The fabrication of luminescent defects in single-crystal diamond upon Sn implantation and annealing is reported. The relevant spectral features of the optical centers (emission peaks at 593.5, 620.3, 630.7, and 646.7 nm) are attributed to Sn-related defects through the correlation of their photoluminescence (PL) intensity with the implantation fluence. Single Sn-related defects were identified and characterized through the acquisition of their second-order autocorrelation emission functions, by means of Hanbury-Brown and Twiss interferometry. The investigation of their single-photon emission regime as a function of excitation laser power revealed that Sn-related defects are based on three-level systems with a 6 ns radiative decay lifetime. In a fraction of the studied centers, the observation of a blinking PL emission is indicative of the existence of a dark state. Furthermore, absorption dependence on the polarization of the excitation radiation with ∼45% contrast was measured. This work shed light on the existence of a new optical center associated with a group-IV impurity in diamond, with similar photophysical properties to the already well-known Si–V and Ge–V emitters, thus, providing results of interest from both the fundamental and applicative points of view.

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Fusion and transfer + breakup channels have been studied in the collision induced by the two-neutron-halo 6 He on a 64 Zn target at energies from below to above the Coulomb barrier. For comparison, the reaction induced by the stable isotope 4 He on the same target has been studied. The fusion cross section has been measured by using an activation technique, detecting off-line the delayed x-ray activity following the electron capture decay of the evaporation residues. New measurements of the 4 He + 64 Zn fusion cross section at sub-barrier energies have been performed in order to cover the same energy range of the 6 He + 64 Zn fusion cross section and to compare the excitation functions for the two systems down to the lowest energy data point measured for 6 He. From the new comparison a sub-barrier fusion enhancement has been observed in the 6 He case with respect to the 4 He one whereas no effect on the 6 He fusion cross section has been seen at energies above the barrier. It has been concluded that such enhancement seems to be due to the diffuse halo structure properties of the 6 He nucleus. Moreover, the reactions induced by 6 He have shown a strong yield of α particles coming from direct processes.

Focused MeV ion beams with micrometric resolution are suitable tools for the direct writing of conductive graphitic channels buried in an insulating diamond bulk, as already demonstrated for different device applications. In this work we apply this fabrication method to the electrical excitation of color centers in diamond, demonstrating the potential of electrical stimulation in diamond-based single-photon sources. Differently from optically-stimulated light emission from color centers in diamond, electroluminescence (EL) requires a high current flowing in the diamond subgap states between the electrodes. With this purpose, buried graphitic electrode pairs, 10 μm spaced, were fabricated in the bulk of a single-crystal diamond sample using a 6 MeV C microbeam. The electrical characterization of the structure showed a significant current injection above an effective voltage threshold of 150 V, which enabled the stimulation of a stable EL emission. The EL imaging allowed to identify the electroluminescent regions and the residual vacancy distribution associated with the fabrication technique. Measurements evidenced isolated electroluminescent spots where non-classical light emission in the 560–700 nm spectral range was observed. The spectral and auto-correlation features of the EL emission were investigated to qualify the non-classical properties of the color centers.

The control of the charge state of nitrogen-vacancy (NV) centers in diamond is of primary importance for the stabilization of their quantum-optical properties, in applications ranging from quantum sensing to quantum computing. In this work buried current-injecting graphitic micro-electrodes were fabricated in bulk diamond by means of a 6 MeV C 3+ scanning micro-beam. The electrodes were exploited to control the variation in the relative population of the negative (NV − ) and neutral (NV 0 ) charge states of sub-superficial NV centers located in the inter-electrode gap regions. Photoluminescence spectra exhibited an electrically-induced increase up to 40% in the NV − population at the expense of the NV 0 charge state, with a linear dependence from the injected current at applied biases smaller than 250V, and was interpreted as the result of electron trapping at NV sites. An * Corresponding author: Tel +39 011 6707306, forneris@to.infn.it, J. Forneris et al., "Electrical control of sub-superficial NV centers in diamond…" p. ! 2 abrupt current increase at ∼300V bias resulted in a strong electroluminescence from the NV0 centers, in addition to two spectrally sharp emission lines at 563.5 nm and 580 nm, not visible under optical excitation and attributed to self-interstitial defects. These results disclose new possibilities in the electrical control of the charge state of NV centers located in the diamond bulk, which are characterized by longer spin coherence times.