Tunable Infrared Phosphors Using Cu Doping in Semiconductor Nanocrystals: Surface Electronic Structure Evaluation

In this Letter, we report the study of the effect of ligands on the surface electronic structure of the nanocrystal by exploiting the mechanism of the Cu-related optical transition, obtained by coupling the nanocrystal conduction band to the Cu ion state in Cu-doped II-VI semiconductor nanocrystals. Systematic study of steady-state luminescence and lifetime decay dynamics of this Cu-related emission in cadmium-based chalcogenides shows that the role of oleic acid in surface passivation is unexpectedly quite different for various chalcogenides. Further, using these leads in Cu-doped CdS nanocrystals, we develop near-infrared-emitting phosphor materials that have tunable, high quantum yield (similar to 35%) emission with a single-exponential lifetime decay. Surprisingly, unlike the emission from other Cu-doped II-VI nanocrystals, emission from Cu doping in CdS nanocrystals is found to exhibit high thermal stability, being essentially unchanged up to 100 degrees C, making them more viable for use in various practical applications.