The role of electron spin resonance in the study of both natural and synthetic diamond is reviewed. A brief survey of the physical significance of the constants in the spin Hamiltonian, as well as experimental technique, is given. The various nitrogen centres are discussed treating exchange-interaction, Jahn-Teller and relaxation effects associated with these centres. The spin Hamiltonian parameters of these centres are tabled and the results are discussed within the framework of the defect molecule approach. In conclusion, the correlation between optical effects and the ESR measurements in the case of four defect centres are discussed in some detail as this seems to be a powerful method of testing the various models suggested for the observed defects.

https://iopscience.iop.org/article/10.1088/0034-4885/41/8/002/pdf

Electron spin resonance in the study of diamond

This review outlines some relevant aspects of theoretical physics-molecular orbital and other calculation of the properties of point defects, symmetry and group theory, zero-phonon lines and the configuration coordinate diagram. The experimentally observed spectra can conveniently be divided into infrared (<1 eV), which are observed in absorption and are mainly vibrational, and 'visible' (1-5.5 eV), which are vibronic and are observed in both absorption and luminescence. 'Visible' spectra include those present naturally, those induced by irradiation, and those induced by irradiation plus annealing. This review covers all the important point defects observed optically in diamond, and includes some results which are not generally available. The relevance of the experimental results to the current controversy about how to calculate the properties of point defects is brought out.

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Optical absorption and luminescence in diamond

Reviews the vibronic properties of point defects (i.e. impurities and radiation-induced defects) in diamond. Cases discussed are: defects where the totally symmetric electron-lattice interaction dominates; cases of dynamic Jahn-Teller distortions; vibronic interactions between nearly degenerate states and a statically deformed defect. Before discussing each of these topics the relevant theory is outlined at an introductory level with the emphasis on features relevant to understanding data. It is shown that a good understanding of the vibronic data is now available in diamond. Compared to defects in silicon, defects in diamond are less prone to static deformations, partly as a result of the high-energy transverse acoustic modes in diamond.

https://iopscience.iop.org/article/10.1088/0034-4885/44/7/003/pdf

The Jahn-Teller effect and vibronic coupling at deep levels in diamond

Employing photoluminescence (PL) spectroscopy, we have carried out a detailed study of the characteristics and origin of the 1.681 eV luminescence center in chemical‐vapor‐deposited (CVD) diamond films. In addition to the zero‐phonon line (ZPL), the fine structure of the PL emission spectrum revealed vibronics corresponding to both phonon emission and phonon absorption. Most of the vibronics can be identified with known lattice phonons in a natural diamond, although a few of the peaks appear to be associated with a local vibrational mode. The emission intensity was found to be a strong function of the CH4/H2 ratio used to grow the diamond films. Decreasing the methane concentration from 2.0% to 0.25% resulted in an increase of about four orders of magnitude in the PL intensity. It has been found that residual stress on the order of 0.5 GPa in the diamond film quenches the PL emission intensity but has no measurable effects on the peak position and half‐width of the 1.681 eV ZPL. Temperature has a marked i...

Characteristics and origin of the 1.681 eV luminescence center in chemical‐vapor‐deposited diamond films

Nitrogen is ubiquitous in both natural and laboratory-grown diamond, but the number and nature of the nitrogen-containing defects can have a profound effect on the diamond material and its properties. An ever-growing fraction of the supply of diamond appearing on the world market is now lab-grown. Here, we survey recent progress in two complementary diamond synthesis methods—high pressure high temperature (HPHT) growth and chemical vapor deposition (CVD), how each is allowing ever more precise control of nitrogen incorporation in the resulting diamond, and how the diamond produced by either method can be further processed (e.g., by implantation or annealing) to achieve a particular outcome or property. The burgeoning availability of diamond samples grown under well-defined conditions has also enabled huge advances in the characterization and understanding of nitrogen-containing defects in diamond—alone and in association with vacancies, hydrogen, and transition metal atoms. Among these, the negatively charged nitrogen-vacancy (NV–) defect in diamond is attracting particular current interest in account of the many new and exciting opportunities it offers for, for example, quantum technologies, nanoscale magnetometry, and biosensing.

Nitrogen in diamond

The GR 1 radiation damage centre in diamond has been studied by means of optical absorption and uniaxial stress. Two zero phonon lines at 1.665 and 1.673 eV have been associated with the defect, and an energy level scheme is proposed to explain the thermal behaviour of the lines. The energy level diagram facilitates the interpretation of the uniaxial stress data, and it is concluded that the defect possesses tetrahedral symmetry. Comparison of the energy level scheme derived experimentally with theoretical treatments of intrinsic defects in diamonds suggests that the GR 1 centre is probably the neutral vacancy.

The Neutral Vacancy in Diamond

The zero-phonon lines GR2, GR3,..., GR8 which are observed in electron-irradiated diamond between 2.8 and 3.1 eV have been studied using optical absorption and uniaxial stress. The relative intensities of these lines correlate with each other and with the GR1 zero-phonon lines at 1.665 and 1.673 eV in all the crystals studied. Changes in intensity with temperature also suggest a link between GR1 and GR2 $\rightarrow $ 8. Uniaxial stress measurements indicate that GR2 (2.881 eV) and GR3 (2.888 eV) are E to T transitions at the GR1 defect. It is concluded that all the transitions GR1 $\rightarrow $ GR8 occur at the vacancy.

J. Walker

Papers

The Neutral Vacancy in Diamond

Electronic transitions at the diamond vacancy