MAGNETO-OPTICAL STUDIES OF CdSe BASED NPLS

Abstract

Solution processed 2D CdSe nanoplatelets (NPLs) exhibit interesting optical properties. The NPLs form in two types of hetrostructures, known as, ”core/ shell” or ”core/ crown” NPLs, based on the growth direction. Here, we investigated the two configurations separately: The formation of core/ shell structures enhances the carrier quantum confinement in these NPLs. However, It also increases the total thickness, which may become a problem for certain applications. Therefore, forming alloyed hetrostrucures offers a way to tune the band gap of the NPLs without changing their dimensions. Here, we report CdSeS/ CdMnS alloy core /shell NPLs with a thickness of 16 ML. The composition of the sulfur range between 0 < x < 1. We expect that the addition of sulfur results in increased delocaliztion of electrons and holes compared to the conventional CdSe/CdMnS core /shell NPLs. The new alloyed structures NPLs exhibit a red shift of the PL emission energy proportional to the sulfur composition and a broadening of the exciton absorption and photoluminescence (PL) features. These results are expected to be beneficial for applications of the NPLs in LEDs. We also investigated core/ crown heterostructure NPLs, with type I and type II band alignment. Starting with CdSe/CdS core/crown NPLs (type I), the transmission spectrum shows the heavy hole–electron and light hole–electron exciton transitions at 2.469 eV and 2.650 eV, respectively occurring in the CdSe core. The CdS crown added for passivation and insure the stability of the NPLs. The sample also maintain a narrow emission peak, (FHMW = 9 nm). Next, CdSe/CdSeTe/CdSe/CdS core / multi crowns structures were studied, The photoluminescence (PL) emission three times broader compared to the PL from core / crown sample . In type II NPLs at 3K, we observe localization of the electrons and holes, this results in a weakening the electron-hole Coulomb interaction. These carrier localization is reduced as the temperature is increased to 20K. Light-emitting devices (LED) that incorporate NPLs were experimentally tested at both room and low temperatures. Our results provide guidelines for further optimization of CdSe hetroustucture-based NPLs for lighting and light-amplification applications.