Abstract
The using of a reliable and accurate new method (called in literatures as derivation of absorption spectrum
fitting (DASF)) for evaluation of the optical band gap (Eg) and also the exact nature of charge carriers optical
transitions, is investigated in ZnSe and ZnSe:Cu nanocrystals (NCs) synthesized by rapid microwave
irradiation. This method can be performed by using the output of UV-Visible spectroscopy. The obtained Eg
values are within the range of 2.985-3.261eV, depending to the microwave irradiation time and Cu dopant
percentage (decreasing trend with increasing of irradiation time and Cu content). The DASF-based obtained
results for ZnSe and ZnSe:Cu nanoparticles, showed the more precise values of band gap, with the same trend
of previously qualitative reported data on the same samples. Also, the direct gap nature of their optical
transitions was justified. To perform the method, there is no any need to the concentration of solutions and
merely one need the direct absorption or transmission spectra. In other word, DASF technique was employed
on ZnSe NCs to confirm its validity and to avoid non-precise reports on optical band gap which can affect on
the device optimizations based on these samples. Moreover, using the values of Eg, refractive index and
dielectric constant of each sample were obtained at the absorption edge. Also, the width of the tailing states in
the gap (Urbach energy: ETail) was estimated and were within the range of 0.049-0.122 eV, which their very
small values in compare with Eg imply to the sharp valence and conduction band edges; it means the good
crystallinity nature of the produced samples