In that particular example, I actually hit my card on the turn, so what started out as a semi-bluff turned into a made hand, so my turn bet was based on the pair of aces with the 20% probability of still making the nut flush.

But in general, you could still attempt a semi-bluff on the turn but it is much more risky. If you attempted a semi-bluff on the flop and your opponent called, then he may have a decent hand. To attempt another semi-bluff on the turn may lead to the same result: your opponent still calling. You can still put out the semi-bluff bet if the bet relative to the pot odds provide a positive expected value.

You will need to combine the probability of hitting your outs plus the probability of your opponent folding (plus the probability of your opponent chasing a weaker draw hand and hitting).