Tellurite And Fluorotellurite Glasses For Active And Passive

6. Optical properties; MDO 240
30 mol. % ZnF2 (over 20 times less than the TeO2-Na2O-ZnO based glasses. The
multiphonon edge did not shift significantly with ZnF2 addition. For glasses of the series
65 TeO2-(25-x)ZnF2-xZnO-10Na2O, for 5 ≤ x ≤ 30 mol. %, increasing the ZnO content
did not significantly shift the multiphonon edge at around 6 µm, however it did increase
the intensity of the OH absorption bands at around 2900 cm -1 (from around 25 dB.m -1 for
ZnO/ZnF2 = 0.4, to around 40 dB.m -1 for ZnO/ZnF2 = 0.6). Therefore, for low optical
loss mid-infrared fibre the glasses of the series (90-x)TeO2-10Na2O-xZnF2 mol. % would
be more suitable. The composition of these glasses can be altered over a wider range (15
to 30 mol. % ZnF2) than the 65 TeO2-(25-x)ZnF2-xZnO-10Na2O mol. % series without
significantly shifting the multiphonon edge or OH absorption band intensities. This
would enable a larger refractive index difference in a core / clad pair, without
compromising other optical properties.
6.3.1.3. Spectroscopy of Er +3 -doped composition
The effect of heat treatment on the emission bands of erbium, particularly at around 1.55
µm is discussed here. These heat treatments were performed in the hope of producing
transparent glass ceramics, analogous to the fluoroaluminosilicate based materials
produced by Kukkonen and Beggiora et al. [34, 35]. In this work, the heat treatments
resulted in the precipitation of a nano-crystalline erbium rich phase, which enhanced the
optical properties and broadened the emission bands of Er +3 .
Fig. (6.44) shows the near-IR spectra of glass MOF017 (69.86TeO2-9.98Na2O-
19.96ZnF2-0.20ErF3 mol. %) untreated, and heat treated for 1 hour at 245, 255, 265 and