Ge-As-S硫系玻璃的结构与性能调控

制备了系列具有不同化学配比特征的Ge-As-S硫系玻璃,并研究了玻璃的结构、折射率和光学带隙(Eg).Ge-As-S玻璃具有以Ge S_4]四面体和As S_3]三角锥为骨架结构单元相互交联形成的连续网络结构,当S过量时,结构中出现S链或S_8环;当S不足时,结构中形成As_4S_4/As_4S_3分子,甚至出现大量AsAs/Ge-Ge同极键.玻璃的组成元素在2—10μm波段的摩尔折射度分别为R_(Ge)=9.83—10.42 cm~3/mol,RAs=11.72—11.87 cm~3/mol和R_S=7.78—7.86 cm3/mol.Ge-As-S玻璃的折射率与密度和组成元素的摩尔折射度之间存在较好的定量关系,可根据该定量关系在1%偏差内对玻璃的折射率进行预测或调控.提出了采用玻璃粉末的漫反射光谱确定可靠Eg的方法,通过该方法可获得玻璃的强吸收数据用于确定Eg.Ge-As-S玻璃的Eg与玻璃的平均键能之间存在较好的关联,S含量较高的玻璃更倾向于具有较大的平均键能,因此具有较大的Eg.

Tailoring structure and property of Ge-As-S chalcogenide glass

Chalcogenide glass has been considered to be a promising optical material for infrared (IR) transmission and nonlinear optics because of its favorable physical properties such as wide IR transparent windows, high linear and nonlinear refractive indices, and tunable photosensitivity. In many optical designs and practical applications, the refractive index (n) and optical bandgap (E_g) are two important parameters. Aiming to evaluate the composition dependence of the n and E_g in Ge-As-S chalcogenide glasses, a series of glasses with different stoichiometric characteristics are synthesized in quartz tubes under vacuum by the melt quenching technique. The structure, n and E_g of the glass are investigated by Raman spectroscopy, ellipsometry, and diffused reflectance spectroscopy, respectively.To eliminate thermal effects on the measured Raman spectra, the data are corrected by the Bose-Einstein thermal factor. Raman spectrum analyses indicate that Ge-As-S glass has a continuous network structure with interconnected GeS₄] tetrahedra and AsS₃] pyramids forming the backbone. When S amount is excess, S chains or S₈ rings emerge. When S amount is deficient, As₄S₄/As₄S₃ molecules are formed, and even a large number of As-As/Ge-Ge homopolar bonds appear in the structure. The n values at different wavelengths are obtained by fitting the ellipsometry data with the Sellmeier dispersion model. The values of molar refractivity (R_i) of Ge, As and S elements are evaluated by using the measured n and density (d) of the investigated glass. The optimal values of R_i at 2-10 μm for each element are R_Ge=9.83-10.42 cm³/mol, R_As=11.72-11.87 cm³/mol, and R_S=7.78-7.86 cm³/mol, respectively; and the values decrease with increasing wavelength. The n of Ge-As-S glass is well quantitatively correlated to the d and the R_i of constituent elements, so that its value can be predicted or tailored within 1% deviation. A method to determine reliable E_g of a glass is proposed based on diffuse reflectance spectrum (DRS) of glass powders. To determine E_g of a glass, the absorption coefficient (α) is required to be as low as ～10⁴ cm^-1. For a 1-mm-thick bulk glass, the detection limit of a spectrophotometer is typically α < 100 cm^-1. To obtain a reasonable E_g, the sample thickness used for the measurement must be less than 10 μm. Such a thin glass sample is difficult to prepare. In comparison, DRS of glass powers measured using a spectrophotometer is able to provide valid absorption data in a 10⁴ cm^-1 range required for E_g determination. In this proposed method, the Kubelka-Munk function F(R), which is proportional to α of the glass, is calculated from the measured DRS on the glass powders. The F(R) is calibrated by using the DRS of a glass (e.g. As₂S₃) with a known E_g. Using the same F(R) absorbance value, E_g of the Ge-As-S glass is determined based on DRS of powders measured under the same condition. The E_g of Ge-As-S glass is broadly correlated to the average bond energy of the glass. The glass containing more S atoms tends to show a higher average bond energy, and therefore exhibits a larger E_g.