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1.
Optically detected EPR investigations have been performed on the recombination luminescence (RL-EPR) of LiBaF 3 crystal, X-irradiated at T=4.2 K. RL-EPR lines of V K- centres were found, as well as further lines of a defect with
and an axial g-tensor with its main axis along a [1 0 0] direction of the crystal. Measurements of the magnetic circular dichroism of the absorption (MCDA) have been performed on LiBaF3 crystals X-irradiated at two temperatures (4.2 K and RT). After irradiation at T=4.2 K, the main MCDA bands peak at 453 and 500 nm, but after irradiation at T=300 K, the main bands peak at 444 and 390 nm, there is a change of the sign between the peaks in both cases. The MCDA-detected EPR (MCDA-EPR) consists of one broad EPR line in both cases and belong to electron trap centres. Analysis of half-widths of MCDA-EPR lines showed that both defects should have g-tensors with their axes along the [1 0 0] direction. This symmetry has to be expected for F-type centres in LiBaF3 crystals. The low-temperature electron centre has a more perturbed ground state as the RT centre. 相似文献
2.
In LiBaF 3 crystals both valence–core transitions (5.4–6.5 eV) and so-called self-trapped exciton luminescence (about 4.3 eV) are important for practical application. Here, we present a study of 4.3 eV luminescence under photo- and thermostimulation after X-irradiation of undoped LiBaF 3 crystals at various temperatures. Optically stimulated luminescence as a result of electron recombination with both self-trapped holes and holes localized at some defects, were observed after X-irradiation below 130 K and that of electron recombination with defect-localized holes was observed after X-irradiation above 130 K. The spectra of thermo-stimulated luminescence (TSL) contain a broad band about 4 eV related to the electron (high-energy side) or hole (low-energy side) recombination depending on TSL peak temperature. 相似文献
3.
The radiation-induced defect types in LaB 3O 6 and Li 6Gd(BO 3) 3:Ce single crystals have been determined taking into account crystal-lattice features, absorption characteristics, photo- and thermostimulated luminescence data. The possible activator center models in Li 6Gd(BO 3) 3:Ce crystals are proposed. 相似文献
4.
We report on the scintillation properties of LiBaF 3 upon irradiation with thermal neutrons. For thermal neutron excitation cross luminescence is not observed, contrary to luminescence under X-ray or γ-ray excitation. 相似文献
5.
On-line measured radiation-induced absorption spectra and their kinetics are presented for the doped PbWO 4, YAlO 3:Ce and CsI crystals. In the doubly doped PbWO 4:Mo,Y crystals the saturation level of the induced absorption increased with Mo concentration up to 2750 ppm. With a higher concentration it again gradually decreased. Yttrium co-doping around 100 ppm improved considerably the radiation hardness of Mo-doped PbWO 4. Characteristic recovery time of these crystals was about 30 min. Positive influence of Zr +4 co-doping on characteristics of a set of YAlO 3:Ce samples resulted in decrease in the induced absorption intensity. The presence of very slow recovery processes was in good agreement with thermoluminescence characteristics above room temperature reported earlier. An absorption band round 420 nm appeared in as-grown CsI crystals doped with Tl, and was related to the oxygen contamination. 相似文献
6.
We have studied thermally and photostimulated recombination processes in PbWO 4 crystals in the temperature interval 90–295 K. We have shown that after x-ray excitation of the crystal at 90 K, the thermally
stimulated luminescence curve shows a relatively intense peak at 110 K and weak peaks at about 173, 191, and 232 K. Exposure
of the PbWO 4 crystal to IR radiation after excitation by x-ray photons leads to the appearance of photostimulated flash luminescence,
a significant decrease in the intensity of the 110 K peak, and a shift of that peak to the 116 K region. But long-wavelength
illumination has less of an effect on the intensity and position of the higher temperature peaks. It is assumed that F − centers are formed in the PbWO 4 crystal at 90 K during x-ray exposure. The thermal light sum released by IR illumination in the temperature region 90–150
K has a maximum at ≈108 K. The nature of this maximum is connected with the complex centers [Pb 3+ + (WO 3-F −)]. Optical and thermal degradation of these centers leads to the appearance of emission in the green region of the localized
exciton spectrum. 相似文献
7.
From the temperature dependence of the line—band luminescence intensity ratio of LiBaF3: Eu2+ a 4 f−5 d activation energy (Δ) of 800 cm −1 is derived, being much higher than the value reported in the literature (100 cm −1). The temperature dependence of the luminescence decay can be well described with Δ = 800 cm−1 and with 4f−4f and 5d−4f radiative probabilities of 4×10 2s−1 and 6×10 5s−1, respectively. 相似文献
8.
