EPR and electronic absorption spectra of copper bearing turquoise mineral

Abstract

Electron paramagnetic resonance and optical absorption spectra of turquoise have been studied both at room and low temperatures. It is concluded from the EPR spectra that the ground state of Cu 2+ ion in turquoise is 2A g(d x 2− y 2 ) and it is sited in an elongated rhombic octahedron (D 2π). The observed absorption bands at 14970 and 18354 cm −1 are assigned at 2A g→ 2B 1 g ( d x 2− y 2 → xy ) and 2A g→[ su2B 3g(d x 2−y 2 →d yz) respectively assuming D 2π symmetry which are inconsistent with EPR studies. The three bands in the NIR region are attributed to combinations of fundamental modes of the H 2O molecule present in the sample.