The transient behavior of photorefractive gratings in the polymer composite poly(N‐vinyl carbazole) (PVK), 2,4,7‐trinitro‐9‐fluorenone (TNF), and N,N‐diethyl‐para‐nitroaniline (EPNA) doped with various amounts of 4‐(diethylamino)benzaldehyde diphenylhydrazone (DEH) is presented. The influence on the hole drift mobility due to the change in the trap density induced by DEH, was directly measured. ©1995 American Institute of Physics.