P1 Centers Research Articles

Electron spin resonance of a tri-nitrogen centre in Cape yellow type Ia diamonds

A di-nitrogen centre has been observed in gem quality Cape yellow diamonds while illuminated with ultraviolet light. Analysis of the spectrum shows that the paramagnetic electron is localised on two neighbouring nitrogens along (111) directions, which suggests that it is most likely a derivative of the non-paramagnetic A centre. Observation of this paramagnetic centre in many diamonds suggests an interplay between it, the A centre, the P2 (or optical N3) and possibly the P1 centre.

13C hyperfine structure and relaxation times of the P1 centre in diamond

EPR measurements are reported for isolated nitrogen atoms substituted for carbon atoms in type-1A diamonds. The EPR lines are exceptionally narrow, (7.5+or-0.4) mu T. The relaxation times measured by continuous saturation methods are T1T2=(2,4+or-1.1)*10-9 s2, T2>or=(0.87+or-0.05) mu s, T1<or=(2.7+or-1.2) ms. Two weak 13C interactions reported previously as being isotropic, are shown to be axially symmetric with a=+or-(0.92+or-0.02) mT, b=+or-(0.04+or-0.01) mT and a=+or-(0.437+or-0.005) mT, b=+or-(0.039+or-0.003) mT where a, b are respectively the isotropic and anisotropic contributions to the hyperfine splitting. Three weaker 13C interactions have also been measured; sites are suggested for the nuclei responsible.

ELECTRON PARAMAGNETIC RESONANCE OF DEFECTS IN ION-IMPLANTED SILICON

The first EPR measurements of the identity of defects in an ion-implanted layer (&amp;lt; 15 000 Å) are reported. The Si–P3 center is the dominant paramagnetic defect produced at room temperature by 400-keV O+ implantation in Al- and B-doped Lopex Si, and it anneals below 200°C. The Si–P1 center is the dominant defect remaining above 200°C, and it anneals near 350°C. Interstitial Al++ (Si–G18) are observed in the Al-doped sample; their number indicate that Si interstitials do not migrate over large distances into the unirradiated Si. Comparison of EPR and infrared data indicates that the Si divacancy is produced in the diamagnetic neutral charge state.

Paramagnetic centres in proton-irradiated silicon

As in the case of neutron irradiation P1, P3 and P6 centres occur in silicon after irradiation with protons of 3 MeV. A new S = 1 2 centre is observed which is axially symmetric along the [111] axis and has the eigenvalues g ‖ = 2.0010 and g ⊥ = 2.0103.

Tinted films for sound positives

More than 200 samples of diamonds from the Snap Lake dyke system in Canada were studied in details using optical and EPR spectroscopy. About 30% of them were colorless or slightly greenish tinted and were related to IaB type with a high aggregation level of defects: N3 (N3V), B nitrogen centers (N4V0) and clusters of interstitials (B′ centers). Traces of heavy plastic deformation in the crystals were found by X-ray techniques. Visual examination of photoluminescence (PL) of another batch of samples shows one type emission: a blue core surrounded by a green shell. As a rule these diamonds were colored in brownish to greenish tints and belong to the IaA type containing predominantly N–N nitrogen aggregates.Specific features of type IaB diamonds are a dominant broad line in the P2 EPR spectrum and an unusually high concentration of nitrogen in a single substitutional form, NS0. We suggest that this uncommon combination was produced naturally by the destruction of B-centers (N4V0) during plastic deformation. When IaA and IaB diamonds are heated, movement of dislocations throughout the crystal causes further decomposition of the complicated nitrogen defects (A, B), producing simpler nitrogen forms: P1, P2 and H3 centers. Analysis of light illumination effects on the IaB type diamonds revealed that some of these defects are in different charge states and the color of plastically deformed crystals is believed to be due to the charge transfer between the nitrogen defects and the dislocation core. Results of the current study suggest that a line broadening in P2/N3 and H3 systems and thus unusual ratio between strengths of the zero phonon lines and vibronic bands in PL spectra are related to the lattice distortion because of nearby dislocations. The sharp 1332 cm− 1 IR peak in these samples is due to NS+ rather than to B-centers.The PL 490.7 nm center, most manifesting itself in plastically deformed IaA diamonds, is first shown to be always accompanied by PL blue systems at 406 and 423 nm and to correlate with EPR signal from dangling bonds in the dislocation cores.