Excited state absorption measurements as a powerful tool for advanced spectroscopy

Examples of the excited state absorption (ESA) spectra measurements along with interpretations are presented and concerned as a tool which can provide answers to questions arising from other spectroscopic data. Author presents several cases where the data taken from the ESA spectra had been successfully working in the above context. The ESA characteristics for Cr3+, Cr4+, Cr6+ or Pr3+ ions in the glass, ceramic and crystalline matrices are demonstrated and discussed.In case of Cr3+ and Cr4+ ions in very different matrices the ESA spectra allowed to determine character of incident and terminal states taking part in the transitions, in case of Cr6+ ions in two different glasses the ESA spectra gave rise for answer to the question on [CrO4]2− group and its luminescence efficiency, and finally, in case of Pr3+ ions in the fluoroaluminate glass the ESA measurements revealed multiple-line gain and its growth with temperature whereas in the LiNbO3 crystal the ESA spectra allowed to identify a trapped exciton taking part in the deexcitation and luminescence process.