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1.
M. D. Volnyanskiĭ M. P. Trubitsyn Yakh’ya A. Kh. Obaĭdat 《Physics of the Solid State》2007,49(8):1453-1456
The temperature-frequency dependences of the permittivity of crystals of lithium heptagermanate Li2Ge7O15 doped with Cr3+ ions are investigated. A dielectric response to reorientation of the dipole moments of the chromium impurity centers is revealed. Anomalies of the permittivity are described within the model of a Debye relaxator. 相似文献
2.
Crystals of the chalcopyrite family, AgGaSe2, AgGaS2, and CdGa2S4, doped with chromium ions have been investigated using high-frequency broad-band EPR spectroscopy in the range 65–530 GHz
at T = 4.2 K. It has been revealed that, in the AgGaSe2 and AgGaS2 crystals, the Cr2+ ions occupy positions with orthorhombic and tetragonal symmetry, whereas the previously investigated CdGaS4 crystals contain only tetragonal centers. The observed spectra have been described in the framework of the spin-Hamiltonian
formalism. Apart from the divalent chromium centers, the EPR lines attributed to non-Kramers ions are observed in the frequency
range 300–450 GHz for all the crystals under investigation. The nature of these lines has been discussed. 相似文献
3.
R. B. Morgunov F. B. Mushenok S. M. Aldoshin N. A. Sanina 《Journal of Experimental and Theoretical Physics》2009,109(4):667-675
The effect of irradiation by ultraviolet light on the effective magnetic moment of a paramagnetic single crystal based on
photochrome spiropyran (Sp) and chromium oxalates Sp3Cr(C2O4)3 molecules is detected. It is shown that the deviation of the temperature dependence of the magnetic moment from the Curie
law is caused not by the exchange interaction, but by electron redistribution between Cr3+ and Cr4+ ions and spiropyran molecules Sp0 and Sp+. Analysis of the angular dependence of EPR spectra makes it possible to determine the contribution of Cr3+ ions to the magnetic properties of the crystals and to determine the crystal field parameters D = 0.619 cm−1 and E = 0.024 cm−1. Irradiation of hydrated samples by ultraviolet light leads to intensity redistribution of EPR lines attributed to Cr3+ and Sp0. Thermally stimulated paramagnetism of triplet states of spiropyran ions Sp+ and the SpI salt is observed. 相似文献
4.
A. A. Konovalov V. F. Tarasov V. B. Dudnikova E. V. Zharikov 《Physics of the Solid State》2009,51(8):1626-1633
Divalent and trivalent chromium ions Cr2+ and Cr3+ replacing magnesium ions at octahedral positions in Mg2SiO4: Cr and Mg2SiO4: Cr: Li crystals are investigated by submillimeter EPR spectroscopy in the frequency range 65–230 GHz. The crystals are grown from the melt by the Czochralski method. The content of mixed-valence chromium species in forsterite is analyzed. It is demonstrated that, in crystals grown in argon (the oxygen partial pressure is \(P_{O_2 } \) = 0.01 kPa), approximately half of the chromium ions are in the divalent form. The Cr2+ ions are distributed over the M1 and M2 positions in a ratio of approximately 2: 1. A change in the oxygen partial pressure \(P_{O_2 } \) and the chromium concentration, as well as an additional doping with lithium, does not lead to substantial changes in the distribution of divalent chromium ions over the positions. It is shown that an increase in the oxygen partial pressure \(P_{O_2 } \) from 0.01 to 2.00 kPa results in a decrease in the coefficient of divalent chromium distribution between the crystal and the melt. Doping with lithium also decreases the concentration of Cr2+ centers. In crystals grown without lithium, approximately half of the trivalent chromium ions are associated with magnesium vacancies. The addition of lithium leads to the destruction of these associates, an increase in the concentration of individual Cr3+ centers, and the formation of lithium associates with trivalent chromium ions. The conditions for the formation of associates of trivalent chromium ions with lithium ions are optimum when the crystal contains approximately identical amounts of Cr3+ and Li+ ions. Doping with lithium increases the concentration of Cr3+ ions and, thus, decreases the fraction of Cr2+ and Cr4+ ions in the total content of chromium centers. 相似文献
5.
