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1.
Calcium aluminate glasses show high sensitivity to ultraviolet radiation without the doping of optically active components. A mechanism is proposed to account for their photosensitivity on the basis of the result that the cause of UV-induced coloring is the emergence of two kinds of paramagnetic centers, an aluminum-oxygen hole center (Al-OHC) and an ozonide (O-3). In this model, a peroxy linkage connecting tetrahedrally coordinated Al3+s and a physically dissolved O2 molecule are assumed to be present in the glasses as structural defects. On exposure to UV rays, the peroxy linkage homolvtically dissociates into a pair of A1-OHC's by absorbing UV quanta and one of the two resulting A1-OHC's combines with a nearby O2 to form an ozonide. Experimental evidences substantiating the mechanism are also reported.  相似文献   

2.
Properties and Structure of Glasses in the System Ge-S   总被引:1,自引:0,他引:1  
Distinct glass-forming composition regions were found in the system Ge-S (1) from GeS2 to GeS9 and (2) from GeS1.21 a to GeS1.5 The properties of these glasses, e.g. ir absorption spectra, thermal expansion, extraction of S8 molecules with CS2, Vickers hardness, density, and optical absorption, led to the conclusion that the structures of glasses in the two regions differ. In region (1), the structure is based on a three-dimensional inorganic polymer of polymeric S chains cross-linked with Ge; in region (2), it involves GeS2 (GeS4 tetrahedra) and GeS (GeS6 octahedra) components that can be regarded as network formers and modifiers, respectively.  相似文献   

3.
Beginning with a 19BaF2−27ZnF2−27YbF3−27ThF4 (mol%) base glass, compositional modifications were made to improve optical properties and glass-forming ability. Replacement of YbF3 by LuF3 removed a strong near-ir electronic absorption band, and small additions of LiF and NaF improved glass quality. The multicomponent BaF2/ThF4 glasses had higher refractive indices and lower expansion coefficients than fluorozirconate and fluorohafnate glasses. In the 6 to 10 μm region, these materials exhibit absorption coefficients an order of magnitude lower than those reported for other heavy-metal fluoride glasses.  相似文献   

4.
CdS-doped SiO2 glasses were prepared via silica gels containing diethyldithiocarbamatocadmium Cd(S2CN(C2H5)2)2. Heat treatment of the gels gave transparent yellow SiO2glasses doped with hexagonal CdS crystals. In optical absorption and fluorescence spectra, the optical absorption edge and the emission peak clearly exhibited a blue shift, which was attributed to the quantum size effect of the carrier confinement, as the CdS content was decreased. In the fluorescence spectra of the CdS-doped silica glasses, the emission peak was observed only near 500 nm and not observed at longer wavelengths which were known to be present if there were sulfur vacancies.  相似文献   

5.
Coloring and bleaching of reduced phosphate glasses in the systems K2O-B2Or Al2O3-P2O5 and K2O-Al2O3-P2O5, containing no silver halide, were studied. The as-cast glasses, which are colorless and transparent, become tinged with red when they are reheated at high temperatures for long times. The bleached specimens (PTC-RP glass) are obtained by heating at >600°C, then quenching. The PTC-RP glasses exhibit coloring phenomena by irradiation of light or by heating above 200°C; the colored glasses are again bleached thermally. Coloring of the glasses by heating is described in this paper in terms of phase change within the colloidal phosphorus formed in the glasses. The apparent activation energy for the thermocoloring is estimated to be ∼15×104 J/mol (35 kcal/mol).  相似文献   

6.
Cerium-activated silica (SiO2) glasses were prepared by plasma torch chemical vapor deposition (CVD). In Ce-doped SiO2 glasses, most Ce exists as Ce4+ ions; the remaining small amount of Ce3+ ions exhibits a broad fluorescence spectrum with a large Stokes shift, ∼9600 cm-1, from the excitation spectrum peak of 324 nm. Aluminum and phosphorus codoping considerably increases the Ce3+ ratio and shifts the peaks of both spectra to shorter wavelengths. P codoping is the more effective way to achieve this result and in some cases produces an absorption spectrum similar to that of a Ce-doped phosphate glass. These findings are consistent with the solvatiorn shell model for codoping, as previously proposed. To codope P, a soot remelting method was devised to deal with the highly volatile P2O5.  相似文献   

