Abstract
The results of investigation of infrared, Raman and UV-Visible absorption spectra of natural topaz crystals from Ukraine before and after fast neutron irradiation are presented. We assume that the ~ 620 nm band in topaz crystals is associated with the presence of Cr3+, Fe2+ and Mn2+ impurities. The broad band with maxima at 650 cm−1 observed in Raman spectra for topaz irradiated by fast neutrons may be connected with lattice disorder. Exchange interaction between radiation defect and impurity ions during neutron irradiation leads to appearance of additional absorption band in UV-VIS spectra and bands broadening in infrared and Raman spectra of investigated crystals.
Highlights
The study the optical properties of topaz can be used to determine the quality of jewelry topaz, for the successful use of these crystals in thermoluminescence dosimetry [1] as well as for evaluation of physical and chemical conditions of formation of mineral [2]
The fluence of fast neutrons with energy 0.1 MeV was in the range 1014 – 5 1017 cm-2
The broad band with maxima at 650 cm-1 observed in Raman spectra for irradiated by fast neutron topaz may be connected with lattice disorder
Summary
The study the optical properties of topaz can be used to determine the quality of jewelry topaz, for the successful use of these crystals in thermoluminescence dosimetry [1] as well as for evaluation of physical and chemical conditions of formation of mineral [2]. Topaz is an aluminium fluorosilicate with a fairly constant chemical composition Al 2SiO4(OH,F). The structure of topaz consists of SiO4 groups linking octahedral chains of Al[O4(F,OH)2] in a zigzag fashion parallel to the crystalline c-axis. Four of six anions surrounding Al3+ ion belong to SiO4 tetrahedron and the remaining two anions are. Topaz crystallizes in the orthorhombic system, space group Pbnm (D162h) [3, 4] with four molecules per unit cell, but the OH/F substitution turns its symmetry into triclinic (P1) [5]. The lattice parameters are a=4.6499 A , b=8.7968 A and c=8.3909 A and is normally found as welldeveloped prismatic crystals with pyramidal terminations
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