Neutron-transmutation doping of GaAs — as studied by ESR

Neutron (n⁰) transmutation doping of GaAs has been monitored by electron spin resonance (ESR). Strong evidence was obtained that, apart from fast neutron impact, As_Ga antisite defects are also created by the γ- and β-emissions following thermal n⁰-capture. The As_Ga defects, forming deep midgap states, anneal out at 500°C.     

ESR study of Gd in TmSb: Determination of the host excited crystalline field splitting levels

The ESR thermal broadening of Gd in the metallic Van Vleck paramagnet, TmSb, is used to extract the excited crystalline field splitting energy level, Θ₅⁽²⁾, of Tm⁺³.     

ESR of selenium pairs (Se+2) in silicon

A slight anisotropy of the Se⁺₂ ESR is resolved, revealing [111] axial symmetry. The pair groundstate is a_2u in D_3d symmetry, consistent with the almost complete s-character at the Se sites. The value of g₆ is correlated with the binding energy of Se⁺₂ in a way recently established for simple deep donors in Si.     

Origin of PL intensity increase of CaMgSi2O6:Eu phosphor after baking process for PDPs application

We have synthesized blue-emitting CaMgSi₂O₆:Eu²⁺ (CMS) and evaluated its thermal stability after baking process. To evaluate its thermal stability, CMS was baked in air at 500 and 600 °C for 20 min, respectively, and compared with BaMgAl₁₀O₁₇:Eu²⁺ (BAM) treated in the same condition. After baking process, CMS showed somewhat increased photoluminescence (PL) intensity with baking temperature. To investigate the reasons behind the increase of PL intensity after baking process, vacuum ultraviolet (VUV)/PL, electron spin resonance (ESR), X-ray photoelectron spectroscopy (XPS) techniques were applied. From the ESR and the XPS analyses, it is noted that spectral intensity of Eu²⁺ ion somewhat increased. It was believed that due to charge balance Eu³⁺ ions reduced to Eu²⁺ ions during the baking process in air. It is clear that the concentration of Eu²⁺ increased after the baking process in air and it leads to slight increase of the VUV/PL intensity of CMS phosphor.     

ESR studies on calcite encrustation on Fili neotectonic fault, Greece

Electron spin resonance (ESR) study was done on calcite encrustation on Fili neotectonic fault surface, Greece. Normally such calcite encrustations on fault surfaces are not observed. Significantly, the ESR study has detected the presence of nitrate NO₃²⁻ radical in this calcite encrustation, havingg _⊥=2.0063±0.0001 and hyperfine coupling constantA _⊥=3.44 mT, the second such detection of nitrate NO₃²⁻ radical following a sample from Scott Glacier, Antarctica. From isochronal thermal annealing measurement the NO₃²⁻ radical was found to be quite stable, only fully annealed at 475°C. This study also shows that the ESR, as a tool, can be suitably applied to date the age of formation of the calcite encrustation with SO₃⁻ as an ESR dating signal by additive γ-ray irradiation. A preliminary estimation indicates the age of formation of calcite precipitation at Fili fault, Greece to be about 5600 years.     

Crystal field narrowing and relaxation rates in the ESR spectra of CePd3:Gd intermediate valence compound

The mechanisms that are responsible for the thermal behaviour of the ESR lines CePd₃:Gd are examined. A complete fitting of the ESR spectra, both for single crystals and powdered samples is obtained. The mechanisms considered in this work are the narrowing of the fine structure of Gd³⁺ in low temperatures, the excitation energy of the 4f⁰ to 4f¹ configurations of Ce, and the possible existence of an hybridization hole. Complete fitting of the ESR spectra is obtained in the whole range of temperatures.     

Mechanism of thermoluminescence in Sm- and Eu-doped barium sulphate

Thermoluminescence, TL emission spectra, ESR and optically excited luminescence of BaSO₄:Sm and BaSO₄:Eu were investigated. The optically excited luminescence studies showed that samarium ions were stabilized in the trivalent state in doped samples, and a fraction of these ions was reduced to the divalent state on γ-irradiation. These reduced ions were reoxidized on thermal annealing. Europium was found to be stabilized in the divalent form in BaSO₄:Eu phosphor, both before and after γ-irradiation. These results were further confirmed from the emission spectra of different glow peaks from BaSO₄:Sm and BaSO₄:Eu samples. The ESR spectra of these samples, recorded after γ-irradiation and various post-irradiation thermal annealings, revealed that anion radicals (such as SO₄^?, SO₃^?, SO₂⁺ and O₃^?) are formed on γ-irradiation and get annihilated at temperatures which corresponds to some of the glow peaks. An attempt is made to explain the results by a mechanism, suggested earlier for other impurity-doped BaSO₄ phosphors, in which holes released on thermal activation from anion radicals recombine with the electrons trapped at certain defect centres and the energy thus released is non-radiatively transferred to the impurity ions, which give their characteristic emission.     

