Power-dependent and ultrafast spectroscopic studies of Ag ion-doped colloidal CdSe nanoplatelets

Atomically precise two-dimensional (2D) semiconductor nanoplatelets (NPLs) are found to be promising materials for next-generation optoelectronic devices due to their excellent optical properties. However, energy loss through phonon emission significantly causes problems in achieving efficient performance. Power-dependent steady-state spectroscopy and ultrafast spectroscopic studies have been performed to understand the influence of Ag ions on ultrafast carrier dynamics and thermalization processes in colloidal CdSe NPLs. An ultrafast transient absorption spectroscopic study shows that the rise time is faster from 410 fs to ∼160 fs after 11% Ag doping in CdSe NPLs. The dopant states act as a trap for the charge carriers that facilitate faster relaxation of electrons in these dopant states. The bleach decay time constant (τ1r) changes from 5 ps to 800 fs, changing the dopant concentration from 0 to 11% Ag, indicating the charge carrier separation through an intra-band dopant-mediated state. Power-dependent steady-state photoluminescence spectroscopic study reveals that the thermalization rate reduces from 159.9 ± 9 mW K^-1 cm^-2 to 27.35 ± 2 mW K^-1 cm^-2 after Ag doping into CdSe NPLs due to the phonon bottleneck effect (PBE). Reducing the thermalization rate and charge carrier separation due to incorporating Ag dopant is beneficial for efficient optoelectronic devices.