7.
To obtain low transmission loss optical fibers from ultrapure multicomponent silicate glasses, it is necessary to add small quantities of As2O3 (or Sb2O3). In optical fibers prepared from glasses without these agents, a significant increase in loss is observed. To investigate this effect, the influence of As2O3 (added to the batch and present in the glass as As2O5) on the optical properties of ultrapure silicate glasses was studied. These properties are the Rayleigh scattering loss coefficient, transition metal absorption, and position of the uv absorption edge. This study showed that the increase in loss of As2O3-free glass cannot be assigned to any of these contributions and was attributed to absorption by electrons, trapped in relatively shallow traps in the glass network. The As5+ ions serve as deep traps and therefore remove the additional absorption. The same phenomenon, although much more pronounced, was observed in optical fibers prepared from alkali borosilicate glasses.  相似文献   

8.
The ultraviolet absorption of vanadium(V) in R2O-B2O3 glasses (R represents Li, Na, or K) and in aqueous buffer solutions was investigated. In glasses of variable R2O:B2O3 ratio, a change in the absorption spectra similar to the [VO4]3- → [VO3(OH)]2- change in aqueous solution was observed. It is suggested that vanadium(V) in these glasses may be present as either [VO4]3- or [VO3O1/2]2- (O1/2 indicates a bridging oxygen ion), depending on the basicity of the melt. The critical R2O concentration, above which this change in vanadium(V) environment occurs with increasing alkalinity, is 24, 26, and ≅30 mol%, for K2O, Na2O, and Li2O, respectively.  相似文献   

9.
10.
Bismuth borate glasses from the system: 40Bi2O3–59B2O3–1Tv2O3 (where Tv=Al, Y, Nd, Sm, and Eu) and three glasses of composition: 40Bi2O3–60B2O3, 37.5Bi2O3–62.5B2O3 and 38Bi2O3–60B2O3–2Al2O3 were prepared by melt quenching and characterized by density, UV-visible absorption spectroscopy and differential thermal analysis (DTA) studies. Bismuth borate glasses exhibit a very strong optical absorption band just below their absorption edge. Glasses were devitrified by heat treatment at temperatures above their glass transition temperatures and the crystalline phases produced in them were characterized by Fourier transform infrared (FTIR) absorption spectroscopy and X-ray diffraction (XRD). Bi3B5O12 was found to be the most abundant phase in all devitrified samples. DTA studies on glasses and FTIR and XRD analysis on crystallized samples revealed that very small amounts of trivalent ion doping causes significant changes in the devitrification properties of bismuth borate glasses; rare-earth ions promote the formation of metastable BiBO3–I and BiBO3–II phases during glass crystallization.  相似文献   

11.
Infrared spectra of glasses of the system R2O-B2O3-SiO2 were investigated. The extinction coefficients of the hydroxyl absorption band ("free OH") were calculated by a method proposed for alkali borate glasses. The results confirmed the applicability of this method to homogeneous and phase-separated alkali borosilicate glasses. The variation of the hydroxyl absorption band position was interpreted according to the structural characteristics of the studied glasses.  相似文献   

12.
Borosilicate glasses, 5B2O3· 95SiO2 (mol%), containing TeO2 and ZnO nominally equivalent to 10 wt% Te and ZnTe were prepared by a solgel method from Si(OC2H5)4, B(OCH3)3, H6TeO6, and Zn(NO3)2. A study by electron spectroscopy for chemical analysis (ESCA) showed that glasses heated at high temperature (450°C) in air contained both Te6+ and Te4+ ions on the surface layer, but that mainly Te4+ ions occurred inside the bulk glass. When solgel-derived borosilicate glasses containing the TeO2 compound were reduced at elevated temperature in a hydrogen atmosphere, Te crystallites ranging in size from 4 to 15 nm were produced at a lower temperature, between 200° and 250°C. The absorption edge moved from the infrared to the visible wavelength region as the particle size decreased to about 4 nm. For glasses containing both TeO2 and ZnO, ZnTe crystallites formed at high temperature—over 300°C—and existed along with the Te phase.  相似文献   

