Ray J?is adamant … he is NOT secretly harboring a stash of sexually explicit photos and video, depicting him and?Whitney Houston?in the throes of passion — because no such stash exists.

There have been reports … Ray is sitting on a hoard of sex tapes and XXX photos — holding them over the Houston family as ransom — because he knows they’re worth a pretty penny.

But Ray J’s rep tells TMZ, “The despicable tabloid report released today claiming the existence of a sex tape between Ray J and Whitney Houston is not true … There is no sex tape.”

Sources extremely close to Ray J tell us the singer insists he NEVER took sexually explicit pics of Whitney … or recorded ANY of their intimate encounters.