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1.
The luminescence spectra of C60 single crystals are studied at T≅10 K and pressure up to 4.0 GPa. It is observed that as the pressure increases, one fine-structure band in the spectrum intensifies
sharply and dominates at pressures P≥1.7 GPa. The pressure shift of this band is much larger than the shift of other bands in the spectrum, and its magnitude
correlates with the pressure dependence of the band gap. It is shown that this band could be due to radiative recombination
of free Frenkel excitons.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 3, 234–238 (10 August 1998) 相似文献
2.
K. P. Meletov A. A. Maksimov I. I. Tartakovskii 《Journal of Experimental and Theoretical Physics》1997,84(1):144-150
Measurements have been made of the Raman, optical absorption, and luminescence spectra of single crystals and pellets of the
fullerite C70 at T=300 K and at pressures up to 12 GPa. The baric shift dω/dP and the Grüneisen parameters of the Raman-active intramolecular phonon modes have been determined. It has been established
that the d
ω/dP value for certain phonon modes abruptly changes at pressures of P
1≈2 GPa and P
2≈5.5 GPa, as do the half-widths of the Raman lines. These features in the Raman spectrum are associated with phase transitions
at high pressure. The baric shifts of the absorption and luminescence edges of C70 crystals have been determined and are −0.12 eV/GPa and −0.11 eV/GPa, respectively, for absorption and luminescence. The baric
shift of the absorption edge decreases significantly with increasing pressure and is −0.03 eV/GPa at 10 GPa. These data have
been used to determine the deformation potential of the fullerite C70, which is about 2.1±0.1 eV.
Zh. éksp. Teor. Fiz. 111, 262–273 (January 1997) 相似文献
3.
A. F. Hebard C. B. Eom R. M. Fleming Y. J. Chabal A. J. Muller S. H. Glarum G. J. Pietsch R. C. Haddon A. M. Mujsce M. A. Paczkowski G. P. Kochanski 《Applied Physics A: Materials Science & Processing》1993,57(3):299-303
The irradiation of sublimed fullerene (C60 and C70) thin films with ultraviolet light in an oxygen-rich ambient has been found to lead to a substantially increased cohesive energy in the fullerene solid. The decreased solubility and lower vapor pressure of the phototransformed material enables wet (organic solvents) or dry (thermal or photon-induced sublimation) development of photo-defined negative images. One micrometer wide lines with good edge definition are demonstrated. X-ray, infrared, optical absorption, and high performance liquid chromatography reveal that photo-oxygenated C60 retains its fcc crystal structure but with a substantial fraction of the C60 molecules modified with carbonyl (C=O) bonds. 相似文献
4.
A. V. Bazhenov S. I. Bredikhin V. V. Kveder Yu. A. Ossipyan R. K. Nikolaev T. N. Fursova A. I. Shalynin 《Journal of Experimental and Theoretical Physics》1999,89(5):923-932
Diffusion of lithium cations in C60 single crystals driven by electric field has been detected and studied. A novel technique for fullerene crystal doping based
on injection of ions through a “superionic crystal/C60 single crystal” heterojunction has been suggested. It has been found that lithium doping of C60 single crystals brings about an ESR signal, and this signal as a function of time has been investigated. The electronic conductivity
in LixC60 crystals has a nonmetallic nature. Reflection spectra measured in the IR band have shown that the reflectivity due to free
electrons gradually decreases with time, which correlates with the evolution of signals due to ESR and microwave conductivity.
Lithium doping of crystals increases the oscillator strength of the T
1u
(4) vibrational mode and shifts it to lower frequencies (from 1429 cm−1 to 1413 cm−1), which indicates that one electron is present at the C60 molecule, and this fact may be treated as evidence that the LiC60 phase is generated in a C60 crystal.
Zh. éksp. Teor. Fiz. 116, 1706–1722 (November 1999) 相似文献
5.