13.
In the Y2O3–Al2O3–B2O3 system, homogeneous glasses were obtained from compositions containing from 50 to 65 mol% B2O3. The density, refractive index, and thermal expansion increase as Y2O3 replaces either B2O3 or Al2O3. These glasses have a dilatometric softening temperature above 665°, and below 300°C their dc electrical resistivity exceeds that of fused silica. The infrared absorption spectra indicate that BO3, BO4, and AlO4, groups are present in these glasses.  相似文献   

14.
The infrared absorption spectra of fused B2O3 and of a series of soda borate glasses are presented. These spectra were obtained using vacuum-pressed briquettes of the powdered glass and powdered KBr. The spectrum of fused B2O3 shows quite definitely that this glass does not consist of a completely continuous triangularly coordinative network. It is shown that hydrogen bonds play an important part in the atomic arrangement of the glasses of zero or low soda content. The B2O3 glass apparently consists of complexes of an approximate unit (B9O14)- held together by hydrogen bonds. One in nine borons is tetrahedrally coordinated. The glasses of low soda content are similar. The spectra for soda concentrations greater than 15% did not permit the determination of the atomic arrangement with exactitude, but it is shown to be quite different from that found in glasses with 10% Na2O or less.  相似文献   

15.
Clear glasses form in the system Ag2O-B2O3 up to about 35 mol% (65 wt%) Ag2O. Infrared absorption, thermal expansion, and density data indicated an analogy to the Na2O-B2O3 system. Pentaborate-triborate group pairs appear to be formed on addition of Ag2O to B2O3 up to 20 mol% Ag2O and diborate groups from 20 to 33 mol% Ag2O. This interpretation is supported by the comparison of the infrared absorption spectra of quenched and crystallized glasses. One crystallization product, Ag2O-4B2O3, was identified previously. A new compound starts to appear at 28 mol% Ag2O. The theory that silver is generally present as a network modifier like sodium was substantiated by the comparison of the molar volume of sodium and silver borate glasses. Above 27 mol% Ag2O some atomic silver is assumed to be present; below 15 mol%, exploratory studies indicate a two-phase structure within an immiscibility gap. A low-temperature internal friction peak in the glasses up to 28 mol% Ag2O corresponds to the alkali peak in other glasses; a high temperature peak appearing in the 34 mol% Ag2O glass is associated with the appearance of nonbridging oxygen in the system.  相似文献   

16.
The integrated absorption cross section, the spontaneous emission probability, and the stimulated emission cross section of Yb3+ were determined in silicate, phosphate, borate, germanate, aluminate, gallate, and ZBLAN host glasses. The compositional dependence of the stimulated emission cross section of the 2F5/22F7/2 transition is determined mainly by the integrated absorption cross section in the glasses. A peak stimulated emission cross section above 1 pm2, which is the highest value in glasses, was obtained in a gallate glass with a composition of 40K2O·20Ta2O5. 40Ga2O3. The factors affecting the integrated absorption cross section are discussed using the Judd-Ofelt parameters of Er3+ calculated in previous studies.  相似文献   

