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1.
I.N. Ogorodnikov V.A. Pustovarov S.A. Yakovlev L.I. Isaenko S.A. Zhurkov 《Journal of luminescence》2012,132(7):1632-1638
We report the results of complex study of luminescence and dynamics of electronic excitations in K2Al2B2O7 (KABO) crystals obtained using low-temperature luminescence-optical vacuum ultraviolet spectroscopy with sub-nanosecond time resolution under selective photoexcitation with synchrotron radiation. The paper discusses the decay kinetics of photoluminescence (PL), the time-resolved PL emission spectra (1.2–6.2 eV), the time-resolved PL excitation spectra and the reflection spectra (3.7–21 eV) measured at 7 K. On the basis of the obtained results three absorption peaks at 4.7, 5.8 and 6.5 eV were detected and assigned to charge-transfer absorption from O2? to Fe3+ ions; the intrinsic PL band at 3.28 eV was revealed and attributed to radiative annihilation of self-trapped excitons, the defect luminescence bands at 2.68 and 3.54 eV were separated; the strong PL band at 1.72 eV was revealed and attributed to a radiative transition in Fe3+ ion. 相似文献
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Polarized IR reflection spectra of Li2B4O7 crystals are studied in a spectral range of 80–1600 cm?1 and compared with their Raman spectra. Based on the results of the dispersion analysis of the spectra, the frequencies, damping constants, and oscillator strengths of all vibrations are determined. The inversion of frequencies of the longitudinal and transverse vibrations of the A 1 and E symmetry in a range of 900–1150 cm?1 is found. Based on the data thus obtained, the effective charges are calculated and the types of chemical bonds are analyzed for structural groups of the Li2B4O7 crystal. 相似文献
3.
A. V. Vdovin V. N. Moiseenko V. S. Gorelik Ya. V. Burak 《Physics of the Solid State》2001,43(9):1648-1654
The polarized infrared reflection spectra of Li2B4O7 were studied in the spectral range 80–1600 cm?1 and compared with Raman spectra. From the spectrum dispersion analysis, the frequencies, damping, and dielectric oscillator strengths were determined for all vibrational modes observed. A calculation of the effective charges and an analysis of the chemical-bond types of the Li2B4O7 crystal structural units were carried out on the basis of the obtained data. 相似文献
4.
A. Yu. Kuznetsov A. V. Kruzhalov I. N. Ogorodnikov A. B. Sobolev L. I. Isaenko 《Physics of the Solid State》1999,41(1):48-50
The results of an investigation of the electronic structure of lithium tetraborate crystals using experimental (x-ray photoelectron
spectroscopy) and theoretical (quantum-chemical modeling) methods are reported. The experimental spectrum of the valence-band
states of the crystal lies 2–15 eV below the Fermi level and is due primarily to boron-oxygen groups (B4O9). The quantum-chemical calculations were performed self-consistently, using the standard variant of the scattered-wave method
in the model of a cluster embedded in a lattice of point charges. The data obtained on the partial contribution of the model
densities to the one-electron spectrum of the [B4O9]6 cluster make it possible to interpret the fine structure of the experimental spectrum of the valence-band states.
Fiz. Tverd. Tela (St. Petersburg) 41, 57–59 (January 1999) 相似文献
5.
Raman spectra of an Li2B4O7 crystal containing potassium and silver impurity ions with a concentration in a range of 0.1–0.2% were studied in detail. In the scattering geometries corresponding to manifestation of totally symmetric polar vibrations, the redistribution of spectral intensity for some lines in a region of 450–570 cm?1 was observed. Using the model of weakly interacting oscillators, parameters of vibrations in this region were determined. On the basis of present-day concepts of the theory of light scattering by impurities, the position of impurity ions in a crystal lattice is discussed. 相似文献
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Single crystals of novel semiorganic material, potassium diboro-oxalate (PDO) have been grown from aqueous solution by slow evaporation technique. The lattice parameters for the grown crystals were determined by the single crystal X-ray diffraction analysis and the crystallinity of the grown crystal was confirmed by powder X-ray diffraction analysis. The presence of functional groups was estimated qualitatively by using Fourier transform infrared (FTIR) analysis. The optical absorption spectrum shows that the UV cut-off wavelength for the grown crystal is at 240 nm and the band gap was calculated. The thermal stability of the grown crystal was studied by using TG/DTA analysis. The second harmonic generation and the phase-matchable tests were performed by Kurtz powder technique. The crystal perfection was analyzed by SEM photographs. 相似文献
8.
