Core-shell phase segregation in Nanocrystals: A pathway for unlocking new internal quantum yield efficiencies Fernando Arteaga Cardona 1 , Eduard Madirov 1 , Dmitry Busko 1 , Radian Popescu 3 , Noopur Jain 4,5 , Sara Bals 4,5 , Sandra Van Aert 4,5 , Bryce S. Richards 1,2 , and Damien Hudry 1 1 KIT-IMT, Germany
2 LTI, Karlsruhe Institute of Technology, Karlsruhe, Germany 3 LEM, Karlsruhe Institute of Technology, Karlsruhe, Germany 4 EMAT, University of Antwerp, Antwerp, Belgium 5 NANOlab Center of Excellence, University of Antwerp, Antwerp, Belgium
Improving the quantum yield of lanthanide-based nanocrystals is crucial for unlocking the full potential of various applications such as bioimaging, biolabeling, anti-counterfeiting, and energy harvesting. However, achieving high quantum yields in nanocrystals presents a significant challenge due to multiple factors that can dampen the emitted energy. These factors include surface quenching, dangling bonds, concentration quenching. One of the most efficient and widely recognized strategies for mitigating the detrimental effects of luminescent quenchers involves the growth of an optically inert shell with the same chemical composition as the luminescent host (homogeneous shell) without the luminescent active centers. However, this approach assumes that the optically active core remains unaffected by the post-synthesis process required to grow the optically inert shell. Recent findings have challenged this assumption, revealing that the integrity of the core is compromised in the majority of the cases, resulting in an intermixed phase that alters interatomic distances, local concentrations, and thus energy migration pathways. Consequently, it becomes challenging to determine the optimal ratio between sensitizers and emitters, preventing to reach high photoluminescence quantum yields. In this study, we present evidence that growing an optically inert heterogeneous shell, instead of a homogeneous one, successfully achieves phase segregation between the luminescent active core and the protective inert shell. The establishment of a genuine core-shell structure significantly enhances the internal downshifting photoluminescence quantum yield (DSPLQY) of lanthanide-based luminescent materials. For samples co-doped with Tm, the heterogeneous shell improved the DSPLQY in the 1,800 nm emission from 1% to 7%. In the case of samples co-doped with Er, the DSPLQY of the 1,550 nm emission improved from 9% to 30%. Furthermore, when Er and Ce were used together, the DSPLQY increased from 26% to 50%. This improvement can be attributed to various factors, including enhanced protection against surface quenching by confining absorbed energy exclusively within the core region. We believe that our results of achieving a well-proven phase segregation between the core and the shell and its heavy impact in the DSPLQY will help to pave the way for the realization of promising applications associated with lanthanide-based nanocrystals.
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© The Author(s), 2023
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