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(a) As concentration increases, absorption corresponding to different indirect transitions shifts to lower energy side. The absorption peak near 480 nm is due to the occurrence of intermediate energy states in the bandgap. (b) Variation of bandgaps with concentration. Bandgap is enhanced with decrease in solute concentration. The broadening in the band tail is expected as due to the presence of high density localized states in the forbidden energy gap.
Schematic density of states for amorphous semiconductors.
Excitation and emission spectra of sample C3. The excitation spectrum which consists of abroad peak around 480 nm shows the presence of localized states.
Normalized transmittance as a function of the position for different concentrations in the open aperture scheme at 532 nm with a laser power of 174 MW/cm2. The solid line shows the theoretical fit.
Schematic of two step photon absorption as well as resonant two photon absorption in nanocolloids.
Optical limiting response of C1, C2, and C3 at 532 nm at an input power density of 174 MW/cm2. The optical limiting threshold is found to decrease with concentration.
(a) and (b) XRD of spin coated nanocolloidal solution “C3” before and after laser exposure showing tendency for crystallization after laser exposure is less.
(a) and (b) SEM image of unexposed and laser exposed nanocolloid.
Variation of nonlinear absorption coefficient with concentration at 174 MW/cm2.
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