ZnSe/ZnS Core/Shell Quantum Dots with Superior Optical Properties through Thermodynamic Shell Growth.

Botao Ji,Ilya Slobodkin,Somnath Koley,Sergei Remennik,Uri Banin

doi:10.1021/acs.nanolett.9b05020

Botao Ji, Ilya Slobodkin + Show 3 more

Open Access

https://doi.org/10.1021/acs.nanolett.9b05020

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Abstract

Epitaxial growth of a protective semiconductor shell on a colloidal quantum dot (QD) core is the key strategy for achieving high fluorescence quantum efficiency and essential stability for optoelectronic applications and biotagging with emissive QDs. Herein we investigate the effect of shell growth rate on the structure and optical properties in blue-emitting ZnSe/ZnS QDs with narrow emission line width. Tuning the precursor reactivity modifies the growth mode of ZnS shells on ZnSe cores transforming from kinetic (fast) to thermodynamic (slow) growth regimes. In the thermodynamic growth regime, enhanced fluorescence quantum yields and reduced on–off blinking are achieved. This high performance is ascribed to the effective avoidance of traps at the interface between the core and the shell, which are detrimental to the emission properties. Our study points to a general strategy to obtain high-quality core/shell QDs with enhanced optical properties through controlled reactivity yielding shell growth in the thermodynamic limit.

Highlights

Epitaxial growth of a protective semiconductor shell on a colloidal quantum dot (QD) core is the key strategy for achieving high fluorescence quantum efficiency and essential stability for optoelectronic applications and biotagging with emissive quantum dots (QDs)
Colloidal quantum dots (QDs) are exceptional fluorescence emitters manifesting continuous color-tunability and narrow emission line widths.[1,2]. These properties, combined with the solution-processability of QDs, are the basis for their widespread implementation as building blocks in optical and optoelectronic applications including in commercial displays, lasing, light-emitting diodes (LEDs), and bioimaging that require high photoluminescence (PL) quantum yields (QY) and photostability.[3−9] For over two decades, the efficient strategy to achieve these stringent demands has been through the formation of core/shell structures.[10,11]
Various approaches were introduced to achieve high quality shell growth. Among these are the growth of alloyed shells, and shells with graded composition designated to relax the strain upon increasing shell thickness.[18−23] These are well developed for the Cd-chalcogenide semiconductor QDs