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A two-dimensional (2D) lamellar Zn metal–organic framework (Zn-MOF, 1) with a fluorescent 1,6-di(pyridin-3-yl)pyrene (3-DPPy) and 1,4-benzenedicarboxylate (BDC2−) bridging linkers was prepared and structurally characterized. The chemical formula of 1 is [Zn(μ-3-DPPy)(μ-BDC)]n. The mononuclear Zn(II) ion, acting as a node, is tetrahedrally coordinated with two 3-DPPy and two BDC linkers. The coordination environment of Zn(II) is a distorted tetrahedral geometry. The Zn-MOF is the sql network structure based on topology analysis. The undulated 2D sheets of 1 tightly pack together to form a lamellar structure. The pyrene moieties are parallelly oriented to each other. The Zn-MOF is not porous, possibly because the mononuclear Zn(II) node did not form cluster-based secondary building units due to the less symmetric 3-DPPy. The steady-state fluorescence measurements indicate that the fluorescence signal of the 1 is slightly blue-shifted compared to the free 3-DPPy in the solid state. The excimer emission band at 463 nm for crystalline 3-DPPy is shifted to 447 nm for 1. The value of 447 nm is also a blue-shift value compared to nonsubstituted pyrene crystals (470 nm). Despite its nonporosity, the surface Lewis acidic sites of 1 could catalyze the transesterification of esters. Surface defect sites are responsible for this catalytic activity. [ABSTRACT FROM AUTHOR]

Perovskite quantum dots (PQDs), as the promising materials for the blue light-emitting diodes (LEDs), own huge advantages as ultra-high color purity, flexibility and whole-spectrum tunability. Through dimensional and compositional engineering, PQD-LEDs have shown superiority in deep-blue light emission. However, compared with the fast development of red and green PeLEDs, the electroluminescent performance of PQD-LEDs has faced more obstacles. In this review, we aim to explore and state the uniqueness and the possible solutions for the bottleneck problems of the PQD-LEDs. [ABSTRACT FROM AUTHOR]

Perovskite quantum dots (PQDs), as the promising materials for the blue light-emitting diodes (LEDs), own huge advantages as ultra-high color purity, flexibility and whole-spectrum tunability. Through dimensional and compositional engineering, PQD-LEDs have shown superiority in deep-blue light emission. However, compared with the fast development of red and green PeLEDs, the electroluminescent performance of PQD-LEDs has faced more obstacles. In this review, we aim to explore and state the uniqueness and the possible solutions for the bottleneck problems of the PQD-LEDs.

The synthesis and characterization of diaquabis[2-(2-hydroxyethyl)pyridine-κ2N,O)nickel(II) dinitrate, [Ni(C7H9NO)2(H2O)2](NO3)2, under ambient conditions is reported and compared with catena-poly[[bis[2-(2-hydroxyethyl)pyridine-κ2N,O]copper(II)]-μ-sulfato-κ2O:O′], [Cu(C7H9NO)2(SO4)]n [Zeghouan et al. (2016). Private communication (refcode 1481676). CCDC, Cambridge, England]. In the two complexes, the 2-(2-hydroxyethyl)pyridine ligands coordinate the metal ions through the N atom of the pyridine ring and the O atom of the hydroxy group, creating a chelate ring. The NiII or CuII ion lies on an inversion centre and exhibits a slightly distorted MO4N2 octahedral coordination geometry, build up by O and N atoms from two 2-(2-hydroxyethyl)pyridine ligands and two water molecules or two O atoms belonging to sulfate anions. The sulfate anion bridges the CuII ions, forming a polymeric chain. The photoluminescence properties of these complexes have been studied on as-synthesized samples and reveal that both compounds display a strong blue-light emission with maxima around 497 nm. From DFT/TDDFT studies, the blue emission appears to be derived from the ligand-to-metal charge-transfer (LMCT) excited state. In addition, the IR spectroscopic properties and thermogravimetric behaviours of both complexes have been investigated.

Electrochemiluminescence (ECL) is a phenomenon in which light is emitted from excited species generated by electrochemical reactions at electrodes. Alternating-current-driven ECL (AC-ECL) devices show good brightness and fast ECL response in comparison to direct-current-driven ECL devices. In this report, we focus on the ECL intensity and long-term stability of blue-light-emitting AC-ECL systems. We used a mixed solvent of propylene carbonate and toluene (volume ratio=1 : 1) to achieve stable blue ECL from 9,10-diphenylanthracene (DPA) molecules. We analyzed the electrochemical, optical, and AC-ECL properties of DPA in this mixed solvent to investigate the effect of the stabilities of redox species on AC-ECL properties. We found that the composition of the electrolyte solution affects the stability of these species. We conclude that stability of generated active species is required to achieve good performance in blue AC-ECL devices. [ABSTRACT FROM AUTHOR]

