Questions are often seen on this list about fluorescence. a recent article Fluorescence of ceramic color standards Annette Koo,1,* John F. Clare,1 Kathryn M. Nield,1 Andrew Deadman,2 and Eric Usadi2 APPLIED OPTICS / Vol. 49, No. 12 / 20 April 2010 may be of interest for those who are concerned -- Jean-Pierre Vial