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1.
S. A. Nemov P. P. Seregin E. A. Tomil’tsev N. O. Tagil’tseva 《Glass Physics and Chemistry》2006,32(2):257-259
The structure of glasses based on fluorides of alkaline-earth metals, aluminum, and europium, in which aluminum fluoride is partially replaced by aluminum nitride, is investigated by 151Eu Mössbauer spectroscopy. It is found that these glasses contain europium atoms in two oxidation states (+2 and +3). The isomer shifts of the Mössbauer spectra of Eu3+ and Eu2+ ions entering into the composition of the fluoride glasses are somewhat different from the isomer shifts of the Mössbauer spectra of EuF3 and EuF2 compounds. This difference is explained by the effect of the alkaline-earth metal and aluminum atoms (not bound directly to the europium atoms) on the electron density at the 151Eu nuclei. The broadening of the Mössbauer spectra of the Eu2+ ions in the fluoride glasses is explained by the nonuniform isomer shift. 相似文献
2.
The influence of the chemical nature of the local environment of Eu3+ ions on the parameters of luminescence of these centers in glasses of the (BaGeO3)1 ? x ? y (Al2O3) x (0.45CaF2 · 0.55MgF2) y (x = 0.25, y = 0; x = 0.17, y = 0.17; x = 0.15, y = 0.22; x = 0.07, y = 37.00; x = 0, y = 0.45) system is investigated. The oxidation state of europium atoms and the degree of homogeneity of their local environment in the glasses are determined using 151Eu Mössbauer spectroscopy. 相似文献
3.
Ya. P. Biryukov R. S. Bubnova S. K. Filatov A. G. Goncharov 《Glass Physics and Chemistry》2016,42(2):202-206
Iron oxoborate Fe3O2(BO4) has been first produced in solid-phase chemical reactions. Its thermal behavior in the temperature range 20–900°C is studied with the use in-situ high-temperature powder X-ray diffraction. It is shown that Fe3O2(BO4) begins decomposing with the formation of Fe2O3 in the temperature range 660–900°C. Thermal expansion is sharply anisotropic at room temperature (αmax/αmin = 7) and becomes more isotropic with an increase in the temperature (αmax/αmin = 1.2). The degree of oxidation of Fe3+ has been confirmed by Mössbauer spectroscopy (at a room temperature), and two nonequivalent positions in the structure have been detected, which are occupied by iron atoms with the octahedral environment of the oxygen atoms. 相似文献
4.
Combined UV-visible and FTIR spectral studies of undoped and Nd2O3 –doped sodium silicophosphate glasses were carried out to characterize the optical and structural properties of such glasses. The base undoped silicophosphate glass exhibits strong UV absorption which is due to the presence of unavoidable trace iron impurities (mainly Fe3+ ions) present contaminated within the raw materials used for the preparation of such glasses. Nd2O3 –doped glasses show characteristic absorption bands extending in the entire visible region which are attributed to the contribution of Nd3+ ions with distinct peaks which are almost constant with the increase of dopant. This comes from the combined compact glass structure containing two glass forming units and the shielding of the rare-earth ions. Infrared absorption spectra of the studied glasses reveal characteristic IR bands due to the combination of both silicate and phosphate groups. The introduction of Nd2O3 within the dopant level (2 %) produces no variations in the IR vibrational bands due to the presence of the two structural silicate and phosphate groups giving compactness of the network structure. The deconvoluted spectra reveal the presence of phosphate groups in a slightly high ratio due to the high content of P2O5 in the composition. 相似文献
5.
G. A. Bordovskii R. A. Castro A. V. Marchenko P. P. Seregin 《Glass Physics and Chemistry》2007,33(5):467-470
Two valence states of tin atoms (namely, the doubly charged Sn2+ and quadruply charged Sn4+ states) in the structure of the (As2Se3)0.4(SnSe)0.3(GeSe)0.3 glasses are identified by 119Sn Mössbauer spectroscopy. It is demonstrated that the concentration ratio of the doubly charged Sn2+ and quadruply charged Sn4+ states in the glass of this composition depends on the rate of quenching of the melt and on the initial temperature of the melt before quenching. The optical band gap and the activation energy for electrical conduction of the studied glass do not depend on the concentration ratio of the Sn2+ and Sn4+ ions. This behavior of the optical band gap and the activation energy is explained within the model according to which the structure of the glasses under investigation is built up of the structural units AsS3/2, As2/2Se4/4, GeSe4/2, SnSe4/2, and SnSe3/3, which correspond to the compounds AsSe3, AsSe, GeSe2, SnSe2, and SnSe, respectively. 相似文献
6.
