Optical Detection Of Electron Paramagnetic Resonance Research Articles

Charge state dynamics and optically detected electron spin resonance contrast of shallow nitrogen-vacancy centers in diamond

Nitrogen-vacancy (NV) centers in diamond can be used for nanoscale sensing with atomic resolution and sensitivity; however, it has been observed that their properties degrade as they approach the diamond surface. Here we report that in addition to degraded spin coherence, NV centers within nanometers of the surface can also exhibit decreased fluorescence contrast for optically detected electron spin resonance (OD-ESR). We demonstrate that this decreased OD-ESR contrast arises from charge state dynamics of the NV center, and that it is strongly surface-dependent, indicating that surface engineering will be critical for nanoscale sensing applications based on color centers in diamond.

Hybrid nanophotonic-nanomagnonic SiC-YiG quantum sensor: II/dark spins quantum sensing with V2 spins and fiber based OP-PELDOR/ODMR

First experiments like optically detected (OD) electron paramagnetic resonance (ODMR), photoluminescence detected RABI oscillations, and optical pumping (OP) assisted pulsed EPR measurements of T2 and T1 of V2 spins in bulk SiC, which were previously demonstrated on various home build EPR spectrometers with free space optics, are here all demonstrated for the first time using a commercial X band pulsed EPR spectrometer combined with a single optical fiber and a standard external photoluminescence setup. Quantum sensing of bulk dark spins dipolar coupled to V2 spins in SiC is also demonstrated here for the first time using single fiber based OP assisted pulsed electron electron double resonance spectroscopy (PELDOR). A spin wave resonance study of model permalloy nanostripes is also presented allowing to check the ferromagnetic nanostripes design. These experiments are first key steps towards the fiber-based integration of the recently proposed SiC-YiG quantum sensor device [J. Tribollet, Eur. Phys. J. Appl. Phys.90, 20102 (2020)], to a commercially available and worldwide used pulsed EPR spectrometer, with important applications expected in structural biology, surface chemistry, and quantum computing.

Point defects in ZnO: Electron paramagnetic resonance study

Abstract The results of electron paramagnetic resonance (EPR), photo-EPR, and optical detection of EPR (ODEPR) investigation of different point defects in ZnO single crystals, ceramics and powders are reported. The main attention is given to EPR and photo-EPR studies of oxygen vacancy (VO) being in scope of many experimental and theoretical investigations. Different EPR and ODEPR spectra related to VO and reported in literature are analyzed and their temperature stability is investigated. The properties of the Pb atoms playing important role in spin dependent recombination process are studied. Specific features of the VO+ and Pb3+ EPR spectra, such as (i) reversal and not reversal change of EPR lines intensity under excitation by light with different wavelengths, (ii) fast increase followed by slow decrease of EPR spectra when light is switched on, (iii) correlation between EPR photoexcitation and persistent microwave photoconductivity are discussed. Spectral and time dependences of the Pb3+ EPR spectrum are explained taking into account double donor nature of Pb in ZnO. Experimental results on the photoexcitation and quench of the VO+ EPR spectrum in different ZnO samples are reported.

Fluorescence and Spin Properties of Defects in Single Digit Nanodiamonds

This article reports stable photoluminescence and high-contrast optically detected electron spin resonance (ODESR) from single nitrogen-vacancy (NV) defect centers created within ultrasmall, disperse nanodiamonds of radius less than 4 nm. Unexpectedly, the efficiency for the production of NV fluorescent defects by electron irradiation is found to be independent of the size of the nanocrystals. Fluorescence lifetime imaging shows lifetimes with a mean value of around 17 ns, only slightly longer than the bulk value of the defects. After proper surface cleaning, the dephasing times of the electron spin resonance in the nanocrystals approach values of some microseconds, which is typical for the type Ib diamond from which the nanoparticle is made. We conclude that despite the tiny size of these nanodiamonds the photoactive nitrogen-vacancy color centers retain their bulk properties to the benefit of numerous exciting potential applications in photonics, biomedical labeling, and imaging.

