ODMR of bismuth and sulphur in GaP

Optically detected magnetic resonance (ODMR) of bismuth and sulphur impurities in GaP is reported. The results are compared to previous measurements by Cavenett et al. on GaP:N and further confirm the model proposed by these authors to explain the observed decrease in photoluminescence.     

光测磁共振及其在研究Ⅲ-Ⅴ族半导体材料中的应用

光测磁共振技术是一种研究半导体中的杂质缺陷的有效工具,它可以提供有关杂质缺陷的电子结构及与辐射复合过程的关系的信息。这篇文章对光测磁共振的原理和技术进行了讨论,着重评述了最近几年来新的认识和进展。对光测磁共振技术在Ⅲ-V族半导体材料的辐射过程的研究中的应用也进行了评述,比较详细地介绍了对l_np:M_n及G_ap:O的研究工作。     

Complementary ODMR and photo-ESR studies of deep donor-acceptor pair recombination processes in ZnS and GaP

The complementary approach to studies of deep donor acceptor pair (DAP) recombination processes is presented. On the basis of supplementary light induced Electron Spin Resonance (photo-ESR) and Optically Detected Magnetic Resonance (ODMR) studies, the nature of radiative recombination transitions is cleared out and the centers participating in these transitions are identified. We also show a new approach to determining the recombination rate for DAP’s of different separations. The latter is possible due to frequency-resolved ODMR experiments. The relevant experimental results for deep DAP transitions in ZnS and GaP are presented.     

Role of free carriers in the application of optically detected magnetic resonance for studies of defects in silicon

The influence of free carriers on optically detected magnetic resonance (ODMR) signals for defects in silicon is discussed. The presence of free carriers induces a strong background signal in the ODMR spectrum due to carrier heating effects in a microwave field. This background signal often obscures a possible detection of a defect-related magnetic resonance signal and is therefore highly undesirable. To avoid this problem, a delayed ODMR (D-ODMR) technique is employed. On the other hand, the presence of free carriers provides a medium for a possible ODMR detection of nonradiative defects. This is realized by a shunt pass of carrier recombination at such defects, which competes with the radiative carrier recombinations detected optically, and gives rise to negative ODMR signals for the defects responsible for the nonradiative recombination. Typical examples from recent studies of these different cases of defects in silicon are demonstrated.Dedicated to H.-J. Queisser on the occasion of his 60th birthday     

ODMR studies of antisite-related luminescence in GaP

By the use of ODMR, we have detected and identified two different antisite defects which contribute to newly-reported infrared luminescence observed in GaP. The antisite proper, P_Ga, gives rise to a spin-$\text{1}\text{2}$ resonance; the associated luminescence originates in the DA pair recombination of an electron trapped at the deep double donor P⁺_Ga with a distant shallow acceptor. An impurity-associated centre of the form P_Ga · Y_P is observed in a spin-triplet state via a distinct luminescence band which originates in electron-hole recombination localised at the defect.     

KCl crystals with a silver impurity: From point defects to oriented AgCl microcrystals in a crystalline host

This paper presents the first unambiguous optically detected magnetic-resonance (ODMR) evidence that AgCl crystals embedded in the KCl lattice and retaining the host orientation are formed in KCl crystals grown with a 2–3 mol % silver impurity. ODMR spectra were obtained of self-trapped holes, shallow electronic centers, and self-trapped excitons, which are typical of AgCl, and a number of substantially different ODMR spectra were also obtained. The differences between the ODMR spectra observed in samples cleaved from different parts of a KCl: AgCl crystal are probably accounted for by embedded AgCl crystals varying in size from large micro-to nanocrystals.     

Optically detected magnetic resonance of Mn-related excitations in (Cd,Mn)Te quantum wells

Optically detected magnetic resonance (ODMR) was applied to reveal the exchange interaction effects between Mn²⁺ ions and confined holes in (Cd,Mn)Te quantum wells with 2D hole gas. Two anisotropic ODMR signals with different angular variations were found and ascribed to isolated manganese ions and to exchange-coupled complexes consisting of manganese and holes. It is shown that calculations on the basis of spin Hamiltonian for these systems are in agreement with the experimental data.     

