Abstract: The threshold energies of photovoltaic response of both doped nano-La0.8Sr0.2FeO3 and undoped nano-LaFeO3 were probed by the vacuum adsorptive surface photovoltage technique. The results show that the threshold energy of nano-La0.8Sr0.2FeO3 is obviously smaller than that of nano-LaFeO3 under exposure to the sensor gas (ethanol vapor). And the difference between threshold energies of the two samples exposed to the sensor gas is increased, compared with that of them exposed to air. Moreover, by means of the difference of the threshold energies before and after doping Sr2＋ ion, the reorganization energy of surface electrons of doped sample can be quantitative calculated, i.e., Ers=b－a (where Ers is reorganization energy of surface electron of the sample, b and a is threshold energy before and after doping Sr2＋ ion respectively). The reason for producing reorganization energy of surface electrons is discussed.

Key words: Doped nanocrystal, Surface electronic reorganization, Photovoltage characters