High Quantum Efficiency and High Concentration Erbium-Doped Silica Glasses Fabricated by Sintering Nanoporous Glasses

A new method was used to prepare erbium-doped high silica （SiO2 % 〉 96 % ） glasses by sintering nanoporous glasses. The concentration of erbium ions in high silica glasses can be considerably more than that in silica glasses prepared by using conventional methods. The fluorescence of 1532 nm has an FWHM （Full Wave at Half Maximum） of 50 nm, wider than 35 nm of EDSFA （erbium-doped silica fiber amplifer）, and hence the glass possesses potential application in broadband fiber amplifiers. The Judd-Ofelt theoretical analysis reflects that the quantum efficiency of this erbium-doped glass is about 0.78, although the erbium concentration in this glass （6 × 10^3） is about twenty times higher than that in silica glass. These excellent characteristics of Er-doped high silica glass will be conducive to its usage in optical amplifiers and microchip lasers.

Photoinduced Second Harmonic Generation of Bi_2S_3 Microcrystallite Doped Silica Glass

Silica glasses doped with Bi2S3 microcystallite was prepared by the sol-gel process. Photoinduced second harmonic generation (SHG) was observed in the glass when it was irradiated with intense 1.06 mum and frequency doubled laser beams from a mode-locked Nd: YAG laser. It was found that the signal intensity increased with the irradiating time and approached a saturation gradually. The effect may be explained reasonably by the DC field model.

Low Temperature Coating of Anatase Thin Films on Silica Glass Fibers by Liquid Phase Deposition

Uniform crystalline TiO2 thin films were coated on silica glass fibers by liquid phase deposition from aqueous solution of ammonium hexafluorotitanate at low temperature. TiO2 thin films and nanopowders were prepared by adding H3BO3 into （NH4）2TiF6 solution supersaturated with anatase nano-crystalline TiO2 at 40 ℃. The effects of the deposition conditions on the surface morphology, section morphology, thickness of the deposited TiO2 thin films were investigated. The results indicate that the growth rate and particle size of the thin films were controlled by both the deposition conditions and the amount of anatase nano-crystalline TiO2.

Effects of Flame Temperature and SiCl_4 Concentration on Particle Characteristics for Synthetic Silica Glass

Effects of flame temperature and SiCl4 concentration on the particle characteristics were studied.The flame temperature distributions were measured using modified sodium line-reversal technology.The particles were collected by quartz supports and were analyzed by scanning electron microscope（SEM） at different locations along the flame centerline.When the SiCl4 concentration is 16 g/min,the particles first grow and then shrink with the flame temperature increasing.When the SiCl4 concentration is 26 g/min,the flame temperature has little influence on the particle characteristics along the flame and many large spherical particles exist all the way.

Preparation and Fluorescent Property of Eu-Doped High Silica Glasses

A method to fabricate europium ions doped-high silica glass for transparent fluorescence materials based on the fabrication and sintering technique of nano-porous silica glass was reported. Glasses impregnated with Eu ions and sintered at above 1150℃in a reduction atmosphere show a very strong blue light from an emission band at about 430 nm due to the 4f65d→4f7(8S7/2) transition of the Eu2+ ions. On the other hand, the Eu-doped glass obtained by co-impregnated with Y3+ and V5+ ions and sintering in oxidation atmosphere behaves a very strong red emission band at about 615 nm with a UV excitation. An appearance of vanadate band in the excitation spectrum of Eu3+ , Y3+ .and V5+ ions co-doped high silica glass implies an effective energy transferring from VO43- to Eu3+ and effective excitation of Eu3+ by about 500 nm strong broad emission of VO43- .

Spectroscopic Properties of Nd^(3+)-Doped High Silica Glass Prepared by Sintering Porous Glass

A new kind of Nd^3＋-doped high silica glass （SiO2 〉 96% （mass fraction）） was obtained by sintering porous glass impregnated with Nd^3 ＋ ions. The absorption and luminescence properties of high silica glass doped with different Nd^3 ＋ concentrations were studied. The intensity parameters Ωt （t = 2, 4, 6）, spontaneous emission probability, fluorescence lifetime, radiative quantum efficiency, fluorescence branching ratio, and stimulated emission cross section were calculated using the Judd-Ofelt theory. The optimal Nd^3＋ concentration in high silica glass was 0.27% （mole fraction） because of its high quantum efficiency and emission intensity. By comparing the spectroscopic parameters with other Nd^3 ＋- doped oxide glasses and commercial silicate glasses, the Nd^3 ＋ -doped high silica glasses are likely to be a promising material used for high power and high repetition rate lasers.