Il Woo Park Hyo Jin Lee Jae Soo Yoo Chang Kyun Choi 《Korean Journal of Chemical Engineering》2007,24(2):294-298
We investigated the optical characteristics of strontium aluminate phosphors excited by near ultraviolet light emitting diodes
(UV LEDs). For UV LEDs applications, strontium aluminates doped with europium were prepared at high temperature in a weakly
reductive atmosphere. The effect of boric acid as a flux was considered. The excitation and emission spectra of these phosphors
indicated that all of them have a broad band and that the main emission peaks, situated at around 490 nm for 4SrO·7Al2O3 : Eu and 520 nm for SrOAl2O3 : Eu, are both due to the 4f65d1 → 4f7 transition of Eu2+. The typical brightness of a phosphor-converted LED, which was made with synthesized phosphors and a blue LED, was 712 mcd.
By using the synthesized phosphors, phosphor-converted white LEDs could be well fabricated with good optical characteristics.
In this case, color coordinates could be controlled from x = 0.1373 and y = 0.4635 to x = 0.2386 and y = 0.6066 at 20 mA and
3.69 V. 相似文献
7.
SrAl2O4: (Eu2+, Dy3+) phosphor was prepared by solid state reaction. B2O5 as a flux was added in SrAl2O4:(Eu
2+, Dy3+) in order to accelerate a solid state reaction. In this paper, the effects of B2O3 on the crystal structure and the phosphorescent properties of the material have been evaluated. The synthesized phosphor
exhibited a broad band emission spectrum peaking at 520 nm, and the spectrum peak showed little effect by the B2O3 contents. The maximum afterglow intensity of the SrAl2O4: (Eu2+, Dy3+) phosphor was obtained at the B2O3 content of 5%. Adding the B2O3 caused uniform distortion to the crystal structure of the phosphor and resulted in reducing the lengths of a and c axes and
Β angle of the SrAl2O4 crystal. The uniform distortion was accompanied with crystal defects which can trap the holes generated by the excitation
of Eu2+ ions. The afterglow characteristic of the SrAl2O4: (Eu2+, Dy3+) phosphor was thus enhanced. 相似文献
8.
Xingdong Lü Wangen Shu Quanmao Yu Qin Fang Xinqiang Xiong 《Glass Physics and Chemistry》2007,33(1):62-67
The polycrystalline Eu2+ and Dy3+ codoped strontium aluminates SrAl2O4: Eu2+,Dy3+ were prepared by a solid-state reaction. The UV-excited photoluminescence, persistent luminescence, and thermoluminescence
of the SrAl2O4: Eu2+,Dy3+ phosphors with different compositions and ion doping was studied and compared. The results showed that the Eu2+ ion doped in SrAl2O4: Eu2+,Dy3+ phosphors is not only the UV-excited luminescent center but also the persistent luminescent center. The Dy3+ ion introduced into SrAl2O4: Eu2+ crystal matrix can hardly yield any luminescence under UV excitation but acts as an electron trap with a suitable depth for
persistent luminescence. The Dy3+ codoping would effectively enhance the persistent luminescence and thermoluminescence. Different codoping RE
3+ ions have a different effect on persistent luminescence. Only the RE
3+ ions (for example, Dy3+ and Nd3+), which have suitable optical electronegativity, can form suitable electron traps and effectively improve the persistent
luminescence of SrAl2O4: Eu2+. Based on the above observations, a persistent luminescence mechanism, electron transfer model, was proposed and illustrated.
The text was submitted by the authors in English. 相似文献
9.