Magnetic-field dependent optically detected ESR in the photoexcited triplet states of bridged Zr(IV) metallocenes

We report on the magnetic-field-dependent optically detected magnetic resonance (ODMR) spectra for polycrystalline samples of the bridged Zr(IV) metallocenes, Me₂Si<(Cp₂)ZrCl₂ ( (dimethylsilylbis(cyclopentadienyl)zirconium-dichloride) and Me₂C<(Cp₂)ZrCl₂ (iso-propylidenebis(cyclopentadienyl)zirconium-dichloride). ODMR spectra at zero magnetic field were recorded by frequency sweeping a microwave source from 0.1 to 10 GHz with the sample contained in a microwave helix. ODMR spectra at finite magnetic fields were recorded with the sample contained in either a helix or a slotted-tube resonator with a fixed microwave frequency and sweeping the magnetic field. For all experiments, the sample and microwave probes were contained in an immersion dewar cryostat, and the temperature was held at about 2 K. All three zero field ODMR transitions (2|E|, and |D| − |E| and |D|+|E|) were observed in the frequency-swept ODMR spectra recorded at zero and small magnetic fields. The zero-field frequency-swept spectra allowed the determination ofD andE values uniquely. For frequency-swept small-field ODMR spectra recorded at successively higher magnetic fields, each of the ODMR line intensities was observed to increase with increasing magnetic field. This intensity increase was observed for all three ODMR lines, reflecting an increase in the total intensity rather than simply a change in the polarization of the triplet sublevels. The latter would result in a change in the relative intensities of the ODMR lines but would not change simultaneously the intensities of all three lines. The ODMR line intensities increase in proportion toB ⁿ, wheren<1. This field dependence is weaker than the expected proportionalB ² dependence from the Zeeman effect, which likely originates from the magnetic field dependence of the spin relaxation rates between the triplet sublevels. Magnetic-field-swept ODMR spectra recorded at fixed microwave frequencies in the X-band frequency range (9.8 GHz) do not show all three expected classic Pake powder pattern line shape profiles, exhibited by the molecules with their magneticZ, Y, andX axes parallel to the external magnetic field. In particular, the intensity for molecular magneticY-axes parallel to the external magnetic field is completely suppressed. In addition, an external magnetic field dependence in field-swept ODMR spectra was observed, which results in a linear decrease of the ODMR intensity with increasing strength of the external magnetic field over and above that would be expected in a polycrystalline spectrum. The data are analyzed by simulation of the continuous-wave ESR spectrum with the eigenvalues and eigenvectors of the spin Hamiltonian matrix characterizing the triplet state exhibiting the ODMR spectrum, in conjunction with homotopy, as a function of the orientations of the magnetic axes of the various molecules in a polycrystalline sample. This approach is useful to interpret the experimentally observed ODMR transition frequencies andg-values but does not take the amplitudes in the ODMR spectrum. The corrections required to modify the continuous-wave ESR spectral amplitudes that reproduce the observed ODMR amplitudes are effects associated with the ODMR processes.     

Saturation of the ODMR effect on singlet exciton induced emission in molecular crystals: Application to crystalline tetracene

We have studied the variation of the ODMR effect according to the intensity of a microwave field. We have highlighted a saturation effect of ODMR lines. This effect has been studied as part of the kinetic theory by developing the pilot equation while utilizing for the first time the formalism of a superoperator coupled with a time dependent sinusoidal perturbation. The agreement of the best fit between the experiment and the theory gives the mixing between singlet and quintuplet states, which seems to depend on the direction of the applied magnetic field.Received: 22 September 2003, Published online: 28 May 2004PACS: 71.35.-y Excitons and related phenomena - 32.30.Dx Magnetic resonance spectra - 76.70.Hb Optically detected magnetic resonance (ODMR)     

Polaron spin-lattice relaxation time in pi-conjugated polymers from optically detected magnetic resonance

We describe a method for obtaining the polaron spin-lattice relaxation time T{SL} in pi-conjugated polymers by measuring the optically detected magnetic resonance (ODMR) dynamics as a function of microwave power and laser intensity. The peculiar ODMR dynamics is well described by a spin dependent recombination model where both recombination and spin relaxation rates determine together the response dynamics. We apply this method to the spin 1/2 ODMR in films of pristine 2-methoxy-5-(2{'}-ethylhexyloxy) phenylene vinylene [MEH-PPV] polymer, as well as MEH-PPV doped with various concentrations of radical impurities. We obtained T{SL} approximately 30 micros in pristine MEH-PPV, but substantially shorter when the magnetic impurities are added.     

Features of High-Frequency EPR/ESE/ODMR Spectroscopy of NV-Defects in Diamond

Physics of the Solid State - The methods of high-frequency electron paramagnetic resonance (EPR), electron spin echo (ESE) and optically detected magnetic resonance (ODMR) are used to study the...     

