Strategies for Isolating Colloidal Quantum Dot Luminescence from External Fluctuations: Alloyed Shells on CdSe and Mn2+ Doping of ZnSe

ZnxCd1-xS alloyed shells and Mn2+ ions were studied as a means to confine charge carriers away from the surface of nanocrystals. In the former case, the electron confinement potential increased with the Zn fraction in CdSe/ZnxCd1-xS colloidal quantum dots and their photoluminescence blueshifted by similar to 50 nm. However, structural defects and polydispersity became important in samples with x >0.7 likely due to a phase transition and to strain increasing with core/shell lattice mismatch reaching 12% when x = 1. In the latter case, the Mn2+ ions diffused within MnyZn1-ySe/ZnSe nanocrystals act as localized luminescent centers and their density can be controlled with the Mn fraction in the alloyed core. The ions are excited through energy transfers from excitons in the ZnSe, and given the long lifetime of the Mn2+ first excited state, thermo-activated reverse energy transfer also occurred and emission from the ZnSe excitons was observed.