Core/Shell Magic-Sized Semiconductor Nanocrystals

Magic-sized semiconductor nanocrystals (MSNCs) grow via discrete jumps between specific sizes. Despite their potential to offer atomically precise structures, their use has been limited by poor stability and trap-dominated photoluminescence. Recently, syntheses have been reported that produce CdSe MSNCs over a larger size series. We exploit such particles and demonstrate a method to grow shells on CdSe MSNC cores. Thin CdS shells lead to dramatic improvements in the emissive properties of the MSNCs, narrowing their fluorescence linewidths, enhancing photoluminescence quantum yields, and eliminating trap emission. While thicker CdS shells lead to decreased performance, CdxZn1-xS alloyed shells maintain efficient and narrow fluorescence lines. These alloyed core/shell crystallites also exhibit a tetrahedral shape, in agreement with a recent model for MSNC growth. Our results indicate that MSNCs can compete with other state-of-the-art semiconductor nanocrystals. Furthermore, these core/shell structures will allow further study of MSNCs and their potential for atomically precise growth.