Luminescent phosphors have been used in biology and imaging for many applications. Interestingly, there is another application that has not been publicized as much. Scientists from Malaysia, Moldova and Russia have made unique persistent phosphors that last for many days and hours in tough environment below the ocean. These are originally made nearly 16 years ago from (Europium) Eu2+ co-doped with (Dysprosium) Dy3+to create a material that emitted light for several hours after the excitation light ended. This material, SrAl2O4.Eu2+, Dy3+, was far more effective than the older materials made from ZnSCu.Co.
This material was made by firing Strontium carbonate, Aluminum oxide, Europium oxide and Dysprosium oxide at 1250 C and then coating it onto rocks that were dropped into oceans. These luminescent rocks attracted wild life and served as artificial reefs and more pictures are located here.