V. A. Nadolinny

New paramagnetic centres containing nickel ions in diamond

Abstract Electron spin resonance (ESR) and optical spectroscopy were used to investigate synthetic diamonds, obtained by a temperature gradient method. Three new ESR spectra were discovered due to Ni + defects in a divacancy position in the diamond lattice. Their optical analogues are S2 and S3 vibronic systems and the system with a zero phonon line at 523.2 nm, well known for natural diamond. The variety of defects is due to the presence of two or three nitrogen atoms in the nearest coordination sphere of the Ni + ion.

EPR study of the transformations in nickel containing centres at heated synthetic diamonds

Electron paramagnetic resonance (EPR) was used to investigate the transformation of as grown nickel and nitrogen defects at the annealing of synthetic diamonds, obtained by the temperature gradient method. Structural models and formation mechanisms of the seven nickel containing paramagnetic centres (NE1-NE7) in synthetic diamonds are discussed. A common structural fragment of NE1-NE4 centres is a double semivacancy, in centre of which Ni+ ion is located. The NE6, NE7 centres are proved to operate as shallow electronic traps. The effects observable for NE5 centres are supposed due to an internal electronic transformation in them. The problem of charge compensators for nickel ions is also discussed. The features observable in the charge transfer processes under X-ray irradiation for nickel and nitrogen containing centres suggest that donor nitrogen serves as a bulk charge compensator for substitutional nickel and NE1 centres.

Effect of HPHT annealing on the photoluminescence of synthetic diamonds grown in the Fe-Ni-C system

Abstract The photoluminescence (PL) spectra of synthetic diamonds (SD) containing high concentrations of nitrogen and nickel impurities have been examined in both as-grown samples and the ones annealed at 1950 or 2200 K. A large number of zero-phonon lines (ZPLs), including two tens of vibronic PL systems, have been identified and their behaviour on annealing has been studied, one-third of documented lines have also been observed in natural diamonds. An analysis of their behaviour on annealing allows their division into three main groups, namely: (I) The systems present in as-grown SD, but which disappear after annealing at 1950 K; (II) The systems, which appear after annealing at approximately 1950 K, but their intensity is lower or they disappear completely after annealing at 2200 K; (III) The system, whose intensity increases after annealing at 1950 K and does not decrease after further annealing at 2200 K. A combined optical and ESR study allowed one to identify the systems of group I with individual impurities, whereas the items within group III were associated with nickel–nitrogen complexes containing a single nickel ion in the divacancy position surrounded by a few (n≥2) nitrogen atoms. The systems within group II are related to a relaxed single nickel defect (nickel ion in divacancy position) and simple nickel–nitrogen complexes, containing a single nitrogen atom. The PL excitation spectra were measured for 15 most intense PL systems. A broad absorption band in the annealed SD, with a peak approximately 450 nm and a superimposed fine structure, was decomposed into individual components, related to the NE1, NE2 and NE3 paramagnetic centres. The lower excited states of these three centres are split with ΔE=125 meV, 62 meV and 221 meV, respectively, while the spin-allowed electronic transitions take place only to the upper sublevel.

Spatial distribution of impurity defects in synthetic diamonds obtained by the BARS technology

Abstract Luminescence and optical transmission topography reveal the inhomogeneities in distribution of impurity nitrogen and nickel-related defects in synthetic diamonds obtained in high-pressure apparatus of the split-sphere type (Russian acronym: BARS). Owing to considerable supersaturations and temperature gradients at growth the lighter areas with higher content of purely nitrogen A-centres and of complex nickel-nitrogen NE1–NE3 defects are present in yellow Ib samples. The coefficients for NE1/NE2/NE3 concentration and strength of absorption in corresponding zero-phonon lines in visual region were determined. These centres were found to be stable relative to 3 MeV electron irradiation and annealing at 1100 K.

New {RuNO} Polyoxometalate [PW11O39RuII(NO)]4-: Synthesis and Reactivity

New Ru-containing polyoxometalate [PW11O39Ru(II)(NO)](4-) (1(4-)) was obtained in high yield by reaction of [Ru(NO)Cl5](2-) with [PW11O39](7-) and characterized by multinuclear NMR, cyclic voltammetry, IR spectroscopy, and electrospray ionization mass spectrometry (ESI-MS). The intrinsic reactivity of the {RuNO} site in 1(4-) toward various reagents has been studied using a versatile and simple ESI tandem mass spectrometric methodology for identification of the L attached at the Ru site; this approach relies on the preferential liberation of the L ligands attached at the Ru sites upon mass-selecting desired intermediates and subsequent promotion of their fragmentation. Reactions with both hydrazine and hydroxylamine lead to elimination of the nitroso group and quantitative formation of [PW11O39Ru(III)(H2O)](4-) (2(4-)) in aqueous solution. In the reaction with hydroxylamine, an intermediate with coordinated dinitrogen has been detected. An easy access to the NH3-coordinated [PW11O39RuNH3](4-) (3(4-)) complex was achieved upon reduction of 1(4-) with Sn(2+) in water.

