Electron irradiation‐induced effects on optical spectra of (NH₄)₂ZnCl₄: x Sr²⁺ single crystals

Abstract

The effect of electron-beam irradiation with different doses on optical constants of (NH 4 ) 2 ZnCl 4 : x Sr 2+ crystals with x=0.000, 0.020, 0.039, 0.087 or 0.144 wt% has been studied. The optical transmission in the energy range 3.4-6.4 eV was measured hence the absorption coefficient was computed as a frequency function. The absorption coefficient was also calculated as a function of electron-beam dose. Irradiation with e-beam did not affect the allowed indirect type of transition responsible for interband transitions of (NH 4 ) 2 ZnCl 4 : x Sr 2+ crystals. Values of the optical energy gap E g and optical moment E p for electronic interband transition of unexposed and (NH 4 ) 2 ZnCl 4 : x Sr 2+ crystals after e-beam exposure were deduced. The area under the absorption band at 5.30 eV was used to evaluate the effect of e-irradiation on optical parameters of samples with x=0.00, 0.020 or 0.039. A shift in the position and a nonmonotonic change in the intensity of this band with increasing e-beam dose was observed. Changes in the E g value were used to evaluate the effect of e-beam exposure dose on (NH 4 ) 2 ZnCl 4 : x Sr 2+ samples with x=0.087 or 0.144. The obtained results were compared with those obtained for the same crystals after irradiation with different γ-doses.

Structure and Physical Properties of Polymer Composite Films Doped with Fullerene Nanoparticles

“…The fundamental absorption is related to band-to-band transitions, and is subject to certain selection rules [13]. The usual method to determine the energy of the band gap is to plot a graph between (ahv) 1/n and hv looking for the value of n (depends on the nature of transition) that gives the best linear fit of a given data set [14]. The allowed direct and indirect transitions are given by the values of n as 1/2 and 2, respectively:…”

“…The other line represents the dependence in the high energy range corresponding to a phonon-emission process and cuts the energy axis at E gi + E p . From the energy intercept of the two straight line portions, the values of E gi and E p could be estimated [14].…”

“…The values of band tails, optical energy gaps, phonon energy, and the phonon equivalent temperature (given by T p = E p /k B , where k B is Boltzmann's constant, at the room temperature[14]) for different fullerene polymer composites.…”