The results of study on luminescence and recombination processes in the large LiB 3O 5 single crystals are reported. It was shown that the luminescence at 295 nm is excited by photons with energy exceeding the band gap energy, by an electron beam, and also in recombination processes. Four peaks of thermoluminescence at 130, 180, 240 and 330 K are revealed, their parameters are fixed, and the origin of the trapping and recombination centers are determined. The most acceptable models of recombination processes and the origin of the LiB 3O 5 luminescence are discussed. 相似文献
9.
The interference of optical transmission spectra of thin CuGaS 2 single crystals is measured in E||c and E⊥c polarizations. The spectral dependencies of the refractive indexes n o, n e and Δn = n o − n e near the absorption edge have been determined from interference spectra. The intersection of refractive indexes at two wavelengths has been revealed at 300 K and 10 K. The characteristics of Band-Pass-Mode Filter and Band-Elimination-Mode Filter have been measured, which possess 7 narrow absorption (transmission) bands and represent a comb filter. The characteristics of these filters have been studied. 相似文献
10.
Photoluminescence (PL), photostimulated luminescence (PSL), thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) studies were carried out on LiYF 4:U 4+ and pure LiYF 4 crystals. The PL and EPR investigations have identified the presence of Eu 3+, Tb 3+ and Gd 3+ ions in both of these crystals possibly due to their existence in the starting materials. The luminescence observed during afterglow, PSL and TSL revealed that emission occurs at wavelength positions 382, 413, 437 and 544 nm, which are characteristic of Tb 3+ ions. The present investigations using PSL and TSL in combination with PL studies before and after gamma irradiation have revealed that selective energy transfer to Tb 3+ ions occurs during electron–hole recombination processes like PSL and TSL. Even though other luminescent ions (U 4+ and Eu 3+) are present in the system and U 4+/U 3+ ions are participating in electron capture/release processes, the selective energy transfer results in Tb 3+ ions acting as luminescence centers. 相似文献
11.
Yb 3+-doped YAlO 3 single crystals were grown by the Czochralski method with a radio frequency heating system. The starting melt compositions of Y 1−xYb xAlO 3 were varied as x=0.02, 0.1, 0.2, 0.3 and 0.45. Photo- and thermo-luminescence characteristics including emission decays were measured within 4–300 K. Very fast charge transfer luminescence of Yb 3+ was found, with the typical double peak spectrum at 345 and 525 nm. At room temperature the photoluminescence and scintillation decay curves show a leading subnanosecond decay component without any additional slower processes. The high density of Yb-rich YAlO 3 makes this material a promising candidate for fast scintillators. 相似文献
12.
The influence of doping (with F, Gd and Mo ions) and co-doping (with F, Gd or F, Gd, Mo ions) of PbWO 4 crystals was investigated. It is shown that even a small amount of specific impurities (especially F ions) causes an important redistribution of the point defects and changes the physical properties of the crystals. The cell parameters were refined from X-ray powder diffraction data. It was found that the cell parameters of F-doped PbWO 4 samples are larger than those of undoped samples. Photoluminescence and optical transmission spectra of pure and doped PbWO 4 were investigated. 相似文献
13.
The EPR g factors g// and g⊥ for Ti 3+ ions at the trigonal octahedral Li + sites of LiNbO 3 and LiTaO 3 crystals are calculated from the third-order perturbation formulas of g factors for 3d 1 ion in trigonal symmetry. In the calculations, the crystal-field parameters are obtained from the structural data by using the superposition model. The calculated values are in reasonable agreement with the observed values. The results are discussed. 相似文献
14.
A red-emitting phosphor of Eu 3+-doped calcium–tellurium–zinc oxide, Ca 3Te 2(ZnO 4) 3, with a garnet-type structure was synthesized by high temperature solid-state reactions. This phosphor exhibited a strong red emission. The photoluminescence excitation spectrum showed that Ca 3Te 2(ZnO 4) 3:Eu 3+ can be effectively excited by UV–visible light. The property of long-wavelength excitation for this material has a benefit as a red phosphor in application of white light-emitting diodes. The colour coordinates were calculated. The excitation and emission spectra and luminescence decay curves were obtained using a pulsed, tunable, narrowband dye laser. Crystallographic sites and charge compensation mechanism of Eu 3+ ions were discussed. The emission line from Eu 3+ in intrinsic crystallographic site in the lattice was located at 579.56 nm. The emission line from Eu 3+ in another disturbed site, which is created by the defects created by the charge-compensation, was located at 580.88 nm. The disordered crystallographic sites of Eu 3+ are benefit for their strong red luminescence corresponding to the 5D 0→ 7F 2 transition. 相似文献
15.