Single crystal of 4-dimethylaminopyridinium picrate was grown by slow evaporation solution growth method. The optical properties of the crystal were studied by using UV–vis absorption and transmittance studies. The emission spectrum indicates that the crystal shows green and red fluorescence emissions. The band gap energy of the crystal was calculated and it is found to be 2.05 eV. The thermal stability of the crystal was studied using thermogravimetry-differential thermal (TG-DTA) analyses. The thermal anomalies observed in the differential scanning calorimetry (DSC) heating and cooling cycles indicate the occurrence of a first order phase transition. FTIR spectrum was used to confirm the presence of various functional groups in the crystal. The synthesized crystal shows SHG efficiency 32 times greater than that of potassium dihydrogen phosphate (KDP). The dielectric constant and dielectric loss of the crystal decreases with increases in frequency. 相似文献
9.
V. Jambunathan X. Mateos M. C. Pujol J. J. Carvajal C. Zaldo U. Griebner V. Petrov M. Aguiló F. Díaz 《Applied physics. B, Lasers and optics》2014,116(2):455-466
We present the crystal growth, optical spectroscopy, and room temperature continuous-wave (CW) laser operation of monoclinic Ho:KLu(WO4)2 crystals. Macro defect-free crystals of several dopant concentrations were grown by top-seeded solution growth slow-cooling method. The evolution of unit cell parameters with holmium doping level and temperature was studied using X-ray powder diffraction. The spectroscopic properties were characterized in terms of room- and low-temperature optical absorption and photoluminescence. From low-temperature optical absorption measurements, the energy of the Stark levels was determined. Calculation of the emission and gain cross sections is presented. CW laser action was realized for 3 and 5 at. % Ho-doped KLu(WO4)2 by in-band pumping using a Tm:KLu(WO4)2 pump laser. A maximum output power of 507 mW with a slope efficiency of ~38 % with respect to the incident power was achieved at 2,080 nm with the Ho:KLu(WO4)2 laser. 相似文献
10.
The results of calculations of the phonon dispersion,
the vibrational density of states and the heat capacity of lithium
tetraborate and lithium triborate crystals are presented. They are
obtained in the framework of a potential model that takes into
account the non-equivalence of boron atoms in different structural
positions (BO3 and BO4 units). A symmetry analysis
of the phonon modes at point was performed, and calculated
frequencies are compared to experimental spectra.
Analysis of Li contributions to the vibrational density of states reveals that
the Li-O bonds in both crystals are relatively weak. This is in line
with the experimentally observed high mobility
of lithium ions at high temperatures. A good agreement between calculated and measured heat capacities from the literature was obtained. 相似文献
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The photoluminescence (PL) of ZrP2O7 and KZr2(PO4)3 phosphate crystalline micro-powders grown by spontaneous crystallization method is studied under vacuum ultra-violet (VUV) synchrotron radiation excitations (4–20 eV region of excitation photon energies) in 8–300 K temperature region. The electronic structures (partial densities of states) and optical absorbance spectra of the crystals are calculated by the Full-Potential Linear Augmented Plane Wave Method. Both phosphate crystals reveal PL emission band in the UV spectral region peaking near 300 and 295 nm for ZrP2O7 and KZr2(PO4)3 respectively. The spectral profile of the band weakly depends on temperature. The excitation spectra of the UV emission in each crystal contain intensive excitation band peaking at 189 and 182 nm for ZrP2O7 and KZr2(PO4)3 respectively. The excitation band of the UV emission is related to band-to-band electronic transitions with charge transfer from O 2p to Zr 4d states. The energy band gaps Eg of ZrP2O7 and KZr2(PO4)3 are estimated as 6.7 and 6.6 eV respectively. 相似文献
13.
