The effect of temperature on the line Shape of the ultraviolet
absorption bands of chromium (VI) in ditrerent
(1-x) Na20, xB20 8 (where x varied from 0.1 to 0.33), and
in a 0.3Na20, 0.7Si02 glass was studied. The ultraviolet
absorption of chromium (VI) in these glasses is characterised
by two charge transfer bands centred around 250-270
nm and 35()....:370 nm, the location of the centre of absorption
and relative intensities of the two bands depending on the
borochromate/chromate ratio in the glass which in turn is
dependent on the chemical composition of the glass. The
35()....:370 nm band has been found to be Gaussian at the top
half of absorption, and exponential with wave-number at
the low-energy tail of the band obeying Urbachs Rule. In
all the glasses, the energy of absorption maximum decreased
linearly with increasing temperature, and the bands became
broader. The change in intensity of chromium (VI) absorption
in ditrerent glasses with varying temperature has a
satisfactory correlation with thermal expansion coefficient
of these glasses strongly indicating a photon-phonon
interaction in these cases. |