Boron doped diamond synthesized from detonation nanodiamond in a C-O-H fluid at high pressure and high temperature

X-ray Excited Optical Luminescence of Eu in Diamond Crystals Synthesized at High Pressure High Temperature

Powder diamonds with integrated europium atoms were synthesized at high pressure (7.7 GPa) and temperature (1800 °C) from a mixture of pentaerythritol with pyrolyzate of diphthalocyanine (C₆₄H₃₂N₁₆Eu) being a special precursor. In diamonds prepared by X-ray fluorescence spectroscopy, we have found a concentration of Eu atoms of 51 ± 5 ppm that is by two orders of magnitude greater than that in natural and synthetic diamonds. X-ray diffraction, SEM, X-ray exited optical luminescence, and Raman and IR spectroscopy have confirmed the formation of high-quality diamond monocrystals containing Eu and a substantial amount of nitrogen (~500 ppm). Numerical simulation has allowed us to determine the energy cost of 5.8 eV needed for the incorporation of a single Eu atom with adjacent vacancy into growing diamond crystal (528 carbons).

A Review of Binderless Polycrystalline Diamonds: Focus on the High-Pressure-High-Temperature Sintering Process

Nowadays, synthetic diamonds are easy to fabricate industrially, and a wide range of methods were developed during the last century. Among them, the high-pressure-high-temperature (HP-HT) process is the most used to prepare diamond compacts for cutting or drilling applications. However, these diamond compacts contain binder, limiting their mechanical and optical properties and their substantial uses. Binderless diamond compacts were synthesized more recently, and important developments were made to optimize the P-T conditions of sintering. Resulting sintered compacts had mechanical and optical properties at least equivalent to that of natural single crystal and higher than that of binder-containing sintered compacts, offering a huge potential market. However, pressure-temperature (P-T) conditions to sinter such bodies remain too high for an industrial transfer, making this the next challenge to be accomplished. This review gives an overview of natural diamond formation and the main experimental techniques that are used to synthesize and/or sinter diamond powders and compact objects. The focus of this review is the HP-HT process, especially for the synthesis and sintering of binderless diamonds. P-T conditions of the formation and exceptional properties of such objects are discussed and compared with classic binder-diamonds objects and with natural single-crystal diamonds. Finally, the question of an industrial transfer is asked and outlooks related to this are proposed.

Fabrication of a boron-doped nanocrystalline diamond grown on an WC–Co electrode for degradation of phenol

Cemented carbide (WC–Co) is applied as the substrate instead of conventional ones such as Si, Ti, and Nb, on which nanocrystalline BDD films are deposited by hot filament chemical vapor deposition. Then the WC–Co/BDD electrodes are investigated by Field Emission Scanning Electron Microscopy (FE-SEM), Micro-Raman Spectroscopy, X-ray photoelectron spectroscopy (XPS), a four-point probe method, accelerated life test (ALT), and electrochemical analysis. According to the results, the BDD films deposited on the WC–Co substrate are highly uniform and pinhole-free with a grain size of 100 nm and a low compressive stress. The WC–Co/BDD electrode has a wide potential window of 3.8 V and low background currents in 0.5 mol L⁻¹ H₂SO₄ electrolytes and shows a quasi-reversible behavior in the K₃[Fe(CN)₆] redox system. The electrode has a service life of more than 400 h in the ALT with 3 mol L⁻¹ H₂SO₄ electrolytes at a constant current density of 1 A cm⁻². These electrochemical performances of BDD films on the WC–Co substrate is similar to or even slightly better than that on the commonly used substrates. Finally, phenol is used as a pollutant to test the activity of the WC–Co/BDD electrode. The results of replicated experiments show that the average COD reduces from the initial 5795 to 85 mg L⁻¹, and the average current efficiency is about 46%. This suggests that the WC–Co/BDD electrode has a good mineralization capacity in phenol with a high concentration.

WC–Co is applied as the substrate instead of conventional ones, on which nanocrystalline BDD films are deposited by HFCVD. WC–Co/BDD electrode like the standard BDD shows a wide potential window and a good mineralization capacity in phenol.

High-Quality Green-Emitting Nanodiamonds Fabricated by HPHT Sintering of Polycrystalline Shockwave Diamonds

We demonstrate a high-pressure, high-temperature sintering technique to form nitrogen-vacancy-nitrogen centres in nanodiamonds. Polycrystalline diamond nanoparticle precursors, with mean size of 25 nm, are produced by the shock wave from an explosion. These nanoparticles are sintered in the presence of ethanol, at a pressure of 7 GPa and temperature of 1300 °C, to produce substantially larger (3-4 times) diamond crystallites. The recorded spectral properties demonstrate the improved crystalline quality. The types of defects present are also observed to change; the characteristic spectral features of nitrogen-vacancy and silicon-vacancy centres present for the precursor material disappear. Two new characteristic features appear: (1) paramagnetic substitutional nitrogen (P1 centres with spin ½) with an electron paramagnetic resonance characteristic triplet hyperfine structure due to the I = 1 magnetic moment of the nitrogen nuclear spin and (2) the green spectral photoluminescence signature of the nitrogen-vacancy-nitrogen centres. This production method is a strong alternative to conventional high-energy particle beam irradiation. It can be used to easily produce purely green fluorescing nanodiamonds with advantageous properties for optical biolabelling applications.

High pressure: a feasible tool for the synthesis of unprecedented inorganic compounds

After a simple classification of inorganic materials synthesized at high-temperature and high-pressure, this tutorial reviews the important research results in the field of high-temperature and high-pressure inorganic synthesis in the past 5 years.

Photoluminescence from NV- Centres in 5 nm Detonation Nanodiamonds: Identification and High Sensitivity to Magnetic Field

The content of nitrogen-vacancy (NV^-) colour centres in the nanodiamonds (DNDs) produced during the detonation of nitrogen-containing explosives was found to be 1.1 ± 0.3 ppm. This value is impressive for nanodiamonds of size < 10 nm with intentionally created NV^- centres. The concentration was estimated from the electron paramagnetic resonance as determined from the integrated intensity of the g = 4.27 line. This line is related with "forbidden" ∆m_s = 2 transitions between the Zeeman levels of a NV^- centre's ground triplet state. Confocal fluorescence microscopy enables detection of the red photoluminescence (PL) of the NV^- colour centres in nanoscale DND aggregates formed from the 5-nm nanoparticles. Subwavelength emitters consisting of NV^- with sizes a few times smaller than the diffraction-limited spot are clearly distinguished. We have further observed an abrupt drop in the PL intensity when mixing and anti-crossing of the ground and excited states spin levels in NV^- occurs under an applied external magnetic field. This effect is a unique quantum feature of NV^- centres, which cannot be observed for other visible domain light-emitting colour centres in a diamond lattice.