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1.
The electron/hole trapped centres created during internal irradiation in239Pu doped K2Ca2(SO4)3 were investigated using electron paramagnetic resonance (EPR), thermally stimulated luminescence (TSL) and photoacoustic spectroscopic studies (PAS). These techniques were used to identify the defects and characterize the thermally induced relaxation processes. TSL studies of self (α)/γ-irradiated239Pu doped K2Ca2(SO4)3 revealed two glow peaks around 400 and 433K. Plutonium introduced as Pu4+ was partly reduced to Pu3+ due to self irradiation. This was ascertained from PAS studies. EPR studies carried out on these samples showed the formation of radical ions SO 4 , SO 3 , O 3 , etc. The thermal destruction of SO 4 ion was found to be associated with the prominent glow peak around 433K. Pu3+ was found to act as luminescent centre for the observed TSL glow. The trap depth for the glow peak at 433K has been determined from TSL and EPR data.  相似文献   

2.
Electron paramagnetic resonance (EPR) and thermally stimulated luminescence (TSL) studies were conducted onγ-irradiated CaSO4:UO 2 2+ to elucidate the role of the electron/hole traps in thermally stimulated reactions and to obtain the trap parameters (trap depth and frequency factor). Intense TSL glow peaks around 140, 375, 400 and 438±2K are observed and their spectral characteristics have shown that UO 2 2+ and UO 6 6− act as luminescent centres. EPR studies have shown the peaks at 140 and 400/438K to be associated with the thermal destruction of O and SO 4 radical ion in two stages respectively. The maximum rate of thermal destruction of SO 4 ions (as seen by EPR) in various alkaline earth sulphate matrices investigated in our laboratory is also summarized. The activation energy which characterizes the electron transfer reaction between SO 4 and the dopant ion lies in the range of (0.95±0.15 eV). This value is independent of the dopant and therefore seems to be characteristic of the binding energy of hole in the SO 4 radical ion.  相似文献   

3.
Thermally stimulated luminescence (TSL) studies of gamma-irradiated uraniumdoped K2Ca2(SO4)3 revealed two glow peaks around 400 K and 435 K. Electron paramagnetic resonance (EPR) studies carried out on these samples have shown the formation of the radical ions SO 4 , SO 3 , SO 2 and O 3 . From the study of the thermal stabilities of these radical ions, it was found that the thermal destruction of SO 2 and SO 4 radical ions are associated with the glow peaks observed around 400 K and 435 K respectively. Uranate ion was identified as the luminescent centre for the observed TSL glow. The trap depth values for the glow peaks have been determined from TSL data.  相似文献   

4.
Er and Yb co-doped ZnAl2O4 phosphors were prepared by solution combustion synthesis and the identification of Er and Yb were done by energy-dispersive X-ray analysis (EDX) studies. A luminescence at 1.5 μm, due to the 4I13/24I15/2 transition, has been studied in the NIR region in Er and Yb co-doped ZnAl2O4 phosphors upon 980 nm CW pumping. Er-doped ZnAl2O4 exhibits two thermally stimulated luminescence (TSL) peaks around 174°C and 483°C, while Yb co-doped ZnAl2O4 exhibits TSL peaks around 170°C and 423°C. Electron spin resonance (ESR) studies were carried out to identify defect centres responsible for TSL peaks observed in the phosphors. Room temperature ESR spectrum appears to be a superposition of two distinct centres. These centres are assigned to an O ion and F+ centre. O ion appears to correlate with the 174°C TSL peak and F+ centre appears to relate with the high temperature TSL peak at 483°C in ZnAl2O4:Er phosphor.  相似文献   

5.
Electron paramagnetic resonance (EPR) evidence is presented for the radiation stabilization of pentavalent uranium in CaO matrix. From the theoretical predictions ofg value for U5+ in axial symmetries, it was concluded that U5+ at Ca2+ site is associated with a second neighbour charge compensating Ca2+ vacancy. EPR measurements also revealed the presence of Mn2+, Mn4+ and Cu2+ impurities in the samples. The thermal stability of U5+ was investigated using EPR and thermally stimulated luminescence (TSL) techniques. The TSL and EPR studies on gamma irradiated uranium doped calcium oxide samples had shown that the intense glow peak at 540 K is associated with the reduction in the intensity of EPR signal of U5+ ion around this temperature. This peak is associated with the process U5++hole→U6+*→U6++hv. The activation energy for this process was determined to be 1.4eV.  相似文献   