I. N. Ogorodnikov V. Yu. Yakovlev A. V. Kruzhalov L. I. Isaenko 《Physics of the Solid State》2002,44(6):1085-1092
This paper reports on a study of the transient optical absorption exhibited by Li2B4O7 (LTB) in the visible and UV spectral regions. Using absorption optical spectroscopy with nanosecond time resolution, it is established that the transient optical absorption (TOA) in these crystals originates from optical transitions in hole centers and that the kinetics of the optical-density relaxation is controlled by interdefect tunneling recombination, which involves these hole centers and electronic Li0 centers representing neutral lithium atoms. At 290 K, the Li0 centers migrate in a thermally stimulated, one-dimensional manner, without carrier ejection into the conduction or valence band. The kinetics of the pulsed LTB cathodoluminescence is shown to be controlled by a relaxation process connected with tunneling electron transfer from a deep center to a small hole polaron migrating nearby, a process followed by the formation of a self-trapped exciton (STE) in an excited state. Radiative annihilation of the STE accounts for the characteristic σ-polarized LTB luminescence at 3.6 eV, whose kinetics is rate-limited by the tunneling electron transfer. 相似文献
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G.D. Patra Mohit Tyagi D.G. Desai Babita Tiwari Shashwati Sen S.C. Gadkari 《Journal of luminescence》2012,132(5):1101-1105
UV excited photo luminescence from Li2B4O7:Cu and Li2B4O7:Cu, Ag single crystals has been investigated in the temperature range from 77 K to 300 K. An excitation band having a doublet structure at 240 nm and 262 nm was observed for the emission at 370 nm that corresponds to 1A1g→1Eg and 1A1g→1T2g crystal field components of the 3d10→3d94s1 transition of Cu+. The relative intensity of these components and their temperature dependence provide a measure of the off-center displacement of the Cu+ ground state in the crystal lattice site. The co-doped Ag plays a role of a sensitizer when doped with Cu and increases the overall emission as the emission between Ag states lies in the excitation region of Cu states. The 370 nm emission in both the crystals slightly decreases with temperature; however a sudden increase in the intensity around 264 K was observed. 相似文献
17.
V.M. Holovey K.P. Popovych M.S. Klenivskyi A.V. Gomonnai 《Journal of luminescence》2012,132(8):1982-1986
The temperature dependence of the photoluminescence (PhL) spectral distributions has been reported for the lithium tetraborate Li2B4O7 (LTB) and Li2B4O7:Cu (LTB:Cu) single crystals and for glassy LTB:Cu. It was found that the emission peaks of the LTB and LTB:Cu single crystals are non-elementary and splittable by temperature increase into several elementary peaks. By the sample heating the temperature quenching of PhL as well as the redistribution of the PhL intensity among elementary peaks was observed. Heating of the LTB:Cu single crystal samples caused no shift of the spectral maxima of the individual PhL peaks. The curve describing the temperature dependency of individual PhL peaks for the LTB:Cu single crystal is characterized by maxima resulting from combination of PhL and thermostimulated luminescence (TSL). The PhL intensity for glassy LTB:Cu is significantly lower than that for LTB:Cu single crystal with the equivalent copper dopant content. As compared to the LTB:Cu single crystal, the PhL spectral maximum for glassy LTB:Cu is wider and shifted to the lower energy range. Heating of the glassy LTB:Cu sample results in the PhL temperature quenching without any shift of the spectral maximum. 相似文献
18.
4-Dimethylaminobenzaldehyde-4-nitrophenylhydrazone (DANPH) single crystals exhibit polymorphism such as DANPH-G form (greenish red) and DANPH-R form (red). The different polymorphic phases of the grown crystals have been identified by X-ray diffraction studies. The functional groups of the crystals have been identified by FT-IR study. Crystallographically independent environment of polymorphs has been confirmed by NMR study. The thermal properties such as melting and decomposition temperatures of the compound have been analyzed. Optical constants of DANPH polymorph crystals have been calculated. 相似文献
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The detailed theoretical studies of electronic,optical,and mechanical properties of γ-Bi_2Sn_2O_7 are carried out by using first-principle density functional theory calculations.Our calculated results indicate that γ-Bi_2Sn_2O_7 is the p-type semiconductor with an indirect band gap of about 2.72 e V.The flat electronic bands close to the valence band maximum are mainly composed of Bi-6s and O-2p states and play a key role in determining the electrical properties of γ-Bi_2Sn_2O_7.The calculated complex dielectric function and macroscopic optical constants including refractive index,extinction coefficient,absorption coefficients,reflectivity,and electron energy-loss function show that γ-Bi_2Sn_2O_7 is an excellent light absorbing material.The analysis on mechanical properties shows that γ-Bi_2Sn_2O_7 is mechanically stable and highly isotropic. 相似文献