Yu. K. Startsev A. A. Pronkin I. A. Sokolov I. V. Murin 《Glass Physics and Chemistry》2011,37(3):263-282
The glasses, in which oxygen was partially replaced with sulfur, have been synthesized in the Na2O-P2O5-Na2S system. The chemical and chromatographic analyses of the glasses synthesized have been performed. The temperature-concentration
dependences of electrical conductivity of the glasses have been studied over a wide temperature range; the glass transition
temperatures and the nature of charge carriers have been determined. The IR spectra and Raman spectra have been recorded at
room temperature; the density and microhardness of the glasses and ultrasound velocity have been measured. A comparison of
the electrical conductivities of the investigated glasses with those of the earlier studied glasses in the Na2O-P2O5 system has shown their fair coincidence. The introduction of sodium sulfide into the Na2O-P2O5 system is accompanied by an approximately threefold increase in electrical conductivity, although the concentrations of charge
carriers (sodium ions) in the glasses amount to ∼17 and ∼26 mmol/cm3, respectively. The rise in electrical conductivity has been assumed to be caused by the increase in the degree of dissociation
of polar structural chemical units including sulfide ions and by the higher mobility of sodium ions in the oxygen-free matrix. 相似文献
10.
The quaternary glasses of mixed divalent oxides including ZnO, MgO, CdO within a phosphate network former were prepared. Vanadium pentoxide was introduced as a dopant in the range from 0.5 to 3%. Optical and infrared absorption studies for all glass samples were carried out. The optical spectra reveal the presence of both V3+ and V4+ ions in the studied host mixed divalent oxides phosphate glass. Fourier transform infrared absorption spectral analysis indicates the appearance of distinct vibrational bands due to the presence of characteristic phosphate groups depending on the glass composition and the ratio of V2O5 content. The optical band gap and Urbach energy were calculated and discussed in relation to the effect of V2O5 content. Finally, the glasses were optically and structurally examined affter gamma irradiation with a dose of 80 KGy. 相似文献
11.
I. A. Sokolov I. V. Murin V. D. Khripun N. A. Valova Yu. K. Startsev A. A. Pronkin 《Glass Physics and Chemistry》2008,34(3):227-239
The concentration dependence of the electrical conductivity of glasses in the Tl2O-B2O3 system is studied. The nature of charge carriers in this system is experimentally investigated for the first time. It is demonstrated using the Hittorf, Tubandt, and Hebb-Liang-Wagner techniques and the Faraday law that neither Tl+ ions nor electrons are involved in the electricity transport. The verification of the Faraday law does not reveal the presence of thallium in the amalgam of the cathode or a change in the sample weight after electrolysis, to within the experimental error. This allows one to make the inference that protons can be charge carriers in glasses of the Tl2O-B2O3 system. It is shown using extended X-ray absorption fine structure (EXAFS) spectroscopy that Tl3+ ions and thallium Tl0 reduced to the metallic state are absent in the structure of the glasses under investigation. This means that thallium in glasses of the Tl2O-B2O3 system occurs only in the form of Tl+ ions. The analysis of the IR spectroscopic data leads to only a qualitative conclusion that the water content in the glasses insignificantly increases with an increase in the thallium oxide content. An increase in the electrical conductivity of glasses in the Tl2O-B2O3 system with an increase in the thallium oxide content is explained by the increase in the number of protons formed upon dissociation of H+[BO4/2]? structural-chemical units, because their concentration increases with increasing Tl2O content. In the structure of boron oxide, impurity hydrogen enters predominantly into the composition of H+[O2/2BO?] structural-chemical units, for which the dissociation energy is higher than that for the H+[BO4/2]? structural-chemical units. The increase in the concentration of H+[BO4/2]? structural-chemical units is accompanied by the increase in the number of dissociated protons, which are charge carriers in glasses of the Tl2O-B2O3 system. 相似文献
12.
Optical absorption spectral investigations have been carried out on Fe3+ ions doped sodium borate, sodium silicate and sodium phosphate glasses before and after gamma irradiation. The UV-visible absorption spectrum exhibits bands characteristic of Fe3+ ions coordination in each system. Interesting aspects of FT-IR spectra were found, and this gives information about the structure changes in the constituent units of these glass systems as a function of Fe2O3 concentration. All glasses reveal characteristic absorption bands due to the addition of different ratios of iron which explain the state of iron in each system in terms of its valence and coordination number. Results indicate that iron favors a higher oxidation state (tetrahedral coordination) in the case of sodium silicate glasses. The doping with progressive Fe2O3 additions (0.5?7.5 %) has some effect on the number and position of the characteristic bands due to formation of FeO4 groups. The IR absorption spectra after irradiation reveal limited changes in the intensity which can be correlated with minor changes in bond angles and /or bond lengths within the structural units by irradiation. 相似文献
13.
