Benefitting from Dopant Loss and Ostwald Ripening in Mn Doping of II-VI Semiconductor Nanocrystals

Annealing or growth at high temperatures for an extended period of time is considered detrimental for most synthetic strategies for high-quality Mn-doped II-VI semiconductor nanocrystals. It can lead to the broadening of size distribution and, more importantly, to the loss of dopants. Here, we examine how ripening can be beneficial to doping in a simple "heat-up" approach, where high dopant concentrations can be achieved. We discuss the interplay of the loss of dopants, Ostwald ripening, and the clustering of Mn near the surface during nanocrystal growth. Smaller nanocrystals in a reaction batch, on average, exhibit higher undesirable band-edge photoluminescence (PL) and lower desirable dopant PL. The optimization of dopant loss and the removal of such smaller undesirable nanocrystals through Ostwald ripening along with surface exchange/passivation to remove Mn clustering lead to high Mn PL quantum yields (45 to 55 %) for ZnSxSe1-x, ZnS, CdS, and CdSxSe1-x host nanocrystals. These results provide an improved understanding of the doping process in a simple and potentially scalable synthetic strategy for achieving "pure" and bright dopant emission.