Stabilization of moisture-reactive raw materials for improved synthesis of Ca-α-SiAlON:Eu2+ phosphor

The raw materials needed to make the Ca-α-SiAlON:Eu²⁺ phosphor contain highly moisture-reactive Ca₃N₂. Exposing them to a preheating process prior to high-temperature synthesis stabilized the raw materials against oxidation. Preheating above 1200 °C in a tube furnace directly connected to a glove box, resulted in the formation of intermediate phases such as CaAlSiN₃, which provided higher moisture resistance to the raw materials. We found that even after exposure to a humid environment, the preheated samples maintained PL characteristics similar to the conventional unexposed samples, while the PL intensity and particle homogeneity of the un-preheated samples were severely deteriorated.     

Optical properties of green-blue-emitting Ca-α-Sialon:Ce,Li phosphors for white light-emitting diodes (LEDs)

Ce³⁺,Li⁺-codoped Ca-α-Sialon phosphors with the formula [Ca_(1−2x)Ce_xLi_x]_m/2Si_12−(m+n)Al_m+nO_nN_16−n (0≤x≤0.25, 0.5≤m≤3.5, and 0.16≤n≤2.0) have been synthesized by gas pressure sintering (GPS). The effects of the activator concentration and the overall composition of host lattice on the phase evolution, morphology, and optical properties were investigated. The single-phase Ca-α-Sialon:Ce³⁺,Li⁺ can be synthesized at x<0.1, 1.0≤m≤2.5, and n≤1.2. The synthesized powders exhibit a relatively dispersive and uniform morphology. Under the near UV excitation, the bright green-blue emission centered at 500-518 nm is observed. The photoluminescence can be tailored by controlling Ce³⁺ concentration and the overall composition of the α-Sialon host lattice. With increasing the Ce concentration and m value both excitation and emission bands show a red shift, which perfectly matches with the near-UV LEDs in the range of 360-410 nm. The strongest luminescence is achieved at x=0.08-0.1, m=2.0-2.5, and n=1.0. Simultaneously, the highest quantum efficiency and better thermal stability are also present.     

Thermal and luminescent properties of Eu2+-doped aluminates prepared by the sol–gel method

Alkaline earth aluminates with the overall nominal compositions Ca_0.5Sr_0.5Al₂O₄, Ca_0.5Mg_0.5Al₂O₄ and Mg_0.5Sr_0.5Al₂O₄ doped with 1 mol% of Eu²⁺ ions were prepared by the modified aqueous sol–gel method. The thermal behaviour of the xerogels was studied by the TG/DSC-MS technique under an argon and a reductive atmosphere (Ar/H₂–5 %). Appropriate luminescent efficiency of the materials was achieved after annealing at temperatures lower than those in conventional solid state reactions. All three aluminates are mixtures of at least two phases; the monoclinic phase of CaAl₂O₄, the hexagonal phase of SrAl₂O₄ and the cubic phase of MgAl₂O₄ were identified. Solid solubility was recognised in the Ca_0.5Sr_0.5Al₂O₄:Eu²⁺ composition due to the similar ionic radii of Ca²⁺ and Sr²⁺. UV excited luminescence was observed in the blue region (λ_max = 441 nm) in the aluminates containing the monoclinic phase of CaAl₂O₄ and in the green region (λ_max = 520 nm) in the Mg_0.5Sr_0.5Al₂O₄:Eu²⁺ composition.     

Synthesis and thermal properties of NiSbS–As doped phase

The substitution of Sb with As in the NiSbS intermetallic compound was studied in the framework of evaluating a possible increase of the thermoelectric properties. Different NiSb_1?xAs_xS samples were synthesized with increasing amounts of As (0 < x < 0.66) employing a simple synthetic route using a muffle furnace. Scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy was used to investigate the microstructure. X-ray powder diffraction techniques were employed in order to study the possible existence of a solid solution between NiSbS and NiAsS compounds, as well as to identify the crystal structure and determine the lattice parameters. All compounds were found to crystallise with the NiSbS prototype (cP12-P2₁3), with lattice parameters varying from a = 0.59341(7) nm (x = 0) to a = 0.56849(6) nm (x = 1). Good agreement with Vegard’s law was evidenced. Thermal measurements on NiSb_1?xAs_xS samples were carried out using DTA instruments to evaluate the thermal stability and the melting temperatures.     

