We study the circularly polarized photoluminescence of negatively charged (${\mathrm{NV}}^{\ensuremath{-}}$) and neutral (${\mathrm{NV}}^{0}$) nitrogen-vacancy ensembles and neutral vacancies (${\mathrm{V}}^{0}$) in diamond crystals exposed to magnetic fields of up to 10 T. We determine the orbital and spin Zeeman splitting as well as the energetic ordering of their ground and first-excited states. The spin-triplet and -singlet states of the ${\mathrm{NV}}^{\ensuremath{-}}$ are described by an orbital Zeeman splitting of about 9 $\ensuremath{\mu}\mathrm{eV}/\mathrm{T}$, which corresponds to a positive orbital $g$-factor of ${g}_{L}=0.164$ under application of the magnetic field along the (001) and (111) crystallographic directions, respectively. The zero-phonon line (ZPL) of the ${\mathrm{NV}}^{\ensuremath{-}}$ singlet is defined as a transition from the ${}^{1}{E}^{\ensuremath{'}}$ states, which are split by ${g}_{L}{\ensuremath{\mu}}_{\text{B}}B$, to the ${}^{1}{A}_{1}$ state. The energies of the zero-phonon triplet transitions show a quadratic dependence on intermediate magnetic field strengths, which we attribute to a mixing of excited states with nonzero orbital angular momentum. Moreover, we identify slightly different spin Zeeman splittings in the ground (gs) and excited (es) triplet states, which can be expressed by a deviation between their spin $g$-factors: ${g}_{S,\text{es}}={g}_{S,\text{gs}}+\mathrm{\ensuremath{\Delta}}g$ with values of $\mathrm{\ensuremath{\Delta}}g=0.014$ and 0.029 in the (001) and (111) geometries, respectively. The degree of circular polarization of the ${\mathrm{NV}}^{\ensuremath{-}}$ ZPLs depends significantly on the temperature, which is explained by an efficient spin-orbit coupling of the excited states mediated through acoustic phonons. We further demonstrate that the sign of the circular polarization degree is switched under rotation of the diamond crystal. A weak Zeeman splitting similar to $\mathrm{\ensuremath{\Delta}}g{\ensuremath{\mu}}_{\text{B}}B$ measured for the ${\mathrm{NV}}^{\ensuremath{-}}$ ZPLs is also obtained for the ${\mathrm{NV}}^{0}$ zero-phonon lines, from which we conclude that the ground state is composed of two optically active states with compensated orbital contributions and opposite spin-1/2 momentum projections. The zero-phonon lines of the ${\mathrm{V}}^{0}$ show Zeeman splittings and degrees of the circular polarization with opposite signs. The magnetophotoluminescence data indicate that the electron transition from the $^{1}T_{2}$ states to the $^{1}A$ ground state defines the zero-phonon emission at 1.674 eV, while the $^{1}T_{2}\ensuremath{\rightarrow}^{1}E$ transition is responsible for the zero-phonon line at 1.666 eV. The $^{1}T_{2}$ ($^{1}E$) states are characterized by an orbital Zeeman splitting with ${g}_{L}=0.071$ (0.128).

We report on detecting continuous 60-GHz microwave radiation with powers in the nanowatt range by the photoluminescence of an ensemble of negatively charged nitrogen vacancy (NV−) centers in diamond at room temperature. The high contrast of the optically detected magnetic resonance and the efficient photon collection yield a magnetic field sensitivity of 86 nT/Hz for continuous-wave laser excitation with a photon energy of 2.33 eV and a power density of 93 W/cm2. The efficiency of the microwave-power-to-magnetic-field conversion amounts to 0.54 mT/W. The microwave excitation also enhances the degree of the linear polarization of NV− photoluminescence at magnetic resonance conditions, and for linearly co-polarized NV− photoluminescence and laser light, the magnetic field sensitivity is improved by about 7%.

EPR studies of Cr impurities in GaAs and intrinsic defects in GaP are reviewed to illustrate the contributions that EPR has made to the materials science and technology of III–V semiconductors. EPR has shown how the Cr impurity acts to compensate residual shallow donors or acceptors to produce semi-insulating GaAs which is used for device substrates. EPR work has identified two intrinsic defects, the PGa antisite and the VGa vacancy, and clarified their role in electrical and stoichiometric properties of GaP.

We report electrically-detected magnetic resonance (EDMR) and electroluminescence-detected magnetic resonance (ELDMR) results on InGaN/AJGaN single-quantum-well light emitting diodes. The dominant feature detected by either technique is a broad resonance (ΔB ≈ 13 mT) at g ≈ 2.01 which is enhanced by high current stressing. Our ELDMR measurements show that, depending on bias, this defect is predominately associated with either an increase or a decrease in electroluminescence at resonance while our EDMR measurements show that this resonance is associated with an increase in current at resonance before stressing and a decrease after stressing. We suggest that this is associated with a nonradiative recombination path, in parallel with the radiative recombination path and with recombination in the depletion region of a contact. A second resonance, more prominent before stressing, with g ≈ 1.99 and ΔB ≈ 7 mT is very similar to the deep donor trap, previously observed in double heterostructure diodes and is associated with a decrease in both the current and electroluminescence at resonance.

