Figure 10: The calculated refractive index (n) and extinction
coefficient (k)
Absorption coefficient
The rate of incident electromagnetic radiations rapt in any material can
generally be determined through the absorption coefficient, i.e.,\(\eta\ =\frac{2k\omega}{c}\). As shown in Fig. (11), the absorption
starts approximately from 6.5 eV frequency because it is prime
characteristic of the absorption coefficient that it remains zero upto
the energy equal to the energy band gap of any solid material. However,
values of the absorption coefficient are found to be increased when
incident radiations gain threshold frequency, then it attains its
maximum value of 280000 cm-1 at 10.25 eV frequency.
Rather increasing the absorption rate after this frequency, its values
decrease sharply and become zero at 17 eV frequency where incident
radiations fall in infrared range of the electromagnetic radiations.
Moreover, the absorption coefficient may be associated with band gap
energy of a certain material which can further be elaborated in a way
that the material having wide band gap could be a best absorber of
incident radiations above Eg and vice versa.