Doped semiconductor nanoparticles – a new class of luminescent materials?

Abstract

Five years ago it was reported that nanocrystalline ZnS : Mn 2+ can yield both high luminescence efficiencies and a spectacular lifetime shortening, which suggested that doped semiconductor nanoparticles form a new class of luminescent materials for various applications. From lifetime measurements and time-resolved spectroscopy we conclude that the Mn 2+ emission of nanocrystalline ZnS : Mn 2+ does in fact not show a spectacular shortening of the decay time upon decreasing particle size. The luminescence of nanocrystalline ZnS : Mn 2+ indeed shows a short decay time component (∼100 ns), but also a long (ms) decay time is observed. The short decay time is ascribed to a defect-related emission of ZnS, and is not from the decay of the 4 T 1– 6 A 1 transition of the Mn 2+ impurity. The 4 T 1– 6 A 1 transition of the Mn 2+ has a `normal’ decay of about 1.9 ms. Based on our observations, we conclude that doped semiconductor nanoparticles do not form a new class of luminescent materials, combining a high efficiency with a short (ns) decay time.