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1.
The manifestations of phase transitions and the spatial modulation of the structure of the (N(CH3)4)2CuCl4 crystal in its absorption spectra have been investigated. It has been established that the thermooptical-memory effect manifesting
itself in the absorption spectra of this crystal entirely corresponds to the model of ordering of defects and impurities in
a sample with a modulated structure. It is shown that, as a result of stabilization of the crystal studied in the incommensurate
phase, its symmetry and the symmetry of the metal-halogen complex in it lower depending on the defect wave. This manifests
itself as a marked shift of the intraionic-absorption bands and an increase in their intensity.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 3, pp. 386–390, May–June, 2005. 相似文献
2.
A. V. Malakhovskii S. L. Gnatchenko I. S. Kachur V. G. Piryatinskaya A. L. Sukhachev V. L. Temerov 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(5):721-723
Optical absorption spectra of the trigonal crystal of TbFe3(BO3)4 in the vicinity of the 7F6 → 5D4 transition in a Tb3+ ion were studied as a function of temperature (2–70 K) and magnetic field strength (0–60 kOe) at 2 K. The splitting of the
excited states of Tb3+ due to both the magnetic ordering of iron and an external magnetic field was determined. Abrupt splitting of the absorption
lines of Tb3+ at temperature TN of the magnetic ordering of the subsystem of iron was revealed, suggesting that the nature of such splitting is not entirely
magnetic. 相似文献
3.
(NH4)3NbOF6 single crystals were grown, polarization-optical studies were performed, and birefringence was measured over the temperature range 90–500 K. A sequence of first-order structural phase transitions was found at temperatures T 1↓ = 259.7 K and T 2↓ = 257.7 K with temperature hysteresis δT 1 = 0.9 K and δT 2 = 1.9 K. The transitions are accompanied by twinning and the following change in the crystal symmetry: cubic ? tetragonal ? monoclinic. Optical second harmonic generation is found to occur at room temperature, which indicates that the cubic phase is not centrosymmetric. It is assumed that the phase transitions are ferroelastic and ferroelectric in nature. 相似文献
4.
L. Kovács M. Mazzera E. Beregi R. Capelletti 《Applied physics. B, Lasers and optics》2009,94(2):273-277
Several weak absorption bands have been observed in the optical absorption spectra of pure and rare-earth-doped YAl3(BO3)4 single crystals in the 3350– 3650 cm−1 wave number region. Two of them, peaking at about 3377 cm−1 and 3580 cm−1 in the 8 K spectra, appear in most of the samples. They are tentatively attributed to the stretching mode of OH− ions incorporated in the crystal during the growth. An additional absorption band at about 5250 cm−1 at 8 K has also been detected in almost all samples. The temperature and polarization dependences of these bands, and their
possible origin, are discussed. 相似文献
5.
M. Aoki K. Miwa T. Noritake N. Ohba M. Matsumoto H.-W. Li Y. Nakamori S. Towata S. Orimo 《Applied Physics A: Materials Science & Processing》2008,92(3):601-605
We have investigated the structural and dehydriding properties of Ca(BH4)2. It was found that Ca(BH4)2 undergoes a structural phase transformation from an orthorhombic low-temperature (LT) modification into a tetragonal high-temperature
(HT) modification between 433 K and 523 K. The amount of hydrogen desorbed from Ca(BH4)2 during the pressure–composition (p–c) isotherm measurement was 5.9 mass%. This hydrogen desorption is caused by the partial dehydrogenation of Ca(BH4)2 accompanied by the formation of CaH2 and orthorhombic intermediate phases. 相似文献
6.
