Facile Atmospheric Pressure Synthesis of High Thermal Stability and Narrow-Band Red-Emitting SrLiAl3N4:Eu(2+) Phosphor for High Color Rendering Index White Light-Emitting Diodes.

Red phosphors (e.g., SrLiAl3N4:Eu(2+)) with high thermal stability and narrow-band properties are urgently explored to meet the next-generation high-power white light-emitting diodes (LEDs). However, to date, synthesis of such phosphors remains an arduous task. Herein, we report, for the first time, a facile method to synthesize SrLiAl3N4:Eu(2+) through Sr3N2, Li3N, Al, and EuN under atmospheric pressure. The as-synthesized narrow-band red-emitting phosphor exhibits excellent thermal stability, including small chromaticity shift and low thermal quenching. Intriguingly, the title phosphor shows an anomalous increase in theoretical lumen equivalent with the increase of temperature as a result of blue shift and band broadening of the emission band, which is crucial for high-power white LEDs. Utilizing the title phosphor, commercial YAG:Ce(3+), and InGaN-based blue LED chip, a proof-of-concept warm white LEDs with a color rendering index (CRI) of 91.1 and R9 = 68 is achieved. Therefore, our results highlight that this method, which is based on atmospheric pressure synthesis, may open a new means to explore narrow-band-emitting nitride phosphor. In addition, the underlying requirements to design Eu(2+)-doped narrow-band-emitting phosphors were also summarized.

Redox-active π-conjugated organometallic monolayers: pronounced Coulomb blockade characteristic at room temperature.

We report the electrical transport characteristics of a series of molecular wires, fc-C≡C-C6H4-SAc (fc = ferrocenyl; Ac = acetyl) and AcS-C6H4-C≡C-(fc)n-C≡C-C6H4-SAc (n = 2, 3), consisting of multiple redox-active ferrocenyl centers. The self-assembled monolayers of these molecular wires on Au surfaces were comprehensively characterized by electrochemistry and conductive atomic force microscopy techniques. Characterization of the wires revealed that electron transport is made extremely efficient by the organometallic redox states. There is a strong electronic coupling between ferrocenyl moieties, and superior electron-transport ability exists through these semirigid molecular wires. Standard rate constants for the electron transfer between the electrode and the ferrocenyl moieties were measured for the monolayers by a potential-step chronoamperometry technique. The electron conduction through the molecular wires was estimated using the monolayers as a bridge from the Au(111) metal surface to the gold tip of a conductive atomic force microscope (CAFM). Using the CAFM, Coulomb blockade behavior arising from the capacitive charging of the multinuclear redox-active molecules was observed at room temperature. The conductance switching was mediated by the presence of various ferrocenyl redox states and each current step corresponded to a specific redox state.

Enhanced recognition of single-base mismatch using locked nucleic acid-integrated hairpin DNA probes revealed by atomic force microscopy nanolithography.

Probe design is a critical parameter in successful DNA and RNA target detection. In this proof-of-concept study, we evaluated the single-base mismatch recognition power of surface immobilized and self-assembled stem-loop hairpin DNA oligonucleotide probes modified to contain locked nucleic acid residues (LNA-HP). The stiffness change in conjunction with the stem opening of the interfacial molecules before and after hybridization led to clear variations of the overall film thickness or miniaturized nanospot height, which could be directly measured using an atomic force microscopy (AFM) nanolithography technique. Particularly, LNA-HP achieved highly differentiable readouts between perfectly complementary and singly mismatched targets (discrimination ratio as high as 2 to 3), outperforming the selectivity of its linear and hairpin counterparts with no LNA modification.

Tracking the chemistry of unsaturated C3H3 groups adsorbed on a silver surface: propargyl-allenyl-acetylide triple bond migration, self-hydrogenation, and carbon-carbon bond formation.

A diverse array of unsaturated C1 (methylene and methylidyne) and C2 (vinyl, vinylidene, ethylidene, and ethylidyne) bound to metal center(s) and surfaces has received much attention. In sharp contrast to the effort devoted to C1 and C2 ligands, complexes or surfaces bearing C3 fragments have been less explored, especially the M-C3H3 systems, which include propargyl (M-CH2C[triple bond]CH), allenyl (M-CH=C=CH2), and acetylide (M-C[triple bond]CCH3) forms. To understand the bonding and reactivity of these C3 species appended to an extended metal structure, proprargyl bromide (Br-CH2C[triple bond]CH) was utilized as a precursor to generate C3H3 fragments on a Ag(111) surface under ultrahigh vacuum conditions. The molecular transformation process was explored by a combination of temperature-programmed desorption (TPD), reflection absorption infrared spectroscopy (RAIRS), and X-ray photoemission spectroscopy (XPS) techniques. In addition, density functional theory (DFT) calculations were conducted to obtain the optimized geometries and energies for the various surface intermediates. The computed IR spectra facilitated the vibrational mode assignments. TPD spectra show that C3H3(ad) self-hydrogenates to C3H4 around 300 and 475 K, respectively. In addition to hydrogenation, a C-C coupling product C6H6 (2,4-hexadiyne) is also unveiled as part of the desorption feature at 475 K. Identification of the possible C3H4 isomers (propyne and/or allene) was equivocal, but it was circumvented by using an alpha,alpha-dimethyl-substituted propargylic species--(CH3)2(alpha)C-C[triple bond]CH, which results in hydrogenation products, alkynic (CH3)2CH-C[triple bond]CH and allenic (CH3)2C=C=CH2, distinguishable by the mass spectrometry. The substitution experiments clarify that in the normal case the convoluted TPD feature around 300 K, in fact, consists of both allene at 260 K and propyne at 310 K, while the last hydrogenation product at 475 K is solely propyne. The RAIR spectroscopy demonstrates that at 200 K C3H3(ad) on Ag(111) readily adopts the allenyl formalism involving concerted CBr bond scission and [1,3]-sigmatropic migration (i.e., Br-*CH2C[triple bond]CH --> *CH2=C=CH-Ag), in which the sigma bond moves to a new metal location across the pi-periphery. Single hydrogen incorporation to the alpha-carbon of the surface allenyl rationalizes the allene formation at 260 K. When the surface is heated to the range of 250-300 K, both RAIR and XP spectra reveal drastic changes, indicative of a new species whose spectral characteristics could be duplicated by separate measurements from 1-propyn-1-yl iodide (CH3-C[triple bond]C-I) being a direct source for the surface methylacetylide (CH3-C[triple bond]C-Ag). It is thus suggested that allenyl is further reorganized to render acetylide presumably via [1,3]-hydrogen shift (i.e., *CH2=C=CH-Ag --> *CH3=C[triple bond]C-Ag). The presence of this third Ag-C3H3 isomeric form demonstrates an unprecedented propargyl-allenyl-acetylide multiple rearrangements on a metal surface. Migration of the triple bond from the remote terminal position into the chain, through the stage of allenic structure, is driven by thermodynamic stabilities, supported by the DFT total energy calculations. Consequently, the evolutions of propyne at 310 and 475 K, as well as 2,4-hexadiyne (bismethylacetylide), can all be reasoned out.