Tellurite And Fluorotellurite Glasses For Active And Passive

6. Optical properties; MDO 243
6.3.2. Refractive index (ellipsometry)
6.3.2.1. Refractive index of oxide tellurite glasses
Table (6.11) shows the refractive index of a selection of the oxide tellurite glasses melted
in this study. Glass MOD007 (78TeO2-12ZnO-10Na2O mol. %) had a lower refractive
index (n = 2.021) than glass MOD010 (75TeO2-10ZnO-10Na2O-5PbO mol. %, n =
2.024). This is a result of the large polarisability of PbO (3.45 Å 3 ) compared to ZnO
(2.612 Å 3 ) [39]. The index of glass MOD012 (75TeO2-10ZnO-10Na2O-5GeO2 mol. %, n
= 1.992) was lower than MOD007 and MOD010. This is due to the low polarisability of
GeO2 (1.72 Å 3 ) compared to ZnO and PbO [39]. MOD014 (90TeO2-5WO3-5Nb2O5 mol.
%), MOD015 (82.5TeO2-7.5WO3-10Nb2O5 mol. %), and MOD016 (70TeO2-25WO3-
5Bi2O3 mol. %) had much higher indices (n = 2.147, 2.152 and 2.157 respectively) than
the ZnO, PbO and GeO2 containing glasses. These glasses contained WO3, Bi2O3 and
Nb2O5 which have high polarisabilties (2.677, 3.507 and 2.679 Å 3 respectively) [39],
resulting in high refractive indices.
6.3.2.2. Refractive index of fluorotellurite glasses
Fig. (6.48) shows the variation in refractive index with increasing ZnF2 batch content for
the glass series (90-x)TeO2-10Na2O-xZnF2 mol. %, for 5 ≤ x ≤ 30 mol. % (MOF001, 004
to 008). The index decreases linearly (with a correlation coefficient of 0.99641) from
2.02 (5 mol. % ZnF2) to 1.85 (30 mol. % ZnF2). This is to be expected as the fluoride and