Magnetic resonance techniques are used to study the recombination processes in GaN-based light emitting diodes (LEDs). Electrically-detected magnetic resonance (EDMR) and electroluminescence-detected magnetic resonance (ELDMR) results on InGaN/AlGaN double heterostructures are presented for blue and green LEDs. In either technique our signals are dominated by a broad feature that we ascribe to a deep Zn-related acceptor. Our ELDMR measurements show that this is associated with the blue or green emission. Our EDMR measurements resolve a second center that is tentatively identified as a deep donor trap.

Nuclear magnetic resonance (NMR) from constituent Ga and As nuclei was optically detected on excitonic recombination in single GaAs quantum dots formed by interface fluctuations in GaAs/Al0.3Ga0.7As quantum wells. Orientation of the nuclear spin system by optical pumping causes an Overhauser shift of the excitonic energy levels proportional to the degree of nuclear orientation. NMR was subsequently detected by monitoring changes in the combined Overhauser plus Zeeman splitting of excitons localized in single quantum dots as the RF frequency was swept through a nuclear resonance. The NMR signals originate from approximately 10(5) nuclei in the quantum dot-with dimensions of approximately 4 nm X 10 nm X 100 nm--illustrating the extreme sensitivity and spatial resolution of the technique. NMR from such small structures provides a chemically specific probe of the local environment on the nanometer scale.

The use of electron paramagnetic resonance to investigate intrinsic defects in the III-V semiconductors is reviewed. Particular attention is given to lattice vacancies, antisites and their complexes in GaP, GaAs, and InP. The role of EPR in arriving at an understanding of these defects is emphasized and the interplay between experiment and theory is discussed.

We propose using mode locking to enable coherent nonlinear optical effects in inhomogenously broadened spin ensembles. We carry out detailed calculations for quantum dot systems in which increased spin coherence via mode locking has been recently observed [A. Greilich et al., Science 313, 341 (2006); 317, 1896 (2007)]. We show how, in the presence of spin locking, a strong pulse-matching effect occurs, providing a powerful tool for high-bandwidth linear optical processing. We then go on to study "slow light" in this system and show that high-bandwidth pulses can be controllably delayed by a time comparable to the pulse width.

We investigate the fine structure of band-edge excitons in PbSe nanocrystals and nanorods using circularly polarized magnetophotoluminescence and optically detected magnetic resonance and, based on the results, propose a singlet-triplet model of exciton photoluminescence from nondegenerate conduction and valence bands. From the data and model we extract g-factors for electrons and holes of +1.2 and +0.8, respectively. The splitting of the triplet ground state, which is responsible for the low-temperature photoluminescence, is 88 mu eV for nanorods, and less than 20 mu eV for nanocrystals. The intervalley splitting of the electron and hole levels in the nanocrystals is much larger than the electron-hole exchange interaction.

Electron spin is envisioned as the useful property for new applications in electronics, optical communications and quantum information technology. Recent work on ensembles of spins in normal (non-magnetic) semiconductors motivated by this vision is reviewed in this paper. The states of the spins are initialized, controlled and read out using light of suitable energy and duration. The recent progress in theory, materials and experimental techniques is substantial. In the area of spin lifetimes, a microsecond T-2 and a millisecond T-1 have been reported in III-V semiconductors. Demonstrations of coherent population trapping and the conversion of light-polarization to electronic spin point the way toward future applications.

School of Computational Sciences, George Mason University, Fairfax, VA 22030, USA(Dated: January 16, 2009)We find that detuning an optical pulse train from electronic transitions in quantum dots controlsthe direction of nuclear spin flips. The optical pulse train generates electron spins that precess aboutan applied magnetic field, with a spin component parallel to the field only for detuned pulses. Thiscomponent leads to asymmetry in the nuclear spin flips, providing a way to produce a stable andprecise value of the nuclear spin polarization. This effect is observed using two-color, time-resolvedFaraday rotation and ellipticity.

Spin g-factors and lifetimes were studied with picosecond pump-probe techniques for a set of samples of InAs quantum dots of uniform height. The samples were grown by MBE with a cap and flush sequence to produce a height of 2.5 nm. Remote doping provided electrons in the dots. Electron coherence was excited by a fast pump pulse and detected through the Faraday rotation of a probe pulse. The results show an in plane g-factor of 0.427 and lifetimes around 1 ns that shorten for increasing magnetic fields. For an undoped sample, signals from singly charged and neutral dots are observed and simulated to provide the hole g-factor and parameters for the neutral exciton. The undoped sample also exhibits signals for negative delays attributed to mode-locking of the spin coherence to the optical pulse train. This observation indicates that the true spin coherence lasts at least 12 ns.