Intrinsic defects in ZnO: A study using optical detection of electron paramagnetic resonance

Intrinsic defects produced in ZnO by 2.5 MeV electron irradiation are studied by optical detection of electron paramagnetic resonance (ODEPR). Observed in the photoluminescence (PL) after electron irradiation in situ at 4.2 K are ODEPR signals that are identified with the oxygen vacancy, V O +, interstitial zinc, Zn i +, and zinc vacancy–zinc interstitial Frenkel pairs. Annealing stages at 65–120 K and at 145–170 K are observed for the defects associated with the zinc sublattice and are identified with the migration of interstitial zinc. The character of their ODEPR signals appears consistent with recent theoretical calculations which predict interstitial zinc to be an effective mass shallow double donor. Interpretation of the PL appears to require a large Jahn–Teller distortion (∼0.8 eV) for V Zn −. ODEPR studies in material after electron irradiation at room temperature reveal a broad PL band at 600 nm associated with V O +. The results are consistent with two different models for the V O (0/+) donor level position, each of which has some theoretical support.

Oxygen vacancies in ZnO

The electronic properties of ZnO have traditionally been explained by invoking intrinsic defects. In particular, the frequently observed unintentional n-type conductivity has often been attributed to oxygen vacancies. We report first-principles calculations showing that the oxygen vacancy VO is not a shallow donor, but has a deep ε(2+∕0) level at ∼1.0eV below the conduction band. The negative-U behavior that causes the 1+charge state to be unstable is associated with large local lattice relaxations. We present a detailed configuration coordinate diagram, which allows us to provide a detailed interpretation of recently reported ODEPR (optically detected electron paramagnetic resonance) measurements [L. S. Vlasenko and G. D. Watkins, Phys. Rev. B 71, 125210 (2005)].

Optical detection of electron paramagnetic resonance for intrinsic defects produced in ZnO by 2.5-MeV electron irradiationin situat 4.2 K

Intrinsic defects produced in ZnO by 2.5-MeV electron irradiation in situ at 4.2 K are studied by optical detection of electron paramagnetic resonance (ODEPR). Observed in the photoluminescence (PL) are ODEPR signals, which are identified with the oxygen vacancy, ${\mathrm{V}}_{\mathrm{O}}^{+}$, interstitial zinc, ${\mathrm{Zn}}_{i}^{+}$, and zinc-vacancy--zinc-interstitial Frenkel pairs. The Frenkel pairs are primarily observed in their $S=1$ exchange-coupled state, supplying strong evidence that interstitial zinc is a shallow effective mass double donor in ZnO. Annealing stages at $\ensuremath{\sim}65\text{--}119\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and $\ensuremath{\sim}145\text{--}170\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ are observed for the defects associated with the zinc sublattice and are identified with the migration of interstitial zinc. Although interstitial oxygen is not observed in the ODEPR, a higher-temperature annealing stage observed in the PL at $\ensuremath{\sim}160\text{--}230\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ is tentatively identified with the onset of its migration. The oxygen vacancy is stable to $\ensuremath{\sim}400\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. The relationship between the spin-dependent processes producing the ODEPR signals and the PL of the material remains unclear.

Optical detection of electron paramagnetic resonance in room-temperature electron-irradiated ZnO

The dominant defect observed in the photoluminescence (PL) of room-temperature electron-irradiated ZnO by optical detection of electron paramagnetic resonance (ODEPR) is determined to be the positively charged oxygen vacancy $({V}_{\mathrm{O}}^{+})$. Its spectrum, labeled L3, was previously observed in a $4.2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ in situ irradiation study [Yu. V. Gorelkinskii and G. D. Watkins, Phys. Rev. B 69, 115212 (2004)], but it was thought there not to be stable at room temperature and was not identified. Here it is found to be stable to $400\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, where it disappears. It is observed as a competing process (negative signal) to the dominant PL band produced by the irradiation at $\ensuremath{\sim}700\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, but is positive in a weaker band at $\ensuremath{\sim}600\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. Models are presented for its electrical level position in the gap to explain the results. Two other ODEPR signals are also detected, one of which is tentatively identified as also associated with the oxygen vacancy.