Optical absorption spectra of thin fullerene (C60) crystals in the range 1.7 to 3.8 eV have been measured at T=300 K and at pressures up to 2.5 GPa. The spectrum shifts toward the red with pressure, and the electron absorption intensity
is redistributed among its bands. The intensity of the band associated with the lowest direct electron interband transition
monotonically increases with pressure, whereas the intensity of the upper interband feature decreases. Bands related to weak
edge absorption in the range between 1.7 and 2.2 eV gradually merge with the band associated with the lowest interband transition,
whose intensity rises with pressure. A similar redistribution of intensity among electron transition bands has been observed
when comparing the spectrum of an isolated C60 molecule and that of a C60 crystal. The results indicate that the crystal-field induced mixing of electron states is present in solid C60, and they can be discussed in terms of the Craig-McClure model, which was suggested to describe crystal-field induced mixing
of electron states in anthracene and naphthalene molecular crystals.
Zh. éksp. Teor. Fiz. 113, 313–322 (January 1998) 相似文献
6.
The features of the intraband luminescence spectrum of wide-gap insulators (KI, KBr, CsCl, etc.) and semiconductors (GaP,
CdS, α-SiC, and ZnS) are studied in the temperature interval 80–760 K. The spectra of the intraband luminescence are compared with
the spectra of the pre-breakdown electroluminescence of GaP and α-SiC surface-barrier diode structures and of a ZnS thin-film electroluminescence indicator. In alkali halide crystals the
short-wavelength boundary hν
m of the intraband luminescence is less than the band gap E
g and is governed by complex excitonic processes. In semiconductors with indirect transitions hν
m>E
g. The differences in the spectra of the intraband luminescence and the intraband pre-breakdown electroluminescence can be
explained by differences in the distributions of the hot charge carriers over levels of the allowed bands and in the maximum
energies of the carriers involved in the formation of the spectra.
Fiz. Tverd. Tela (St. Petersburg) 39, 613–617 (April 1997) 相似文献
7.
I. N. Ogorodnikov A. V. Kruzhalov E. A. Radzhabov L. I. Isaenko 《Physics of the Solid State》1999,41(2):197-201
A study of the luminescence characteristics of crystalline lithium triborate LiB3O5 (LBO) is reported. Investigation of the excitation and photoluminescence spectra of nominally pure, oriented LBO crystals
within broad spectral (1.2–10.5 eV) and temperature (8–500 K) regions, complemented by optical spectroscopy at the long-wavelength
fundamental-absorption edge, has revealed that the broad-band LBO luminescence in the 3.5–4.5-eV region is efficiently excited
by photons having energies above 7.5 eV in recombination processes and under corpuscular or x-ray irradiation. The totality
of the experimental data obtained permitted a conclusion that the LBO luminescence has an intrinsic nature and that it originates
from radiative decay of relaxed electronic excitations.
Fiz. Tverd. Tela (St. Petersburg) 41, 223–228 (February 1999) 相似文献
8.
K. P. Meletov V. A. Davydov J. Arvanitidis D. Christofilos K. S. Andrikopoulos G. A. Kourouklis 《Journal of Experimental and Theoretical Physics》2008,107(4):620-631
Stability of the linear orthorhombic polymer of C60 under pressure and laser irradiation is studied by Raman scattering and X-ray diffraction measurements. The Raman spectrum
at ambient pressure remains unchanged, in the time scale of the experiment, up to an intensity of 3200 W/cm2 of the 514.5 nm line of an Ar+ laser, but irreversible changes are observed at higher intensities. The Raman spectra recorded at increased pressure show
similar irreversible changes even at the laser intensity as low as 470 W/cm2. The X-ray diffraction and Raman measurements of the pressure-treated samples, performed after pressure release, show that
the nonirradiated material does not exhibit any changes in the crystal structure and phonon spectra. This behavior indicates
a pressure-enhanced photo-induced transformation to a new polymeric phase characterized by a Raman spectrum that differs from
those of the other known polymeric phases of C60. The Raman spectra of the phototransformed linear orthorhombic polymer of C60 were measured at a pressure of up to 29 GPa. The pressure dependence of the Raman mode frequencies show singularities near
4 GPa and 15 GPa, respectively, related to a reversible phase transition and an irreversible transformation to a metastable
disordered phase. The diffuse Raman spectrum of the disordered phase does not exhibit substantial changes with an increase
in pressure up to 29 GPa. The high-pressure phase transforms to a mixture of pristine and dimerized C60, after pressure release and exposure to ambient conditions for 30 h.
