We present the results of experiments performed on K1-xLixTaO3 as well as o
n Nb-doped and nominally pure KTaO3 single crystals, in which we compared o
bservations of thermally stimulated currents and photoconductivity. In the
Li-doped compounds, the large enhancement of conductivity caused by ultravi
olet excitation at low temperature was found to correlate with the tilling
of shallow trapping centres, giving intense charge release below 30-40 K. N
o sign of a corresponding release was shown by pure or Nb-doped KTaO3, cons
istently with a very low yield of photocurrent which one observes in these
cases. The depth of the trapping levels in K1-x LixTaO3 crystals was found
to be between 50 and 70 meV. On the basis of past models and recent calcula
tions, these levels can be identified with hole traps, originating from the
perturbation of O2- states at the top of the valence band. They are a plau
sible source of enhanced photoconductivity, via the quenching of electron-h
ole recombination.