ESR of X-ray irradiated boracites

Defect centers induced by X-ray irradiation in zinc-halogen boracites have been observed for the first time by ESR spectroscopy. Four types of defects have been observed: O^?, BO^2?₃, B²⁺ and Zn⁺ O^? and BO^2?₃ centers have been strictly identified as unpaired spins localized, respectively, on a particular oxygen and on a triangular BO₃ unit of the covalent network of the noncubic species. Computer simulations and comparisons with previous results have allowed the formulation of models for these centers. Thermal studies have been carried out. Vanishing of the different signals with temperature is connected either to thermal bleaching or to structural changes.     

A photoluminescence study on lithium ternary compounds

Summary The photoluminescence spectra of LiInS₂ and LiInSe₂ single crystals are investigated in this work. The origin of the coloration and deep emission at 460 nm on LiInS₂ is estimated through ESR measurements to be due to Fe³⁺ ions. The so-called ?near-band-edge emission? was observed at 600 nm and at 77 K on the light yellow LiInSe₂ single crystals. Through a comparison between the results of electrical and photoluminescence measurements it is shown that the red LiInSe₂ has a tailing band structure with high-density residual impurities. Some deep emissions are obtained on yellow and red LiInSe₂. Paper presented at the ?V Intenrational Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

Electron spin resonance study of a CuIr2S4 single crystal

A spinel sulphide CuIr₂S₄ single crystal, which exhibits an orbitally induced Peierls phase transition at ～230?K, is investigated by electron spin resonance (ESR) spectroscopy. The phase transition is clearly manifested on the ESR spectra. It is suggested that the ESR signals are produced by a few non-dimerized Ir⁴⁺ ions. Moreover, an extra ESR spectrum appears at low temperature in addition to the paramagnetic ESR signals of Ir⁴⁺ ions, which is suggested to be caused by the Jahn–Teller effect of the non-dimerized Ir⁴⁺ ions. From the ESR results, it is found that the Jahn–Teller splitting energy ΔE _JT is much smaller than the spin-dimerization gap.     

Filling of the 3d band of the manganese in GdAl2−xMnxforx < 0.2

X-ray, magnetic, electrical resistivity and ESR studies of GdAl_2?xMn_x compounds were performed. The transition temperatures, effective mass, thermal broadening of resonance linewidth and g-factors were obtained. For low concentration of GdMn₂ in GdAl₂ up to 20%, Mn is nonmagnetic. Increasing of the effective mass and the thermal broadening linewidth ESR with increasing x can be explained by the presence of d-electrons.     

深能级对AlGaInP/GaAs异质结双极晶体管性能的影响

用深能级瞬态光谱和光致发光(PL)方法研究了AlGaInP/GaAs异质结双极晶体管(HBT)发射区AlGaInP中的深能级.得到了两个深能级,分别为E_c-E_t1＝0.42eV和E_c-E_t2＝0.59eV,其复合截面为σ_n1＝6.27×10^-17cm²和σ_n2＝6.49×10^-20cm². 关键词：     

Laser-induced shifts and splittings of hyperfine structure lines in electron spin resonance spectra of 35Cl atoms

Laser-induced shifts and splittings of the hyperfine structure (hfs) lines in the electron spin resonance (ESR) spectra of ³⁵Cl atoms have been studied using both dressed-atom theory and semiclassical dispersion theory. In resonant cases, the calculated results by the dressed-atom theory of the ac Stark effect indicate that laser-induced hfs ESR shifts of ³⁵Cl atoms in the ground state 3p^{5 2}P⁰ _3/2 can be more than 1 MHz W^?1 cm², and a single ESR hfs line is split into four lines under the action of a laser beam with intensity 10 W cm^?2. In non-resonant cases, the two theories give similar results for the shifts. The laser-induced broadening of the ESR hfs lines is also calculated and is less than the shifts. The laser-induced shifts in ESR can be observable within the resolution of ESR experiments.     

ESR and Optical Absorption of Ag in a N2 Matrix

Ag atoms isolated in N₂ matrices were studied by simultaneous observation of optical absorption and electron spin resonance (ESR). In matrices with low Ag/N₂ ratios two ESR signals were observed, both of which could be correlated to the well known absorption triplet corresponding to the 5s ²S → 5p ²P resonance transition. One of the two ESR signals disappeared irreversably upon annealing up to 20 K. The stable species is attributed to Ag atoms in a nanocrystalline environment whereas the unstable species corresponds to atoms in the non-crystalline regions between the crystallites. In higher doped matrices a new Ag spectrum showed up, both in the optical absorption and in the ESR. It is assigned to Ag atoms with near-by complexes, possibly Ag clusters.     

