Tellurite And Fluorotellurite Glasses For Active And Passive

6. Optical properties; MDO 172
where I0 = incident intensity, [J] = molar concentration of absorbing species J, and ε =
extinction coefficient or molar absorption coefficient. ε has units mol. -1 cm -1 , therefore the
product of ε[J]l is dimensionless, and known as absorbance, γ. Transmittance, ϕ, of the
sample is given by I/I0. The relation between transmittance and equation (6.8) is shown
by equation (6.9) [3].
log ϕ = −γ
(6.9)
The absorbance of the sample can be easily obtained by determining I and I0 (and hence
ϕ) experimentally. As equation (6.8) implies, sample absorption decreases exponentially
with sample thickness, l, and concentration, [J] [3].
Molecular explanation of vibrational spectroscopy
If a molecule possesses a permanent electric dipole moment, P, with particles of charges
+e and –e separated by distance r, shown by equation (6.10) [2].
P = er
(6.10)
A heteronuclear diatomic molecule above absolute 0K vibrates at a particular frequency.
The molecular dipole also vibrates about its equilibrium position. This dipole can only
absorb energy from an electric field (i.e. incident IR radiation) if the dipole oscillates at
the same frequency. A resonant energy transfer occurs, for example, between the net