Two-dimensional CdX (X = Se, Te) nanosheets: controlled synthesis and their photoluminescence properties

Two-dimensional (2D) CdX (X = Se, Te) nanosheets are potential candidates for novel optoelectronic applications. Herein, oleic acid (OA), stearic acid (SA) and typical Cd precursors were chosen to synthesize high-quality 2D CdX nanosheets. Their unique absorption (or excitation) and photoluminescence (PL) properties were studied. The PL profiles are differentiated as band-edge and trap-state PL. These trap-states emanated from the intrinsic surface defect sites (Cd²⁺ or Se^2-). The intrinsic defect sites were generated because of the bonding termination at the surface of the nanosheets. A complex formed by the Cd-interstitial (Cd_i-V_Cd) acts as a donor-acceptor pair according to the Prener-Williams model and is accountable for the large Stokes-shifted trap-state PL peak. Our experimental findings imply that these surface trap-states follow the configurational coordinates model. Inevitably, the PL dynamics of CdSe nanosheets depend strongly on the surface trap-states in addition to their size and shape.