Dopant-Directed Surface Energy Modulation for Controlled Growth and Color-Tunable Photoluminescence in Cu+-Doped Two-Dimensional CdSe Nanoplatelets.

Two-dimensional (2D) semiconductor nanoplatelets (NPLs) are promising building blocks for optoelectronic applications due to their strong 1D quantum confinement and large lateral dimensions. While the growth mechanisms of pristine CdSe NPLs have been extensively studied, the influence of transition-metal dopants on 2D NPL growth remains poorly understood. Here, we investigate the growth behavior of Cu+-doped CdSe NPLs synthesized via a nucleation-doping colloidal approach. The introduction of Cu+ induces a dopant-modulated three-stage growth process. At 230 °C, Cu+ dopants initially decelerate NPL growth, stabilizing 2-monolayer (ML) CdSe NPLs in stage I. In stage II, these 2 ML NPLs undergo a dissolution-ripening process, ultimately leading to the formation of 3 ML NPLs in stage III. The resulting Cu-doped CdSe NPLs exhibit color-tunable photoluminescence (PL) arising from both the CdSe host excitonic emission (∼390-465 nm) and a broad, Stokes-shifted Cu+ dopant emission (∼520-640 nm), enabled by thickness-dependent bandgap modulation. This dopant-directed three-stage growth behavior is also observed in thicker Cu:CdSe NPLs (e.g., 4 ML). Theoretical simulations reveal that Cu+ doping increases the relative surface stabilization energy, stabilizing thinner NPLs and delaying the transition to thicker structures. This dopant-driven control over 2D NPL growth offers opportunities for engineering color-tunable and dopant-emissive optoelectronic materials.