Phosphorescence and donor-acceptor pair recombination in laboratory-grown diamonds

Intense "blue-green" phosphorescence is commonly observed in near colourless lab-grown high-pressure high-temperature (HPHT) diamonds following optical excitation at or above the indirect bandgap. We have employed a holistic combination of optically-excited time-resolved techniques (in addition to standard spectroscopic characterisation techniques) to study the physics of this long-lived phosphorescence and understand luminescence-related charge transfer processes. It is shown that the properties of the broad "blue-green" luminescence and phosphorescence band can be fully explained by emission from neutral substitutional nitrogen-boron donor-acceptor pairs ($\text{N}_\text{S}^0$...$\text{B}_\text{S}^0$) , once the configurational change between charge states is considered, and both tunneling between defects and thermal ionization of donors and acceptors is considered. Significant concentrations of metastable $\text{N}_\text{S}^-$, are identified after optical excitation at or above the indirect bandgap. $\text{N}_\text{S}^-$ is much shallower ($\sim$0.2 eV) than previously thought and plays a key role in resetting the $\text{N}_\text{S}^0$...$\text{B}_\text{S}^0$ donor-acceptor pairs.Comment: 15 pages, 13 figure

All-optical hyperpolarization of electron and nuclear spins in diamond

Low thermal polarization of nuclear spins is a primary sensitivity limitation for nuclear magnetic resonance. Here we demonstrate optically pumped (microwave-free) nuclear spin polarization of $^{13}\mathrm{C}$ and $^{15}\mathrm{N}$ in $^{15}\mathrm{N}$-doped diamond. $^{15}\mathrm{N}$ polarization enhancements up to $-2000$ above thermal equilibrium are observed in the paramagnetic system $\mathrm{N_s}^{0}$. Nuclear spin polarization is shown to diffuse to bulk $^{13}\mathrm{C}$ with NMR enhancements of $-200$ at room temperature and $-500$ at $\mathrm{240~K}$, enabling a route to microwave-free high-sensitivity NMR study of biological samples in ambient conditions.Comment: 5 pages, 5 figure

Controlling palladium morphology in electrodeposition from nanoparticles to dendrites via the use of mixed solvents

By changing the mole fraction of water (χwater) in the solvent acetonitrile (MeCN), we report a simple procedure to control nanostructure morphology during electrodeposition. We focus on the electrodeposition of palladium (Pd) on electron beam transparent boron-doped diamond (BDD) electrodes. Three solutions are employed, MeCN rich (90% v/v MeCN, χwater = 0.246), equal volumes (50% v/v MeCN, χwater = 0.743) and water rich (10% v/v MeCN, χwater = 0.963), with electrodeposition carried out under a constant, and high overpotential (−1.0 V), for fixed time periods (50, 150 and 300 s). Scanning transmission electron microscopy (STEM) reveals that in MeCN rich solution, Pd atoms, amorphous atom clusters and (majority) nanoparticles (NPs) result. As water content is increased, NPs are again evident but also elongated and defected nanostructures which grow in prominence with time. In the water rich environment, NPs and branched, concave and star-like Pd nanostructures are now seen, which with time translate to aggregated porous structures and ultimately dendrites. We attribute these observations to the role MeCN adsorption on Pd surfaces plays in retarding metal nucleation and growth

Laser spectroscopy of NV- and NV0 colour centres in synthetic diamond

In this paper, we analyse the prospects for using nitrogen-vacancy centre (NV) containing diamond as a laser gain material by measuring its key laser related parameters. Synthetic chemical vapour deposition grown diamond samples with an NV concentration of ~1 ppm have been selected because of their relatively high NV concentration and low background absorption in comparison to other samples available to us. For the samples measured, the luminescence lifetimes of the NV- and NV0 centres were measured to be 8±1 ns and 20±1 ns respectively. The respective peak stimulated emission cross-sections were (3.6±0.1)×10-17 cm2 and (1.7±0.1)×10-17 cm2. These measurements were combined with absorption measurements to calculate the gain spectra for NV- and NV0 for differing inversion levels. Such calculations indicate that gains approaching those required for laser operation may be possible with one of the samples tested and for the NV- centre

A closed bipolar electrochemical cell for the interrogation of BDD single particles : electrochemical advanced oxidation

