  Direct holographic recording in undoped Bi$_{12}$TiO$_{20}$ crystal at 1064
nm is investigated aiming the characterization of diffraction efficiency under
action of applied dc electric field ($E_0$). An enhancement of 12-fold in the
diffraction efficiency was revealed when $E_0$ increased from 0.0 to 4.2 kV/cm.
The theoretical dependence of the diffraction efficiency upon $E_0$ was
investigated using the standard model for photorefractivity and the results
showed a good experimental data fitting, allowing the computation of the
effective trap concentration $(N_D$$)_{eff}$ $\approx$ $5.3\times 10^{15}$
cm$^{-3}$ which is responsible by the recording mechanism into the BTO crystal
sample. The type of charge carrier involved in the recording mechanism in the
nearinfrared region is also discussed.
