Telluride nanocrystals with adjustable amorphous shell thickness and core-shell structure modulation by aqueous cation-exchange

TL;DR

This study presents a method to synthesize telluride core-shell nanoparticles with tunable amorphous shell thickness using aqueous cation exchange, enabling control over crystallinity and enhanced optical properties.

Contribution

It introduces a temperature-controlled synthesis approach for telluride CSNPs with adjustable amorphous shells via aqueous cation exchange, overcoming temperature sensitivity challenges.

Findings

Crystallinity controlled from perfect crystals to core-shell structures.

Amorphous shell thickness tunable up to 7-8 nm.

Highest Raman enhancement observed at 60°C synthesis.

Abstract

Engineering the structure of core-shell colloidal semiconductor nanoparticles (CSNPs) is attractive due to the potential to enhance photo-induced charge transfer (PICT) and induce favourable optical and electronic properties. Nonetheless, the sensitivity of telluride CSNPs to high temperatures makes it challenging to precisely modulate their surface crystallinity. Herein, we have developed an efficient strategy for synthesising telluride CSNPs with thin amorphous shells using aqueous cation exchange (ACE). By changing the synthesis temperature in the range 40 to 110C, the crystallinity of the CdTe nanoparticles was controllable from perfect crystals with no detectable amorphous shell (c-CdTe) to a core-shell structure with a crystalline CdTe NP core covered by an amorphous shell of tunable thickness up to 7-8nm (c@a-CdTe) . A second ACE step transformed the c@a-CdTe to crystalline CdTe@HgTe core-shell NPs. The c@a-CdTe nanoparticles synthesized at 60C and having a 4-5 nm thick amorphous shell, exhibited the highest surface-enhanced Raman scattering activity with a high enhancement factor around 8.82x10^5, attributed to the coupling between the amorphous shell and the crystalline core.