A closed bipolar electrochemical cell containing two conductive boron-doped diamond (BDD) particles of size ∼ 250 – 350 μm, produced by high-pressure high-temperature (HPHT) synthesis, has been used to demonstrate the applicability of single BDD particles for electrochemical oxidative degradation of the dye, methylene blue (MB). The cell is fabricated using stereolithography 3D printing and the BDD particles are located at either end of a solution excluded central channel. Platinum wire electrodes placed in each of the two outer solution compartments are used to drive electrochemical reactions at the two BDD particles, which, under bipolar conditions do not require direct electrical connection to a potential source. Experiments using ultra high-performance liquid chromatography coupled with mass spectrometry (UHPLC-MS) show that the anodic pole BDD particle is able to electrochemically remove > 99 % of the dye (originally present at 1 × 10−4 M) to undetectable UHPLC-MS products in 600 s. Monitoring of the time dependant change in MB peak area, from the UHPLC chromatograms, enables a pseudo first order rate constant of 0.54 min−1 to be determined for MB removal. Given the large scale at which such particles can be produced (tonnes), such data bodes well for scale up opportunities using HPHT-grown BDD particles, where the particles can be assembled into high surface area electrode formats

Long Spin Coherence and Relaxation Times in Nanodiamonds Milled from Polycrystalline 12^{12}C Diamond

The negatively charged nitrogen-vacancy centre (NV$^-$) in diamond has been utilized in a wide variety of sensing applications. The centre's long spin coherence and relaxation times ($T_2^*$, $T_2$ and $T_1$) at room temperature are crucial to this, as they often limit sensitivity. Using NV$^-$ centres in nanodiamonds allows for operations in environments inaccessible to bulk diamond, such as intracellular sensing. We report long spin coherence and relaxation times at room temperature for single NV$^-$ centres in isotopically-purified polycrystalline ball-milled nanodiamonds. Using a spin-locking pulse sequence, we observe spin coherence times, $T_2$, up 786 $\pm$ 200 $\mu$s. We also measure $T_2^*$ times up to 2.06 $\pm$ 0.24 $\mu$s and $T_1$ times up to 4.32 $\pm$ 0.60 ms. Scanning electron microscopy and atomic force microscopy measurements show that the diamond containing the NV$^{-}$ centre with the longest $T_1$ time is smaller than 100 nm. EPR measurements give an N$_{s}$$^{0}$ concentration of 0.15 $\pm$ 0.02 ppm for the nanodiamond sample.Comment: 13 pages, 3 figure

Electron paramagnetic resonance for the detection of electrochemically generated hydroxyl radicals : issues associated with electrochemical oxidation of the spin trap

For the detection of electrochemically produced hydroxyl radicals (HO·) from the oxidation of water on a boron-doped diamond (BDD) electrode, electron paramagnetic resonance spectroscopy (EPR) in combination with spin trap labels is a popular technique. Here, we show that quantification of the concentration of HO· from water oxidation via spin trap electrochemical (EC)-EPR is problematic. This is primarily due to the spin trap oxidizing at potentials less positive than water, resulting in the same spin trap-OH· adduct as formed from the solution reaction of OH· with the spin trap. We illustrate this through consideration of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a spin trap for OH·. DMPO oxidation on a BDD electrode in an acidic aqueous solution occurs at a peak current potential of +1.90 V vs SCE; the current for water oxidation starts to rise rapidly at ca. +2.3 V vs SCE. EC-EPR spectra show signatures due to the spin trap adduct (DMPO-OH·) at potentials lower than that predicted thermodynamically (for water/HO·) and in the region for DMPO oxidation. Increasing the potential into the water oxidation region, surprisingly, shows a lower DMPO-OH· concentration than when the potential is in the DMPO oxidation region. This behavior is attributed to further oxidation of DMPO-OH·, production of fouling products on the electrode surface, and bubble formation. Radical scavengers (ethanol) and other spin traps, here N-tert-butyl-α-phenylnitrone, α-(4-pyridyl N-oxide)-N-tert-butylnitrone, and 2-methyl-2-nitrosopropane dimer, also show electrochemical oxidation signals less positive than that of water on a BDD electrode. Such behavior also complicates their use for the intended application

Childhood socioeconomic position and objectively measured physical capability levels in adulthood: a systematic review and meta-analysis