Influence of Annealing on the Structure of Silica Glass

Two types of high-purity synthetic silica glasses were annealed with different processes in precision annealing furnace. The thermal stress and structure of samples were analyzed by two types of stress instruments and Fourier transform infrared spectrometer. After being annealed at1 070 ℃ for 6 days and then cooled slowly, optical path difference （OPD） caused by stress in the center and edge of Type III silica glass with a diameter of 150 mm and thickness of 50 mm decreased from 6 to 2 nm/cm. Meanwhile, with the same annealing process, fictive temperature of small-size Type III glass decreased to 939 ℃, and structural stability of silica glass was improved. In addition, after being annealed at 1 100 ℃ for 5 hours and then cooled slowly, internal stress in Type IV silica glass with a thickness of 1 mm was basically eliminated, and its fietive temperature decreased from 1 421 to 966 ℃.

Structure Characterization of F-doped Silica Glass

Pure and fluorine-doped silica glass were fabricated by plasma chemical vapour deposition （PCVD） and characterized using Raman and infrared spectrum. The change in Raman intensity of 945 cm-1 peak, relating to ≡Si-F stretching vibration, agrees with the change of F content. Compared with measured wavenumber in IR spectrum, the calculated absorption wavelength confirms the incorporation form of F into the glass, the detail of which is a tetrahedron with a Si atom in the center coupled with one F atom and three network O atoms. Such structure identification may be useful for explaining some properties of F-doping silica glass.

Atomistic study on tensile fracture of densified silica glass and its dependence on strain rate

Densification is a major feature of silica glass that has received widespread attention.This work investigates the fracture behavior of densified silica glass upon uniaxial tension based on atomistic simulations.It is shown that the tensile strength of the silica glass approximately experiences a parabolic reduction with the initial density,while the densified samples show a faster power growth with the increase of strain rate.Meanwhile,the fracture strain and strain energy increase significantly when the densification exceeds a certain threshold,but fracture strain tends to the same value and strain energy becomes closer for different densified samples at extreme high strain rate.Microscopic views indicate that all the cracks are formed by the aggregation of nanoscale voids.The transition from brittleness fracture to ductility fracture can be found with the increase of strain rate,as a few fracture cracks change into a network distribution of many small cracks.Strikingly,for the high densified sample,there appears an evident plastic flow before fracture,which leads to the crack number less than the normal silica glass at the high strain rate.Furthermore,the coordinated silicon analysis suggests that high strain rate tension will especially lead to the transition from 4-to 3-fold Si when the high densified sample is in plastic flow.

The charging stability of different silica glasses studied by measuring the secondary electron emission yield

This paper reports that the charging properties of lead silica, Suprasil silica and Infrasil silica are investigated by measuring the secondary electron emission （SEE） yield. At a primary electron beam energy of 25 keV, the intrinsic SEE yields measured at very low injection dose are 0.54, 0.29 and 0.35, respectively for lead silica, Suprasil and Infrasil silica glass. During the first e-beam irradiation at a high injection current density, the SEE yields of lead silica and Suprasil increase continuously and slowly from their initial values to a steady state. At the steady state, the SEE yields of lead silica and Suprasil are 0.94 and 0.93, respectively. In Infrasil, several charging and discharging processes are observed during the experiment. This shows that Infrasil does not reach its steady state. Two hours later, all samples are irradiated again in the same place as the first irradiation at a low current density and low dose. The SEE yields of lead silica, Suprasil and Infrasil are 0.69, 0.76 and 0.55, respectively. Twenty hours later, the values are 0.62, 0.64 and 0.33, respectively, for lead silica, Suprasil and Infrasil. These results show that Infrasil has poor charging stability. Comparatively, the charging stability of lead silica is better, and Suprasil has the best characteristics.