W -band Fabry–Pérot microwave reasonators for optical detected electron paramagnetic resonance and electron nuclear double resonance of paramagnetic defects in solids

The designs of W-band (∼95 GHz) Fabry–Pérot microwave resonators for optically detected electron paramagnetic resonance (ODEPR) and electron nuclear double resonance (ODENDOR) as well as the ODEPR/ODENDOR spectrometer are described. The Fabry–Pérot resonator was mainly designed for W-band EPR and ENDOR detected via the magnetic circular dichroism of the optical absorption (MCDA), but can also be used with slight modifications for photoluminescence (PL) detection of EPR/ENDOR. The microwave resonators were tested and successfully used for the first high-field MCDA-EPR/ENDOR investigation applied to the investigation of the paramagnetic EL2 defect in semi-insulating GaAs in which higher order effects could be suppressed which prevented the unambiguous analysis of previous K-band experiments. W-band PL-EPR was used to investigate dopants in SiC. The excellent performance of the microwave resonators encourages their use in wider applications of ODEPR and ODENDOR spectroscopy.

Correlation of irradiation-induced yellow color with the O - hole center in tourmaline

Tourmaline with the general formula XY 3 Z 6(BO3)3Si6O18(OH,O)3(OH,F) and the trigonal space group R3m (C 3 v 5) is known as a gemstone with great variety of colors. Some color centers are related to transition metal ions, and others to electron or hole traps. In this paper we report on a combined study using electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR), and the optical detection of EPR (ODEPR) on a yellow color center produced by γ-irradiation in colorless Li-bearing elbaite tourmaline from Brazil. The color center is an O− hole trap center, which is stabilized within the plane spanned by three Y sites, and is located in the structural channels formed by Si6O18. We suggest that two of the Y sites are substituted by 27Al and the other by 6,7Li. During the irradiation process atomic hydrogen H0 is also produced, which shows the same thermal stability as the hole center (250 °C). Therefore, we assign H0 to be the local charge compensator for the hole trap. From the ODEPR measurements we conclude that the yellow color is caused by the O− hole center. The large negative isotropic Al superhyperfine interaction of the O− hole trap center is consistent with a calculation of the transferred hyperfine interactions by exchange polarization supporting the proposed defect model of an O− at the O1 sites, whereby the O− is relaxed into the plane formed by three Y ions.

Defects produced in ZnO by 2.5-MeV electron irradiation at 4.2 K: Study by optical detection of electron paramagnetic resonance

The effect of 2.5 MeV electron irradiation in situ at 4.2 K on the properties of single crystalline ZnO is studied by photoluminescence (PL) and optically detected electron paramagnetic resonance (ODEPR). A new PL band is produced by the irradiation, and several annealing stages are observed upon annealing to room temperature, the first starting at $\ensuremath{\sim}110\mathrm{K}.$ Three new ODEPR signals are observed in the PL whose emergence and disappearance correlate with the PL changes. The annealing stages are taken as evidence of host interstitial atom migration beginning at the 110 K anneal. No hyperfine structure is observed for the ODEPR signals, so the defects involved cannot be identified at this stage.

Intrinsic defects in GaN. I. Ga sublattice defects observed by optical detection of electron paramagnetic resonance

Irradiation of GaN by 2.5-MeV electrons in situ at 4.2 K produces a broad photoluminescence (PL) band centered at 0.95 eV. Optical detection of electron paramagnetic resonance (ODEPR) in the band reveals two very similar, but distinct, signals, L5 and L6, which we identify as interstitial ${\mathrm{Ga}}^{2+}$ in two different lattice configurations. L5, present immediately after the irradiation, is seen via a spin-dependent electron transfer process from the shallow effective-mass donor (EM) which competes with the PL (negative signal). L6 emerges upon annealing at various stages starting at $\ensuremath{\sim}60\mathrm{K},$ possibly assisted by optical excitation, as a spin-feeding process (positive signal) not involving the EM donor. Both L5 and L6 disappear upon prolonged annealing at room temperature, with L6 disappearing first. Most of the 0.95-eV band $(\ensuremath{\sim}85%)$ also disappears in this anneal, the remaining fraction being stable to $\ensuremath{\sim}500\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}.$ Two tentative models are presented, each of which identifies L5 and L6 with ${\mathrm{Ga}}^{2+}$ in different interstitial sites near the gallium vacancy from which they were created. Both models ascribe the 0.95-eV PL band, along with an ODEPR signal observed in it L1 as arising from the Ga vacancy, which in its isolated form is therefore stable to $\ensuremath{\sim}500\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}.$

