Boron clusters in luminescent materials

In recent times, luminescent materials with tunable emission properties have found applications in almost all aspects of modern material sciences. Any discussion on the recent developments in luminescent materials would be incomplete if one does not account for the versatile photophysical features of boron containing compounds. Apart from triarylboranes and tetra-coordinate borate dyes, luminescent materials consisting of boron clusters have also found immense interest in recent times. Recent studies have unveiled the opportunities hidden within boranes, carboranes and metalloboranes, etc. as active constituents of luminescent materials. From simple illustrations of luminescence, to advanced applications in LASERs, OLEDs and bioimaging, etc., the unique features of such compounds and their promising versatility have already been established. In this review, recent revelations about the excellent photophysical properties of such materials are discussed.

Stimuli and shape responsive `boron-containing' luminescent organic materials

Recent advancements of material science and its applications have been immensely influenced by the modern development of organic luminescent materials. Among all organic luminogens, boron containing compounds have already established their stature as one of the indispensable classes of luminescent dyes. Boron, in its various forms e. g. triarylboranes, borate dyes and boron clusters, has attracted considerable attention owing to its several unique and excellent photophysical features. In very recent times, beyond the realms of solution-state studies, luminescent boron-containing compounds have emerged as a large and versatile class of stimuli responsive materials. Based on several fundamental concepts of chemistry, researchers have come up with an admirable variety of boron-containing materials with AIE (aggregation-induced emission), mechano-responsive luminescence, thermoresponsive-luminescence as well as a number of purely organic phosphorescent materials and other standalone examples. The unique chemical as well as physical properties of boron-containing compounds are largely responsible for the development of such materials. In this review these new findings are brought together.

Efficient Gate-tunable light-emitting device made of defective boron nitride nanotubes: from ultraviolet to the visible

Boron nitride is a promising material for nanotechnology applications due to its two-dimensional graphene-like, insulating, and highly-resistant structure. Recently it has received a lot of attention as a substrate to grow and isolate graphene as well as for its intrinsic UV lasing response. Similar to carbon, one-dimensional boron nitride nanotubes (BNNTs) have been theoretically predicted and later synthesised. Here we use first principles simulations to unambiguously demonstrate that i) BN nanotubes inherit the highly efficient UV luminescence of hexagonal BN; ii) the application of an external perpendicular field closes the electronic gap keeping the UV lasing with lower yield; iii) defects in BNNTS are responsible for tunable light emission from the UV to the visible controlled by a transverse electric field (TEF). Our present findings pave the road towards optoelectronic applications of BN-nanotube-based devices that are simple to implement because they do not require any special doping or complex growth

A balloon measurement of the isotopic composition of galactic cosmic ray boron, carbon, and nitrogen

The isotopic compositions of galactic cosmic ray boron, carbon, and nitrogen have been measured at energies near 300 MeV amu^-1, using a balloon-borne instrument at an atmospheric depth of ~5 g cm^-2. The calibrations of the detectors comprising the instrument are described. The saturation properties of the cesium iodide scintilla tors used for measurement of particle energy are studied in the context of analyzing the data for mass. The achieved rms mass resolution varies from ~ 0.3 amu at boron to ~ 0.5 amu at nitrogen, consistent with a theoretical analysis of the contributing factors. Corrected for detector interactions and the effects of the residual atmosphere, the results are ^(10)B/B = 0.33^(+0.17)_(-0.11), ^(13)C/C = 0.06^(+0.13)_(-0.01), and ^(15)N/N = 0.42 (+0.19)_(-0.17). A model of galactic propagation and solar modulation is described. Assuming a cosmic ray source composition of solar-like isotopic abundances, the model predicts abundances near earth consistent with the measurements.

Triel Bonds, pi-Hole-pi-Electrons Interactions in Complexes of Boron and Aluminium Trihalides and Trihydrides with Acetylene and Ethylene

MP2/aug-cc-pVTZ calculations were performed on complexes of aluminium and boron trihydrides and trihalides with acetylene and ethylene. These complexes are linked through triel bonds where the triel center (B or Al) is characterized by the Lewis acid properties through its -hole region while -electrons of C2H2 or C2H4 molecule play the role of the Lewis base. Some of these interactions possess characteristics of covalent bonds, i.e., the Al--electrons links as well as the interaction in the BH3-C2H2 complex. The triel--electrons interactions are classified sometimes as the 3c-2e bonds. In the case of boron trihydrides, these interactions are often the preliminary stages of the hydroboration reaction. The Quantum Theory of Atoms in Molecules as well as the Natural Bond Orbitals approach are applied here to characterize the -hole--electrons interactions.

Mechanical and tribological properties of epitaxial cubic boron nitride thin films grown on diamond

电子邮箱nataliya.deyneka@uni-ulm.de

Comparison and combination of several stress relief methods for cubic boron nitride films deposited by ion beam assisted deposition

Cubic boron nitride (c-BN) films were prepared by ion beam assisted deposition (IBAD) technique, and the stresses were primary estimated by measuring the frequency shifts in the infrared-absorption peaks of c-BN samples. To test the possible effects of other factors, dependencies of the c-BN transversal optical mode position on film thickness and c-BN content were investigated. Several methods for reducing the stress of c-BN films including annealing, high temperature deposition, two-stage process, and the addition of a small amount of Si were studied, in which the c-BN films with similar thickness and cubic phase content were used to evaluate the effects of the various stress relief methods. It was shown that all the methods can reduce the stress in c-BN films to various extents. Especially, the incorporation of a small amount of Si (2.3 at.%) can result in a remarkable stress relief from 8.4 to similar to 3.6 GPa whereas the c-BN content is nearly unaffected, although a slight degradation of the c-BN crystallinity is observed. The stress can be further reduced down below I GPa by combination of the addition of Si with the two-stage deposition process. (c) 2008 Elsevier B.V. All rights reserved.

