IV Optical Reflectance:
The practical usuability of the nonlinear optical is mainly decided by
the material’s transparency range in the UV-Vis-IR region. Fig. 3a shows
the UV–Vis reflectance spectrum obtained for the DAT2 compound in
200–1600 nm spectral region. DAT2 shows maximum reflectance of 80%
between 750 and 1100 nm. The lower cut-off wavelength of the crystal was
found to be 500 nm.The optical band gap (Eg ) was
evaluated from the reflectance spectrum as shown in Fig 3b. The optical
absorption coefficient (α) near the absorption edge was estimated by
using the relation,
(αhν) = A ( Eg – hν)1/2————(1)
where A is a constant, Eg is the optical
band gap. Fig. 3 b shows the Kubelka’s plot for the absorption
coefficient and the incident photon energy
(αhν )2 with the photon energy (hν ). It
can be considered as evidence for the indirect transition. The band gap
value has been obtained by extrapolating the linear portion of the plot
to intercept the photon energy axis and found to be 1.69 eV.