ODMR Study of Zn1−x Mn x Se/Zn1−y Be y Se and (Cd1−x ,Mn)Te/Cd1−y Mg y Te Diluted Magnetic Semiconductor Quantum Wells

The effects of microwave pumping with a frequency of 60 GHz on the magneto-optical properties of diluted magnetic semiconductors (DMSs) are studied in (Zn,Mn)Se/(Zn,Be)Se and (Cd,Mn)Te/(Cd,Mg)Te quantum wells. Resonant heating of the Mn²⁺ ions in the electron spin resonance conditions leads to an increase in the Mn-spin temperature, which exceeds the bath temperature by up to 5.2 K, as detected by the shift of exciton emission line and decrease of its integral intensity. Nonresonant heating mediated by free carriers is also observed through variation of the polarization degree of emission. Direct measurements of spin–lattice relaxation times for both materials using time-resolved optically detected magnetic resonance (ODMR) technique have been performed. The mechanisms of ODMR in nanostructures of DMSs are discussed.     

Spin resonance spectroscopy of grown-in defects in Ga(In)NP alloys

We employ the optically detected magnetic resonance (ODMR) technique to study and identify important grown-in defects in Ga(In)NP grown by molecular-beam epitaxy (MBE). Several types of defects were revealed from ODMR studies. The dominant defects were found to be related to Ga interstitials, evident form their characteristic hyperfine interaction arising from the spin interaction between the electron and the Ga nucleus. Some other as yet unidentified intrinsic defects were also found to be commonly present in the alloys. The effects of growth conditions (ion bombardment, N₂ gas flow, etc.) and post-growth rapid thermal annealing on the formation of these defects were studied in detail, shedding light on the formation mechanism of defects.     

Effect of substrate temperatures and annealing on optically detected magnetic resonance in glow-discharge amorphous silicon

Optically detected magnetic resonance experiments have been performed at 2 K in glow-discharge amorphous silicon with different substrate temperatures. Effects of annealing and illumination on ODMR have been examined. A broad line is interpreted in terms of a three-centre bond model.     

Defects in Nanodiamonds: Application of High-Frequency cw and Pulse EPR,ODMR

Different aspects of applications of electron paramagnetic resonance (EPR) based techniques including high frequency (HF) electron spin echo (ESE), electron-nuclear double resonance (ENDOR) and optically detected magnetic resonance (ODMR) approaches to study diamond nanostructures are examined.     

Optically detected magnetic resonance of α-deuterated 2-indanone

When 2-indanone is optically pumped into the phosphorescent triplet state, the excitation remains localized on the carbonyl moiety. Hence, the hydrogens at the α carbons play an important role in the electronic relaxation. Subtle perturbations can be introduced by exchanging these slightly acidic hydrogens with deuteriums. Various deuterated 2-indanone molecules were synthesized and the properties of their phosphorescent triplet state were experimentally determined by optically detected magnetic resonance (ODMR). Theoretical calculations showed that the shifts in the observed zero-field splitting parameters as a function of deuteration are a result of spin-orbit coupling. Finally, unexpected features in the ODMR spectra are explained in terms of the molecule's crystal structure.     

(GaP)n,(GaP)+n和(GaP)-n(n=1～6)团簇的几何结构与稳定性

用密度泛函理论(DFT)的B3L YP方法,在6-31G*水平上,对(GaP)n,(GaP)n 和(GaP)n-(n=1~6)团簇的几何结构、红外光谱和热力学稳定性及电子态进行了研究.得到了(GaP)n,(GaP)n 和(GaP)n-(n=1~6)团簇的基态结构.结果表明:团簇的电荷状态对簇合物的结构有影响;在(GaP)n,(GaP)n 和(GaP)n-(n=1~6)团簇中,n=3,5团簇的基态结构较稳定.     

ODMR study of the nature of iron-red photoluminescence in ZnS crystals

Basing upon the ODMR (optically detected magnetic resonance) measurements on the so-called iron-red (Fe-R) luminescence in ZnS it is shown that the emission is due to the radiative capture of either free or weakly bound electron by substitutional Fe³⁺ associated with an unknown defect residing in n.n. Zn position.     

ODMR study of recombination processes in ionic crystals and silicon carbide

The paper presents the results of optically detected magnetic resonance (ODMR) study of tunneling and photostimulated recombination processes in irradiated ionic crystals, observation of resonance effects using optically pumped F-centres, and investigation of spin-dependent recombination processes in silicon carbide doped with boron, aluminium, gallium and scandium.     

Application of optically detected magnetic resonance to low temperature solid state photoreactions of halogenated coumarines

Optically activated solid state reactions are observed in doped molecular crystals of p-dibromobenzene. The photoreactions result in the formation of stable photoproducts. These products are identified and characterized by a combination of optically detected magnetic resonance methods such as ODMR and ODNQR. Especially optically detected nuclear quadrupole resonance on chlorine and bromine nuclei demonstrates the possibilities to reveal structural information concerning the reaction cage with high sensitivity and spectral resolution.