A D–A structured thermally activated delayed fluorescence (TADF) emitter, CyFbCz , was developed. The combination of 4-fluorocyanophenyl acceptor and carbazolyl donor resulted in an appropriate energy gap for efficient blue emitting. The well separated HOMO and LUMO contributed to a small Δ E ST (0.09 eV) and effective reverse intersystem crossing from lowest triplet state (T 1 ) to singlet state (S 1 ). The OLED with CyFbCz dopant achieved a maximum luminance of 2526.8 cd/m 2 , a maximum current efficiency of 6.64 cd/A, and a CIE coordinate of (0.18, 0.13). [ABSTRACT FROM AUTHOR]

In this study, a highly efficient fluorescent/phosphorescent white organic light-emitting device (WOLED) was fabricated using exciplex light emission. The hole-transport material 4,4ʹ,4ʺ-tris(N-carbazolyl)triphenylamine (TCTA), and electron-transport material, 4,7-diphenyl-1,10-phenanthroline (Bphen), were mixed to afford a blue-emitting exciplex. The WOLED was fabricated with a yellow phosphorescent dye, Ir(III) bis(4-phenylthieno [3,2-c] pyridinato-N,C 2 ʹ ) acetylacetonate (PO-01), combined with the exciplex. In this structure, the energy can be efficiently transferred from the blend layer to the yellow phosphorescent dye, thus improving the efficiency of the utilization of the triplet exciton. The maximum power efficiency of the WOLED reached a value 9.03 lm/W with an external quantum efficiency of 4.3%. The Commission Internationale de I'Eclairage (CIE) color coordinates ( x , y ) of the device were from (0.39, 0.45) to (0.27, 0.31), with a voltage range of 4–9 V. [ABSTRACT FROM AUTHOR]

This study was concerned with the synthesis and properties of new soluble copolyimides containing naphthalene, oxadiazole and tetramethyldisiloxane units. These copolyimides were prepared by two-step polycondensation reaction in solution of aromatic diamines containing preformed oxadiazole ring with a mixture 1 : 1 of naphthalene tetracarboxylic dianhydride and tetramethyldisiloxane- [1,3-bis(4′-phthalic anhydride)]. The structure of these polymers was confirmed by Fourier transform infrared and 1H-NMR spectroscopy. The solubility, thermal stability and glass transition temperature of these copolyimides were measured and compared with those of related polyimides which do not contain siloxane groups. All these polymers emitted an intense blue color light upon irradiation with UV light. These copoly(oxadiazole-naphthylimide)s could be considered promising candidates for organo-soluble high-performance polymers for use in novel technological applications. [ABSTRACT FROM AUTHOR]

As majority of polyheteroarylenes based on bis(naphthalic anhydrides), are difficult to process due to their infusiblity and insolubility in common organic solvents and solubility only in strong acids, this study is concerned with the synthesis and properties of new, easily processable polyimides and copolyimides containing naphthalene and oxadiazole rings. These polymers have been synthesized and their properties have been compared with regard to the influence of oxadiazole and naphthalene units on their physical properties. The polyimides were prepared by polycondensation reaction in solution of the aromatic diamines containing preformed oxadiazole ring with two dianhydrides having naphthalene units, at high temperature. Also, copolyimides were prepared by using a mixture of each naphthalene-containing dianhydride, with hexafluoroisopropylidene-dianhydride in the polycondensation reaction with the same diamino-oxadiazoles. Most of the resulting polyimides and copolyimides were soluble in polar amidic solvents and in less polar solvents, and their solutions gave flexible films when spread onto glass plates. The thermal stability and glass transition temperature of these polyimides and copolyimides were measured and compared. The quality and the roughness of the spin-coated films of these polymers were investigated by atomic force microscopy. The photoluminescence properties of the polymers in solution were studied to determine the color of emission. The UV absorption was also studied to determine the Stokes shift, and hence the possible reabsorption effects. The properties of the present polyimides make them attractive for applications in advanced optoelectronics and other related fields. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: We report the structural and photoluminescence characteristics of a high energy Ar+-irradiated SrTiO3 single crystal. High resolution X-ray reciprocal space mapping, cross-section scanning electron microscopy and photoluminescence measurements suggest that thick amorphous and oxygen-deficient SrTiO3 layers are formed after irradiation. Due to the highly accelerated Ar+ (∼100keV), electrical conductivity of the oxygen-deficient SrTiO3 layer seems to be highly reduced, which results in the absence of 440nm (blue-light) emission at 300K, and broad and weak 380nm emission at 20K. [Copyright &y& Elsevier]

