Range-extended EXAFS at theLedge of rare earths using high-energy-resolution fluorescence detection: A study of La in LaOCl

We present extended x-ray absorption fine structure (EXAFS) data at the La L₂ edge in LaOCl that were recorded on the Lβ₁ fluorescence line with an analyzer energy bandwidth of 1.30.3em0exeV. We show that by taking advantage of the high-energy-resolution fluorescence detection (HERFD) it is possible to extend the energy range for L₂ EXAFS analysis beyond the L₁ edge if the sample is optically thin. The arguments presented here generally apply to fluorescence-detected absorption spectroscopy if the fluorescence lines are sufficiently separated in energy. Calculations using an atomic multiplet model show that intensity due to $2p4d$ multiple-electron excitations is reduced in HERFD spectra. The technique has the potential of considerably improving EXAFS analyses at low energies (<100.3em0exkeV) when absorption edges lie within a few hundred electron volts.