  Nanocrystals are often described as an interesting strategy for the design of
low-cost optoelectronic devices especially in the infrared range. However the
driving materials reaching infrared absorption are generally heavy
metalcontaining (Pb and Hg) with a high toxicity. An alternative strategy to
achieve infrared transition is the use of doped semiconductors presenting
intraband or plasmonic transition in the short, mid and long-wave infrared.
This strategy may offer more flexibility regarding the range of possible
candidate materials. In particular, significant progresses have been achieved
for the synthesis of doped oxides and for the control of their doping
magnitude. Among them, tin doped indium oxide (ITO) is the one providing the
broadest spectral tunability. Here we test the potential of such ITO
nanoparticles for photoconduction in the infrared. We demonstrate that In2O3
nanoparticles presents an intraband absorption in the mid infrared range which
is transformed into a plasmonic feature as doping is introduced. We have
determined the cross section associated with the plasmonic transition to be in
the 1-3x10-13 cm2 range. We have observed that the nanocrystals can be made
conductive and photoconductive due to a ligand exchange using a short
carboxylic acid, leading to a dark conduction with n-type character. We bring
further evidence that the observed photoresponse in the infrared is the result
of a bolometric effect.
