Optically detected x-ray absorption spectroscopy of luminescent materials

Abstract

X-ray absorption near edge and extended fine structure (EXAFS/XANES) has been observed from luminescence excitation spectra of crystals and glasses using synchrotron radiation. The luminescence may either be intrinsic (recombination radiation from alkaki halides, alkaline earth fluorides, oxides) or from activator ions (rare earths, transition metals, organic dyes) excited directly or indirectly. Core electron excitations of cations and anions in luminescent materials have been investigated in the energy range from the VUV to hard x-rays. Absorption features may appear as an increase or decrease in the luminescence intensity depending on the sample thickness with respect to the x-ray absorption length, observation geometry, and intermediate relaxation processes. For materials with multiple sites, conventional x-ray absorption spectroscopy measures some average of different site populations. Since luminescence spectra vary with the local environment, using optical detection measurements can be both atom specific via the characteristic x-ray absorption edge energy and site and valence specific via the optical wavelength.