The H3 zero-phonon line in diamond is generally broader when measured in absorption than in emission. It is shown that a nonradiative energy transfer from the H3 centres to nitrogen impurity accounts qualitatively for this behaviour.
Uniaxial stress perturbations establish the 1.257 eV 'H2' zero-phonon line as an electric-dipole allowed transition at the centre of a C 2v point group. Taken in conjunction with a simple one-electron model, the magnitudes of the perturbations support recent suggestions that the H2 centre is a negative charge state of the well-known nitrogen-vacancy-nitrogen 'H3' centre. The H2 zero-phonon line is 0.9 meV higher in energy in 13 C diamond than in 12 C diamond. The shift is consistent, within large uncertainties, with the shift expected from the temperature dependence of the line. A local vibrational mode involving predominantly carbon atoms is identified.
With the creation of nitrogen (NV) in 1b diamond it is common to find that the absorption and emission is predominantly of negatively charged NV centres. This occurs because electrons tunnel from the substitutional nitrogen atoms to NV to form NV−–N+ pairs. There can be a small percentage of neutral charge NV0 centres and a linear increase of this percentage can be obtained with optical intensity. Subsequent to excitation it is found that the line width of the NV− zero-phonon has been altered. The alteration arises from a change of the distribution of N+ ions and a modification of the average electric field at the NV− sites. The consequence is a change to the Stark shifts and splittings giving the change of the zero-phonon line (ZPL) width. Exciting the NV− centres enhances the density of close N+ ions and there is a broadening of the ZPL. Alternatively exciting and ionizing N0 in the lattice results in more distant distribution of N+ ions and a narrowing of the ZPL. The competition between NV− and N0 excitation results in a significant dependence on excitation wavelength and there is also a dependence on the concentration of the NV− and N0 in the samples. The present investigation involves extensive use of low temperature optical spectroscopy to monitor changes to the absorption and emission spectra particularly the widths of the ZPL. The studies lead to a good understanding of the properties of the NV−–N+ pairs in diamond. There is a critical dependence on pair separation. When the NV−–N+ pair separation is large the properties are as for single sites and a high degree of optically induced spin polarization is attainable. When the separation decreases the emission is reduced, the lifetime shortened and the spin polarization downgraded. With separations of <12 A0 there is even no emission. The deterioration occurs as a consequence of electron tunneling in the excited state from NV– to N+ and an optical cycle that involves NV0. The number of pairs with the smaller separations and poorer properties will increase with the number of nitrogen impurities and it follows that the degree of spin polarization that can be achieved for an ensemble of NV− in 1b diamond will be determined and limited by the concentration of single substitutional nitrogen. The information will be invaluable for obtaining optimal conditions when ensembles of NV− are required. As well as extensive measurements of the NV− optical ZPL observations of Stark effects associated with the infrared line at 1042 nm and the optically detected magnetic resonance at 2.87 GHz are also reported.
With the creation of nitrogen (NV) in 1b diamond it is common to find that the absorption and emission is predominantly of negatively charged NV centres. This occurs because electrons tunnel from the substitutional nitrogen atoms to NV to form NV − –N + pairs. There can be a small percentage of neutral charge NV 0 centres and a linear increase of this percentage can be obtained with optical intensity. Subsequent to excitation it is found that the line width of the NV − zero-phonon has been altered. The alteration arises from a change of the distribution of N + ions and a modification of the average electric field at the NV − sites. The consequence is a change to the Stark shifts and splittings giving the change of the zero-phonon line (ZPL) width. Exciting the NV − centres enhances the density of close N + ions and there is a broadening of the ZPL. Alternatively exciting and ionizing N 0 in the lattice results in more distant distribution of N + ions and a narrowing of the ZPL. The competition between NV − and N 0 excitation results in a significant dependence on excitation wavelength and there is also a dependence on the concentration of the NV − and N 0 in the samples. The present investigation involves extensive use of low temperature optical spectroscopy to monitor changes to the absorption and emission spectra particularly the widths of the ZPL. The studies lead to a good understanding of the properties of the NV − –N + pairs in diamond. There is a critical dependence on pair separation. When the NV − –N + pair separation is large the properties are as for single sites and a high degree of optically induced spin polarization is attainable. When the separation decreases the emission is reduced, the lifetime shortened and the spin polarization downgraded. With separations of <12 A 0 there is even no emission. The deterioration occurs as a consequence of electron tunneling in the excited state from NV – to N + and an optical cycle that involves NV 0 . The number of pairs with the smaller separations and poorer properties will increase with the number of nitrogen impurities and it follows that the degree of spin polarization that can be achieved for an ensemble of NV − in 1b diamond will be determined and limited by the concentration of single substitutional nitrogen. The information will be invaluable for obtaining optimal conditions when ensembles of NV − are required. As well as extensive measurements of the NV − optical ZPL observations of Stark effects associated with the infrared line at 1042 nm and the optically detected magnetic resonance at 2.87 GHz are also reported.
The work presents the results of optical studies of Xe-related defect in diamond. This defect is one of a few having narrow zero-phonon line in the near-infrared part of the photo-luminescence spectra. It appears in diamond after Xe+ ion implantation followed by thermal annealing. Given unique physical properties of diamond (hardness, optical transparency in wide spectral range, chemical inertness, high thermal conductivity, low thermal expansion coefficient) and stability of Xe-related center it can be viewed as an potential candidate for the source of single-photons, or as optically manipulated qubit, not unlike nitrogen-vacancy center. However, compared to the latter Xe-related center is not as well understood and it is necessary to gain thorough understanding of its spatial structure, symmetry, electronic states and mechanisms of interaction with the host diamond lattice. This thesis addresses several questions, in regard to Xe-related center: 1) How efficiently this center is formed in the implantation/annealing process; 2) How does it interact with the host lattice to produce both homogeneous and inhomogeneous shape of the 811.7 nm zero-phonon line; and 3) What is the type and nature of transitions responsible for the 811.7 nm zero-phonon line. In answering the first question two methods for measuring the conversion efficiency of any kind of optically active defect have been developed and applied to Xe-related center in diamond. The study of line-broadening mechanisms showed how this center interacts with the strain produced by other neighboring Xe-centers, distributed in a plane-like geometry. Also, interaction with vibrational motions of the diamond lattice localized in the vicinity of the Xe-centers is analyzed and the parameters of this pseudo-local mode are found. Finally, using the effects of optical saturation in photo-luminescence under excitation with Gaussian laser beams it has been shown that 811.7 nm zero-phonon line is due to absorption and emission by circular magnetic dipole. Also, the site symmetry of Xe-related center has been confirmed as trigonal with the threefold axis oriented alongdirection in the diamond crystal.
The realisation of an efficient spin-photon interface using the negatively charged nitrogen-vacancy centre (NV-) in diamond requires the resonant coupling of the zero phonon line (ZPL) of the centre to an optical microcavity [1]. The cavity serves to encourage emission into the ZPL in preference to the phonon sidebands, and potentially also to increase the homogeneous linewidth via a reduction of the lifetime (the Purcell effect) thus assisting in the generation of indistinguishable photons. Cavity coupling thus has potential to improve by orders of magnitude the speed with which entanglement can be created between spatially remote NV- centres [2], and to enable other mechanisms for realising spin-photon interfaces via non-demolition measurements [3].