Relationship between electronic states of nickel-containing centres and donor nitrogen in synthetic and natural diamonds

Abstract Some features of the charge transfer process in donor nitrogen and nickel centres on exposure to X-ray and light illumination, have been examined in natural and synthetic diamonds by EPR and optical absorption. Donor nitrogen has been shown to serve as a bulk charge compensator of the paramagnetic substitutional (NiS) and NE1 nickel centres. The ionized states of Ns and Nis were found to exist in unexcited diamond crystals.

Study of local concentration of single substitutional nitrogen atoms in microdiamonds from the Kokchetav massif

In this communication we present an estimation of the concentration of single substitutional nitrogen atoms (P1 centre) from EPR data in Kokchetav diamonds. We first performed an analysis of local P1 centre concentrations using van Wyk’s treatment (van Wyk et al ., 1997) of the line width of the resolved EPR spectrum. Also by analysing the dependence of the line-width of the broad exchange line on the P1 concentration in range higher than 1000 ppm in synthetic diamonds, we obtained a calibration curve allowing the estimation of the local P1 centre concentration higher than 1000 ppm and the local volumes occupied by substitutional nitrogen atoms without taking measurements of microcrystalline volume. In addition to the development of a method for calculating high local nitrogen concentrations, the aggregation process in P,T-treated Kokchetav diamonds has been given considerable attention and it was shown that the rate of nitrogen aggregation in these diamonds is consistent with data given in Evans (Evans & Qi, 1982).

Distribution of OK1, N3 and NU1 defects in diamond crystals of different habits

Comprehensive studies of diamond crystals with a low nitrogen concentration from the placer deposits and kimberlite pipes of Yakutia have facilitated the detection of three titanium-nitrogen-related centers: OK1/S1, N3/440.3 nm and NU1/485 nm in the EPR and photoluminescence spectra. Additional proof of titanium presence in the structure of EPR N3 center was obtained from the hyperfine structure of titanium magnetic isotopes 47 Ti and 49 Ti. Titanium-nitrogen-related centers in the neighboring substitutional sites (N3/440.3 nm) and in the structure of the interstitial (NU1/485 nm) are not found in cubic habit crystals, which are characterized by the presence of the OK1/S1 center with a double semi-vacancy structure. All three types of nitrogen-titanium-related centers are present in cuboctahedral habit diamonds. It is assumed that these habit-specific distributions of defects in diamond are a result of the peculiarities of incorporating nitrogen and titanium impurities into the different growth sector of crystals and aggregation thereof at high pressure and temperature.

EPR studies of a nickel-boron centre in synthetic diamond

Abstract Possible models are discussed for a new EPR centre (NOL1) observed in a diamond grown from a nickel-containing solvent catalyst with a titanium nitrogen getter. Nickel and boron are the most prevalent impurities in the diamond. The centre has trigonal (C 3v ) symmetry about 〈111〉, S =1, g ∣∣ =2.0235(5), g ⊥ =2.0020(10) and D =−171(1) GHz. The EPR lineshape is unusual and we tentatively attribute this to partially resolved 11 B hyperfine structure. This centre may be the same as NIRIM-5, observed in boron doped synthetic diamond. The most likely structure for this centre is an interstitial Ni 2+ with a substitutional B − ion at the nearest neighbour site along 〈111〉.

Influence of photoexcitation on the EPR spectra of Mo5+ in Li2Zn2(MoO4)3: Ce3+,Cu2+ crystals annealed in a CO2 atmosphere

The influence of recovery annealing in a CO2 atmosphere at 700°C on the properties of Li2Zn2(MoO4)3 crystals doped with cerium and copper ions has been studied. The EPR investigation of Li2Zn2(MoO4)3 crystals annealed in a CO2 atmosphere has revealed that the annealing leads to the formation of oxygen vacancies in positions adjacent to the oxygen octahedron of lithium, M3, and the oxygen tetrahedron of molybdenum, Mo1. In this case, the charge state of molybdenum becomes Mo5+ and appears in the EPR spectra in the form of one magnetically nonequivalent position. The analysis of the angular dependence of the EPR spectrum of Mo5+ made it possible to calculate the spectral parameters g∥ = 1.862, g⊥ = 1.933, A∥ = 71.8 G, and A⊥ = 34.1 G. The cross relaxation on the hyperfine structure from the molybdenum isotope 97Mo is found in the EPR spectra. The photoexcitation of Li2Zn2(MoO4)3 crystal doped with cerium ions leads to the saturation of the EPR spectrum of Mo5+ and to the formation of the hyperfine structure from one lithium ion with a hyperfine structure constant of 14 G. For Li2Zn2(MoO4)3 crystals doped with copper ions, a very weak EPR spectrum of Mo5+ is observed in the initial crystals. As a result of the photoexcitation, an increase in the intensity of this spectrum by an order of magnitude and manifestation of the EPR spectrum of Cu2+ ions take place. It is assumed that such a behavior of the EPR spectra of molybdenum ions in Li2Zn2(MoO4)3 crystals doped with cerium and copper ions under photoexcitation is caused by different positions of the energy levels of cerium and copper ions with respect to the energy level of the molybdenum ion.