Synthetic single crystals of chromium-and lithium-doped forsterite, namely, (Cr,Li): Mg2SiO4, are studied using electron paramagnetic resonance spectroscopy. It is revealed that, apart from the known centers Cr3+(M1) and Cr3+(M2) (with local symmetries Ci and Cs, respectively), these crystals involve two new types of centers with C1 symmetry, namely, Cr3+(M1)′ and Cr3+(M2)′ centers. The standard parameters D and E in a zero magnetic field [zero-field splitting (ZFS) parameters expressed in GHz] and principal components of the g tensor are determined as follows: D=31.35, E=8.28, and g=(1.9797, 1.9801, 1.9759) for Cr3+(M1)′ centers and D=15.171, E=2.283, and g=(1.9747, 1.9769, 1.9710) for Cr3+(M2)′ centers. It is found that the lowsymmetric effect of misalignment of the principal axes of the ZFS and g tensors most clearly manifests itself (i.e., its magnitude reaches 19°) in the case of Cr3+(M2)′ centers. The structural models Cr3+(M1)-Li+(M2) and Cr3+(M2)-Li+(M1) are proposed for the Cr3+(M1)′ and Cr3+(M2)′ centers, respectively. The concentrations of both centers are determined. It is demonstrated that, upon the formation of Cr3+-Li+ ion pairs, the M1 position for chromium appears to be two times more preferable than the M2 position. Reasoning from the results obtained, the R1 line (the 2E → 4A2 transition) observed in the luminescence spectra of (Cr,Li): Mg2SiO4 crystals in the vicinity of 699.6 nm is assigned to the Cr3+(M1)′ center. 相似文献
6.
The luminescent properties of Eu3+ and Eu2+ ions in sodium pyrophosphate, Na4P2O7, have been studied. The excitation spectrum of the Eu3+ emission in Na4P2O7 consists of several sets of bands in the range 280–535 nm due to 4f–4f transitions of Eu3+ ions and a broad band with a maximum at about 240 nm interpreted to be due to a charge transfer (CT) transition from oxygen
2p states to empty states of the Eu3+ 4f6-configuration. Although the CT band energy is large enough, the quantum efficiency (η) of the Eu3+ emission in Na4P2O7 under CT excitation was estimated to be very low (η ≤ 0.01). In terms of a configurational coordinate model, this fact is
interpreted as a result of the high efficiency of a radiationless relaxation from the CT state to the 7F0 ground state of Eu3+ ions occupying sodium sites in Na4P2O7. A strong reducing agent is required in order to stabilize Eu2+ ions in Na4P2O7 during the synthesis. Several nonequivalent Eu2+ luminescence centers in Na4P2O7 were found. 相似文献
7.
V. F. Lebedev I. D. Ryabov A. V. Gaister A. S. Podstavkin E. V. Zharikov A. V. Shestakov 《Physics of the Solid State》2005,47(8):1504-1506
Based on the results of a comparative analysis of luminescence spectroscopy and EPR spectroscopy data, it was found for the first time that the wide-band luminescence of Cr3+ ions in a forsterite crystal is due to the Cr3+-VMg center or, in a crystal additionally doped with lithium, to a Cr3+-Li+ center. For the first time, tunable laser action was obtained with Cr3+-Li+ centers responsible for the wide-band luminescence. 相似文献
8.
T. N. Vasilevskaya A. A. Kaplyanskii A. B. Kulinkin S. P. Feofilov 《Physics of the Solid State》2003,45(5):961-968
The properties of Cr3+-doped Li2Ge7O15 (LGO) lithium germanate nanocrystals produced in lithium germanate glasses under isothermal heating were studied. The samples were characterized by x-ray diffraction and small-angle scattering, as well as by transmission electron microscopy. The luminescence spectra of the impurity chromium measured in lithium germanate glasses containing LGO crystals revealed transitions in Cr3+ ions residing in the glass phase and in LGO crystallites starting from extremely small clusters. This provided the possibility of following the process of crystallization of the lithium germanate glass from Cr3+ luminescence spectra. The effects observed in the Cr3+ luminescence spectrum revealed a ferroelectric phase transition in LGO nanocrystals embedded in the glass. 相似文献
9.
The broadband luminescence of chromium optical centers with strongly overlapping spectral lines and similar emission probabilities
from excited 4
T
2 states of red and green Cr3+ centers in stoichiometric magnesium-doped lithium niobate crystals has been separated for the first time. The spectral-luminescence
characteristics and parameters of intracenter interaction between red and green optical Cr3+ centers in stoichiometric lithium niobate have been calculated. The luminescence quantum efficiencies of red and green chromium
centers are determined. 相似文献
10.