ESR study of the undoped heavy-fermion compound YbRh2Si2

The electron spin resonance (ESR) of the heavy-fermion metal YbRh₂Si₂ has been studied. The angular variation and the temperature dependence of the ESR line width have been measured in YbRh₂Si₂ single crystals in the temperature range of 4–25 K. The characteristic spin-fluctuation temperatureT ^* ～ 17 K estimated from these studies coincides very well with other experimental data. A well-behaved ESR signal due to local Yb³⁺ moments strongly supports the localized moment scenario for heavy-fermion quantum critical points.     

ESR investigation of structure and dynamics of paramagnetic centres in lime mortars from Budinjak,Croatia

This study presents the preliminary results of investigation of the types and dynamics of paramagnetic centres in lime mortars from Sveta Petka church in Budinjak, Croatia, using Electron Spin Resonance (ESR) spectroscopy. The excavation in Budinjak discovered a very unique four lobed plan object Sveta Petka, with no additional finds or reliable historical records about the time of its construction. The lime mortars from the church were chosen for analysis in order to characterize the building material and to verify the site chronology by dating them. Lime mortar is valuable but problematic material for luminescence and radiocarbon dating. This type of material has not been dated before using ESR; therefore, careful studies are required to identify the useful paramagnetic centres. The ESR approach suggested in this work concentrates on a calcium carbonate signal. All samples were γ-irradiated in ⁶⁰C bomb with the doses of 1, 10, 20, 50, 80 and 100 kGy. In all spectra signals from Fe³⁺ and Mn²⁺ ions have been observed. Paramagnetic centres which give the ESR signals may be interpreted as CO₂^?, CO₃^?, CO₃^3?, HCO₃^2?, SO₂^?, SO₃^?, PO₂^? and PO₃^2? species. However, all spectra are complex and signals are interfering; therefore, computer resolution enhancement method will be needed in further research. The changes in ESR signals amplitude measured at magnetic field range about 3440–3450 G were analysed versus the dose of irradiation, using Mn²⁺ signals as a reference. Exponential growth of the curve and saturation for doses above 20 kGy were observed; therefore, irradiation with smaller doses is required. These preliminary studies will be helpful in future attempts of dating lime mortars by ESR method.     

KCl:OH-中O2-色心实验研究

通过调制吸收光谱和电子自旋共振(ESR)谱的测量得知,在被高能射线辐照前后,KCl:OH^-中氧的成分主要以O₂^-的形式存在。O₂^-在样品中的浓度随辐照时间增加而增加,直至(OH)^-完全被辐照分解。O₂^-有相当强的稳定性。其存在与产生过程对增加F₂⁺激光色心的稳定性无直接作用。本文还根据ES 关键词：     

Study of ESR spectra of Ce<Superscript>3+</Superscript> ions in polycrystalline Sr<Subscript>2</Subscript>B<Subscript>5</Subscript>O<Subscript>9</Subscript>Br

ESR spectra of Ce³⁺ ions in polycrystalline Sr₂B₅O₉Br were studied, and the two crystallographic positions of the Ce³⁺ ion in this compound were identified on the basis of the data obtained. The ESR spectrum of Ce³⁺ ions with local charge compensation contains a broad line indicating the existence of several types of charge compensation. ESR spectra of Ce³⁺ ions in samples activated additionally by K⁺ ions are similar to those of the regular Ce³⁺ centers, which indicates that the effect of the univalent cation on Ce³⁺ is negligible.     

ESR study of the ferrimagnetic spinel selenide CuCr2Se4

Ferrimagnetic spinel selenide CuCr₂Se₄ has been investigated by the electron spin resonance (ESR) spectroscopy. Experimental results reveal that ESR signals originate from the localized d-shell electrons of Cr³⁺ ions. In addition, the ESR linewidth ΔH _PP increases linearly with decreasing temperature. It is suggested that the spin-orbit coupling may be one of the contributions to the broadening of ΔH _PP . Our ESR results support the model of the ferrimagnetic hybridization between localized 3d ³ electrons of Cr³⁺ with delocalized holes of Se 4p band.     

Thermoluminescence and ESR phenomena in X-ray irradiated mixed alkaline-alkaline earth metal sulfates—I

Abstract

Thermoluminescence (TL) and ESR phenomena induced by X-ray irradiation of the mixed samples of K₂SO₄ and alkaline earth metal sulfate (MgSO₄ or BaSO₄) were investigated in terms of the reactivities and the crystallogrpahic properties. A high intensive TL resulted from the diffusion of a small amount of Mg²⁺ into K₂SO₄ crystals. The amount formed of K₂Mg₂(SO₄)₃, langbeinite, compound had a maximum at the stoichiometric composition. From the ESR measurements, SO^? ₃ radicals were found to be easily formed in the langebeinite by excitation. Both the TL and the ESR phenomena were hardly observed in the K₂SO₄–BaSO₄ system due to little diffusion of Ba²⁺ with much larger radius than Mg²⁺. The results were mainly discussed on the basis of the radii of the component cations in these systems. In addition, the fundamental data as to the application to the ESR dosimetry were obtained.