Lanthanide Doping in II-VI Colloidal Nanoplatelets: Synthesis and Optical Characterization

Physical and Analytical Chemistry Seminar

Lecturer: Morin Mor, Schulich Faculty of Chemistry, Technion (group of Prof. Efrat Lifshitz)

05-05 Jan 2020 @ 15:30

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Colloidal semiconductor nanoparticles (NPs) are tiny crystalline particles within the nanoscale dimension, capped with organic molecules, promoting their solubility in various solvents. Unlike bulk semiconductors, these tiny crystallites exhibit size and shape dependent properties owing to the three-dimensional quantum confinement of charge carriers, namely quantum size effect, manifesting size-dependent quantization of the semiconductor energy levels. Colloidal semiconductor NPs can be easily synthesized utilizing low-cost wet chemistry techniques, such as hot injection, enabling control over the size, shape, and size distribution of the obtained quantum dots (QDs). Subsequently, these materials can potentially be implemented in various application, including optoelectronic devices and solar cell-based appliances.

Over the last decade, special attention has been given to the study of two-dimensional (2D) semiconductor nanocrystals, particularly to nanoplatelets (NPLs), as they exhibit one-dimensional (1D) quantum confinement, providing them optical characteristics that are similar to quantum wells and permitting the engineering of their optoelectronic properties by monitoring the particle thickness.

A particular interest has been given to the exploration of II-VI colloidal semiconductor nanoplatelets embedded with transition metal impurities, such as Mn+2, owing to the formation of sp-d interactions between the host and dopants energy level. Consequently, diluted magnetic semiconductor (DMS) are established, allowing their application in spintronics devices.

However, only few studies of lanthanides introduction into II-VI semiconductor nanocrystals have been performed in the past, despite their intriguing features, such as sharp 4f-4f emission lines, that may potentially exhibit enhancement through antenna effect when embedded within wide bandgap sensitizers.

This work describes the successful development of synthesis procedure as well as morphological and optical characterization of colloidal II-VI nanoplatelets embedded with Gd+3 ions. CdSe/CdS core/shell particles were selected for the current study due to their quasi-type II characteristic, providing major localization of the hole at the core area, while the electron is being delocalized over the entire substance, as well as the passivation of CdSe core surface defects by CdS shell. Structural investigation of the obtained particles reveals modifications of the crystal lattice upon the introduction of Gd+3 impurities, whereas optical measurements demonstrate elongated photoluminescence decay lifetime owing to the formation of vacancy trap states following Gd+3 insertion.