Tuning Equilibrium Compositions in Colloidal Cd_1–xMn_xSe Nanocrystals Using Diffusion Doping and Cation Exchange

Abstract

The physical properties of semiconductor nanocrystals can be tuned dramatically via composition control. Here, we report a detailed investigation of the synthesis of high-quality colloidal Cd1-xMnxSe nanocrystals by diffusion doping of preformed CdSe nanocrystals. Until recently, Cd1-xMnxSe nanocrystals proved elusive because of kinetic incompatibilities between Mn(2+) and Cd(2+) chemistries. Diffusion doping allows Cd1-xMnxSe nanocrystals to be prepared under thermodynamic rather than kinetic control, allowing access to broader composition ranges. We now investigate this chemistry as a model system for understanding the characteristics of nanocrystal diffusion doping more deeply. From the present work, a Se(2-)-limited reaction regime is identified, in which Mn(2+) diffusion into CdSe nanocrystals is gated by added Se(2-), and equilibrium compositions are proportional to the amount of added Se(2-). At large added Se(2-) concentrations, a solubility-limited regime is also identified, in which x = xmax = ∼0.31, independent of the amount of added Se(2-). We further demonstrate that Mn(2+) in-diffusion can be reversed by cation exchange with Cd(2+) under exactly the same reaction conditions, purifying Cd1-xMnxSe nanocrystals back to CdSe nanocrystals with fine tunability. These chemistries offer exceptional composition control in Cd1-xMnxSe NCs, providing opportunities for fundamental studies of impurity diffusion in nanocrystals and for development of compositionally tuned nanocrystals with diverse applications ranging from solar energy conversion to spin-based photonics.

High performance of Mn-doped CdSe quantum dot sensitized solar cells based on the vertical ZnO nanorod arrays

“…1(c), inset), it can be seen that the MneCdSe QDs have an average diameter of 6.1 ± 0.6 nm, which is slightly larger than that of 5.5 ± 0.7 nm of CdSe QDs. Recently, Gamelin et al have shown that the diameter of Mn 2þ doped CdSe nanocrystals can grow larger with the addition Mn 2þ precursors, which is consistent with our result [30]. The elemental analysis show in Fig.…”

Efficient and Stable Luminescence from Mn2+ in Core and Core–Isocrystalline Shell CsPbCl3 Perovskite Nanocrystals

“…% Mn 2+ were realized. 28 It can be expected that with different synthesis methods also for CsPbCl 3 NCs, higher Mn 2+ doping levels are possible.…”

Excited-State Dynamics in Colloidal Semiconductor Nanocrystals

“…Doping of bulk materials is a very well developed field, which underpins most of our present technologies, since the properties of materials for lighting, electronic and optoelectronic applications are largely controlled by dopants. In contrast, the precise doping of NCs is still an underdeveloped field, which is however booming and has delivered great successes and many novel materials in recent years [28, 91–100]. …”