Effects of crystalline quality on the phase stability of cubic boron nitride thin films under medium-energy ion irradiation

To investigate the effect of radiation damage on the stability and the compressive stress of cubic boron nitride (c-BN) thin films, c-BN films with various crystalline qualities prepared by dual beam ion assisted deposition were irradiated at room temperature with 300 keV Ar+ ions over a large fluence range up to 2 x 10(16) cm(-2). Fourier transform infrared spectroscopy (FTIR) data were taken before and after each irradiation step. The results show that the c-BN films with high crystallinity are significantly more resistant against medium-energy bombardment than those of lower crystalline quality. However, even for pure c-BN films without any sp(2)-bonded BN, there is a mechanism present, which causes the transformation from pure c-BN to h-BN or to an amorphous BN phase. Additional high resolution transmission electron microscopy (HRTEM) results support the conclusion from the FTIR data. For c-BN films with thickness smaller than the projected range of the bombarding Ar ions, complete stress relaxation was found for ion fluences approaching 4 x 10(15) cm(-2). This relaxation is accompanied, however, by a significant increase of the width of c-BN FTIR TO-line. This observation points to a build-up of disorder and/or a decreasing average grain size due to the bombardment. (c) 2005 Elsevier B.V. All rights reserved.

Enhancement of boron removal in treatment of spent rinse from a plating operation using RO

Boron removal is a critical issue in the production of drinking water and of ultra-pure water in the electronics industry. Boron rejection in a RO process is typically in the range of 40-60%. The objective of this study was to distinguish the factor contributing to enhanced boron rejection in reclamation of a spent rinse stream from a plating operation. The effects of different known components used in the feed on boron removal were investigated in the laboratory. The results indicated that glycolic acid and antifoulants could not individually enhance boron rejection in a RO process. A high boron rejection of 95% was achieved as the concentration of iron in the feed was 10 times higher than that of boron, which might be due to formation of a complex between iron oxide and boron. The finding was confirmed in a pilot study.

Locating hexagonal and cubic phases in boron nitride using wavelength-selective optically detected x-ray absorption spectroscopy

Locating hexagonal and cubic phases in boron nitride using wavelength-selective optically detected x-ray absorption spectroscopy, D.A. Evans, A.R. Vearey-Roberts, N.R.J. Poolton Appl Phys Lett 89, (2006) 161107

Determination of the optical band-gap energy of cubic and hexagonal boron nitride using luminescence excitation spectroscopy

Sponsorship: EPSRC, STFC

Synchrotron-laser interactions in hexagonal boron nitride: an examination of charge trapping dynamics at the boron K-edge

Poolton, Nigel; Towlson, B.M.; Hamilton, B.; Evans, D.A., (2006) 'Synchrotron-laser interactions in hexagonal boron nitride: an examination of charge trapping dynamics at the boron K-edge', New Journal of Physics 8 pp.76 RAE2008

Stereocomplexed poly(lactic acid)-poly(ethylene glycol) nanoparticles with dual-emissive boron dyes for tumor accumulation.

Responsive biomaterials play important roles in imaging, diagnostics, and therapeutics. Polymeric nanoparticles (NPs) containing hydrophobic and hydrophilic segments are one class of biomaterial utilized for these purposes. The incorporation of luminescent molecules into NPs adds optical imaging and sensing capability to these vectors. Here we report on the synthesis of dual-emissive, pegylated NPs with "stealth"-like properties, delivered intravenously (IV), for the study of tumor accumulation. The NPs were created by means of stereocomplexation using a methoxy-terminated polyethylene glycol and poly(D-lactide) (mPEG-PDLA) block copolymer combined with iodide-substituted difluoroboron dibenzoylmethane-poly(L-lactide) (BF2dbm(I)PLLA). Boron nanoparticles (BNPs) were fabricated in two different solvent compositions to study the effects on BNP size distribution. The physical and photoluminescent properties of the BNPs were studied in vitro over time to determine stability. Finally, preliminary in vivo results show that stereocomplexed BNPs injected IV are taken up by tumors, an important prerequisite to their use as hypoxia imaging agents in preclinical studies.

Boron and strontium isotopic characterization of coal combustion residuals: validation of new environmental tracers.

In the U.S., coal fired power plants produce over 136 million tons of coal combustion residuals (CCRs) annually. CCRs are enriched in toxic elements, and their leachates can have significant impacts on water quality. Here we report the boron and strontium isotopic ratios of leaching experiments on CCRs from a variety of coal sources (Appalachian, Illinois, and Powder River Basins). CCR leachates had a mostly negative δ(11)B, ranging from -17.6 to +6.3‰, and (87)Sr/(86)Sr ranging from 0.70975 to 0.71251. Additionally, we utilized these isotopic ratios for tracing CCR contaminants in different environments: (1) the 2008 Tennessee Valley Authority (TVA) coal ash spill affected waters; (2) CCR effluents from power plants in Tennessee and North Carolina; (3) lakes and rivers affected by CCR effluents in North Carolina; and (4) porewater extracted from sediments in lakes affected by CCRs. The boron isotopes measured in these environments had a distinctive negative δ(11)B signature relative to background waters. In contrast (87)Sr/(86)Sr ratios in CCRs were not always exclusively different from background, limiting their use as a CCR tracer. This investigation demonstrates the validity of the combined geochemical and isotopic approach as a unique and practical identification method for delineating and evaluating the environmental impact of CCRs.