X-ray emission spectroscopy (XES)
From Online Dictionary of Crystallography
Detection of the X-rays that are emitted from the sample with an instrumental energy bandwidth that is on the order of the core hole lifetime broadening. XES can be performed by taking advantage of various modes of core hole creation, the most common being photo-excitation, but also ion/electron bombardment and radioactive isotopes (K capture decay) have been used. XES following photo-excitation is a second-order optical process that is theoretically treated using the Kramers-Heisenberg equation. XES thus includes high energy resolution X-ray fluorescence spectroscopy (e.g. Kβ spectroscopy), resonant X-ray emission spectroscopy (RXES) and resonant inelastic X-ray scattering (RIXS).
In the hard X-ray regime instruments based on perfect crystal Bragg optics are used to analyze the emitted X-rays. Common geometries are Rowland or von Hamos. Applications of XES include electronic structure studies (e.g. chemical characterization) but also spectral sharpened XAFS (see HERFD) and range-extended EXAFS. The instrumentation for XES provides the possibility to perform X-ray Raman spectroscopy.