17.
The gamma-ray-induced optical absorption in a series of cabal (calcium-boron-aluminum) glasses was studied and is interpreted, wherever possible, in terms of structural concepts. A resolution of the observed absorption spectra showed that three Gaussian-shaped bands were induced with their maxima at about 2.3, 3.5, and 5.0 e.v. (550, 350, and 250 mμ). The 2.3-e.v. band decreased in intensity with increasing CaO content, reaching a minimum intensity at a composition corresponding to the four-coordination of about 20% of the boron. Further increase in CaO content was associated with an increase in the intensity of this band. The intensity of the 3.5-e.v. band decreased gradually with increased mole per cent of CaO and increased with increased Al2O3. The 5.0-e.v. band showed an abrupt increase in intensity which corresponded to the appearance of non-bridging oxygens in the network. Replacing Ca2+ by Mg2+, Sr2+, or Ba2+ or replacing Li+ by Na+ or K+ showed that glasses containing large ions of low field strength give less induced absorption than glasses containing small ions of high field strength. A potassium alumina borate glass melted under reducing conditions gave a considerably higher ultraviolet transmission, before irradiation, as compared with the same glass melted under normal conditions. The gamma-induced absorption of these two glasses showed that reducing conditions resulted in a decrease in the intensity of the 2.3- and 3.5-e.v. bands, whereas it caused an increase in the far-ultraviolet-induced absorption. The effect of additions of arsenic, thallium, titanium, germanium, and some rare-earth oxides is discussed.  相似文献   

18.
Soda-silica glasses melted under strong reducing conditions (graphite crucible) contain the precursor of a 570-nm color center. Glasses thus prepared under an N2 atmosphere are readily colored by exposure to ultraviolet light; the uv-generated color fades rapidly at room temperature, giving phototropic response. However, with glasses melted under N2-free atmospheres (for example, Ar), this phototropic response is greatly attenuated or absent. The precursor of the 570-nm center evidently results from strong reduction of the glass independent of the covering atmosphere, since X irradiation generates the same characteristic optical absorption in glasses melted under both N2 and Ar. For compositions melted under N2, the amount of N dissolved correlates positively with increasing SiO2 content and phototropic response. The dissolution of N markedly affects the uv absorption of otherwise "clean" glass. An N-free reduced soda-silica glass exhibits essentially the same uv absorption as a similar oxidized glass. However, as N dissolves in the glass, the uv cutoff moves to longer wavelengths. The phototropic response of reduced glasses under long-wavelength uv light is greatly enhanced by incorporation of europium. Again, an N2 atmosphere during melting yields improved phototropic response. Dissolved N lowers the dissolved H2O content and increases the concentration of Eu in the lower valence state (Eu2+).  相似文献   

19.
Single-phase glasses containing 37.5 mol% Y2O3, 7 mol% La2O3, and 1 mol% Pr, Ho, Nd, Er, Sm, Tm, Eu, or Yb oxide substituted for part of the Y2O3 were synthesized by containerless melting. The spectral transmission and absorption cross sections of the glasses were determined at wavelengths from 360 to 3300 nm. The electronic transitions were broadened compared with results obtained in a crystalline yttrium aluminum garnet (YAG) host. The infrared transmission of the host glass extended to 6000 nm. The optical and physicochemical properties of these glasses are well suited for optical device applications.  相似文献   

20.
Crystallization sequences of glasses with compositions in the tridymite primary phase field of the MgO-Al2O3-SiO2 system were studied by DTA, X-ray diffraction, and other techniques. Crystallization was catalyzed by the addition of 7 wt% of either ZrO2 or TiO2. Up to 10 wt% CeO2 was also added to some glasses. Metastable solid solutions with the high-quartz structure exhibiting varying lattice parameters commonly occurred at low temperatures, transforming into a high cordierite at higher temperatures. Depending on the composition and heat treatment, other phases also appeared, e.g. Ce2Ti2O4 (Si2O7). The rate of crystallization was markedly dependent on the catalyst. Colloidal precipitation of the catalyst accompanied by bulk crystallization of the glass was observed with ZrO2, but no crystalline TiO2 was detected. In the presence of CeO2, TiO2 was a more effective catalyst than ZrO2. Although CeO2 lowered the melting temperatures of the glass-ceramics, it increased the stability of the glasses and inhibited volume nucleation, causing coarse structures to form on crystallization.  相似文献   

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