Mechanical and microstructural response of densified silica glass under uniaxial compression: Atomistic simulations

We investigate the mechanical and microstructural changes of the densified silica glass under uniaxial loading-unloading via atomistic simulations with a modified BKS potential. The stress–strain relationship is found to include three respective stages: elastic, plastic and hardening regions. The bulk modulus increases with the initial densification and will undergo a rapid increase after complete densification. The yield pressure varies from 5 to 12 GPa for different densified samples. In addition, the Si–O–Si bond angle reduces during elastic deformation under compression, and 5-fold Si will increase linearly in the plastic deformation. In the hardening region, the peak splitting and the new peak are both found on the Si–Si and O–O pair radial distribution functions, where the 6-fold Si is increased. Instead, the lateral displacement of the atoms always varies linearly with strain, without evident periodic characteristic. As is expected, the samples are permanently densified after release from the plastic region, and the maximum density of recovered samples is about 2.64 g/cm^3, which contains 15 % 5-fold Si, and the Si–O–Si bond angle is less than the ordinary silica glass. All these findings are of great significance for understanding the deformation process of densified silica glass.

Preparation and Spectroscopic Properties of Ce-Doped High-Silica Glass

In order to develop a novel electric light source, the doped high-silica glass was studied on the preparation and spectroscopic properties. ne porous glasses were made firstly and were then immersed in the solution containing Ce ion. Thereafter, the high-silica glasses containing Ce ion were prepared by sintering the porous preform. The spectroscopic properties were studied before and after heath treatment in H-2. The experimental results indicate that the suitable temperature schedules are the most important to prepare doped high-silica glass. The study of the spectra shows that Ce ion can be reduced to low valence state when it is heat-treated in H-2. It can be used to adjust the UV cut-off wavelength of high-silica glass by changing the valence state of Ce ion.

Determination of surface structure and the depth profile of silica glass by infrared spectroscopy

The surface structure and properties are different from those of the bulk, depending on the substrate materials and deposition condition, and playing an important role in precise optical components. The conventional spectroscopic methods to monitor the surface structure are restricted only in several layers of molecules. It is known that the penetration depth of the incident light increases with its wavelength and decreases with the angle of incidence. Thus infrared spectroscopy provides a powerful means for determination of surface structure and the depth profile up to micrometers. By recording the reflection spectra at different angles of incidence, the surface structure and its depth profile can be monitored successively. Further, the incident field has the subcomponents parallel and perpendicular to the surface, which excite the transverse and longitudinal optic modes, respectively. Change of the polarization direction of the incident light provides a practical function to study anisotropic property of the surface and the interaction between the transverse and longitudinal optic modes. In this work, infrared spectrophotometer was applied to investigate the depth profile in microstructure of silica glass. Combining with the glass fiber system, this technique can be used for in-situ control of the deposition process. In comparing with ellipsometry, this method reveals both structural and constitutional information.

Radiation-induced change of OH content in Yb-doped silica glass

Yb-doped silica glasses containing low, medium, and high content of OH arc prepared through nanoporous glass sintering technology. High-OH sample exhibits better X-ray irradiation resistivity than low- and medium-OH samples. After irradiation, OH content of low- and medium-OH samples increases 37.5% and 11%, respectively; in contrast, OH content of high-OH sample decreases dramatically. The different OH content changes among the samples are discussed regarding the proposed inter-conversion reactions involving Si-H and Si-OH during the irradiation.

Effect of Different Forms of Silica on Sintering, Microstructure and Properties of Borosilicate Glass/Al_2O_3 Composites

The effects of the introduction of silica glass and silica ceramic into Ca-Al-B-Si-O glass/ Al2O3 composites on decreasing the shrinkage and the dielectric constant of samples were investigated by FTIR, DSC, XRD and SEM. The results show that silica ceramic filler can better improve the formation of Si- O-Si network in the composites under high temperature, which leads to increased continuity of glass network at high temperature, and deduces the increase of viscosity of composites and further results in the decrease in the shrinkage of samples. Densification, three-point strength, and dielectric constant of samples decrease with the increase of silica glass or silica ceramic content. By contrast, Ca-Al-B-Si-O glass/Al2O3 composites with 4 wt% silica ceramic exhibit better properties of a bulk density of 2.81 g.cm-3, a porosity of 0.3%, a 3dp value of 202 MPa, a er value of 7.41 , a tan d value of 8.3 ×10^-4 at 10 MHz and a well matching with Ag electrodes. This material is suitable to be used as the LTCC material for the application in wireless communications.

