Optical absorption spectra and related parameters of ammonium zinc chloride crystal in the antiferroelectric and commensurate phases

Abstract

Optical absorption along the three crystallographic axes of (NH 4 ) 2 ZnCl 4 single crystals is reported over a temperature range from 276 K to 350 K. Our results clearly confirm the antiferroelectric to commensurate phase transition at 319 K. Analysis reveals that at the absorption edge the type of transition is the indirect allowed one. The indirect band gaps at various temperatures are determined and their temperature dependence is estimated in the antiferroelectric and commensurate phases. Optical parameters related to the temperature dependence of the energy gap are evaluated. The single-effective oscillator model was used to describe the imaginary part of the dielectric constant, which facilitate calculation of the dipole moment parameters. The steepness parameter is given, its value is used to estimate the temperature dependence of the indirect energy gap and the result is compared with that calculated graphically. In the region of the absorption edge, the absorption coefficient obeys Urbach's rule. Urbach characteristic parameters are determined and their temperature dependence is investigated. Correlation between different parameters is considered. Most of the results confirm the optical isotropic nature of AZC crystals.

Substrate temperature effect on the optical properties of amorphous Sb2S3 thin films

“…It can be seen that the refractive index, in general, has a tendency to increase with the substrate temperature, which may be to the change in transmittance. The dispersion of refractive index was found to be normal and well described by a single oscillator model [22,23]. It was observed that the refractive index increased steadily from 2.37 to 2.62 at the wavelength above λ=600 nm when the substrate temperature varied from 300 to 473 K.…”

Crystallization and optical properties of CaWO4 and SrWO4

“…The extinction coefficient (K) and the refractive index (n) have been calculated via the following relations [21];…”

Growth and characterization of undoped, Sr2+-, and Mn2+-doped ammonium tetrachlorozincate

“…It is worthy to know that amount of ZnCl 2 needed for exact chemical stoichiometry is difficult to define and the growth run might be completed in a medium with excess ZnCl 2 . Details about the effect of chemical non-stoichiometry on growth and morphology of AZC may be found elsewhere [11]. The dopant concentration was measured by the atomic absorption technique (Pye Unicam, Atomic Absorption Spectrometer, type Sp 1900).…”