Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
darken [dɑːkn] vt затемня́ть (затемни́ть perf)
vi (sky, room) темне́ть (потемне́ть perf)
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.
Русский: