Usually a peak which occurs in excitation spectrum along with ground state absorption (GSA) peak is readily used as signature for Excited State absorption mechanism.
I would like to know how to identify this peak and upto what energy range from GSA.
Can you please elaborate a bit. I could not understand it completely. Are you dealing about pump probe spectroscopy? What excitation spectrum are you talking about? In normal fluorescence, excitation spectrum is just an absorption spectrum of an emissive molecule. In pump probe spectroscopy ground state bleach is the inverted ground state absorption signal. Excited state absorption spectrum is generally very broad. What is ETU and upconversion in this context?
No I am not talking about Pump probe spectroscopy.
Just luminescence measurement using CW lamp as an excitation source.
The upconversion (UC) is one of the phenomenon of luminescence in which a higher energy of photon will be emitted after absorption of two or more low energy photons. ETU (energy transfer upconversion) and ESA ( excited state absorption) are the two dominant mechanism of UC.
Excited state absorption spectrum in case of rare earth ion doped material is not broad. It is possible to denote each peak in it by the possible energy transitions.
For further information you may refer
c Riedener T, Egger P, Hulliger J, and Gudel H U, “Upconversion mechanisms in Er3+-doped Ba2YCl7”, Phys. Rev. B 56 (1997) 1800