Three different photomagnetic effects caused by ultraviolet light in paramagnetic crystals based on molecules of spiropyrans
(Sp) Sp3Cr(C2O4)3 and SpI have been revealed and separated: (1) in the high-temperature range (30–300 K), the photomagnetic effect in Sp3Cr(C2O4)3 is determined by the charge transfer between chromium ions and spiropyran molecules; (2) in the low-temperature range (2
K), the photomagnetic effect in Sp3Cr(C2O4)3 is due to the photoisomerization of spiropyran molecules, the change in the crystal field, and the splitting of the levels
of Cr3+ ions in zero field; and (3) in the temperature range 2–20 K, the generation of radiation-induced paramagnetic defects contributes
to the magnetic moment of the organic sublattice Sp+. 相似文献
11.
K. A. Subbotin V. A. Smirnov E. V. Zharikov A. V. Gaĭster I. A. Shcherbakov L. D. Iskhakova 《Optics and Spectroscopy》2000,89(1):56-61
Single crystals of a new promising laser material, Cr4+-doped germanium eucryptite Cr4+:LiAlGeO4, are grown from the melt for the first time. The crystals grown exhibit nonlinear optical properties. Absorption and luminescence spectra of the crystals and their luminescence decay are studied at various temperatures. The luminescence lifetime at 1.2 μ m at 300 K is 10 μ s. Active centers in the crystal are identified, and crystal field parameters are estimated. 相似文献
12.
The effects of dopant on the electrochemical properties of spinel-type Li3.97M0.1Ti4.94O12 (M = Mn, Ni, Co) and Li(4-x/3)CrxTi(5-2x/3)O12(x = 0.1, 0.3, 0.6, 0.9, 1.5) were systematically investigated. Charge-discharge cycling were performed at a constant current
density of 0.5 mA/cm2 between the cut-off voltages of 3.0 and 1.0 V, the experimental results showed that Cr3+ dopant improved the reversible capacity and cycling stability over the pristine Li4Ti5O12. The substitution of the Mn3+ and Ni3+ slightly decreased the capacity of the Li4Ti5O12. Dopants such as Co3+ to some extent worsened the electrochemical performance of the Li4Ti5O12. 相似文献
13.
The results of studying the characteristics of an intracavity laser spectrometer based on a polycrystalline Cr2+:ZnSe laser operating in a pulse-periodic regime with the pulse-repetition rate of 3 kHz and pulse duration of ∼50 ns are
presented. Intracavity spectra of absorption of NH3 and CH4 gases in the vicinity of 2.35 μm are measured. The estimate of the spectrometer sensitivity is provided. 相似文献
14.
The electron paramagnetic resonance (EPR) parameters (g-factors g
‖, g
⊥ and zero-field splitting D) of two tetragonal 3d3 impurity centers M3d-VMg and M3d-Li+ (where M3d = Cr3+ or Mn4+, VMg is the Mg2+ vacancy) in M3d-doped MgO crystals are calculated from the high-order perturbation formulas including both the crystal-field (CF) and the
charge-transfer (CT) mechanisms for 3d3 ions in the tetragonal symmetry. The calculated results are in reasonable agreement with the experimental values. From the
calculations, it can be found that the relative importance of the CT mechanism for EPR parameters increases with increasing
valence state of the 3d3 ion. So, for the high-valence 3d
n
ions in crystals, a reasonable explanation of EPR parameters should take into account both CF and CT mechanisms. The defect
structures (characterized by the displacement ΔR of O2− in the intervening M3d and VMg or Li+ at the Mg2+ site) for these tetragonal impurity centers are obtained from the calculations. The results are consistent with the expectations
based on the electrostatic interactions. 相似文献
15.
Yu. V. Zorenko V. P. Savchin V. I. Gorbenko T. I. Voznyak T. E. Zorenko V. M. Puzikov A. Ya. Dan’ko S. V. Nizhankovskii 《Physics of the Solid State》2011,53(8):1620-1625
Luminescence and scintillation properties of Y3Al5O12:Ce single crystals grown from the melt by the Czochralski and horizontal directed crystallization methods in various gas
media and Y3Al5O12:Ce single-crystal films grown by liquid-phase epitaxy from a melt solution based on a PbO-B2O3 flux have been comparatively analyzed. The strong dependence of scintillation properties of Y3Al5O12:Ce single crystals on their growth conditions and concentrations of YAl antisite defects and vacancy defects has been established. Vacancy defects are involved in Ce3+ ion emission excitation as the centers of intrinsic UV luminescence and trapping centers. It has been shown that Y3Al5O12:Ce single-crystal films are characterized by faster scintillation decay kinetics than single crystals and a lower content
of slow components in Ce3+ ion luminescence decay during high-energy excitation due to the absence of YAl antisite defects in them and low concentration of vacancy defects. At the same time, the light yield of Y3Al5O12:Ce single-crystal films is comparable to that of single crystals grown by directed crystallization due to the quenching effect
of the Pb2+ ion impurity as a flux component and is slightly lower (∼25%) than the light yield of single crystals grown by the Czochralski
method. 相似文献
16.
