Profile analysis of experimental x‐ray fluorescence spectra

Abstract

A systematic study has been made of the line shapes of x‐ray fluorescence spectra obtained with a conventional spectrometer using various analysing crystals and experimental conditions. It was found that each component of the K and L spectra can be closely matched by the sum of an asymmetric Gaussian and Lorentzian, namely the pseudo‐Voigt function. Analysis of spectra in the 0.4–3 Å range showed that profile shapes are functions of 2θ, the analysing crystal and the collimating system, but nearly independent of chemical state, specimen thickness and operating voltage. For a fixed analysing crystal and collimator, larger values of 2θ exhibited lower Gaussian content and higher asymmetry. Using an LiF (200) crystal, spectra obtained for 2θ° < 20° were found to be pure Gaussian and symmetric, indicating the dominance of the instrumental effects. As 2θ increased, the Lorentzian component or the spectral effects emerged and the shapes became asymmetric. The analysing crystal has a pronounced effect on the experimental profile shapes. Use of a graphite (002) instead of an LiF (200) crystal yielded profiles three times wider and with twice the Lorentzian content. The differences between PET and LiF crystals were smaller. The accuracy achieved in using the pseudo. Voigt function to describe the experimental XRF spectra demonstrates the convenience and effectiveness of the function in obtaining precise fluorescence intensities, especially in the case of poor counting statistics and/or overlaps. Copyright © 1986 John Wiley & Sons, Ltd.