Tellurite And Fluorotellurite Glasses For Active And Passive

6. Optical properties; MDO 242
Fig. (6.45) shows the near-IR spectra of glass MOF017 (69.86TeO2-9.98Na2O-
19.96ZnF2-0.20ErF3 mol. %) heat treated at 240°C for 1, 5 and 11 hours. The peak
intensity decreased slightly with time, however the shape or positions of the bands did
not change significantly.
Fig. (6.46) shows the visible spectra of glass MOF017 (69.86TeO2-9.98Na2O-
19.96ZnF2-0.20ErF3 mol. %), untreated, and heat treated for 1 hour at 245 and 255°C. It
can be seen scattering losses increased with increasing temperature of heat treatment
1
towards the ultraviolet region, as scattering losses are proportional to (n = 4 for
n
λ
Rayleigh scattering (nano-particulate), and n = 2 for Mie scattering (micro-particulate)).
As heat treatment temperature increases, more crystalline phase will be present for a
given time of heat treatment. This will result in more scattering centres. Fig. (6.47) shows
a similar trend with increasing time of heat treatment (240°C for 1, 5 and 11 hours). As
time of heat treatment increases, the number of crystal and hence scattering centers will
increase.
However, no further work was done to investigate the nature of the phase crystallising,
and whether Er +3 partitioned to nano-crystals. The preliminary work reported here
suggests further work should be done, particularly in compositional development.