Structural, photoluminescence and dielectric investigations of phosphatic shale.

Abstract

In the current study, the structural and spectroscopic properties of phosphatic shale samples obtained from the Atomic Minerals Directorate for Exploration and Research were probed for potential use as a phosphor material. X-ray diffraction and Raman and Fourier transform infrared spectroscopy revealed that the beneficiated phosphatic shale samples were primarily monophasic consisting of fluorapatite [Ca5 (PO4 )3 F, (FAP)] with minor traces of haematite (α-Fe2 O3 ) and calcite (CaCO3 ). Energy dispersive X-ray fluorescence revealed the presence of U, Eu, Dy and Tb in the FAP matrix substituted at Ca(I) and Ca(II) sites of FAP. A reduced optical direct band gap of 4.46eV was calculated from the Tauc plot. Photoluminescence spectral studies revealed multicolour emissions (red, yellow, green and blue) on ultraviolet light excitation that were attributed to luminescence spectra from rare earth ions Eu3+ , Tb3+ , U4+ and U6+ in the FAP matrix. The overall emissions for the rare earth and actinide-doped FAP were obtained in the cool white region and the corresponding Commission Internationale de l'Eclairage chromaticity coordinates were calculated to be (0.274, 0.317). The corresponding colour correlated temperature obtained was 9342K. Furthermore, phosphatic shale had a high room temperature dielectric constant of 11 at a frequency of 1kHz that demonstrated its suitability for use in biological sensors. The study showed that natural phosphatic shale could be a potential material for optical, biological and dielectric applications.