Tellurite And Fluorotellurite Glasses For Active And Passive

6. Optical properties; MDO 241
275°C. The erbium (III) band centered at 1.5 µm consists of two main peaks, both with
some degree of asymmetry. The peak intensity decreased with increasing temperature.
The asymmetry of the bands became more distinct with increasing temperature, making
additional bands more visible. The bands also shifted to lower wavenumbers with
increasing temperature.
Jha and Shen et al. [36, 37] observed an enhancement (i.e. broadening) of this Er +3
band with increasing Er +3 concentration in TeO2-ZnO-Na2O glasses. This was thought to
be due to a number of reasons:
i. The range of structural units present in the glass ([TeO4], [TeO3] and [TeO3+1]).
This results in a range of Te-O bond lengths in the equatorial and axial directions.
Addition of Er2O3 will therefore change the ion host field strength as it changes
the range of polyhedra present [36].
ii. The interaction between the Te +4 lone electron pair and other cations (Zn +2 and
Na + ) will change with Er2O3 addition [36].
iii. Er +3 coordination changes with increasing concentration [36].
Hirano et al. [38] also observed broadening of the Er +3 bands after heat treatment of Er +3
doped TeO2-K2O-Nb2O5 glass. This indicated that the environment surrounding the
erbium ion in glass MOF017 (69.86TeO2-9.98Na2O-19.96ZnF2-0.20ErF3 mol. %) had
changed with increasing heat treatment temperature. The erbium (III) could have been
preferentially segregating into the crystalline phase [34, 35], resulting in the enhancement
of the bands.