High‐Throughput Fabrication of Au–Cu Nanoparticle Libraries by Combinatorial Sputtering in Ionic Liquids

Materials libraries of binary alloy nanoparticles (NPs) are synthesized by combinatorial co‐sputter deposition of Cu and Au into the ionic liquid (IL) 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([C₁C₄im][Tf₂N]), which is contained in a micromachined cavity array substrate. The resulting NPs and NP‐suspensions are investigated by transmission electron microscopy (TEM), X‐ray diffraction (XRD), UV‐Vis measurements (UV‐Vis), and attenuated total reflection Fourier transformed infrared (ATR‐FTIR) spectroscopy. Whereas the NPs can be directly observed in the IL using TEM, for XRD measurements the NP concentration is too low to lead to satisfactory results. Thus, a new NP isolation process involving capping agents is developed which enables separation of NPs from the IL without changing their size, morphology, composition, and state of aggregation. The results of the NP characterization show that next to the unary Cu and Au NPs, both stoichiometric and non‐stoichiometric Cu–Au NPs smaller than 7 nm can be readily obtained. Whereas the size and shape of the alloy NPs change with alloy composition, for a fixed composition the NPs have a small size distribution. The measured lattice constants of all capped NPs show unexpected increased values, which could be related to the NP/surfactant interactions.     

Scrutinizing Design Principles toward Efficient,Long‐Term Stable Green Light‐Emitting Electrochemical Cells

Enhancing the efficiency and lifetime of light emitting electrochemical cells (LEC) is the most important challenge on the way to energy efficient lighting devices of the future. To avail this, emissive Ir(III) complexes with fluoro‐substituted cyclometallated ligands and electron donating groups (methyl and tert ‐butyl)‐substituted diimine ancillary (N^{^}N) ligands and their associated LEC devices are studied. Four different complexes of general composition [Ir(4ppy)₂(N^{^}N)][PF₆] (4Fppy = 2‐(4‐fluorophenyl)pyridine) with the N^{^}N ligand being either 2,2′‐bipyridine ( 1 ), 4.4′‐dimethyl‐2,2′‐bipyridine ( 2 ), 5.5′‐dimethyl‐2,2′‐bipyridine ( 3 ), or 4.4′‐di‐tert ‐butyl‐2,2′‐bipyridine ( 4 ) are synthesized and characterized. All complexes emit in the green region of light with emission maxima of 529–547 nm and photoluminescence quantum yields in the range of 50.6%–59.9%. LECs for electroluminescence studies are fabricated based on these complexes. The LEC based on ( 1 ) driven under pulsed current mode demonstrated the best performance, reaching a maximum luminance of 1605 cd m^?2 resulting in 16 cd A^?1 and 8.6 lm W^?1 for current and power efficiency, respectively, and device lifetime of 668 h. Compared to this, LECs based on ( 3 ) and ( 4 ) perform lower, with luminance and lifetime of 1314 cd m^?2, 45.7 h and 1193 cd m^?2, 54.9 h, respectively. Interestingly, in contrast to common belief, the fluorine content of the Ir‐iTMCs does not adversely affect the LEC performance, but rather electron donating substituents on the N^{^}N ligands are found to dramatically reduce both performance and stability of the green LECs. In light of this, design concepts for green light emitting electrochemical devices have to be reconsidered.     

Highly doped alkaline earth nanofluorides synthesized from ionic liquids

Bulk alkaline earth fluorides co-doped with optically active ions are prominent materials for luminescent applications. However, for phosphor materials the changeover to the nanoscale is a tightrope walk between achieving desirable features of small particles such as reduced light scattering and unwanted drawbacks such as a high surface defect concentration which is likely to result in quenching of luminescence. A new preparation route via ionic liquids allows obtaining pure and oxygen-free alkaline earth fluorides co-doped with Eu³⁺ and Gd³⁺ on the nanoscale with excellent quantum cutting abilities.     

Facile ultrasound-assisted synthesis of ZnO nanorods in an ionic liquid

ZnO nanocrystals have been synthesized by ultrasound-assisted synthesis from Zn(CH₃COO)₂2H₂O and NaOH in the neat room-temperature ionic-liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide, [C₄mim][Tf₂N]. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that the formed ZnO nanocrystals are of rod like shape with lengths from 50 to 100 nm and diameters of about 20 nm. X-ray diffraction (XRD) confirms the crystallinity as well as the sample purity. The band gap of the as-prepared ZnO nanorods was estimated to be 3.31 eV from UV–Vis absorption measurements. The photoluminescence spectrum shows the characteristic greenish emission of ZnO at room temperature (λ_max = 563 nm). The ZnO bonding levels have been determined by X-ray photoelectron spectroscopy (XPS). Nitrogen adsorption–desorption measurements show typical samples to have a specific surface area of 49.93 m²/g.     