The optical absorption spectra of undoped soda lime silicate glass together with two glasses doped with either (1 % nano Fe2O3 ) or with both (1 % Nano Fe2O3 + 5 % cement dust) have been measured from 200 to 2400 nm before and after gamma irradiation with a dose of 8 Mrad. The undoped glass reveals strong UV absorption with two distinct peaks which are attributed trace ferric iron ions present as impurity. Upon gamma irradiation , this base glass exhibits three peaks at 240,310 and 340 nm and the resolution of an induced broad visible band centered at 530 nm. The two doped glasses show an additional small visible band at about 440 nm and followed by a very broad band centered at 1050 nm. Upon gamma irradiation, the two doped samples reveal the decrease of the intensities of the spectrum. The two additional bands are related to ferric (Fe+3) ions to the band at (440 nm) while and the broad band at 1050 nm is due to ferrous iron (Fe+2) ions. The decrease of the intensities of the UV-visible spectrum upon irradiation can be related to of capturing freed electrons during irradiation . Infrared spectra of the glasses reveal repetitive characteristic absorption bands of silicate groups including bending modes of Si–O–Si or O–Si–O, symmetric stretching , antisymmetric stretching and some other peaks due to carbonate , molecular water , SiOH vibrations . Upon gamma irradiation, the IR spectra reveal a small change in the base spectrum while the IR spectra of the two doped glasses remain unchanged. The change of the IR spectrum of the base glass is related to suggested changes in the bond angles or bond lengths of the mid band structural units. The doped glasses show resistance to gamma irradiation because the nano Fe2O3 can capture released electrons and positive holes. 相似文献
14.
An optical material, namely, the potassium aluminosilicophosphate glass activated with trivalent titanium ions, is synthesized and studied. The optimum concentration range (0.2–10.0 wt % Ti2O3) that provides the best physical, luminescent, and kinetic properties of glasses is determined. This makes it possible to use the sensitizing properties of Ti3+ ions to the greatest extent.Original Russian Text Copyright © 2004 by Fizika i Khimiya Stekla, Batyaev, Leonov. 相似文献
15.
Structure and crystalline behavior of the ternary system ZnO-B2O3-P2O5 glasses were investigated by means of X-ray diffraction (XRD) and infrared Raman spectra. The research showed that number
of the planar [BO3] units increases with the increase of B2O3 content. When the B2O3 content is above ≥10 mol %, the relative content of planar [BO3] units increases rapidly and causes weakening of the glass structure and decrease in the chemical stability. In the crystallized
glasses the predominant crystal phase Zn2P2O7 decreases with the increase of B2O3 content, while the crystal phase BPO4 increases with it, which cause the declining of chemical stability and the decrease of thermal coefficients of expansion. 相似文献
16.
Dy3 + -doped lead phosphate glasses were prepared by a melt quenching technique and investigated through Infrared absorption spectra (IR), photoluminescence (PL), and UV-Visible optical absorption measurements (UV-Vis). The luminescence spectra show two intense bands at 483 and 575 nm, which are attributed to 4FH15/2 (blue) and 4FH13/2 (yellow) transitions, respectively. The optical spectra data was used to evaluate the values of indirect allowed transitions. It was found that the optical band gap increases with Dy2O3 content. Variation in optical gap energy with the variation in localized state tails, confirms the theories for localized states in the energy gap of amorphous semiconductors. The characteristic infrared absorption bands of these glasses due to the stretching and bending vibrations were identified and analyzed by the increasing of the Dy2O3 content. This fact allowed us to identify the specific structural units which appear in these glasses. 相似文献
17.
