Optical detection of x-ray-absorption spectra: Sodium salicylate as an example

In the optical detection of extended x-ray-absorption fine structure (EXAFS), x-ray radiation is absorbed, followed by the generation of ``intermediate'' electron-hole pairs. These e-h pairs may excite luminescent centers or recombine radiatively. The optical radiation produced upon decay of excited luminescent centers or radiative recombination of e-h pairs is detected. In the interpretation of the optical detection of EXAFS only the scattering and absorption of exciting x rays and generated light have hitherto been considered. This paper discusses the effect of diffusion of the intermediate e-h pairs to the surface of a single crystal or powder grains followed by radiationless recombination. The theory developed here is used to eliminate an apparent inconsistency between published measurements on the efficiency of sodium salicylate.