Orientational information from unoriented metalloproteins by optically detected electron paramagnetic resonance

The electronic structure of metalloproteins can be analysed with optically detected electron paramagnetic resonance (ODEPR). This relatively young technique combines electron paramagnetic resonance (EPR) and magnetic circular dichroism (MCD) with a coherent Raman scattering experiment. It can complement conventional EPR and MCD in the deconvolution and assignment of optical transitions. Information about the relative orientation of optical and magnetic transition dipoles in metalloproteins can be extracted with considerably higher resolution than by alternative techniques such as MCD. We discuss how these features provide information about the environment of metal ions in metalloproteins.

Optical detection of electron paramagnetic resonance in low-dislocation-content GaN grown by hydride vapor-phase epitaxy

Three broad overlapping photoluminescence bands, centered at $\ensuremath{\sim}1.75 \mathrm{eV}$ (red), $\ensuremath{\sim}2.2 \mathrm{eV}$ (yellow), and $\ensuremath{\sim}2.33 \mathrm{eV}$ (green), are observed in low-dislocation-content GaN grown by the hydride vapor-phase epitaxy method. Optical detection of electron paramagnetic resonance (ODEPR) studies reveal that each is fed by a spin-dependent electron transfer from a shallow donor to a deeper defect, which is different for each of the bands, and different from defects previously found in GaN grown by the more conventional epitaxy methods (metal-organic vapor-phase epitaxy and molecular beam epitaxy). The g-value progression for the deeper defects suggests a two-stage luminescence process in which the luminescence arises from hole capture at the specific defect in each case, after the spin-dependent electron capture process observed by ODEPR. This model also fits for the deep level usually found in the yellow band for more heavily dislocated materials, as originally suggested by Glaser. An additional weak anisotropic ODEPR signal is also observed in the red and yellow bands. None of the signals show resolved hyperfine interactions, and their chemical and/or lattice structures remain unknown.

ODEPR and yellow luminescence intensity in GaN under high pressure

Optically detected electron paramagnetic resonance (ODEPR) measurements in the yellow luminescence (YL) under pressures up to 7 GPa have been performed. A non-magnetic diamond anvil cell was designed, into which microwaves in the 4 mm band (72 GHz) could be coupled. One of the main limiting factors for the ODEPR measurements in the YL at high pressures is the strongly decreased the YL intensity at low temperatures. At normal pressure, when cooling the sample, the YL intensity increases. Under pressures of 5–10.8 GPa, the YL intensity decreases significantly upon cooling. ODEPR spectra of the undoped MOVPE GaN layer on sapphire measured in YL at 1.5 K at normal pressure showed resonance lines at g ||=1.989, and g ||=1.952 and a shoulder with g ||=1.958, respectively. At low temperatures under pressures of 5–10.8 GPa, a part of the YL intensity remains, but only the ODEPR line at g ||=1.989 is measured while that at g ||=1.952 disappears. The disappearing part of the YL is due to a donor–acceptor recombination from a DX-like donor, which is attributed to the oxygen on nitrogen sites (O N) in agreement with theory and other experiments.