6.
YAG phosphor powders doped/codoped with Er3+/(Er3+ + Yb3+) have been synthesised by using the solution combustion method. The effect of direct pumping into the 4I11/2 level under 980 nm excitation of doped/codoped Er3+/Yb3+−Er3+ in Y3Al5O12 (YAG) phosphor responsible for an infrared (IR) emission peaking at ∼1.53 μm corresponding to the 4I13/24I15/2 transition has been studied. YAG exhibits three thermally-stimulated luminescence (TSL) peaks at around 140°C, 210°C and 445°C. Electron spin resonance (ESR) studies were carried out to identify the centres responsible for the TSL peaks. The room temperature ESR spectrum of irradiated phosphor appears to be a superposition of two distinct centres. One of the centres (centre I) with principal g-value 2.0176 is identified as O ion, while centre II with an isotropic g-factor 2.0020 is assigned to an F+ centre (singly ionised oxygen vacancy). An additional defect centre is observed during thermal-annealing experiments and this centre (assigned to F+ centre) seems to originate from an F-centre (oxygen vacancy with two electrons) and these two centres appear to correlate with the observed high-temperature TSL peak in YAG phosphor.  相似文献   

7.
Yttrium borate doped with uranium was prepared by mixing and heating yttrium oxide obtained through oxalate precipitation route, boric acid and requisite amount of nuclear-grade uranium oxide at high temperature. Photoluminescence (PL), thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) studies were carried out on gamma-irradiated doped/undoped yttrium borate samples in the temperature range 300-600 K. TSL studies showed the presence of two glow peaks at 414 and 471 K. PL studies along with lifetime decay investigation suggested uranium goes in the matrix as UO22+. EPR studies showed the presence of O2radical ion along with electron trapped in defect centres, which might have been produced for charge compensation. Apart from this, CO2 radical was also observed in the system having its origin from residual oxalate ion. Temperature dependence EPR studies of the observed radical confirmed the involvement of the CO2 and dioxide radical ion in the observed glow peaks. By correlating the TSL, PL and ESR data, probable mechanism is proposed for the observed TSL glow in the system.  相似文献   

8.
Mg1−x CuxO solid solutions having an NaCl structure with 0⩽x⩽0.20 are synthesized and Cu-Mg1−x CuxO structures are prepared for superconductivity studies. The magnetic susceptibility χ, electron paramagnetic resonance (EPR), and electrical conductivity of the solid solutions are studied at temperatures of 5–550 K. It is shown that χ −1(T) obeys the Curie-Weiss law with a paramagnetic Curie temperature Θ close to zero and an effective magnetic moment μ eff=1.9 μ B, close to the 1.73 μ B of a Cu2+ ion with spin S=1/2. The width ΔH of the EPR line depends weakly on temperature and increases as x is raised. The volume narrowing of the EPR linewidth ΔH is used to estimate the exchange interaction parameter, 3×10−4 eV. The g-factor is close to 2 and is temperature independent. The electrical conductivity of Mg1−x CuxO at T=300 K is ≈10−11–10−12−1 cm−1 for x=0 and increases to 10−5–10−6−1 cm−1 for x=0.15–0.20. The conductivity is p-type. Magnetic shielding is observed in Cu-Mg1−x CuxO structures with x=0.15 and 0.20. The possible connection of this phenomenon with interference superconductivity in the contact layer of the structure is discussed. Fiz. Tverd. Tela (St. Petersburg) 41, 293–296 (February 1999)  相似文献   

9.
The field dependence of the nuclear spin-lattice relaxation (SLR) of cold implanted 82Br (T ≤ 25 mK) in α-Fe single crystals was investigated with nuclear magnetic resonance of oriented nuclei (NMR/ON) at low temperatures as experimental technique. The SLR at the lattice sites with the hyperfine fields found by earlier NMR/ON experiments was measured as a function of the applied external magnetic field B ext parallel to the three principle axes [100], [110] and [111] of the iron single crystal. The data were evaluated with the full relaxation formalism in the single impurity limit and for comparison also with the often employed model of a single exponential function with an effective relaxation time T 1′. With a phenomenological model the high field values of the relaxation rates r ∞, [100]′ = 6.6(2) · 10−15 T2sK−1, r ∞, [110] = 5.4(2) · 10−15 T2sK−1 and r ∞, [111] = 5.2(1) · 10−15 T2sK−1 were obtained.  相似文献   

10.
11.
ZnAl2O4:Tb phosphor was prepared by combustion synthesis. ZnAl2O4:Tb exhibits three thermally stimulated luminescence (TSL) peaks around 150, 275 and 350 °C. ZnAl2O4:Tb exhibits optically stimulated luminescence (OSL) when stimulated with 470 nm light.Electron spin resonance (ESR) studies were carried out to identify defect centres responsible for TSL peaks observed in ZnAl2O4:Tb. Two defect centres are identified in irradiated ZnAl2O4:Tb phosphor and these centres are assigned to V and F+ centres. V centre appears to correlate with the 150 °C TSL peak, while F+ centre could not be associated with the observed TSL peaks.  相似文献   

