Temperature–dependent linear and non-linear optical and physical properties of borosilicate 7059 glasses using ellipsometry

Abstract

Vacuum temperature-dependent ellipsometric studies on borosilicate 7059 glasses and across a temperature range of 111 to 473 K are reported. The refractive index (n), reflection loss (RL), molar refraction (Rm), electronic polarizability (αe), thermo optic coefficient (δn/δT), coefficient of temperature dependence of density (δρ/δT), metallization criterion (Ḿ), optical band gap (Eg), oxide ion polarizability (αo2), optical basicity (A) and electronegativity values are computed. Both the non-linear susceptibility (χ(3)) and non-linear refractive index (n2) are also evaluated over the reported range of temperature. The values of n, RL and Rm are decreased from 1.5317 to 1.5283, from 0.3097 to 0.3079 and from 7.035 to 6.994, respectively over the temperature range 111 - 473 K. The measured values of Ḿ and Eg are increased from 0.6903 to 0.6920 and from 9.53 to 9.58 eV, respectively over the same temperature range. It is noted that the value of αe is decreased from 2.791 to 2.775 × 10−24 cm3, but both δn/δT and δρ/δT are increased from -1.189 to -0.791 × 10−5 K−1 and from -5.212 to -3.46 × 10−5g cm−3 K−1, respectively over the temperature range 111-473 K. Similarly, both n and Eg based oxide ion polarizability {α02-(n)andα02-(Eg)} values are decreased from 1.4326 to 1.4374 and from 1.4275 to 1.44191, respectively. Both the optical basicities, A(n) and A (Eg) are also decreased from 0.5082 to 0.5013 and from 0.5002 to 0.4932, respectively over the reported temperature range. Next, the values of electronegativity (ζ1av) measured using Zahid model on the base of αO2-(n) and A(n) are increased from 5.002 to 5.011 and from 4.7855 to 4.8396, respectively over the temperature range 111-473 K. The values of (ζ1av) measured using Reddy model on the base of αO2-(n) and A(n) are increased from 4.9558 to 4.9691 and from 4.7468 to 4.7771, respectively over the same temperature range. Both χ(3) and n2 are decreased from 1.31620 to 1.27347 × 10−14 esu and from 1.5654 to 1.5274 × 10−14 esu, respectively over the temperature range 111-473 K. Analysis of the above new findings indicates that all the evaluated values of n, RL and Rm, αe,α02-(n)andα02-(Eg), A(n) and A (Eg), have decreasing trend with increasing temperature causing a small increase in Eg values. Further, both the refractive index and energy band gap based Ḿ values are found to be less than one, so, the reported glasses exhibit insulating behaviour over the temperature range 111-473 K. In addition, the rigorous structural changes have not occurred in the glass network over the reported temperature range. Next, due to the low values of δn/δT and δρ/δT, borosilicate 7059 glasses are less subject to stress caused by thermal expansion and thus less vulnerable to cracking from thermal shocks. Also, the calculated values of electronegativity show that these glasses have an ionic character. The new findings also indicate that the generated values for both third-order nonlinear optical susceptibility and non-linear refractive index are very small which don't support the nonlinearity phenomena in these glasses.