Experimental Study of Material Removal Process of Fused Silica Glass Using MR Jet Polishing System

Recently,there has been an investigation of polishing processes that has considered new ultra-precision polishing technology for micro parts and optical parts such as those with aspheric and complex shapes.One suitable means of polishing complex shapes is to use a jet of abrasive fluid.However,aerodynamic disturbances and radial spreading are generated by the unstable polishing process of the jet on the surface of the workpiece when it is being polished.A method of jet stabilization has been proposed in which the original nozzle form of a jet of magnetorheological(MR)fluid contains abrasive particles that are magnetized using a magnetic.This paper details the design of an MR jet polishing system that uses an electromagnet,a nozzle,and a hydraulic unit to stabilize a slurry jet based on MR fluid, Second,for silica glass,the polishing spot and section profile are analyzed and the effect of the MR fluid jet polishing process is evaluated.The results of the experiment show that the removal profile is W-shaped and that,in this case,a stable can be proof of a distance of several tens of millimeters from the nozzle.Such results show the possibility of applying the proposed polishing method using MR fluids in ultra-precision micro and optical parts production processes. MR jet polishing shows great potential for use as a new type of precision surface polishing technology.In particular,this is a highly valuable process for the polishing of complex shapes such as micro parts,concaves parts,and cavities.

Influence of an equimolar amount of aluminium and phosphorus on spectroscopic properties of neodymium under local phosphorus environment in silica glass

To exhibit large emission cross sections of Nd in silica glass, Nd surroundings were regulated in AI/P codoped silica glass prepared by our multi-step method. The influence of an equimolar amount of AI and P on spectroscopic properties was studied under the local phosphorus coordination environment of Nd.The uniformity of composition distribution was characterized by energy dispersion spectra（EDS） and the coordination environment of Nd ions was characterized by the electron paramagnetic resonance（EPR）spectra. The results indicate that the composition distribution is of high uniformity and Nd has a stronger interaction with P atoms than AI atoms regardless of Al/P molar ratio. Local phosphorus coordination environment of Nd ions in silica glass is achieved. Large σ（em） can be achieved when Al or P is excessive,and larger σ（em） is more likely achieved when P is much more than Al. This work brings new possibilities for obtaining large stimulated cross sections of Nd in silica glass.

KINETIC FACTORS AFFECTING THE CORROSION OF SiO_2 IN SILICATE GLASSES CAUSED BY ALKALINE SOLUTIONS

The corrosion of a ZrO2 containing alkali re-sistant silicate glass, float glass and silica glass caused by the aqueous solution of NaOH was studied by use of correlation method with spectrophotometry. Effects of the corroding tem-perature, time and solution concentration on the rate of reac-tion and the degree of corrosion were investigated; effects of the apparent activation energy and the experimental value of frequency factor on the rate constant were discussed.

OH Diffusion in Silica Glass Preform During Jacketing Process by Oxy-Hydrogen Burner

Radial distribution of OH diffusion in silica glass preform during jacketing process using a oxy-hydrogen burner was investigated by FTIR spectroscopy. The OH peaks at the jacketing boundary and the surface of the preform were found to be due to diffusion of OH incorporated from the burner.

Femtosecond laser induced defects in various silica glasses

The mechanism of near infrared (IR) focused femtosecond (fs) laser induced defects in silica glasses produced by different methods is systematically investigated through measurements of absorption, fluorescence, and electronic spin resonance (ESR) spectra. The influence of impurities and hydroxyl groups on defects is discussed. The results show that ES silica glasses containing high OH and few defects are much stable under fs laser irradiation. It is also verified that Si E_δ~′center formation has no direct relation with chloride ions.