Mark,
The real answer is that a very few emeralds flouresce, and even then only a hint of it. They really couldn't be detected at depth because of their small size. IF it was pitch black, with perfect viz, and you had an insanely powerful U/V light, and the emerald happened to be laying on top of the sand...then you'd have about a 1 in a million shot at seeing it. U/V is just not the way to go about finding them. I bounced an idea off of some of our aerospace engineers for locating them...and they thought it had some merit, so we checked into it. It works on cut emeralds, but I don't have any rough emeralds to try it on.
There are still billions of dollars worth of them out there...even at PegLeg's market value (which are much more correct than Mel Fishers, but hey, Mel sells them at his prices, so who's to say).
Jason