High-resolution spectrometric analysis of rare earth elements-activated cathodoluminescence in feldspar minerals

Cathodoluminescence (CL) investigations of igneous, metamorphic and sedimen tary feldspars indicate that rare earth elements (REE)-activated CL in feld spars is more common than previously assumed. Hot-cathode CL microscopy com bined with high-resolution spectrometric analysis of CL emission allow to d etect some REE below the detection limits of electron microprobe and proton -induced X-ray emission analysis (PIXE) and reveal variations in the REE di stribution within single feldspar crystals. Differently luminescing zones c an reflect changes during feldspar crystallization and/or element fluctuati ons during secondary alteration processes which are not discernible using c onventional polarizing microscopy. The results of the study document Eu2+, Sm3+, Dy3+, Tb3+, and Nd3+-activated CL in feldspars of different origin. T he influence of the crystal field on shape and position of REE luminescence spectra significantly differs for divalent and trivalent REE ions. Whereas Eu2+ shows a broad band emission (similar to 420 nm) which is influenced b y the local crystal field, trivalent ions of the rare earth show narrow emi ssion lines which reflect the transitions between excited state wave functi ons lying inside closed electronic shells. The positions of these peaks and the characteristic energies are described for the different REE3+. (C) 199 9 Elsevier Science B.V. All rights reserved.