<p><b>Background:</b> Grip strength, walking speed, chair rising and standing balance time are objective measures of physical capability that characterise current health and predict survival in older populations. Socioeconomic position (SEP) in childhood may influence the peak level of physical capability achieved in early adulthood, thereby affecting levels in later adulthood. We have undertaken a systematic review with meta-analyses to test the hypothesis that adverse childhood SEP is associated with lower levels of objectively measured physical capability in adulthood.</p> <p><b>Methods and Findings:</b> Relevant studies published by May 2010 were identified through literature searches using EMBASE and MEDLINE. Unpublished results were obtained from study investigators. Results were provided by all study investigators in a standard format and pooled using random-effects meta-analyses. 19 studies were included in the review. Total sample sizes in meta-analyses ranged from N = 17,215 for chair rise time to N = 1,061,855 for grip strength. Although heterogeneity was detected, there was consistent evidence in age adjusted models that lower childhood SEP was associated with modest reductions in physical capability levels in adulthood: comparing the lowest with the highest childhood SEP there was a reduction in grip strength of 0.13 standard deviations (95% CI: 0.06, 0.21), a reduction in mean walking speed of 0.07 m/s (0.05, 0.10), an increase in mean chair rise time of 6% (4%, 8%) and an odds ratio of an inability to balance for 5s of 1.26 (1.02, 1.55). Adjustment for the potential mediating factors, adult SEP and body size attenuated associations greatly. However, despite this attenuation, for walking speed and chair rise time, there was still evidence of moderate associations.</p> <p><b>Conclusions:</b> Policies targeting socioeconomic inequalities in childhood may have additional benefits in promoting the maintenance of independence in later life.</p&gt

Using ecological and field survey data to establish a national list of the wild bee pollinators of crops

The importance of wild bees for crop pollination is well established, but less is known about which species contribute to service delivery to inform agricultural management, monitoring and conservation. Using sites in Great Britain as a case study, we use a novel qualitative approach combining ecological information and field survey data to establish a national list of crop pollinating bees for four economically important crops (apple, field bean, oilseed rape and strawberry). A traits data base was used to establish potential pollinators, and combined with field data to identify both dominant crop flower visiting bee species and other species that could be important crop pollinators, but which are not presently sampled in large numbers on crops flowers. Whilst we found evidence that a small number of common, generalist species make a disproportionate contribution to flower visits, many more species were identified as potential pollinators, including rare and specialist species. Furthermore, we found evidence of substantial variation in the bee communities of different crops. Establishing a national list of crop pollinators is important for practitioners and policy makers, allowing targeted management approaches for improved ecosystem services, conservation and species monitoring. Data can be used to make recommendations about how pollinator diversity could be promoted in agricultural landscapes. Our results suggest agri-environment schemes need to support a higher diversity of species than at present, notably of solitary bees. Management would also benefit from targeting specific species to enhance crop pollination services to particular crops. Whilst our study is focused upon Great Britain, our methodology can easily be applied to other countries, crops and groups of pollinating insects.LH was funded by NERC QMEE CDT. EJB was funded by a BBSRC Ph.D. studentship under grant BB/F016581/1. LB was was supported by the Scholarship Program of the German Federal Environmental Foundation (Deutsche Bundesstiftung Umwelt, DBU, AZ 20014/302). AJC was funded by the BBSRC and Syngenta UK as part of a case award Ph.D. (grant no. 1518739). AE was funded by the Swiss National Science Foundation (grant number 405940-115642). DG and A-MK were funded by grant PCIN2014-145-C02-02 (MinECo; EcoFruit project BiodivERsA-FACCE2014-74). MG was supported by Establishing a UK Pollinator Monitoring and Research Partnership (PMRP) a collaborative project funded by Defra, the Welsh and Scottish Governments, JNCC and project partners’. GAdG was funded via research projects BO-11-011.01-051 and BO-43-011.06-007, commissioned by the Dutch Ministry of Agriculture, Nature and Food Quality. DK was funded by the Dutch Ministry of Economic Affairs (BO-11-011.01-011). AK-H was funded by the NKFIH project (FK123813), the Bolyai János Fellowship of the MTA, the ÚNKP-19-4-SZIE-3 New National Excellence Program of the Ministry for Innovation and Technology, and together with RF by the Hungarian Scientific Research Fund OTKA 101940. MM was funded by Waitrose & Partners, Fruition PO, and the University of Worcester. MM was funded by grant INIA-RTA2013-00139-C03-01 (MinECo and FEDER). BBP and RFS were funded by the UK Natural Environment Research Council as part of Wessex BESS (ref. NE/J014680/1). NJV was funded by the Walloon Region (Belgium) Direction générale opérationnelle de l’Agriculture, des Ressources naturelles et de l’Environnement (DGO3) for the "Modèle permaculturel" project on biodiversity in micro-farms, FNRS/FWO joint programme EOS — Excellence Of Science CliPS: Climate change and its impact on Pollination Services (project 30947854)". CW was funded by the Deutsche Forschungsgemeinschaft (DFG) (Project number 405945293). BW was funded by the Natural Environment Research Council (NERC) under research programme NE/N018125/1 ASSIST – Achieving Sustainable Agricultural Systems www.assist.ceh.ac.uk. TB and TO are supported by BBSRC, NERC, ESRC and the Scottish Government under the Global Food Security Programme (Grant BB/R00580X/1)