Abstract: Much attention has been paid to carbazole derivatives for their potential applications as optical materials. For the first time, the blue-light-emitting carbazole chromophore has been covalently bonded to the ordered mesoporous SBA-15 (The resultant hybrid mesoporous materials are denoted as carbazole–SBA-15) by co-condensation of tetraethoxysilane (TEOS) and prepared compound 3-[N-3-(triethoxysilyl)propyl]ureyl-9-ethyl-carbazole (denoted as carbazole–Si) in the presence of Pluronic P123 surfactant. The results of 1H NMR and Fourier transform infrared (FTIR) reveal that carbazole–Si has been successfully synthesized. Small-angle X-ray diffraction patterns (XRD) and Nitrogen (N2) adsorption/desorption measurements were employed to characterize the mesostructure of carbazole–SBA-15. Solid-state 29Si magic-angle spinning (MAS) NMR was used to confirm the preservation of the carbazole group and estimate the degree of hydrolysis-condensation. Photoluminescence (PL) measurements show that carbazole–SBA-15(0.07) [carbazole–Si:(TEOS+carbazole–Si) molar ratio is 0.07] hybrid mesoporous material exhibits a monomeric emission in the “light blue” region with a PL quantum yield ∼31%. Compared with carbazole–Si, the I car/C car (relative luminescence intensity divided by the content of carbazole) of carbazole–SBA-15(0.07) increases 24 times. The luminescence decays for 3-amino-9-ethyl-carbazole (denoted as carbazole–NH2) and carbazole–Si are single-exponential functions of time, while those for carbazole–SBA-15 mesoporous materials are fitted by double-exponential functions. The stability studies on carbazole–Si and carbazole–SBA-15(0.07) show that the carbazole chromophore in the resultant hybrid mesoporous material exhibits better thermal stability than in carbazole–Si compound. The excellent luminescent properties and thermal stability enable the hybrid mesoporous material to have potential use as blue-light-emitting material in optical field. [Copyright &y& Elsevier]

Abstract: Well-crystalline Pb(Zr0.52Ti0.48)O3 square platelets, with dimensions of about 1×0.65×0.16 μm3, have been synthesized by hydrothermal method at low temperature. X-ray diffraction, micro-Raman spectrometry, and field emission scanning electron microscope were employed to study the crystal structure and morphologies of the products. Energy dispersive X-ray spectroscopy was used to analyze the elemental composition of the products. The photoluminescence of the products showed a strong narrow blue-light emission at 453 nm and a weak one at 468 nm at room temperature. The possible mechanisms for the blue-light emission are proposed in this report. The photoluminescence of this ferroelectric material is one more interesting property for technological applications. [Copyright &y& Elsevier]

Abstract: This study presents the synthesis and characterisation of a series of fluorene-based conjugated copolymers, together with the preparation and characterisation of the corresponding light-emitting devices. The polymers consist of alkoxyphenyl-substituted fluorene units together with different amounts of a hole-transporting triphenylamine-substituted fluorene unit: 0%, 10%, 25% and 50%. All polymers (P0, P1, P2, and P3) show high photoluminescence efficiency (η PL) and light emission (both PL and EL) in the blue spectral region. Electrochemical studies show improved hole injection as the ratio of the triphenylamine-substituted segment is increased. The electroluminescence quantum efficiencies (EQEs) of the devices increase six times going from P0 to P1. Compared with P1, polymers P2 and P3 show lower efficiencies in devices. These findings indicate the presence of an optimal polymer composition, where balance between the charge-carrier mobilities has been reached. [Copyright &y& Elsevier]

Abstract: Well-crystalline Pb(Zr0.52Ti0.48)O3 (PZT) nanorolls with typical wall thicknesses in the range of 300–900nm and the length up to 10μm have been synthesized by a surfactant-assisted hydrothermal method at a low temperature of 190°C. The “rolling mechanism” for the formation of PZT nanorolls was discussed. X-ray diffraction, micro-Raman spectrometry, and field emission scanning electron microscope demonstrated the PZT nanostructures and morphology. The photoluminescence measurements showed that a strong and narrow blue-light at 453nm emits and a weak one at 470nm at room temperature for the samples, indicating that PZT nanorolls have potential applications in nano-optical devices. [Copyright &y& Elsevier]

Semiconductor nanometer-scale dots were created by postgrowth hydrogen treatment of GaN films grown on sapphire and silicon substrates with AlN or GaN buffer layers and CdTe and HgCdTe films grown on CdZnTe substrates. HRSEM and AFM measurements confirmed that the nanometer-scale dots were formed by the treatment both on flat and inclined faces regardless of a lattice mismatch between the materials used. Changing hydrogenation conditions controls a density and size of the dots. The blue-light emissions observed from GaN quantum dots were attributed to the presence of a piezoelectric field in the dots. [Copyright &y& Elsevier]

