Xin-Hui Zhou

Blue-yellow ZnO homostructural light-emitting diode realized by metalorganic chemical vapor deposition technique

We report on the realization of ZnO homojunction light-emitting diodes (LEDs) fabricated by metalorganic chemical vapor deposition on (0001) ZnO bulk substrate. The p-type ZnO epilayer was formed by nitrogen incorporation using N2O gas as oxidizing and doping sources. Distinct electroluminescence (EL) emissions in the blue and yellow regions were observed at room temperature by the naked eye under forward bias. The EL peak energy coincided with the photoluminescence peak energy of the ZnO epilayer, suggesting that the EL emissions emerge from the ZnO epilayer. In addition, the current-voltage and light output-voltage characteristics of ZnO homojunction LEDs have also been studied.

Lanthanide metal–organic frameworks assembled from a fluorene-based ligand: selective sensing of Pb2+ and Fe3+ ions

Fast and selective detection of heavy metal ions in the aqueous phase plays a key role in meeting human health and environmental concerns. Herein we report a series of fluorene-based lanthanide metal–organic frameworks ([Ln2(FDC)3DMA(H2O)3]·DMA·4.5H2O, Ln = Sm (1), Eu (2), Gd (3) and Tb (4), H2FDC = 9,9-dimethyl-2,7-fluorenedicarboxylic acid, DMA = dimethylacetamide). Single crystal X-ray diffraction reveals that 1–4 are isostructural and display a 3D neutral framework. 2 exhibits intense characteristic red emission of Eu3+ ions in the solid state and high selectivity for Pb2+ and Fe3+ ions through fluorescence enhancement and the quenching effect in aqueous solutions, respectively. Interestingly, the fluorescence intensity of 2 shows a good linear relationship with Pb2+ concentration in the range of 0.02–0.1 mM. Furthermore, the dynamic and static quenching constants are calculated to be 320 M−1 and 10 680 M−1 by the fluorescence lifetime and titration experiments in low concentration of Fe3+. In addition, 4 exhibits different fluorescence response behaviors in the presence of Sm3+ or Eu3+ in aqueous solution.

Dynamically Adaptive Characteristics of Resonance Variation for Selectively Enhancing Electrical Performance of Organic Semiconductors

Increased resonance: The selective tuning of the optoelectronic properties of organic semiconductors is possible by enantiotropic resonance variation. Using resonance forms of N(+)=P-O(-) in a series of arylamine-phosphine oxide hybrids afforded low-voltage-driven phosphorescent OLEDs with outstanding performances.

Rational design of metallophosphors with tunable aggregation-induced phosphorescent emission and their promising applications in time-resolved luminescence assay and targeted luminescence imaging of cancer cells

A series of Pt(II) complexes with different N⁁O ligands have been synthesized and characterized by NMR, mass spectroscopy, and X-ray diffraction studies. All complexes are non-emissive in dilute solution. Interestingly, they exhibit aggregation-induced phosphorescent emission (AIPE) with an absolute quantum efficiency of up to 38% in the crystal state. In addition, their AIPE properties can be tuned significantly by changing the chemical structures of N⁁O ligands. Furthermore, an AIPE mechanism of “restricted distortion of excited-state structure (RDES)” was proposed through experimental and theoretical investigations, which provided a rational design strategy for metallophosphors with tunable aggregation-induced phosphorescent emission. Considering their excellent emissive properties in aggregation state, the promising applications of these AIPE-active Pt(II) complexes in time-resolved luminescence assay utilizing the long emission lifetime of phosphorescent signal and targeted luminescence imaging of cancer cells have been demonstrated.

Dynamic response and hysteresis dispersion scaling of ferroelectric SrBi2Ta2O9 thin films

The dynamic hysteresis response of ferroelectric SrBi2Ta2O9 thin films versus periodically varying electric field over a frequency range of f=10−1–106 Hz and amplitude range of E0=15–158 kV/cm is measured utilizing the Sawyer–Tower method. The dynamic order parameter Q shows anomalous behavior against the field amplitude, and a single-peaked hysteresis dispersion is identified. The field response of hysteresis area 〈A〉 in the form of 〈A〉∝f2/3E02/3 over the low frequency range is evaluated, while the response over the high frequency range takes the form of 〈A〉∝f−1/3E02. We demonstrate that the hysteresis dispersion spectrum exhibits single-parameter scaling, and predicts a characteristic time for domain reversal that is inversely correlated to the field amplitude.