Review of Income and WealthVolume 1962, Issue 1 p. 350-432 ON THE CALCULATION AND INTERPRETATION OF NATIONAL ACCOUNTING MATERIAL IN EAST AFRICA1 T. A. Kennedy, T. A. Kennedy University College of East AfricaSearch for more papers by this authorH. W. Ord, H. W. Ord University College of East AfricaSearch for more papers by this authorDavid Walker, David Walker University College of East AfricaSearch for more papers by this author T. A. Kennedy, T. A. Kennedy University College of East AfricaSearch for more papers by this authorH. W. Ord, H. W. Ord University College of East AfricaSearch for more papers by this authorDavid Walker, David Walker University College of East AfricaSearch for more papers by this author First published: March 1962 https://doi.org/10.1111/j.1475-4991.1963.tb01012.x 1 The bracketed numerals to be found in the text refer to the numbered items in the bibliography, but not all the items are indicated, since many of them are of a general character. We wish to state that although from time to time we are critical of the material produced by the East African Statistical Department we acknowledge our great indebtedness to the Department's work. In our view it is an outstanding achievement for the Statistical Department to have produced so much material of such high quality in extremely difficult conditions and with such limited resources. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Volume1962, Issue1March 1962Pages 350-432 RelatedInformation

Magnetic resonance of electrons in lightly doped GaAs layers has been detected at 5.8 T by magneto-optical Kerr rotation. A study over a wide range of microwave powers shows (1) resonance without dynamic nuclear polarization (DNP), (2) resonance enhanced by DNP, and (3) DNP pinning of the resonance to the external magnetic field. The dependences of the resonance on donor concentration and on the wavelength and intensity of the probing optical beam were also studied. For optimal conditions, the electron g factor is -0.428 and the inhomogeneous dephasing time is 5.4 ns. This time is limited by the fluctuation in the local fields produced by the host nuclei.

We examine the impact of growth kinetics on the incorporation of Mn dopants into ZnSe nanocrystals. We synthesize such particles, also known as colloidal quantum dots, and use optical spectroscopy to extract information about the average number of Mn impurities per nanocrystal as the reaction proceeds. We find that this number increases with particle growth until the Zn and/or Se precursors are depleted in the reaction solution. If the reaction is continued further, then ripening of the colloid begins and the average number of Mn per nanocrystal decreases, even as the particles slowly increase in size. We show that this effect, which is detrimental for enhanced doping, can be avoided if the reactant concentration is maintained by addition of more reactants. We consider several explanations and conclude that intraparticle ripening, in which material is redistributed on the same nanocrystal due to evolution of the particle shape, is the most consistent with experimental observations.

The spin of a photoluminescent nitrogen centre in diamond has a long life-time that could be useful as a qubit, for example. It's difficult enough to image such a single spin — imagine using that bright spin to detect nearby invisible 'dark' spins.

The excitation of electron spin polarization and coherence by picosecond light pulses and their dynamics in a wide remotely doped quantum well are studied theoretically and experimentally. Assuming that all electrons in the quantum well are localized, the theory considers the resonant interaction of light pulses with the four-level system formed by the electron spins of the ground state and the hole spins of the trion excited state. The theory describes the effects of spontaneous emission, a transverse magnetic field and hole spin relaxation on the dynamics detected by the Kerr rotation of a probe pulse. Time resolved Kerr rotation experiments were carried out on a remotely doped 14 nm GaAs quantum well in the frequency range of optical transitions to the heavy hole (HH) trion and to the light-hole (LH) trion degenerate with the HH exciton. The experiments on the resonant excitation of the HH trion show a very slow heavy hole spin relaxation and, consequently, a weak electron spin polarization after the trion relaxation. In contrast, the resonant excitation of the LH trion/HH exciton results in a fast hole spin relaxation that increases electron spin polarization.

The coherent dynamics of locally interacting spins of carriers and magnetic atoms in the crystal matrix of self-assembled CdMnSe/ZnSe quantum dots was analyzed by means of time resolved Kerr rotation. We demonstrate that even in such a system of tightly interacting spins a coherent transfer of spin between the different subsystems is possible. Strong evidence for an enhancement of the spin coherence time of both the carrier and the manganese system with respect to higher dimensional structures is found.

The spin of a photoluminescent nitrogen centre in diamond has a long life-time that could be useful as a qubit, for example. It's difficult enough to image such a single spin - imagine using that bright spin to detect nearby invisible 'dark' spins.