The text was submitted by the authors in English. 相似文献
9.
The process of phototransformation in C60 was analysed by means of Raman spectroscopy for single crystals irradiated at various temperatures between 80 K and 450 K. The activation window for the transformation process was found to be between the temperature of the first order phase transition of 260 K and an upper temperature of about 400 K. Detailed features of the resulting spectra were found to depend on the transformation temperature. From a comparison with ab initio calculations of Porezag et al. the material irradiated at high temperatures could be assigned to a C60 dimer whereas the material phototransformed at room temperature could not be identified with a simple cluster. 相似文献
10.
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
11.
Data presented on the influence of the temperature in the range 80–650 K on the spectral kinetics of the luminescence and
transient absorption of unactivated CsI crystals under irradiation by pulsed electron beams (〈E〉=0.25 MeV, t
1/2=15 ns, j=20 A/cm2). The structure of the short-wavelength part of the transient absorption spectra at T=80–350 K exhibits features, suggesting that the nuclear subsystem of self-trapped excitons (STE’s) transforms repeatedly
during their lifetime until their radiative annihilation at T⩾80 K, alternately occupying di-and trihalide ionic configurations. It is established that a temperature-induced increase
in the yield of radiation defects, as well as F and H color centers, and quenching of the UV luminescence in CsI occur in the same temperature region (above 350 K) and are characterized
by identical thermal activation energies (∼0.22 eV). It is postulated that the STE’s in a CsI crystal can have a trihalide
ionic core with either an on-center or off-center configuration; the high-temperature luminescence of CsI crystals is associated
with the radiative annihilation of an off-center STE with the structure (I−(I0I−
e
−))*.
Fiz. Tverd. Tela (St. Petersburg) 40, 640–644 (April 1998) 相似文献
12.
V. V. Kveder V. D. Negrii É. A. Shteinman A. N. Izotov Yu. A. Osip’yan R. K. Nikolaev 《Journal of Experimental and Theoretical Physics》1998,86(2):405-411
Photoluminescence, optical absorption spectra, and photoluminescence excitation spectra were measured on large (2–3 mm), very
pure crystals of fullerene C60 at 5 K. It is shown that the main contribution to the photoluminescence of these crystals is from singlet and triplet excitons
captured on crystal defects. The concentration of these defects does not exceed 1018 cm−23, and the lifetime of triplet excitons on these defects is about 3 ms. It is shown that the symmetry distortion of the C60 molecules at the defects is rather large and causes the oscillator strength of the zero-phonon optical transitions to be
comparable to the most intense optical transitions with the participation of intramolecular vibrations.
Zh. éksp. Teor. Fiz. 113, 734–746 (February 1998) 相似文献
13.
V. V. Brazhkin A. G. Lyapin R. N. Voloshin S. V. Popova Yu. A. Klyuev A. M. Naletov S. C. Bayliss A. V. Sapelkin 《JETP Letters》1999,69(11):869-875
The results of an investigation of the transformation of C60 fullerite to diamond under pressure through intermediate three-dimensionally polymerized and amorphous phases are reported.
It is found that treatment of fullerite C60 at pressures 12–14 GPa and temperatures ∼1400°C produces a nanocrystalline graphite-diamond composite with a concentration
of the diamond component exceeding 50%. At lower temperatures (700–1200°C) nanocomposites consisting of diamondlike (sp
3) and graphitic (sp
2) amorphous phases are formed. The nanocomposites obtained have extremely high mechanical characteristics: hardness comparable
to that of best diamond single crystals and fracture resistance two times greater than that of diamond. Mechanisms leading
to the transformation of C60 fullerite into diamond-based nanocomposites and the reasons for the high mechanical characteristics of these nanocomposites
are discussed.
