reaching 74820 cd/m2 and 5.65%, respectively, indicating a huge potential applications in developing high-performance all-fluorescent WOLEDs. Herein, we employ above yellow emitter Y to demonstrate a series of all-fluorescent WOLEDs, where the devices are fabricated by doping yellow emitter Y in blue-emitting thermally activated delayed fluorescent (TADF) host of mCP:PO-T2T-forming exciplex. And white emission are realized by the combination of blue and yellow emissions from mCP:PO-T2T host and yellow emitter Y through the incomplete energy transfer. By simply adjusting the doping ratio of yellow emitter Y in mCP:PO-T2T host, the optimized all-fluorescent white device achieves high device performance with maximum current efficiency, power efficiency, and EQE reaching 20.78 cd/A , 24.25 lm/W, and 8.22%, respectively. The EQE obviously exceed the theoretical limit value of 5% for all-fluorescent WOLEDs, and is comparable to some fluorescent/phosphorescent or all-phosphorescent WOLEDs in reported literatures. The achievement of such high performance is mainly ascribed to the highly efficient exciton utilization derived from excellent yellow fluorescent emitter Y and effective reverse intersystem crossing (RISC) from triplet level to singlet level in mCP:PO-T2T exciplex host.
关键词： white emission,exciplex host,all-fluorescent emission,organic light-emitting diodes,external quantum efficiency
更新于2025-09-23 15:19:57
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Synthesis and properties of hyperbranched polymers for white polymer light-emitting diodes
摘要： In this work, a series of hyperbranched copolymers with fluorene-alt-carbazole as the branches, three-dimensional-structured spiro[3.3]heptane-2,6-dispirofluorene (SDF) as the core, and iridium 1-(4-bromophenyl)-isoquinoline (acetylacetone) (Ir(Brpiq)2acac) as the dimming group were synthesized by one-pot Suzuki polycondensation for white emission. All copolymers show great thermal stabilities and high hole-transporting ability due to the introduction of the carbazole unit. The hyperbranched structures for copolymers can suppress the interchain interactions efficiently, and help to form amorphous films. The fabricated polymer light-emitting devices (PLEDs) based on the above synthesized copolymers realize good white light emission, and achieve high electroluminescence (EL) performance. For example, for the optimized PLED, the maximum luminance and current efficiency reach 6210 cd m?2 and 6.30 cd A?1, respectively, indicating the synthesized hyperbranched copolymers have potential application in solution-processable white polymer light-emitting diodes.
关键词： hyperbranched copolymers,electroluminescence,white emission,Suzuki polycondensation,polymer light-emitting devices
更新于2025-09-16 10:30:52
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Hybrid Quantum Dot Light-Emitting Diodes for White Emission Using Blue Phosphorescent Organic Molecules and Red Quantum Dots
摘要： Hybrid quantum dot light-emitting diodes (QLEDs) with no buffer layer were developed to achieve white emission using red quantum dots by spin-coating, and blue phosphorescent organic molecules by thermal evaporation. These unique bichromatic devices exhibit two distinct electroluminescent peaks with similar intensities at 10.5 V. For white emission, these hybrid QLEDs present a maximum luminance of 6195 cd/m2 and a current efficiency of 2.02 cd/A. These results indicate that the unique double emission layers have the potential for bright and efficient white devices using fewer materials.
关键词： quantum dots,phosphorescent molecules,white emission
更新于2025-09-11 14:15:04
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3.4: Room Temperature Dual Emission of Fluorescence and Phosphorescence in the Solid State
摘要： A white light emission comprised of fluorescence and phosphorescence was observed at room temperature in the solid state. The OLED device used the dual emission material was fabricated and showed white EL light.
关键词： Dual emission OLED device,White emission,Dual emission,Solid state
更新于2025-09-10 09:29:36
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Controlling the white phosphorescence ZnGa2O4 phosphors by surface defects
摘要： White phosphorescence that lasted ≈ 212 seconds, being the longest phosphorescence time reported so far for any Ga based material, has been observed in undoped ZnGa2O4 (ZGO) phosphors. The samples were synthesized by a simple combustion method by using two different Gallium precursors (Gallium nitrate and Gallium Acetylacetonate). According to the X-ray diffraction analysis, the samples prepared with the two different precursors presented the same single cubic phase. TEM images demonstrated that the ZGO phosphors made with both precursors are formed by nanoparticles with quasi-spherical shape, and they have nanoparticle sizes in the range of 17-43 nm. When excited with UV light (400 nm), these phosphors produced a broad blue-green-yellow luminescence. The blue band was associated to transitions from the Ga-O levels, while that of green-yellow band was attributed to radiative transitions from oxygen vacancies. Particularly, the sample synthesized with Gallium acetylacetone precursor presented the highest phosphorescent emission intensity and had a CIE coordinates of (x= 0.27, y= 0.33), which is close to that for pure white light (x=0.33, y=0.33). Since the ZGO presented a white phosphorescent emission without doping with rare earths, they could be good candidates for lighting or signaling applications.
关键词： White emission,Zinc-gallate,phosphorescence,Oxygen-vacancies,luminescence
更新于2025-09-09 09:28:46
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Near-ultraviolet excited Tm3+ and Dy3+ ions co-doped barium lanthanum silica oxide phosphors for white-light applications
摘要： Nowadays, trivalent rare-earth ions activated inorganic luminescent materials have been widely investigated owing to their important applications in solid-state lighting field. Tm3+ and Dy3+ ions single- or co-doped Ba3La6(SiO4)6 (BLSO) phosphor materials for white light application were synthesized by a citrate-based sol-gel method. The prepared samples were examined by X-ray diffraction (XRD), scanning electron microscopy and Fourier-transform infrared spectroscopy to analyze the phase purity, surface morphology and existence of functional groups, respectively. The XRD pattern confirmed that the BLSO host lattice exhibited a hexagonal crystal structure with P63/m (176) space group, which is well indexed with standard JCPDS data. From photoluminescence results, the BLSO:Tm3+ phosphors exhibited purplish blue emission at 453 nm (1D2/3F4) and the BLSO:Dy3+ phosphors showed predominant yellow emission at 575 nm (4F9/2 / 6H13/2) compared to their shoulder blue emission at 479 nm (4F9/2 / 6H15/2), indicating that the Dy3+ ions occupied lattice sites with low inversion symmetry. The determined Commission Internationale de I’Eclairage (CIE) (0.3391, 0.3302) values for the Tm3+ and Dy3+ co-doped BLSO phosphors were near to the standard sun light CIE values (0.33, 0.33) under near-ultraviolet (364 nm) excitation. The energy transfer process from Dy3+ to Tm3+ ions was discussed and it was proved by their corresponding decay curves. Additionally, thermal study was carried out for the optimized phosphor and it maintained superior thermal PL properties.
关键词： Citrate-based sol-gel technique,Ba3La6(SiO4)6 phosphors,Pure white emission,Thermal stability
更新于2025-09-04 15:30:14