Synthesis and characterization of thiophene and fluorene based donor–acceptor conjugated polymer containing 1,3,4-oxadiazole units for light-emitting diodes

A new donor–acceptor (D–A) conjugated polymer (PDTOF) containing 3,4-didodecyloxythiophene, fluorene and 1,3,4-oxadiazole units is synthesized by using Wittig reaction methodology. The synthesized polymer is characterized by ¹H NMR, FTIR, GPC, and elemental analysis. The optical energy band gap of the polymer is found to be 2.42 eV as calculated from the onset absorption edge. The electrochemical studies of PDTOF reveal that, the HOMO and LUMO energy levels of the polymer are ?5.45 eV and ?3.58 eV, respectively. The polymer is thermally stable up to 320 °C. Polymer light-emitting diode devices are fabricated with a configuration of ITO/PEDOT: PSS/PDTOF/Al using PDTOF as the emissive layer. The electroluminescence (EL) spectrum of the device showed green emission with CIE coordinate values (0.34, 0.47). By current density–voltage characteristics, threshold voltage of the PLED device is found to be 6.5 V.     

Synthesis and properties of a luminescent organic material with triphenylamine and pentiptycene units

A donor–bridge–donor compound for blue light-emitting with triphenylamine as donor and pentiptycene derivative units as bridge was synthesized via Sonogashira reaction. The chemical structure was confirmed by NMR and MALDI-TOF MS. It emits blue light peaked at 442 nm with a FWHM of 59 nm in CH2Cl2. Fluorescent quantum efficiency in THF is 82% relative to 9,10- diphenylanthracene. A slight hypsochromic shift was found in its drop-cast film. Cyclic voltammetry revealed that it has high HOMO level corresponding to hole transporting character.     

Synthesis and light-emitting properties of 2-(N-phenyl-α-naphthylamino) and 2-dimesitylboron-7-(N-phenyl-α-naphthylamino)-9,9-diethylfluorene

A fluorescent organic triarylamine with a symmetric structure, 2,7-bis(N-α-naphthyl-phenylamino)-9,9- diethylfluorene (NPAEF) was synthesized using two methods, modified Ullmann coupling and modified palladium-catalyzed amination. An activated copper and a combination of Pd(OAc)2/P(t-Bu)3 and Pd(dba)2/P(t-Bu)3 were selected as catalysts to improve yields of reactions. These synthetic procedures were also successfully applied to an asymmetric 2-dimesitylboron-7-(N-phenyl-α-naphthylamino)-9,9-diethylfluorene ...     

Synthesis,structure and photoluminescence properties of Ho3+ doped TTB–BaTa2O6 phosphors

Ho³⁺ doped TTB–BaTa₂O₆ phosphors were produced by the solid state reaction method. XRD analysis confirmed the formation of BaTa₂O₆ single phase which was accomplished by heat treatment at 1425 °C for 20 h. The crystal structure of TTB–BaTa₂O₆ allowed doping concentration of Ho³⁺ ions up to 10 mol%, maintaining a single phase composition. A second phase of HoTaO₄ begins to appear at 15 mol%. The lattice structure and the crystallite sizes changed with the concentration of Ho³⁺. In SEM analysis, it was also shown that BaTa₂O₆ grain sizes changed with the concentration of Ho³⁺. EDS analysis revealed that the Ta/Ba ratio increased on the grains depending on Ho³⁺ concentration. Charge balance of the structure was formulated through the EDS results. In fluorometer analysis, a strong green emission (λ_em = 546.9 nm) was observed in the visible spectral region. The emission increased with the doping concentration of up to 2.5 mol%, and above this level decreased due to concentration quenching.     