A. V. Malakhovskii S. L. Gnatchenko I. S. Kachur V. G. Piryatinskaya A. L. Sukhachev V. L. Temerov 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,80(1):1-10
Optical absorption spectra of trigonal crystal TbFe3(BO3)4 have been studied in the region of 7F6 → 5D4 transition in Tb3+ ion depending on temperature (2–220 K) and on magnetic field (0–60 kOe). Splitting of the Tb3+ excited states, both under the influence of the external magnetic field and effective exchange field of the Fe-sublattice,
have been determined. Landé factors of the excited states have been found. Stepwise splitting of one of the
absorption lines has been discovered in the region of the Fe-sublattice magnetic ordering temperature. This is shown to be
due to the abrupt change of equilibrium geometry of the local Tb3+ ion environment only in the excited state of the Tb3+ ion. In general, the magnetic ordering is accompanied by temperature variations of the Tb3+ local environment in the excited states. The crystal field splitting components have been identified. In particular, it has
been shown that the ground state (in D
3 symmetry approximation) consists of two close singlet states of A
1 and A
2 type, which are split and magnetized by effective exchange field of the Fe-sublattice. Orientations of magnetic moments of
the excited electronic states relative to that of the ground state have been
experimentally determined in the magnetically ordered state of the crystal. A pronounced shift of one of absorption lines
has been observed in the vicinity of the TbFe3(BO3)4 structural phase transition. The temperature interval of coexistence of the phases is about 3 K. 相似文献
7.
R. M. Shymkiv S. A. Sveleba I. V. Karpa I. N. Katerynchuk I. M. Kunyo E. I. Phitsych 《Journal of Applied Spectroscopy》2012,78(6):823-828
Optical absorption spectra in thin [N(CH3)4]2CuCl4 crystals in the thickness range 10 μm ≤ d < 100 μm have been studied. Strengthening of the crystal field has been found with
a decrease in the [N(CH3)4]2CuCl4 crystal size. The reasons for absorption band shifts in the visible region depending on the [N(CH3)4]2CuCl4 crystal thickness and the manifestation of a size effect in crystals with an incommensurate superstructure are discussed. 相似文献
8.
F. Guo J. Ru H. Li N. Zhuang B. Zhao J. Chen 《Applied physics. B, Lasers and optics》2009,94(3):437-441
Lithium terbium molybdate (LiTb(MoO4)2) single crystal was grown by the Czochralski method. The lattice parameters of the crystal were determined by X-ray diffraction
analysis. The absorption coefficient and the Faraday rotation spectrum (B=1.07 T) were investigated at wavelengths of 400–1500 nm at room temperature. Verdet constants of LiTb(MoO4)2 crystal at 532-, 633- and 1064-nm wavelengths were measured by the extinction method. The results show that LiTb(MoO4)2 crystal has a larger magneto-optical figure of merit than that of terbium gallium garnet at wavelengths of 600–1500 nm. 相似文献
9.
I. N. Ogorodnikov N. E. Poryvai I. N. Sedunova A. V. Tolmachev R. P. Yavetskiy 《Optics and Spectroscopy》2011,110(2):266-276
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
10.
A. M. Pashaev B. G. Tagiev O. B. Tagiev Kh. B. Ganbarova 《Journal of Applied Spectroscopy》2011,78(2):266-271
We have ground bulk samples to obtain nanoparticles of (Ga2S3)1–x
(Eu2O3)
x
solid solutions, the sizes of which were determined using an atomic force microscope. The photoluminescence spectra of the
nanoparticles were studied in the temperature interval 77–300 K. We have established the mechanisms for emission and transfer
of energy from the matrix to the rare-earth ion, and we determined the Stokes shift (ΔS = 0.7 eV), the Huang–Rhys parameter
(S = 16), and the optical phonon energy (ħ−ω = 23 meV). 相似文献
11.
V. D. Fokina E. V. Bogdanov M. V. Gorev M. S. Molokeev E. I. Pogorel’tsev I. N. Flerov N. M. Laptash 《Physics of the Solid State》2010,52(4):781-788
The thermal and dielectric properties of the (NH4)2NbOF5 oxyfluoride have been investigated. It has been established that the structural phase transitions Cmc21 → C2 → Ia observed at the temperatures T
1 = 258.0 K and T
2 = 218.9 K exhibit a nonferroelectric nature. The hydrostatic pressure, which stabilizes the initial phase and destabilizes
the low-temperature phase, hardly affects the temperature range of stability of the intermediate phase. The model of sequential
ordering of the structural elements due to phase transitions has been analyzed using experimental data on the entropies of
the phase transitions. 相似文献
12.