On the problem of the EL2 structure in semi-insulating GaAs: high-frequency ODEPR/ODENDOR measurements in W-band

For almost two decades the structure model of the EL2 defect in semi-insulating (SI) GaAs has been controversially discussed. Neither the isolated As Ga with T d symmetry, nor the As Ga–As i pair model nor any other As Ga-related defect model could be unambiguously established. The reason was that the analysis of previous optically detected electron nuclear double resonance (ODENDOR) and optically detected electron paramagnetic resonance (ODEPR) spectra measured at 24 GHz was difficult and not unambiguous because of forbidden transitions, pseudo-dipolar couplings and higher order effects. However, the ODEPR spectra of the EL2 defect measured in W-band (93 GHz) can be fitted by first order perturbation calculation of the spin Hamiltonian thus allowing a much simpler analysis compared to X- or K-band. From ODEPR measurements in different SI GaAs samples both in K- and W-band we show that the ODEPR spectra of the EL2 defect together with the K-band ODENDOR data are not consistent with the As Ga–As i pair model, but the highly symmetric isolated As Ga model has to be excluded as well. First ODENDOR measurements in W-band are also reported.

Magnetic resonance investigations of oxygen-related luminescence centres in AlN ceramics

The structure of oxygen-related luminescence centres in nominally undoped and Y2O3-doped AIN ceramics were investigated by electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR) and optically-detected EPR. The photoluminescence-detected EPR lines having g values of 1.990 and 2.008 were attributed to neighbouring donor and acceptor pairs causing the recombination luminescence excited in the ultraviolet. The two EPR lines at g = 1.987 and g = 2.003, detected via the recombination luminescence in the afterglow, are thought to be due to a recombination between the same, but more distant donor and acceptor pairs. The donor is supposed to be an electron trapped at an oxygen impurity which substitutes for a nitrogen (ON)−. The defect structure of the acceptor was established by ENDOR to be a hole trapped at an ON-VAl complex (VAl = Al vacancy).

Detection of interstitial Ga in GaN

We report the direct detection of interstitial Ga by optical detection of electron paramagnetic resonance (ODEPR) in the photoluminescence of n-type GaN after irradiation in situ at 4.2 K with 2.5 MeV electrons. It is stable upon annealing until room temperature, where it becomes mobile and trapped to form a new defect which is observed to emerge as the interstitial disappears. The time constant of the process at room temperature is approximately 200 min. The emergence of another ODEPR center beginning at approximately 135 K suggests even easier migration of one of the other intrinsic defects in the GaN lattice.

Frenkel pairs on the two sublattices of ZnTe

Study of the polarization of a dominant 1.0 $\ensuremath{\mu}\mathrm{m}$ photoluminescence band produced by 2.5 MeV electron irradiation of ZnTe in situ at 4.2 K reveals it to arise from a Frenkel pair produced on the Zn sublattice. Optical detection of electron paramagnetic resonance (ODEPR) studies reveal Frenkel pairs on the Te sublattice. All pairs disappear in various annealing stages from 35 K to 120 K. The Te-sublattice pairs can also be made to disappear by optical injection at 1.5 K. Deconvoluting the Te interstitial contribution to the $S=1$ ODEPR spin Hamiltonian parameters leads to a model for it as ${\mathrm{Te}}_{i}^{\ensuremath{-}},$ which is only slightly distorted off-center from a ${T}_{d}$ interstitial site. The distortion, viewed as partially of Jahn-Teller origin, provides a logical explanation for its optically induced migration.

Investigation of Oxygen-Related Luminescence Centres in AlN Ceramics

The structure of oxygen-related luminescence centres in nominally undoped and Y 2 O 3 doped AlN ceramics was investigated by electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR) and optically-detected EPR. The photoluminescence-detected EPR lines having g-values of 1.990 and 2.008 were assigned to a recombination between neighbouring donor and acceptor pairs. The two EPR lines at g = 1.987 and 2.003 detected via the recombination luminescence in the afterglow are thought to be due to a recombination between the same, but distant donor and acceptor pairs. The donor was previously speculated to be an electron trapped on an oxygen impurity which substitutes for a nitrogen on a regular lattice site. The defect structure of the acceptor was established by ENDOR to be a hole trapped on an O N -v Al complex (ON oxygen on a regular N site, v Al Al vacancy). The measured superhyperfine interaction is caused by two equivalent 27 Al nuclei both with a = ±29.6 MHz and one 27 Al nucleus with a = ±27.0 MHz.