Rational design of donor–π–acceptor n-butyl-1,8-naphthalimide-cored branched molecules as charge transport and luminescent materials for organic light-emitting diodes

Four D–π–A bipolar molecules with n-butyl-1,8-naphthalimide (BNI) fragments as acceptors, acetylenes as π-spacers, and different aromatic groups as donors have been designed to explore their optical, electronic, and charge transport properties as charge transport and luminescent materials for organic light-emitting diodes (OLEDs). The frontier molecular orbitals (FMOs) and local density of states analysis have turned out that the vertical electronic transitions of absorption and emission are characterized as intramolecular charge transfer (ICT). The calculated results show that their optical and electronic properties are affected by the different donors of the bipolar molecules. Our results suggest that D–π–A 1,8-naphthalimide derivatives with donors triphenylamine (1), 1-nitrobenzene (2), anisole (3), and 4-phenylbenzo[c][1,2,5]thiadiazole (4) fragments are expected to be promising luminescent materials. Furthermore, 2–4 are expected to be promising candidates for both electron and hole transport materials as well as potential ambipolar charge transport material, whereas BNI and 1 can serve as hole transfer materials only. We have also predicted the mobility of 4 with better performance in three different space groups. On the basis of investigated results, we proposed a rational way for the design of charge transport and/or luminescent materials simultaneously.     

Synthesis and luminescence examination of β-NaCaPO<Subscript>4</Subscript>:Eu<Superscript>2+</Superscript>, phosphor promising for white light-emitting diode applications

The morphology, particle-size distribution, and luminescence properties of β-NaCaPO₄:Eu²⁺ were examined in relation to the synthesis conditions by electron-microscopic, X-ray phase, and luminescence analyses. The distribution of the Eu ions over the metal sites in the β-NaCaPO₄ structure was analyzed.     

Synthesis and characterization of two new metal–organic frameworks with interpenetrated structures and luminescent properties

Two new metal–organic compounds, [Ag₂(HADC)₂(bimh)] (1) and [Cd(ADC)(bpp)]_n (2) [H₂ADC = 1,3-adamantanedicarboxylic acid, bimh = 1,6-bis(2-methyl-imidazole-1-yl)hexane, bpp = 1,3-bis(4-pyridyl)propane], have been synthesized and characterized. Compound 1 exhibits a discrete symmetric unit with 0D→2D interpenetrating structure. Compound 2 crystallizes in a chiral space group P212121 and presents a threefold interpenetrated 3D diamondoid network containing three helical chains. Thermal stability, X-ray powder diffraction, and luminescence for 1 and 2 are also measured and discussed.     

Optical properties of yellow-light-emitting LiZnVO4:Eu3+ phosphor prepared by sol–gel method

Europium-doped nanocrystals of lithium zinc vanadium oxide (LiZnVO₄) prepared via the sol–gel method are characterized. The X-ray power diffraction results reveal that a pure phase is obtained at 500 °C. The photoluminescence spectra of LiZnVO₄:xEu (x = 7 mol%) exhibit emission peaks at 526, 597 and 620 nm. The emission shifts from bluish-green to yellow when the doping concentration is increased from 0 to 7 mol%, due to the emission peak at 620 nm from the ⁵D₀ → ⁷F₂ transition, which originated from charge transfer transitions from VO₄ ^3? to Eu³⁺ ions.     

