Tao Haizheng

Structure, Upconversion and Fluorescence Properties of Er3+-Doped TeO2-TiO2-La2O3 Tellurite Glass

Tellurite glasses were generally applied in rare earth optical materials due to their excellent physical and chemi- cal properties. In this study, novel tellurite glasses composed of Te02-Ti02-La203 were prepared by conventional melting- quenching method. Some basic physical parameters such as density, refractive indices, transition temperature and crystal- line temperature were measured. The structure was analyzed by Raman spectra. The absorption, upconversion and fluores- cence spectra were measured by UV-Vis-NIR spectrophotometer and spectrofluorimeter . Under 980 nrn laser excitation, upconversion luminescence centered at 531, 545 and 657 nm corresponding to the transition 4Hll/2-+4115/2, 4s3/2+4115/2 and 4Fg/244115/2 respectively, were observed. The effects of Ti02 concentration on structure and upconversion lumines- cence intensity were discussed. The result indicated that the upconversion intensity increased as the phonon concentration decreased. The fluorescence properties of Er3+ doped glass were also studied. The dominant peak centered at 1531 nm and full width at half maximum (FWHM) was 64 nm. The E? + stimulated emission cross-section was calculated on the basis of McCumber theory. The possible mechanism of upconvesion and fluorescence were proposed.

Broadband infrared luminescence from bismuth-doped GeS2-Ga2S3 chalcogenide glasses

Near-infrared luminescence is observed from bismuth-doped GeS2—Ga2S3 chalcogenide glasses excited by an 808 nm laser diode. The emission peak with a maximum at about 1260 nm is observed in 80GeS2-20Ga2S3:0.5Bi glass and it shifts toward the long wavelength with the addition of Bi gradually. The full width of half maximum (FWHM) is about 200 nm. The broadband infrared luminescence of Bi-doped GeS2-Ga2S3 chalcogenide glasses may be predominantly originated from the low valence state of Bi, such as Bi+. Raman scattering is also conducted to clarify the structure of glasses. These Bi-doped GeS2-Ga2S3 chalcogenide glasses can be applied potentially in novel broadband optical fibre amplifiers and broadly tunable laser in optical communication system.

Microstructural probing of (1−x) GeS2−x Ga2S3 system glasses by Raman scattering

Raman scattering measurement of (1−x) GeS2−xGa2S3 system glasses was conducted in order to understand the microstructural change caused by the addition of Ga2S3. According to the change of Raman spectra with the addition of Ga2S3, two main structural transformations were deduced: the gradual enhancement of ethane-like structural units S3Ge−GeS3 (250 cm−1) and S3 Ga−GaS3 (270 cm−1) and the appearance of charge ambalanced units [Ga2S2(S1/2)4]2− and [Ga(S1/2)4]− And this change of structural aspect seems to give us a clue to understanding the cause of the increased rare-earth solubility.

Microstructure and thermal properties analysis of (1−x) As2S3−xCdBr2 glass system

The homogeneous glass sample for the (1−x)As2S3−xCdBr2, where x=0.015, 0.035, 0.05, was prepared by the conventional melt-quenched method. Amorphous (1−x)As2S3−xCdBr2 alloys were determined by X-ray diffraction, thermal comprehensive analysis and Raman scattering. The glass transition temperature (Tg) decreases a bit with the addition of CdBr2. Based on the experimental data, the microstructure is considered to be the discrete molecule species of AsBr3 and Cd−S atomic bonds or clusters are homogeneously dispersed in a disordered polymer network formed by AsS3 pyramids interlinked by sulfur bridges.

Microstructure and thermal properties of (1−x) As2S3−xCdCl2 glassy system

The homogenous glass samples of the (1−x) As2S3−xCdCl2 where x=0 and 0.05 were prepared by the conventional melt-quenched method. The addition of 5 mol% CdCl2 enhanced the glass transition temperature of pure As2S3 glass sample by about 30°C. Based on the experimental data, the microstructure is considered to be that the discrete molecule species of AsCl3 and nanocrystal CdS is homogeneously dispersed in the disordered polymer network formed by AsS3 pyramids interconnected by sulfur bridges.

