X-ray levels have various degrees of
ionization -- single, double or higher -- and may in some cases also be electrically neutral. An excitation level (
exciton) is an electrically neutral
X-ray level with an expelled electron bound in the field of a core electron vacancy.
Source:
PAC, 1991, 63, 735
(Nomenclature, symbols, units and their usage in spectrochemical analysis - VIII. Nomenclature system for X-ray spectroscopy (Recommendations 1991))
on page 738