V. V. Golubkov V. L. Stolyarova Z. G. Tyurnina N. G. Tyurnina 《Glass Physics and Chemistry》2010,36(5):554-560
The structure of single-phase glasses in the BaO-B2O3-SiO2 system has been studied by the large- and small-angle X-ray scattering techniques. The glasses containing 40 mol % BaO upon equimolar replacement of B2O3 by SiO2 have been investigated. It has been demonstrated that the incorporation of barium ions into structural groupings fixes their position and provides ordering in the distribution of barium ions at interatomic distances up to at least 5 Å. The glasses under investigation are homogeneous, and their inhomogeneity is determined by thermal density fluctuations and fluctuations of the concentration of a part of barium ions distributed in a statistically random manner in the volume of the glass. The observed ordering in the distribution of barium ions is not reduced to the formation of local clusters with an increased concentration of barium ions but is most likely a characteristic feature of the bulk glass structure. The glass structure is consistent with the model of ideal associated solutions. 相似文献
18.
Xin‐Yuan Sun Da‐Guo Jiang Shi‐Wei Chen Guo‐Tai Zheng Shi‐Ming Huang Mu Gu Zhi‐Jun Zhang Jing‐Tai Zhao 《Journal of the American Ceramic Society》2013,96(5):1483-1489
Eu3+‐activated borogermanate scintillating glasses with compositions of 25B2O3–40GeO2–25Gd2O3–(10?x)La2O3–xEu2O3 were prepared by melt‐quenching method. Their optical properties were studied by transmittance, photoluminescence, Fourier transform infrared (FTIR), Raman and X‐ray excited luminescence (XEL) spectra in detail. The results suggest that the role of Gd2O3 is of significance for designing dense glass. Furthermore, energy‐transfer efficiency from Gd3+ to Eu3+ ions can be near 100% when the content of Eu2O3 exceeds x = 4, the corresponding critical distance for Gd3+–Eu3+ ion pairs is estimated to be 4.57 Å. The strongest emission intensities of Eu3+ ions under both 276 and 394 nm excitation are simultaneously at the content of 8 mol% Eu2O3. The degree of Eu–O covalency and the local environment of Eu3+ ions are evaluated by the value of Ωt parameters from Judd–Ofelt analysis. The calculated results imply that the covalency of Eu–O bond increases with the increasing concentration of Eu3+ ions in the investigated borogermanate glass. As a potential scintillating application, the strongest XEL intensity under X‐ray excitation is found to be in the case of 6 mol% Eu2O3, which is slightly different from the photoluminescence results. The possible reason may be attributed to the discrepancy of the excitation mechanism between the ultraviolet and X‐ray energy. 相似文献
19.
The temperature-concentration dependence of the electrical conductivity of glasses in the Na2SO4-NaPO3 and Na2O-P2O5 systems has been investigated. Based on the obtained experimental data (IR spectra, density, microhardness, sound velocity,
and paper chromatography), it has been demonstrated that SO42− ions form terminal groups through the incorporation into polyphosphate fragments of the structure of glasses in the Na2SO4-NaPO3 system. An increase in the electrical conductivity of glasses in this system by a factor of ∼1000 (as compared to NaPO3) at 25°C and a decrease in the activation energy for electrical conduction from 1.40 to 1.10 eV have been interpreted from
the viewpoint of the decrease in the dissociation energy E
d of polar sulfate phosphate structural chemical fragments formed in the glass bulk upon introduction into sodium metaphosphate
Na2SO4. This leads to an increase in the number of dissociated sodium ions, which are charge carriers, and to a decrease in the
energy (E
a) of their activation shift in the sublattice formed by sulfate phosphate fragments of the structure. 相似文献
20.
The crystal structure of Pb6O[(Si6Al2)O20)] is investigated using X-ray diffraction. The compound has tetragonal symmetry, space group I4/mmm, a = 11.7162(10) Å, c = 8.0435(12) Å, and V = 1104.13(2) Å3. The structure is refined to R 1 = 0.036 for 562 unique reflections with [F 0] ≥ 4σF. The structure contains two symmetrically independent positions of the Pb2+ cations coordinated by five O atoms (Pb2+-O2? = 2.34–2.68 Å). The TO4 tetrahedra (T = Si, Al) form tubular [(Si6Al2)O20] chains extended along the c axis. The O4 oxygen atom is not bonded to the Si and Al atoms and is octahedrally coordinated by six Pb atoms with the formation of an oxo-centered OPb6 octahedron. The assumption is made that, in some of lead silicate and aluminosilicate glasses, a number of oxygen atoms are located outside the tetrahedral structure and represent segregation centers of the Pb2+ cations due to the formation of oxo-centered complexes. 相似文献