A study of¹³C hyperfine structure in the EPR of nickel-nitrogen-containing centres in diamond and correlation with their optical properties

Abstract

Electron paramagnetic resonance (EPR) and optical spectroscopy have been used to determine the structure and electronic state of nickel-nitrogen centres in natural diamonds and in synthetic diamonds enriched in 13C. The latter were grown in an Fe-Ni-C solvent/catalyst system at 1750 K, under stabilizing pressure, by the temperature gradient method and afterwards treated at high temperature and pressure. The parameters and directions of the 13C hyperfine structure (HFS) tensors for the NE1 centre were found to confirm the previously proposed model for this defect, with a nickel ion at the centre of a double semivacancy as the basic structural unit. In this unit the nickel atom has six atoms in its coordination shell. The NE1 centre has C2h symmetry, and the two equivalent nitrogen atoms in the coordination shell lie in the symmetry plane. New data on the HFS of 14N and 13C for the NE5 centre, also with C2h symmetry, indicated the same structural unit, but the two equivalent nitrogen atoms (and two equivalent carbon atoms) lie out of the symmetry plane and are related to one another by reflection in it. A new paramagnetic centre was found, labelled NE8, also with C2h symmetry, with four equivalent nitrogen atoms in the coordination shell all lying out of the symmetry plane. This centre is responsible for the 793.6 nm vibronic system in absorption and luminescence spectra. The new data have allowed a reinterpretation of the HFS tensors for the NE2 centre, which has C1 symmetry, suggesting that it has the same structure as NE1 but with one additional nitrogen atom in the coordination shell. The electronic states of these nickel-containing centres are discussed using the approach of Ludwig and Woodbury to transition metal ions in covalent crystals.

Diamond Nanophotonics

“…A multitude of color centers containing nickel is known, especially in nitrogen rich high pressure high temperature (HPHT) diamond, where nickel is used as a catalyst and forms several complexes with nitrogen [69] . The only of these complexes identified as single emitter is the so called NE8 center [70][71][72] , consisting of a nickel atom, two vacancies and four nitrogen atoms.…”

Incorporation of Large Impurity Atoms into the Diamond Crystal Lattice: EPR of Split-Vacancy Defects in Diamond

“…At the same time, the HPHT annealing procedure of diamonds was elaborated in detail. Using these new techniques, diamond crystals were synthesized in the Fe-Ni-C and Ni-C systems in Novosibirsk, Russia [19][20][21][22]. The P1 and W8 centers were observed in the EPR spectra of diamond crystals synthesized at a temperature of 1700 K and a pressure of 5.5 GPa.…”

“…Table 1. Parameters of the spin Hamiltonian for different nickel-containing centers with S = 1/2 in diamond [19][20][21][22]. The directions are for a C 2h symmetry site with (1-10) as its plane of reflection symmetry.…”

Investigation of nickel lattice sites in diamond: Density functional theory and x-ray absorption near-edge structure experiments

“…From an experimental point of view, the various lines detected by electronic paramagnetic resonance (EPR) [31][32][33][34][35][36] or by magneto-optical (including magnetic circular dichroism) or piezo-optical spectroscopy 21,[37][38][39] have been attributed to specific incorporation sites of Ni in diamond. This has been a challenge since the early days when it was recognized that an isolated Ni atom was incorporated in a site of trigonal symmetry at low temperatures (below 25 K) changing over to a tetrahedral symmetry at higher temperatures.…”