Synthesis and photoluminescent properties of Y1 − x La x PO4:Eu3+ nanophosphor

In this paper, Y_{1 ? x} La _x PO₄:Eu³⁺ (x = 0.5, 0.7, and 0.3) nanophosphors were synthesized by a rather simple method. The products present different morphologies. For Y_{1 ? x} La _x PO₄:Eu³⁺, they have similar phase composition of a mixture of monoclinic LaPO₄ and tetragonal YPO₄. Furthermore, the luminescence behavior of Eu³⁺ has been investigated in this type of matrices. In Y_{1 ? x} La _x PO₄:Eu³⁺, the ⁵D₀-⁷F₁ magnetic dipole transition is dominant, indicating that the Eu³⁺ site is inversion symmetry. The difference in the Eu-O charge transfer (CT) band with La³⁺ ion concentration suggests the difference in the ionicity of the Eu-O bond. Among those products, the red to orange intensity ratio (R/O) of ⁵D₀-⁷F₂ to ⁵D₀-⁷F₁ value of Eu³⁺ is different, furthermore, for La³⁺ x = 0.3, the R/O value of Eu³⁺ is the biggest on the contrary, indicating that the inversion symmetry Eu³⁺ is lowest.     

Synthesis and some properties of diethoxyaluminum α,α-dimethylbenzyl peroxide

Summary The previously undescribedorganoaluminum peroxide of composition (C₂H₅O)₂AlOOC₉H₁₁ was synthesized, and some of its properties were studied.     

A serial of 2D Co-Zn isomorphous metal–organic frameworks for photodegradation and luminescent detection properties

A series of 2D isomorphous MOFs [M (HBTC)(BMIOPE)·DMF·H₂O]_n (M = Zn ( 1 ), Zn_0.7Co_0.3 ( 2 ), Zn_0.5Co_0.5 ( 3 ), Zn_0.3Co_0.7 ( 4 ), Co ( 5 ), H₃BTC = 1,3,5-benzenetricarboxylic acid, BMIOPE = 4,4′-bis(2-methylimidazol-1-yl)diphenyl ether) were synthesized to investigate the correction between the center metal ions and the photocatalytic behaviors. The photocatalytic results show that with the increase of Co²⁺ content, the photodegradation properties are continuously improved from 1 to 5 , which fully indicate that only changing metal ions could regulate the photodegradation properties. In detail, 1 is an inactive photocatalyst to degrade methylene blue (MB), while 5 exhibits preeminent photocatalytic properties under visible light irradiation. Moreover, 1 shows good selective sensing toward Fe³⁺, Cr³⁺, UO₂²⁺, CrO₄²⁻ and Cr₂O₇²⁻ ions in aqueous solution. To the best of our knowledge, 1 is the first MOF example for the optical detection of Fe³⁺, Cr³⁺, UO₂²⁺, CrO₄²⁻ and Cr₂O₇²⁻ ions in aqueous solution.     

Triptycene scaffolds: Synthesis and properties of triptycene-derived Schiff base compounds for the selective and sensitive detection of CN− and Cu2+

A series of triptycene-derived Schiff bases were synthesized by condensation between amino triptycenes with an appropriate aldehyde and were isolated in good to excellent (85–90%) yields. Amongst these, a triptycene-hydroxybenzaldehyde Schiff base compound proved to be a selective sensor for cyanide. It exhibited a “turn-on” fluorescence response at 490 nm to CN^? facilitated by the nucleophilic addition of CN^? to the aldehyde group, accompanied by a visible color change from orange to yellow. Likewise, a triptycene salicylaldehyde adduct was shown to be highly sensitive towards the detection of the CN^? ion with a detection limit of 0.9 μM. On the other hand a triptycene-BODIPY Schiff base compound could be used for the detection of Cu²⁺ ions over other competing, biologically relevant metal ions in acetonitrile. Photophysical studies revealed a 1:1 binding model for the triptycene-BODIPY compound.     

Synthesis and blue light-emitting properties of 4,4''''-bis(diphenylamino)-quinque(p-phenyl)s

An excellent organic blue light-emitting diode based on 4,40-bis(diphenylamino)-quinque( p-phenylene)s (OPP(5)-NPh) with a maximum luminance of up to 5000 cd/m2 and a luminanous efficiency of 1.3 cd/A was reported. This diode was made by using a wide band-gap hole-blocking layer, F-TBB instead of PBD in the OLED devices. We attribute the good performance to the one trade-off involved in the use of F-TBB to obtain higher luminance is the increased turn-on voltages and slightly decreased device efficiencies.