G. A. Komandin A. S. Prokhorov V. I. Torgashev E. S. Zhukova B. P. Gorshunov A. A. Bush 《Physics of the Solid State》2011,53(4):736-744
The spectra of complex permittivity of a Ba2Mg2Fe12O22 single crystal belonging to the family of Y-type hexaferrites have been measured over a wide temperature range (10–300 K) with the aim of determining the dynamic parameters
of the phonon and magnetic subsystems in the terahertz and infrared frequency ranges (3–4500 cm−1). A factor-group analysis of the vibrational modes has been performed, and the results obtained have been compared with the
experimentally observed resonances. The oscillator parameters of all nineteen phonon modes of E
u
symmetry, which are allowed by the symmetry of the Ba2Mg2Fe12O22 crystal lattice, have been calculated. It has been found that, at temperatures below 195 and 50 K, the spectral response
exhibits new absorption lines due to magnetic excitations. 相似文献
13.
A. V. Malakhovskii E. V. Eremin D. A. Velikanov A. V. Kartashev A. D. Vasil’ev I. A. Gudim 《Physics of the Solid State》2011,53(10):2032-2037
The magnetic properties of the Nd0.5Gd0.5Fe3(BO3)4 single crystal have been studied in principal crystallographic directions in magnetic fields to 90 kG in the temperature
range 2–300 K; in addition, the heat capacity has been measured in the range 2–300 K. It has been found that, below the Néel
temperature T
N = 32 K down to 2 K, the single crystal exhibits an easy-plane antiferromagnetic structure. A hysteresis has been detected
during magnetization of the crystal in the easy plane in fields of 1.0–3.5 kG, and a singularity has been found in the temperature
dependence of the magnetic susceptibility in the easy plane at a temperature of 11 K in fields B < 1 kG. It has been shown that the singularity is due to appearance of the hysteresis. The origin of the magnetic properties
of the crystal near the hysteresis has been discussed. 相似文献
14.
S. A. Sveleba I. V. Karpa I. M. Katerynchuk O. V. Semotyuk R. M. Shymkiv I. M. Kunyo O. I. Fitsych 《Journal of Applied Spectroscopy》2011,78(2):228-233
This a study of the optical transmission of [N(CH3)4]2ZnCl4 and [N(CH3)4]2CuCl4 crystals in the incommensurate phase when a defect density wave is present. It is found that an anomalous reduction in the
transmission coefficient is caused by scattering of light owing to a realignment of the superstructure during transitions
between metastable states. When a defect density wave is present, the anomalous optical transmission of the crystal is related
to the scattering of light on superstructure inhomogeneities produced by a superposition of existing modulation waves. 相似文献
15.
I. N. Ogorodnikov N. E. Poryvay I. N. Sedunova A. V. Tolmachev R. P. Yavetskiy 《Physics of the Solid State》2011,53(2):263-270
The thermally stimulated recombination processes and luminescence in crystals of the lithium borate family Li6(Y,Gd,Eu)(BO3)3 have been investigated. The steady-state luminescence spectra under X-ray excitation (X-ray luminescence spectra), the temperature
dependences of the X-ray luminescence intensity, and the glow curves for the Li6Gd(BO3)3, Li6Eu(BO3)3, Li6Y0.5Gd0.5(BO3)3: Eu, and Li6Gd(BO3)3: Eu compounds have been measured in the temperature range 90–500 K. In the X-ray luminescence spectra, the band at 312 nm
corresponding to the 6
P
J
→ 8
S
7/2 transitions in the Gd3+ ion and the group of lines at 580–700 nm due to the 5
D
0 → 7
F
J
transitions (J = 0–4) in the Eu3+ ion are dominant. For undoped crystals, the X-ray luminescence intensity of these bands increases by a factor of 15 with
a change in the temperature from 100 to 400 K. The possible mechanisms providing the observed temperature dependence of the
intensity and their relation to the specific features of energy transfer of electronic excitations in these crystals have
been discussed. It has been revealed that the glow curves for all the crystals under investigation exhibit the main complex
peak with the maximum at a temperature of 110–160 K and a number of weaker peaks with the composition and structure dependent
on the crystal type. The nature of shallow trapping centers responsible for the thermally stimulated luminescence in the range
below room temperature and their relation to defects in the lithium cation sublattice have been analyzed. 相似文献
16.