12.
We used the spin-Hamiltonian method for the analysis of the electron paramagnetic resonance (EPR) spectrum of Fe3+ as a probe ion in (NH4)2AlF5·H2O single crystalline basic material. The theoretical expressions for the magnetic field (at which the fine structure transition lines appear) versus the angle between the magnetic field and the axis of symmetry of the magnetic complex are also given. These values were calculated by applying the perturbation theory to the second-order terms. From the experimental results (at 300 K and 9.21 GHz), the spin-Hamiltonian parameters were deduced:D=(668±10)·10−4 T,E=(−56±10)·10−4 T,a=(−54±10)·10−4 T,F=(30±10)·10−4 T. An isotropic superhyperfine structure was evidenced for the five fluorine ions. The obtained EPR data were used to determine the local symmetry of the Al3+ ion. A good agreement with X-ray diffraction measurements was found.  相似文献   

13.
A method for studying the reactions of surface alkoxy radicals with O2 at temperatures of 230 to 300 K is described. Alkoxy radicals were generated directly in the cavity of an EPR spectrometer. Surface organic radicals, prepared from paraffin wax ((CH3)2(CH2) n , n = 16–20), were applied to Aerosil particles from a solution in heptane. The Aerosil sample was placed in the cavity of the EPR spectrometer in a cylindrical cup with a central hole for pumping out gases and exposed to H atoms. In this way, it is possible observe a steady increase in the EPR signal from the surface radicals. To measure the rate constant at tropospheric temperatures, the reaction tube was placed in a Teflon jacket, through which cool nitrogen vapor was pumped. The temperature in the reactor was varied from 230 to 300 K. The recorded EPR spectra belong to the (RO) s radical. After obtaining a stable EPR signal from the surface radicals, treatment with H atoms was stopped, additional flow of O2 was introduced ([O2] = 1014–1016 cm−3), and the reaction of O2 with the surface organic radicals was studied by monitoring the EPR signal decay. The temperature dependence of the rate constant for the (RO) s + O2 → HO2 + ketone was obtained within T = 230–300 K. The extrapolation of the data to real tropospheric conditions ([O2] = 1018 cm−3) was performed.  相似文献   

14.
In the paper the dependence of the photorefraction (PhR) in LiNbO3 and LiNbO3−Fe (0.1 wt%, 0.3wt%) crystals on light intensity (within 1016–1023 quanta·cm−2·s−1 at wavelengths 496.5 nm and 600 nm) and temperature (in the region 100–500 K) is studied. For all the crystals the limiting values of PhR are similar and atT=293 K Δn sat lim ≈3·10−3. In LiNbO3 the temperature dependence of PhR in the range 100–500 K requires to take into account at least two trapping centres.  相似文献   

15.
EPR investigation on xV2O5 · (100 −x)[2P2O5 · Na2O] and xV2O5 · (100 −x)[P2O5 · mNa2O] (m = 1.5 and 2) glass systems was performed. The changes observed in the EPR spectra of xV2O5× (100 −x)[2P2O5 · Na2O] glasses with increasing content of vanadium oxide are explained supposing that these spectra consist of two superposed EPR signals, one with hyperfine structure typical for isolated ions and another one consisting of a broad line without hyperfine structure characteristic for clustered ions. The clustered V4+ ions are not evidenced at low V2O5 contents (x = 5 mol%). The EPR spectra of xV2O5 · (100 −x)[P2O5 · mNa2O] glasses indicate a superposition of two or three hyperfine structures attributed to nonequivalent VO2+ centers. Spin Hamiltonian parameters (g, A), dipolar hyperfine coupling parameter (P) and Fermi contact interaction term (K) have been evaluated. The ratio between the number of clustered and isolated ions was also determined.  相似文献   

16.
The new heteronuclear crystal CuPr2(CCl3COO)8·6H2O, constructed of chains containing copper and praseodymium atoms, has been synthesized and investigated by EPR at 9.3 GHz at temperatures ranging from room temperature down to 10 K. At temperatures T∼300–130 K, EPR spectra are observed which are characteristic of isolated polyhedra of copper ions with g z=2.330±0.005, g x,y =2.053±0.005, A z=139×10−4 cm−1, and A x,y <26×10−4 cm−1. At temperatures T<130 K a complex spectrum is observed, associated with the appearance of weak exchange interactions between the copper ions in the chain (J Cu-CuΣS i·S i+1), comparable in magnitude with the hyperfine interactions J Cu-Cu=0.015 cm−1 at T=10 K. The magnitude of the exchange interaction decreases smoothly as the temperature is raised. It is conjectured that orbitals of the praseodymium ions participate in the process of indirect exchange between the copper ions. Fiz. Tverd. Tela (St. Petersburg) 41, 2154–2157 (December 1999)  相似文献   