IR spectra analysis of SiO2−TiO2−GeO2 gel glass of CO2 laser transmitting hollow waveguide

Both titanium and germanium were introduced into silicon dioxide system by sol-gel method to move its region of anomalous dispersion caused by IR resonance absorption towards the wavelength of CO2 laser. It is indicated by IR absorption spectra that as the content of SiO2 decreases in this glass system TiO2 and GeO2 tends to exist in their own phases. As for the gel glass with a composition of 40 SiO2·30TiO2·30GeO2, when the temperature is below 600°C, germanium atoms exist mainly in Ge−O−Ge bonds. With the temperature increasing from 800°C to 1000°C, titanium atoms in Si−O−Ti bonds abmost transform into Ti−O−Ti bonds. Furthermore, a large number of Si−O−Ti and Si−O−Ge bonds formed when the temperature approaches 800°C, which makes a notable IR absorption band round the wavelength of CO2 laser. Therefore, sol-gel based SiO2−TiO2−GeO2 gel glass is a candidate material for CO2 laser hollow waveguide.

Large and Ultrafast Third-Order Nonlinear Optical Properties of Ge-S Based Chalcogenide Glasses

We report ultrafast third-order nonlinear optical (NLO) properties of several chalcogenide glasses GeSx (x = 1.8, 2.0, 2.5) measured by femtosecond time-resolved optical Kerr gate technique at 820 nm. The third-order nonlinear susceptibility of GeS1.8 glass is determined to be as large as 1.41×10−12 esu, which is the maximum value of the third order nonlinear susceptibility χ(3) for the three compositions investigated. The symmetric Gauss profiles of optical Kerr signals reveal the nature of ultrafast nonlinear response of these samples, which are originated from the ultrafast polarization of the electron clouds. By detailed microstructural analysis of these glasses based on the chain-crossing model (CCM) and the random-covalent-network model (RCNM), it can be concluded that χ(3) value of GeSx glasses can be enhanced greatly by S–S covalent bonds or S3Ge–GeS3 ethane-like units.

Microstructure and optical properties of the (1−x) GeS2−xP2S5 glasses

To find materials with larger second-order nonlinearity, the Ge−P−S chalcogenide glasses with various ratios of GeS2:P2S5 were prepared by the melt-quenching method. The microstructure and optical properties of these glasses were characterized by XRD, Raman, Vis-NIR spectroscopy and Maker fringe technique. The second harmonic generation (SHG) was observed in the as-prepared chalcogenide glasses which was ascribed to the thermal stress gradient and/or the microanisotropic defects (such as the lone-pair orbital or the valence alternative pairs) prefer-orientation of the as-prepared glasses.

Effects of nitric acid concentration on the stability of alumina sols

Alumina sols with a molar ratio of 1:50 between aluminum sec-butoxide (ASB) and H2O were fabricated by adding various amounts of nitric acid. The particle shape, zeta potential, polydispersity and effective particle size of alumina sol were examined by a TEM, a zeta PALS granularity analyzer and a zetaPALS zeta potential analyzer, respectively. By analyzing the change of zeta potential and double-layer thickness with nitric acid concentration, the potential energy curves of colloidal particles were mapped on the basis of DLVO theory, and the effects of nitric acid concentration on the stability of alumina sols were intensively studied. The results show that for the alumina sols with a mol ratio of 1:50 between ASB and H2O, the total interaction energy of the colloidal particle is at a maximum when the nitric acid concentration is 0.22 mol/L. Therefore, the stability of the colloid reaches optimum at the nitric acid concentration of 0.22 mol/L.

Properties and microstructure of GeS2−Ga2S3−CdS glasses

The samples of the GeS2−Ga2S3−CdS pseudo-ternary glassy system were prepared by conventional melt-quenching techniques. The microstructure of the GeS2−Ga2S3−CdS glasses was analyzed thoroughly using Raman spectra and the relationships among the composition, microstructure and properties (such as thermal properties, densities, optical properties) were probed. The experimental results indicate that the GeS2 acts as the network former, the Ga2S3 as the net intermediate, and the CdS as the net modifier. The GeS2 and Ga2S3 exist in the form of [GeS4/2], [GaS4/2] tetrahedra or S3 Ge(Ga)−(Ga)GeS3 ethane-like units within the glassy network, and the addition of CdS mainly breaks the Ge(Ga)−(Ga) Ge bonds among the ethane-like units, leading to the formation of [GeS4/2], [GaS4/2] tetrahedra. The Tg and Tx have tight relations on the congregated degree of glassy network, however, λris, n and d are hardly involved into the connectional dependence of the space arrangement.