Gamma irradiated [(CH 3) 4N]InCl 4 and [(CH 3) 4N] 2CdCl 4 single crystals were investigated by electron paramagnetic resonance at ambient temperature, and it has been found that both compounds indicate the existence of (CH 3) 3N + radicals. The g factors were found to be isotropic, and the hyperfine constant for H atoms was measured as 2.86 mT and is isotropic for this radical in these substances. The hyperfine coupling constant of the N nucleus with the hole in (CH 3) 3N + in [(CH 3) 4N]InCl 4 was found to be anisotropic with the Azz=2.92, Ayy=1.62 and Axx=1.40 mT. From these, it has been revealed that the C3v-axis of (CH 3) 3N + radical performs rotational or jumping reorientational motions around a fixed axis, in addition to the rotations of protons in CH 3 groups and the rotational motions of CH 3 groups around the C3v-axis of the radical. The g, and the hyperfine coupling factors of the N nucleus were isotropic in (CH 3) 3N + in [(CH 3) 4N] 2CdCl 4. This indicates the motional behaviour of the radical in this compound is as in a liquid. This isotropic behaviour of the hyperfine coupling constants was found to be same until the attainable lowest temperature of 113 K in our laboratory. 相似文献
16.
研究了提拉法生长的Er3+/Yb3+:Gd3Sc2Ga3O12和Er3+:Gd3Sc2Ga3O12晶体在室温下320—1700nm范围的吸收光谱和500—750nm范围内的上转换荧光谱,同时对其上转换荧光的可能发生机制、途径以及上转换过程可能对Er3+相似文献
17.
本文采用Novocontrol宽频介电谱仪在-100 ℃–100 ℃温 度范围内、0.1 Hz–10 MHz频率范围内测量了表面层打磨前 后CaCu 3Ti 4O 12陶瓷的介电特性, 分析了CaCu 3Ti 4O 12陶瓷的介电弛豫机理. 首先, 基于对宏观“壳-心”结构的定量分析, 排除了巨介电常数起源于表面层效应的可能性; 其次, 基于经典Maxwell-Wagner夹层极化及其活化能物理本质的分析, 排除了巨介电常数起源于经典Maxwell-Wagner极化的可能性; 最后, 依据晶界Schottky势垒与本征点缺陷的本质联系, 提出了巨介电常数起源于Schottky势垒边界陷阱电子弛豫的新机理. 陷阱电子弛豫机理反映了CaCu 3Ti 4O 12陶瓷本征点缺陷、 电导、介电常数之间的本质关系.
关键词:
3Ti 4O 12')" href="#">CaCu 3Ti 4O 12
介电弛豫
Schottky势垒
点缺陷 相似文献
18.
An organic-inorganic hybrid perovskite (C 4H 9NH 3) 4Pb 3I 4Br 6 was synthesized and studied by X-ray diffraction, Raman and infrared spectroscopies, optical transmission and photoluminescence. The title compound, abbreviated (C 4) 4Pb 3I 4Br 6, crystallises in a periodic two-dimensional multilayer structure with P2 1/a space group. The structure is built up from alternating inorganic and organic layers. Each inorganic layer consists of three sheets of Pb X6 ( X=I, Br) octahedra. Raman and infrared spectra of the title compound were recorded in the 100-3500 and 400-4000 cm −1 frequency ranges, respectively. An assignment of the observed vibration modes is reported. Optical transmission measurements, performed on thin films of (C 4) 4Pb 3I 4Br 6, revealed two absorption bands at 474 and 508 nm. Photoluminescence measurements have shown a green emission peak at 519 nm. 相似文献
19.
From measurements of the decrease in the heat (enthalpy) of transition in the solid phase using differential scanning calorimetry, the apparent molar heats of solution, slope Δ Ht/ x, the partial molar heats of solution at infinite dilution, χ, and the heats of solution, Δ Hs°, of Tl + in CsNO 3 crystal and Cs + in TlNO 3 crystal and Rb + in CsNO 3 crystal and Cs + in RbNO 3 crystal along with their recovered lattice energies, Δ HL°, are reported. Δ Hs° of Tl + and Rb + in CsNO 3 crystal are each found to be negligible or zero representing an ideal solid solution, i.e. Δ Hmix=0. The complete phase diagrams of the TlNO 3-CsNO 3 and RbNO 3-CsNO 3 systems with details of the sub-solidus regions are included. The properties of Tl (1−x)Cs xNO 3 and Rb (1−x)Cs xNO 3 compositions are discussed in terms of a ‘mixed crystal’ or ‘crystalline solid solution’ in relation to parallel compositions of Tl (1−x)Rb xNO 3. 相似文献
20.
Surface properties of indium subselenide (In 4Se 3) were studied. It was confirmed, that the superstructure of this crystal is characterized by nanowire-like cylindrical clusters with diameter dimensions of about 20 nm and stairs along the a-axis up to 5 nm, depending on the cleavage conditions. 相似文献
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