• The efficiency of the devices is increased with the additional quantum well. • The current efficiency reported is pretty high as compared with other published data. • The device with quantum well structure shows purer blue-light emission. • The color temperature stability of the device is highly improved. Currently, exciplex has drawn a great deal of attention due to its potential for efficient electroluminescence and for use as a host. In this study, we used 4,4′,4"-Tris(carbazol-9-yl) triphenylamine (TCTA) and 1,3,5-Tri(m-pyridin-3-ylphenyl) benze nee (TmPyPB) to form an exciplex host, where Bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III)(FIrpic) was used as the dopant to emit blue phosphorescent light. Additional FIrpic and Bis(1phenylisoquinoline) (acetylacetonate) iridium(III) emission layers were inserted in the proposed structure to investigate how the recombination area of carriers shifts with the increase of voltage. TCTA and non-doped FIrpic layers were then inserted in both sides of the emission layer to confine the carriers, and the thickness of the emission layer was also optimized to improve the current efficiency of the proposed devices. The efficiency of the devices was increased from 56 cd/A to 63.6 cd/A with the additional quantum well structure and an emission layer thickness of 15 nm. The current efficiency reported in this paper was fairly high as compared with other published data on blue-emission exciplex-based organic light-emitting diodes. In addition, the device with the quantum well structure exhibited purer blue-light emission, and the color temperature stability was also highly improved. [ABSTRACT FROM AUTHOR]

Abstract: We fabricated fused-silica substrates which emit blue light by using Si-ion implantation and high-temperature annealing. Photoluminescence peak wavelengths are around 400nm, and the peak intensities can be remarkable after annealing above 1150°C. [Copyright &y& Elsevier]

Thermally activated delayed fluorescent (TADF) materials are considered as the competitive alternative to traditional fluorescent and noble-metal-based phosphorescent materials due to their high electroluminescence (EL) efficiency and low cost. Solution-processable TADF OLEDs have drawn great research attention and can be potentially applied in both flat-panel displays and lighting sources in the near future. However, the blue light emitting TADF materials with high luminance, satisfying color purity and excellent stability are still rare. Herein, two blue light emitting TADF molecules (CzAC-TRZ, DFAC-TRZ) are designed and synthesized. Due to the modified acridine units by introducing 9-phenylcarbazole and dibenzofuran as σ-groups into the molecular skeletons, CzAC-TRZ, DFAC-TRZ possess high energy states and rigid molecular configuration. Solution-processed OLEDs based on CzAC-TRZ and DFAC-TRZ achieved high EL efficiency with the external quantum efficiency (EQE) up to 11.8% and 11.5%, respectively. Moreover, compared with the analogue emitter (DMAC-TRZ) fabricated control devices, CzAC-TRZ and DFAC-TRZ OLEDs presented lower roll-offs, blue-shift and narrower EL spectra. These results have shown that introducing high energy state building blocks into the donor units via σ bonds offers a promising approach of developing stable deeper blue TADF emitters. Image 1 • σ-link strategy was employed to construct two blue TADF emitters: CzAC-TRZ and DFAC-TRZ. • In contrast to DMAC-TRZ, CzAC-TRZ and DFAC-TRZ possess blue-shift photoluminescence and improved thermal stability. • The fabricated OLEDs demonstrated blue electroluminescence with improved color purity and reduced efficiency roll-offs. [ABSTRACT FROM AUTHOR]

Lead‐based perovskite nanocrystals (NCs) are promising candidates for use in lighting and display applications; however, the toxicity of lead is one critical issue that needs to be solved for its commercialization. Consequently, less toxic tin and bismuth‐based perovskite NCs have been developed, but these materials exhibit low photoluminescence quantum yields (PLQYs) and large full width at half maximum (FWHM) values. Due to their similarity in size for Eu2+ and Pb2+, the more environmental‐friendly europium shows the potential to replace lead. Herein, the synthesis of Eu2+ doped CsBr NCs with an average size of 51.5 nm via a facile hot‐injection method is reported. The prepared CsBr:Eu2+ NCs exhibit an emission peak at 440 nm with an FWHM of 31 nm and PLQY up to 32.8%, which is persistent for at least 60 d. Moreover, the size and FWHM of CsBr:Eu2+ NCs can be tuned to 18.9 and 29 nm, respectively, by co‐doping of Ca2+ ions into the NCs. It is also demonstrated that the prepared CsBr:Eu2+ NCs can be employed as efficient color conversion materials for fabricating white light‐emitting diodes. [ABSTRACT FROM AUTHOR]