Electron paramagnetic resonance (EPR) has been used to monitor oxygen vacancies and zinc vacancies in a ZnO crystal irradiated near room temperature with 1.5MeV electrons. Out-of-phase detection at 30K greatly enhances the EPR signals from these vacancies. Following the electron irradiation, but before illumination, Fe3+ ions and nonaxial singly ionized zinc vacancies are observed. Illumination with 325nm laser light at low temperature eliminates the Fe3+ signal while producing spectra from singly ionized oxygen vacancies, neutral zinc vacancies, and axial singly ionized zinc vacancies. This light also produces EPR spectra from zinc vacancies having a OH− ion at an adjacent oxygen site. The low-temperature response of the irradiated crystal to illumination wavelengths between 350 and 750nm is described. Wavelengths shorter than 600nm convert Fe3+ ions to Fe2+ ions and convert neutral oxygen vacancies to singly ionized oxygen vacancies. Neutral zinc vacancies are formed by wavelengths shorter than 500nm as electrons are removed from isolated singly ionized zinc vacancies. Warming above 120K in the dark reverses the effect of the illuminations. These wavelength-dependence results suggest that the ground state of the neutral oxygen vacancy is deep, approximately 1.3eV above the valence band, and that the ground state of the singly ionized zinc vacancy is also deep, about 0.9eV above the valence band.

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An electron paramagnetic resonance (EPR) spectrum from Er3+ ions has been observed in a bulk single crystal of aluminum nitride (AlN). These Er3+ ions were introduced into the crystal during growth and had a concentration of approximately 2×1016 cm−3. The Er3+ EPR signal, monitored at 4.5 K, exhibits axial symmetry (the unique axis is parallel to the c axis in this wurtzite lattice) and shows well-resolved hyperfine splittings due to E167r nuclei. An absence of site splittings in the EPR angular dependence indicates that these erbium ions, replacing aluminum ions in the AlN crystal, have no nearby defects. Principal values for the g and hyperfine matrices are g∥=4.337, g⊥=7.647, |A∥|=454 MHz, and |A⊥|=796 MHz. Forbidden transitions, appearing in the low-field portion of the hyperfine spectrum when the magnetic field is rotated a few degrees away from the c axis, give |P|=7.8 MHz for the nuclear electric quadrupole parameter.

Electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) spectra are obtained from a donor in aluminum nitride (AlN) crystals. Although observed in as-grown crystals, exposure to x rays significantly increases the concentration of this center. ENDOR identifies a strong hyperfine interaction with one aluminum neighbor along the c axis and weaker equivalent hyperfine interactions with three additional aluminum neighbors in the basal plane. These aluminum interactions indicate that the responsible center is a deep donor at a nitrogen site. The observed paramagnetic defect is either a neutral oxygen substituting for nitrogen (ON0) or a neutral nitrogen vacancy (VN0).

The Coral Triangle in the Indo-Pacific is a region renowned for exceptional marine biodiversity. The area could have acted as a ‘centre of origin’ where speciation has been prolific or a ‘centre of survival’ by providing refuge during major environmental shifts such as sea-level changes. The region could also have acted as a ‘centre of accumulation’ for species with origins outside of the Coral Triangle, owing to it being at a central position between the Indian and Pacific oceans. Here, we investigated support for these hypotheses using population-level DNA sequence-based reconstructions of the range evolution of 45 species (314 populations) of Indo-Pacific reef-associated organisms. Our results show that populations undergoing the most ancient establishment were significantly more likely to be closer to the centre of the Coral Triangle than to peripheral locations. The data are consistent with the Coral Triangle being a net source of coral-reef biodiversity for the Indo-Pacific region, suggesting that the region has acted primarily as a centre of survival, a centre of origin or both. These results provide evidence of how a key location can influence the large-scale distributions of biodiversity over evolutionary timescales.

Electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) . The Mn2+ ions substitute for the Cd 2+ ions in this tetragonal chalcopyrite lattice, and form "deep" isoelectronic centers. Their g values and crystal-field parameters are g ║ = 2.0025, g ⊥ = 2.0011, D = 118.8 MHz, a + 2/3F = 18.4 MHz, and a = −0.3 MHz. The hyperfine and nuclear electric quadrupole parameters for the 55 Mn nucleus are A ║ = −154.94 MHz, A ⊥ = −155.69 MHz, and P = 0.622 MHz. Hyperfine parameters for one set of nearby Cd nuclei and two sets of nearby As nuclei were also determined using ENDOR. No evidence was found in these doped bulk crystals to suggest that Mn 4+ ions substitute for Ge 4+ ions.

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