|
Journal of Physical Studies 27(4), Article 4702 [8 pages] (2023)
DOI: https://doi.org/10.30970/jps.27.4702 OPTICAL AND ELECTRONIC PARAMETERS OF POTASSIUM SULPHATE CRYSTALS DOPED WITH MANGANESE IMPURITY
V. Yo. Stadnyk1
1Ivan Franko National University of Lviv, 19, Drahomanov St., Lviv, UA-79005, Ukraine,
|
 |
The simplest method for changing and improving the dielectric properties of crystals involves introducing various substitutional impurities or subjecting the crystals to external influences. This allows us to uncover the potential for expanding the practical applications of crystals as optical filters, acousto-optic modulators, temperature and pressure sensors, piezo transducers, scintillators, etc. Currently, the effect of manganese admixture on the dielectric parameters of K$_2$SO$_4$ crystals remains unstudied. Therefore, the objective of this work is to investigate the effect of introducing a manganese admixture into potassium sulfate crystals on their band-energy and refractive properties.
In this study, a potassium sulfate crystal with a manganese admixture was synthesized, and its crystal structure was determined. The dispersion of refractive indices was investigated, and the band-energy structure was calculated. It was established that the crystal structure of K$_2$SO$_4$ impurity crystals can be considered a result of multiple heterovalent replacement of two K$^+$ atoms by one Mn$^{2+}$ atom in the framework of stacking of SO$_4^{2-}$ tetrahedra. The study reveals that the conduction band's bottom is formed by $s$- and $p$-states of sulfur and potassium atoms, while the valence band's top is formed by $p$-states of oxygen and $s$-states of oxygen. The manganese impurity in the density of states of the potassium sulfate crystal is represented by a narrow intense $d$-electron peak, which corresponds to impurity levels in the band gap near the top of the valence band. The calculated band gap for the impurity crystal is $E_g = 5.92$ eV.
It was found that the introduction of the admixture results in a reduction in the volume of the unit cell and a decrease in the refractive indices for three crystal physical directions, with an average decrease of $1.9\times 10^{-3}$. Additionally, it causes a shift in the position of the centers of ultraviolet oscillators in the long-wavelength spectrum region, leading to a decrease in the strength of the corresponding oscillators and electronic polarizability compared to pure crystals.
Key words: crystal, crystal structure, band-energy structure, density of states, refractive index, dispersion.
