Mechanistic insights into hole spin dynamics in colloidal Ag+-doped CdSe nanosheets: Interplay between two counteracting surface effects

We present a mechanistic study of hole spin dynamics in colloidal cadmium selenide (CdSe) nanosheets, aiming to gain insights into the elusive interplay between two counteracting surface effects, i.e., hole-trapping interaction [between the valence-band heavy-hole (HH) state and its nearby localized surface trap (LST) state] vs spin-exchange interaction [between the HH spin state and the surface dangling-bond spin (DBS) state]. Differently from our previous work adopting a strategy of ligand engineering [see Wu et al., Adv. Opt. Mater. 12, 2400583 (2024)], we here implement an alternative strategy of element doping to regulate the LST and DBS states in the Ag+-doped CdSe nanosystem. It is observed that the hole spin-flip lifetime is shortened when the Ag+-doping level is elevated, demonstrating that the hole-DBS exchange interaction can effectively compete against the coexisting hole-LST trapping interaction, mainly due to the doping-induced increase in the density of the DBS state. Markedly, this observation is contrary to that in the ligand-engineering case, where the hole-trapping interaction plays a predominant role due to the strong ligand/CdSe orbital hybridization. This work elucidates the interplay between the two surface effects and enriches the understanding about the subtle DBS-related effect, providing valuable mechanistic information for rational design and optimization of spintronic applications based on colloidal nanostructures.