Record-high near-band-edge optical nonlinearities and two-level model correction of poled polymers by spectroscopic electromodulation and ellipsometry

The determination of nonlinearities near the band edge of organic and polymeric electro-optic(EO)materials is important from the viewpoint of molecular nonlinear optics(NLO)and photonic device applications.Based on transmission-mode Stark effect electromodulation(EM)spectroscopy,we study the electric-field-induced changes in optical absorption and refraction of newly developed EO polymers from the visible to near-infrared(NIR)wavelengths and report record-high near-band-edge complex EO effects from poled thin films.Values ofΔn andΔk up to 10^-3 and 10^-2 are found at an applied electric field of 2.0×10⁵-3.0×10⁵V/cm.The study of linear optical properties of poled films by spectroscopic ellipsometry shows large polinginduced birefringence and a nearly two-fold increase in the extinction coefficients at the extraordinary polarization.Through the Kramers-Kronig analysis,we obtained the real and imaginary second-order nonlinear coefficients up to~3,500 and~5,600 pm/V,respectively,which are believed to be the highest NLO coefficients of poled polymers through the resonance enhancement.Our approach goes beyond the previous works,applicable only to several discrete wavelengths,to a full-spectral analysis with independent verification of slab waveguide measurements.By considering both the electroabsorption and electrorefraction effects,our study overcomes the limitation of the classic qualitative two-level model and provides a quantitative understanding of near-resonance optical nonlinearities of organic EO materials.It can inspire the exploration of high-speed,absorptive,or phase-shifting light-modulators using EO polymers for on-chip applications.     

超导磁共振仪器设备国产化现状及挑战

磁共振在化学分析和医学影像等领域发挥着不可或缺的作用，而磁共振仪器设备是开展磁共振研究的必要前提.长期以来，国外仪器厂商在我国磁共振仪器市场居于垄断地位.近年来，随着我国在磁共振仪器研发和产业化方面不断取得进展，市场份额为外商垄断的局面已大为改观.本文调研综述了我国磁共振仪器设备研制的现状，以及面临的若干挑战.     

Going Off the Grid: Iterative Model Selection for Biclustered Matrix Completion

We consider the problem of performing matrix completion with side information on row-by-row and column-by-column similarities. We build upon recent proposals for matrix estimation with smoothness constraints with respect to row and column graphs. We present a novel iterative procedure for directly minimizing an information criterion to select an appropriate amount of row and column smoothing, namely, to perform model selection. We also discuss how to exploit the special structure of the problem to scale up the estimation and model selection procedure via the Hutchinson estimator, combined with a stochastic Quasi-Newton approach. Supplementary material for this article is available online.     

Bis-tridentate IrIII Phosphors Bearing Two Fused Five-Six-Membered Metallacycles: A Strategy to Improved Photostability of Blue Emitters

Iridium complexes bearing chelating cyclometalates are popular choices as dopant emitters in the fabrication of organic light-emitting diodes (OLEDs). In this contribution, we report a series of blue-emitting, bis-tridentate Ir^III complexes bearing chelates with two fused five-six-membered metallacycles, which are in sharp contrast to the traditional designs of tridentate chelates that form the alternative, fused five-five metallacycles. Five Ir^III complexes, Px-21 – 23 , Cz-4 , and Cz-5 , have been synthesized that contain a coordinated dicarbene pincer chelate incorporating a methylene spacer and a dianionic chromophoric chelate possessing either a phenoxy or carbazolyl appendage to tune the coordination arrangement. All these tridentate chelates afford peripheral ligand–metal–ligand bite angles of 166–170°, which are larger than the typical bite angle of 153–155° observed for their five-five-coordinated tridentate counterparts, thereby leading to reduced geometrical distortion in the octahedral frameworks. Photophysical measurements and TD-DFT studies verified the inherent transition characteristics that give rise to high emission efficiency, and photodegradation experiments confirmed the improved stability in comparison with the benchmark fac-[Ir(ppy)₃] in degassed toluene at room temperature. Phosphorescent OLED devices were also fabricated, among which the carbazolyl-functionalized emitter Cz-5 exhibited the best performance among all the studied bis-tridentate phosphors, showing a maximum external quantum efficiency (EQE_max) of 18.7 % and CIE_x,y coordinates of (0.145, 0.218), with a slightly reduced EQE of 13.7 % at 100 cd m⁻² due to efficiency roll-off.     

Quantitative analysis of precious metals in automotive shredder residue/combustion residue via EDX fluorescence spectrometry

The recovery of precious metals from automotive shredder residue (ASR) dust/combustion residue is an option that is not usually considered due to the lack of available information. Therefore, before any disposal or recovery application can be considered, it is necessary to determine the significance of the levels and distribution of precious metal in ASR dust/ASR combustion residue. In the present study, quantitative analysis of precious metals (Pt, Pd, Au, Ag and Cu) in the ASR residue samples was performed using energy dispersive X-ray (EDX) fluorescence spectrometer. With the fundamental parameter (FP) method, the X-ray intensity is obtained and the quantitative analysis is performed using theoretical calculation. This method is very effective for quantitative analysis of unknown samples without standard samples. Further, in order to analyse the precious metal distribution within the ASR combustion residues, the microstructural characterisation and elemental mapping were also carried out with the aid of field emission scanning election microscopy combined with electron dispersive spectroscopy (FE-SEM EDS). Significant amount of Pt, Pd, Au, Ag and Cu element concentrations in the ASR residue were identified. Total precious (Pt, Pd, Au, Ag and Cu) metals obtainable values are representing about 12.23 wt% from its initial ASR dust/combustion residues. Considering their relevant concentrations, these metals should be properly recovered for recycling purposes before to dispose or landfill.     

Pincer‐Type Platinum(II) Complexes Containing N‐Heterocyclic Carbene (NHC) Ligand: Structures,Photophysical and Anion‐Binding Properties,and Anticancer Activities

Two classes of pincer‐type Pt^II complexes containing tridentate N‐donor ligands ( 1 – 8 ) or C‐deprotonated N^C^N ligands derived from 1,3‐di(2‐pyridyl)benzene ( 10 – 13 ) and auxiliary N‐heterocyclic carbene (NHC) ligand were synthesized. [Pt(trpy)(NHC)]²⁺ complexes 1 – 5 display green phosphorescence in CH₂Cl₂ (Φ: 1.1–5.3 %; τ: 0.3–1.0 μs) at room temperature. Moderate‐to‐intense emissions are observed for 1 – 7 in glassy solutions at 77 K and for 1 – 6 in the solid state. The [Pt(N^C^N)(NHC)]⁺ complexes 10 – 13 display strong green phosphorescence with quantum yields up to 65 % in CHCl₃. The reactions of 1 with a wide variety of anions were examined in various solvents. The tridentate N‐donor ligand of 1 undergoes displacement reaction with CN^? in protic solvents. Similar displacement of the N^C^N ligand by CN^? has been observed for 10 , leading to a luminescence “switch‐off” response. The water‐soluble 7 containing anthracenyl‐functionalized NHC ligand acts as a light “switch‐on” sensor for the detection of CN^? ion with high selectivity. The in vitro cytotoxicity of the Pt^II complexes towards HeLa cells has been evaluated. Complex 12 showed high cytotoxicity with IC₅₀ value of 0.46 μM , whereas 1 – 4 and 6 – 8 are less cytotoxic. The cellular localization of the strongly luminescent complex 12 traced by using emission microscopy revealed that it mainly localizes in the cytoplasmic structures rather than in the nucleus. This complex can induce mitochondria dysfunction and subsequent cell death.