S. V. Mel’nikova A. S. Krylov A. L. Zhogal’ N. M. Laptash 《Physics of the Solid State》2009,51(4):817-822
Polarization-optical study of twinning and measurements of the Raman spectra and birefringence in oxyfluoride (NH4)3Ti(O2)F5 were carried out over the temperature range 90–350 K. Phase transitions were detected at temperatures T 01 = 266 K (second-order transition) and T 02 = 225 K (first order). It is assumed that the crystal symmetry is changed as follows: Fm3m ? I4/mmm ? I4/m. Anomalies of the spectral parameters are established in the frequency range of internal vibrations of ammonium ions and Ti(O2)F5 complexes. An analysis of the results shows that the transition at T 01 is likely due to small shifts of the tetrahedral groups from their position on the triad axis and that the transition at T 02 is due to fluorine-oxygen ordering of Ti(O2)F5 complexes. 相似文献
17.
The [N(CH3)4][N(C2H5)4]ZnCl4 compound has been synthesized by a solution-based chemical method. The X-ray diffraction study at room temperature revealed
an orthorhombic system with P21212 space group. The complex impedance has been investigated in the temperature and frequency ranges 420–520 K and 200 Hz–5 MHz,
respectively. The grain interior and grain boundary contribution to the electrical response in the material have been identified.
Dielectric data were analyzed using the complex electrical modulus M
* for the sample at various temperature. The modulus plots can be characterized by full width at half height or in terms of
a non-exponential decay function ϕ(t) = exp[(−t/τ)
β
]. The detailed conductivity study indicated that the electrical conduction in the material is a thermally activated process.
The variation of the AC conductivity with frequency at different temperatures obeys the Almond and West universal law. 相似文献
18.
L. N. Korotkov T. N. Korotkova R. R. Levitskii S. I. Sorokov A. S. Vdovych 《Bulletin of the Russian Academy of Sciences: Physics》2011,75(10):1331-1334
The time dependences of polarization of K0.88(NH4)0.12H2PO4 mixed crystal have been studied within the temperature range of 74–100 K. Two mechanisms of polarization relaxation were
found. The first mechanism is caused by domain walls lateral motion and their interaction with point lattice defects. The
second one supposedly is due to polar regions infiltration through the regions of frustrated paraelectric phase. 相似文献
19.
We have studied photoluminescence and thermoluminescence (PL and TL) in CaGa2Se4:Eu crystals in the temperature range 77–400 K. We have established that broadband photoluminescence with maximum at 571 nm
is due to intracenter transitions 4f6 5d–4f7 (8S7/2) of the Eu2+ ions. From the temperature dependence of the intensity (log I–103/T), we determined the activation energy (E
a = 0.04 eV) for thermal quenching of photoluminescence. From the thermoluminescence spectra, we determined the trap depths:
0.31, 0.44, 0.53, 0.59 eV. The lifetime of the excited state 4f6 5d of the Eu2+ ions in the CaGa2Se4 crystal found from the luminescence decay kinetics is 3.8 μsec.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 112–116, January–February, 2009. 相似文献
20.
F.B. Xiong X.H. Gong Y.F. Lin Y.J. Chen Q.G. Tan Z.D. Luo Y.D. Huang 《Applied physics. B, Lasers and optics》2007,86(2):279-286
A Pr3+-doped La2(WO4)3 crystal grown by the Czochralski method has been investigated as a promising laser material. The principal axes of the optical
indicatrix and Pr3+ concentration of the crystal were determined. The polarized absorption, fluorescence spectra and fluorescence decay curves
of the main emission multiplets of the crystal were measured at room temperature. The spectroscopic parameters were obtained
by the modified Judd–Ofelt theory combined with the normalized method. The peak stimulated emission cross-sections of the
major emission lines were estimated. The good spectroscopic properties imply that the Pr3+:La2(WO4)3 crystal is a potential laser gain medium for solid-state laser and self-stimulated Raman laser applications.
PACS 78.20.-e; 42.70.Hj 相似文献