Imaging rare-earth elements in minerals by laser-induced plasma spectroscopy: Molecular emission and plasma-induced luminescence

Abstract

Laser-induced breakdown spectroscopy (LIBS) of atoms and ions of rare earth elements (REEs) appears to be an effective tool for REE detection and identification, specifically in imaging applications. We propose to combine this technique with the molecular emissions of LaO and YO and the plasma-induced luminescence (PIL) of REEs in luminescent matrixes. Presently, PIL is mostly sensitive to Eu, Sm, Dy, Gd, and Pr. The main advantage of the proposed technique is that both molecular emission and PIL are characterized by long plasma lifetimes, tens and hundreds of microseconds, when nearly all interfering emissions do not practically exist. Furthermore, the relatively broad emission and luminescence bands and lines enable us to use spectroscopic equipment with a relatively low spectral resolution. It is important to emphasize that the proposed experiments (atomic LIBS, molecular LIBS and PIL) are performed with the same experimental setup and from the same plasma source. Only the detection parameters (spectral range and spectrometer slit, as well as the ICCD gain, delay and width) are modified. As result, imaging of REEs becomes more sensitive and less sophisticated. As an illustration, two imaging experiments are shown to emphasize the high complementarity of these three approaches for the detection of REEs.