Pis’ma Zh. éksp. Teor. Fiz. 69, No. 11, 822–827 (10 June 1999) 相似文献
14.
Two-photon-excited luminescence (TEL) spectra have been recorded in the blue (400–500 nm) and near-ultraviolet (300–400 nm)
ranges for diamond particles with 4 nm average size, which were obtained by detonation synthesis from explosives. The observed
TEL bands are attributed, by comparing the obtained spectra with the impurity luminescence spectra in large diamond crystals,
to N2 and N3 defects associated with the presence of nitrogen impurities in diamond. The TEL spectra presented are found to have certain
distinguishing features: short-wavelength shift of the maximum and changes in the shape and width of the spectral bands for
ultradispersed diamond compared with the spectrum in bulk crystals.
Fiz. Tverd. Tela (St. Petersburg) 41, 1110–1112 (June 1999) 相似文献
15.
The energy level structure of F
3
+
laser color centers in crystals of LiF is discussed. A high-power laser (λ
ex=920 nm) is used to excite luminescence from LiF crystals with F
3
+
centers via two-photon absorption, and the dependence of the polarization and intensity of this luminescence on the polarization
of the laser light is measured and calculated. It is shown that the two-photon transition involves the excitation of a previously
unknown state of the F
3
+
center—a spin singlet whose wave function has 1
A
1 symmetry.
Fiz. Tverd. Tela (St. Petersburg) 39, 1373–1379 (August 1996) 相似文献
16.
It is shown that deuteration of C60 fullerite followed by thermal decomposition of the resulting deuteride C60D24 leads to the formation of an fcc lattice with a
0=14.52 Å in the final product, which according to the IR spectra consists mainly of C60 fullerene molecules.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 3, 239–242 (10 August 1998) 相似文献
17.
S. S. Novosad 《Technical Physics》1999,44(1):124-125
The effect of the conditions of preparation, temperature, and the action of x rays on the luminescence properties of calcium-iodide
scintillation crystals is investigated. On the basis of the results of a study of the spectral characteristics of CaI2 and CaI2:H2 crystals for optical and x-ray excitation in the temperature range 90–400 K, also taking into account the results of a study
of the luminescence properties of CaI2 crystals activated by Cl−, Br−, OH−, and Ca2+ impurities, it is suggested that the 236-nm band observed in the excitation spectra of crystals of calcium iodide may be
caused by an uncontrollable hydrogen impurity. The luminescence of these crystals with maximum at 395 nm is ascribed to radiative
recombination of excitons trapped at H− ions.
Zh. Tekh. Fiz. 69, 135–136 (January 1999) 相似文献
18.
A. A. Klochikhin 《Physics of the Solid State》1998,40(5):819-820
A unified method is developed for describing the steady-state luminescence of exciton fluctuation states for weak excitation
in different disordered systems. The phononless luminescence band is found to be formed by “radiative” states of the fluctuation
tail in the density of states, i.e., by states for which nonradiative states are either nonexistent or have a low probability.
The shape of the emission spectra calculated including the phonon interaction is in good agreement with experimental luminescence
spectra of α Si:H and of solid solutions of ZnSe(1−c)Tec and CdS(1−c)Sec.
Fiz. Tverd. Tela (St. Petersburg) 40, 890–891 (May 1998) 相似文献
19.
V. D. Blank A. A. Nuzhdin V. M. Prokhorov R. Kh. Bagramov 《Physics of the Solid State》1998,40(7):1261-1263
Measurements of the specific heat and elastic wave velocities for a C60 fullerene sample treated at high pressure and temperature are used to estimate the Debye temperature and the function ΔC=C
p−C
v, and also to calculate the thermal expansion work in the ideal approximation. Similar calculations were made for graphite,
diamond, silicon, germanium, and various refractory metals. The results were used to draw qualitative conclusions on the structural
stability of a new material obtained from fullerene C60 which possesses extremely high hardness.
Fiz. Tverd. Tela (St. Petersburg) 40, 1387–1389 (July 1998) 相似文献
20.
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