Syntheses, structures, photoluminescence, and magnetic properties of nanoporous 3D lanthanide coordination polymers with 4,4′-biphenyldicarboxylate ligand

Six three-dimensional nanoporous lanthanide coordination polymers, [Ln2(bpdc)3(HCOOH)2]n [Ln = Eu (1), Sm (2), La (3), Ce (4), Gd (5) and Nd (6)], were prepared by the solvothermal reactions of the LnIII ions with 4,4′-biphenyldicarboxylate (H2bpdc) in DMF solution. Crystallographic data show that compounds 1–6 are isomorphous and crystallize in monoclinic, space groupC2. Each LnIII is eight-coordinated to seven O atoms from six bpdc2− ligands and one O atom from HCOOH molecule in distorted bisdisphenoid coordination geometry. The adjacent LnIII ions are intraconnected by the carboxylate groups of the bpdc2− ligands to form a 1D inorganic rod-shaped chain [Ln(CO2)3]n. The inorganic chains are interconnected by the biphenyl groups, giving rise to a 3D framework that consists in two types of 1D open channels, with 15.11 × 27.05 A rhombic channels along the b axis and 8.66 × 15.91 A quadrate channels along the c axis without interpenetration. Compounds 1 and 6 are strong luminescent materials which exhibit characteristic EuIII emission bands in the visible region for 1 and NdIII emission bands in the near IR region for 6 upon excitation at 360 nm. The absence of the ligand emission can be ascribed to the energy transfer from the bpdc2− ligand to the LnIII ion during photoluminescence. The magnetic properties of compounds 1, 4, 5 and 6 have been investigated through the measurement of their magnetic susceptibilities over the temperature range of 1.8–300 K.

Guest-induced reversible structural transitions and concomitant on/off luminescence switching of an Eu(III) metal–organic framework and its application in detecting picric acid

We report a flexible metal–organic framework (MOF), (Me2NH2)3[Eu3(MHFDA)4(NO3)4(DMF)2]·4H2O·2MeCN (1) (H2MHFDA = 9-methyl-9-hydroxy-fluorene-2,7-dicarboxylic acid), which was synthesized by a hydrothermal method and structurally characterized. This MOF has a three-dimensional framework structure with one-dimensional rhombic channels and the framework can be reversibly transformed between two phases upon release/uptake of the guest molecules. The vacuum drying process is accompanied by the loss of luminescence of the MOF, while the luminescence is recovered upon resoaking in DMF. The potential of the material for PA sensing was studied in DMF through the luminescence quenching experiments, which elucidate that this material is a potential turn-off luminescent sensory material for the selective detection of PA.

Hydrothermal syntheses and structures of three novel coordination polymers assembled from 1,2,3-triazolate ligands

Three new coordination polymers with 1,2,3-triazolate ligands, [Cd3(ta)3Cl3]n (1), {[Cd3(ta)6]·6H2O}n (2) and [Cu6(ta)3I3]n (3) (Hta = 1,2,3-triazole), have been hydrothermally synthesized and structurally characterized. In complex 1, the Cd2+ and Cl− ions form a 3D [(Cd3Cl3)3+]n inorganic framework with (82.12)(4.8.10) topology while the Cd2+ ions and ta− ligands give a {[Cd3(ta)3]3+}n double helical chain. The two moieties are fused with each other by sharing “hinge” Cd2+ ions leading to a 3D organic–inorganic hybrid structure. The 3D porous metal–organic framework of complex 2 shows the topology of the diamond net with the Cd-centered CdCd4 tetrahedron units as the connecting nodes. The desolvated structure of 2 has 48% solvent accessible space of the total volume. Complex 3 is an undulating 1D organic–inorganic hybrid complex consisting of interesting discrete five-capped [Cu6I5]− triangular prism clusters and arched metallacycle [Cu6(ta)6I]+ moieties.

Direct silicon–nitrogen bonded host materials with enhanced σ–π conjugation for blue phosphorescent organic light-emitting diodes

Silicon-containing ultrahigh-energy gap hosts (UGHs) have emerged as important candidates of high-performance host materials with high thermal stability and triplet energy for blue phosphorescent organic light-emitting diodes (PhOLEDs). However, the highest occupied molecular orbital (HOMO) of these UGHs are generally too deep to support balanced hole injection and transportation in devices. Here, we propose a new design strategy of UGHs by multiple introduction of strong electron-donating and high-triplet-energy units of carbazoles into the electron-accepting arylsilanes in the N–Si–N structure. The facilely synthesized carbazole-arylsilanes in one-step show high thermal stability, triplet energy and charge mobilities with high-lying HOMOs due to enhanced σ–π conjugation in the N–Si–N structure as revealed by combined experimental and theoretical investigations. Impressively, blue PhOLEDs hosted by these novel N–Si–N bonded UGHs exhibit an improved maximum current efficiency up to 39.5 cd A−1, a power efficiency of 27.4 lm W−1, and an external quantum efficiency of 24.2%, demonstrating significant advances in the design of UGHs by adjusting the d-orbital participation of π-conjugation to enhance the σ–π conjugation in donor (D)–acceptor (A) molecular architectures.

Miniature spectrometer based on diffraction in a dispersive hole array.

We present an ultra-compact spectrometer that uses a 10×10 hole array as the dispersive component. Our analysis shows that the two-dimensional intensity distribution can be modeled by a system of simultaneous linear equations when the size of each hole in the dispersive component has been pre-designed appropriately. One can readily recover the spectral contents of the input radiation by solving the linear equation system with regularized procedure. Experimental results show that the reconstruction range is at least within the entire visible band, which can be further extended if a near-infrared CCD is used. One therefore envisions strong potential for many wavelength analysis applications.