Ho3+–Yb3+ co-doped Y2O3 nanocrystals were synthesized by firing hydroxy carbonate precursors. Yb3+-concentration-dependent up-conversion properties of Ho3+ in Y2O3 nanocrystals have been investigated. The relative intensity of up-converted red emission increases more quickly than that of the green and the near-infrared ones with the enhancement of the concentration of Yb3+. It is believed that the energy process 5
S
2 (5F4) (Ho) + 5
I
7 (Ho) →5
I
6 (Ho)+5
F
5 (Ho) plays an important role in the population of the 5
F
5 level of Ho3+. The result indicates that the intensity ratio of the green emission to the red one can be tuned by changing the sensitizer concentration. PACS 78.55.-m 相似文献
17.
A. M. Ulyashenko N. V. Nikonorov A. K. Przhevuskii 《Bulletin of the Russian Academy of Sciences: Physics》2007,71(2):159-163
Forsterite nano glass-ceramics doped with tetravalent chromium ions is synthesized, and the spectral and luminescence properties of this material are investigated. A technique for measuring the absolute quantum yield of Cr4+ luminescence is proposed and implemented experimentally. The luminescence spectra and the absolute quantum yield of Cr4+ luminescence of the forsterite nano glass-ceramics are compared with those of the forsterite single crystal and calcium aluminate glass doped with tetravalent chromium ions. 相似文献
18.
We have investigated the photoluminescence (PL) and photostimulated luminescence (PSL) spectra at 300 K to study the effect
of isoelectronic impurities K+ and I− on the formation and energy structure of Eu2+-VCs isolated dipole centers and aggregate centers in the form of single crystals of CsEuBr3 in CsBr:Eu2+ single crystals. We have shown that K+ and I− impurities in a concentration of 5 mol% do not have a substantial effect on the energy spectrum of isolated dipole centers
in CsBr:Eu2+ single crystals and the processes for the formation of such centers during growth of CsBr:Eu single crystals from the melt
by the Bridgman method. We have established that in Cs0.95K0.05Br:Eu2+, more favorable conditions are realized for the formation of aggregate centers than in CsBr:Eu2+ and CsBr0.95K0.05Br:Eu2+ single crystals. So in order to improve the storage properties of phosphors based on CsBr:Eu2+, in particular for increasing the efficiency of PSL excitation, it is expedient to dope them with K+ impurity in a concentration up to 5 mol%.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 5, pp. 627–630, September–October, 2007. 相似文献
19.
A. P. Voitovich V. S. Kalinov N. N. Naumenko L. P. Runets A. P. Stupak 《Journal of Applied Spectroscopy》2010,77(2):247-254
A method is developed for determining the mean lifetime of anion vacancies in dielectric crystals following irradiation. This
method is used to study the temporal kinetics of the concentrations of vacancies and F
2+ color centers in lithium fluoride crystals irradiated by ionizing radiation. It is then possible to study the dependences
of the vacancy lifetime on the concentration of F
1 color centers, temperature, and impurity content of a crystal. Vacancy and F
2+ color lifetimes determined by this method are given. 相似文献
20.
I. N. Ogorodnikov I. N. Sedunova L. I. Isaenko S. A. Zhurkov 《Physics of the Solid State》2012,54(3):485-492
This paper reports on a study of the luminescence emitted by Li6Gd(BO3)3: Ce3+ crystals under selective photoexcitation to lower excited states of the host ion Gd3+ and impurity ion Ce3+ within the 100–500-K temperature interval, where the mechanisms of migration and relaxation of electronic excitation energy
have been shown to undergo noticeable changes. The monotonic 10–15-fold increase in intensity of the luminescence band at
3.97 eV has been explained within a model describing two competing processes, namely, migration of electronic excitation energy
over chains of Gd3+ ions and vibrational energy relaxation between the 6
I
j
and 6
P
j
levels. It has been shown that radiative transitions in Ce3+ ions from the lower excited state 5d
1 to 2
F
5/2 and 2
F
7/2 levels of the ground state produce two photoluminescence bands, at 2.08 and 2.38 eV (Ce1 center) and 2.88 and 3.13 eV (Ce2
center). Possible models of the Ce1 and Ce2 luminescence centers have been discussed. 相似文献