With 9 diamonds and 3 more 4 and 9's = 15 outs I like your bet. You will likely take down the pot here. You are also drawing to the nuts until a pair hits the board. Good.
If you don't win it here, your odds drop off huge if only one person calls.
I'd bet the pot again on the turn, thus thoroughly decieving any caller.
If you hit it on the river, I'm all in.
If you don't hit it on the river, I'd still make a large bet, as many times the other caller is also drawing and will fold figuring you for trips or an over pair.

There is a qualifier here though. I only do this with TAG players, as they seldom call. LAG's call far more often.