Efficient and Long Lived Green Light‐Emitting Electrochemical Cells

The combination of high efficiencies and long lifetime in a single light‐emitting electrochemical cell (LEC) device remain a major problem in LEC technology, preventing its application in commercial lighting devices. Three green light‐emitting cationic iridium‐based complexes of the general composition [Ir(C^{^}N)₂(N^{^}N)][PF₆] with 4‐Fppy (2‐(4‐fluorophenyl)pyridinato) as the cyclometalating C^{^}N ligand and 1,10‐phenanthroline ( 1 ), 4,7‐diphenyl‐1,10‐phenanthroline (bathophenanthroline, bphen, 2 ), and 2,9‐dimethyl‐4,7‐diphenyl‐1,10‐phenanthroline (bathocuprione, dmbphen, 3 ) as ancillary N^{^}N ligands are synthesized and characterized. Computational studies are carried out in order to compare the electronic structure of the three ionic transition metal complexes (iTMCs) and provide insights into their potential as LEC emitter materials. LECs are then fabricated with complexes 1 – 3 . Driven under a pulsed current, they display a high luminance and current and power efficiencies. As the LEC based on complex 2 displays the overall best device performance, including the longest lifetime of 474 h, it is selected for subsequent driving conditions optimization. An extraordinary power efficiency of 25 lm W^?1 and current efficiency of 30 cd A^?1 are achieved under optimized operation conditions with reduced current density, resulting in a long device lifetime of 720 h. Altogether, ligand design in iTMCs and optimization of the device driving conditions leads to a significant improvement in LEC performance.     

Praseodymium diiodide, PrI2, revisited by synthesis, structure determination and theory

Praseodymium diiodide, PrI₂, is obtained from the triiodide, PrI₃, by reduction with praseodymium metal at elevated temperatures. The two modifications, PrI₂-IV and -V, are obtained in different ratios upon fast and slow cooling, respectively. PrI₂-IV crystallizes with the CdCl₂ type of structure (trigonal, R-3m, a=426.5(1), c=2247.1(8) pm) while PrI₂-V (cubic, F-43m, a=1239.9(2) pm) represents an own structure type that may be considered as a structural variant of the CdCl₂ type with tetrahedral Pr₄ clusters. To elucidate the electronic properties of the modifications of PrI₂ first principles electronic band structure calculations have been carried out using the tight-binding linear-muffin-tin-orbital method (LMTO) as well as the full potential augmented plane wave method (FP-LAPW). The band structure and the bonding were analysed in terms of projections of the bands onto orthogonal orbitals. It was especially focussed on Pr–Pr interactions by crystal orbital Hamiltonian population (COHP) analysis. The calculations show accordingly that a configurational crossover between a [Xe]6s⁰5d⁰4fⁿ and a [Xe]6s⁰5d¹4f^n-1 configuration can be observed in the case of PrI₂, depending upon the structure adopted. A higher d orbital contribution results in stronger Pr–Pr interactions. Thus, the driving force appears to be an optimisation of bonding.     

One‐Pot Synthesis of Luminescent Polymer‐Nanoparticle Composites from Task‐Specific Ionic Liquids

A multifunctional polymerizable ionic liquid, diallyldimethylammonium tetrafluoroborate (DADMA BF₄), is used in a one‐pot synthesis of novel luminescent polymer‐nanoparticle composites. First, small monodisperse lanthanide fluoride nanoparticles are formed by microwave irradiation in the presence of Ln(OAc)₃·xH₂O (Ln = Gd, Eu, Tb; OAc = acetate) in the ionic liquid. The nanoparticles can be precipitated for structural characterization or kept in the solution, which yields after irradition by high intensity UV light colorless, processable polymer materials with good photophysical properties. Both green‐emitting Tb‐containing and red‐emitting Eu‐containing IL‐ polymers are described.     

Sonochemical preparation of TiO2 nanoparticles in the ionic liquid 1-(3-hydroxypropyl)-3-methylimidazolium-bis(trifluoromethylsulfonyl)amide

Spherical shaped anatase nanoparticles (ø 5 nm) have been synthesized in the ionic liquid 1-(3-hydroxypropyl)-3-methylimidazolium-bis(trifluoromethanesulfonyl)amide from titanium tetraisopropoxide by ultrasound assisted synthesis under ambient conditions. XRD, EDX, TEM, XPS, Raman, UV–vis, PL and BET measurements have been employed for characterization of the nanostructure of as-prepared TiO₂. XRD and Raman measurements both show that the obtained material is crystalline with anatase structure. The morphology of TiO₂ nanoparticles was characterized by transmission electron microscopy (TEM). The bandgap of the TiO₂ nanocrystals estimated from XRD and UV–vis measurements is about 3.3 eV. The surface area of a typical sample is 177 m² g⁻¹. The synthesized anatase nanocrystals show good photocatalytic activity in the degradation of methylorange.     

Facile preparation of Ag/ZnO nanoparticles via photoreduction

Ag/ZnO nanoparticles can be obtained via photocatalytic reduction of silver nitrate at ZnO nanorods when a solution of AgNO₃ and nanorods ZnO suspended in ethyleneglycol is exposed to daylight. The mean size of the deposited sphere like Ag particles is about 5 nm. However, some of the particles can be as large as 20 nm. The ZnO nanorods were pre-prepared by basic precipitation from zinc acetate di-hydrate in the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide. They are about 50–300 nm in length and 10–50 nm in width. Transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDS), X-ray powder diffraction (XRD), UV–Vis spectroscopy, X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) were used to characterize the resulting Ag/ZnO nanocomposites.