Long-lived Mn2+ emission in nanocrystalline ZnS : Mn2+

Recently, it has been reported that doped semiconductor nanoparticles can y ield both high luminescence efficiencies and a spectacular lifetime shorten ing, which suggests that doped semiconductor nanoparticles form a new class of luminescent materials for various applications. From lifetime measureme nts and time-resolved spectroscopy we conclude that the Mn2+ emission does not show a spectacular shortening of the decay time upon decreasing particl e size as reported earlier. The luminescence of nanocrystalline ZnS:Mn2+ in deed has a short decay time (similar to 100 ns), but also shows a long ms r ange decay time. The short decay time is ascribed to a defect-related emiss ion of ZnS, and is not from the decay of the T-4(1)-(6)A(1) transition of t he Mn2+ impurity as suggested by other authors. The T-4(1)-(6)A(1), transit ion of the Mn2+ has a ''normal'' decay of about 1.9 ms. Based on our observ ations, we conclude that doped semiconductor nanoparticles do not form a ne w class of luminescent materials, combining a high efficiency with a short (ns) decay time. [S0163-1829(98)52038-6].