17.
Two lead-phosphate glass systems doped with both copper and vanadium ions in different ratios were studied by EPR (electron paramagnetic resonance) method. EPR spectra and parameters (g = 2.44, g = 2.08 andA = 117.6 · 10−4 cm−1) obtained for x(CuO · V2O5)(l−x)[2P2O5 · PbO] glasses withx ≤ 10 mol% suggest a tetrahedral (Td) coordination of Cu2+ ions and not a tetragonally elongated octahedron as has been assumed in previous works. The ground state of the paramagnetic electron is thed xy copper orbital with a 4pz contribution of 6%. For 20 ≤x ≤ 40 mol% a broad line (ΔB = 307 G) characteristic for clustered ions appears atg = 2.18. The V4+ ions are evidenced only in the spectra of x(CuO · 2V2O5)(1 −x)[2P2O5 · PbO] glasses and the resonance parameters suggest a pentacoordinated C4v local symmetry for these ions. The hyperfine structures characteristic for Cu2+ and V4+ ions disappear for 10 ≤x ≤ 40 mol% due to the mixed exchange Cu2+−V4+ pair formation in these glasses.  相似文献   

18.
Electron paramagnetic resonance studies were conducted on the photoinduced charge transfer and also hyperfine interaction of U5+ stabilized in photorefractive matrix LiNbO3. This work deals with: (i) first observation of hyperfine structure due to233U (I=5/2) in its pentavalent state at octahedral sites and comparison with other possible site symmetries, (ii) photoinduced charge transfer as observable by EPR and its relevance to photorefractive behaviour of LiNbO3. The effect of chemical bonding on the hyperfine interaction of 5f 1 configuration was also studied by converting the existing literature data on235U5+ to that of233U5+ by standard methods. This suggests that progressive substitution of oxygen by F, in the series UO 6 7− , (UO5F)6− and (UO4F2)5− drastically decreases the hyperfine coupling constantA , along the local distortion axis. This trend is explained as being due to the absence of ligand ion along the distortion axis at U5+ site in trigonal LiNbO3. The effects of illumination by copper vapor laser (CVL) on the intensity of the U5+ signal was studied in the 10–300K region. The kinetics of decay and restoration of U5+ was also studied between 10–100K range. The decay kinetics was found to obey double exponential. The reduction of concentration of U5+ with CVL-illumination and its restoration in the absence of light show that pentavalent uranium takes part in the photorefractive effects in LiNbO3.  相似文献   

19.
The luminescence and thermally stimulated recombination processes in lithium borate crystals Li6Gd(BO3)3 and Li6Gd(BO3)3:Ce have been studied. The steady-state luminescence spectra under X-ray excitation (X-ray luminescence), temperature dependences of the intensity of steady-state X-ray luminescence (XL), and thermally stimulated luminescence (TSL) spectra of these compounds have been investigated in the temperature range of 90–500 K. The intrinsic-luminescence 312-nm band, which is due to the 6 P J 8 S 7/2 transitions in Gd3+ matrix ions, dominates in the X-ray luminescence spectra of these crystals; in addition, there is a wide complex band at 400–420 nm, which is due to the d → f transitions in Ce3+ impurity ions. It is found that the steady-state XL intensity in these bands increases several times upon heating from 100 to 400 K. The possible mechanisms of the observed temperature dependence of the steady-state XL intensity and their correlation with the features of electronic-excitation energy transfer in these crystals are discussed. The main complex TSL peak at 110–160 K and a number of minor peaks, whose composition and structure depend on the crystal type, have been found in all crystals studied. The nature of the shallow traps that are responsible for TSL at temperatures below room temperature and their relation with defects in the lithium cation sublattice are discussed.  相似文献   

20.
We studied the spectral-luminescent characteristics of the luminescence of mixed-ligand polypyridine-phosphine complexes of ruthenium(II) cis-[Ru(bpy)2(PPh3)X](BF4) n with ligands 2,2′-bipyridyl (bpy) and triphenylphosphine (PPh3) and X = Cl, Br, CN, NO2, NH3, MeCN, pyridine (py), 4-aminopyridine (pyNH2), and 4,4′-bipyridyl (4,4′-bpy) in a 4: 1 EtOH-MeOH alcoholic mixture at 77 K. The radiative and nonradiative deactivation rate constants of the lowest electronically excited state of the complexes are determined. We find that triphenylphosphine has a greater effect on the photophysical characteristics of ruthenium(II) complexes compared to π-acceptor strong-field ligands, such as MeCN, CN, and NO2. At the same time, the characteristics of complexes cis-[Ru(bpy)2(PPh3)X] n+ considerably depend on the nature of the second monodentate ligand X, which is coordinated to ruthenium(II), and correlate with its position in the spectrochemical series of ligands.  相似文献   

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