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Different from the narrow band emission based on free excitons in lead-perovskite nanocrystals (NCs), the low electronic dimensionality in lead-free double perovskite NCs can lead to self-trapped excitons (STEs), giving a broadband emission.

To date, how the singlet/triplet STEs influence the photoluminescence (PL) properties and whether triplet STEs can give efficient emission in double-perovskite NCs are still unclear.

Recently, a research team led by Prof. HAN Keli and YANG Bin from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences synthesized double perovskite NCs with bright PL emission based on triplet STEs.

This study was published in Nano Letters on Oct. 11.

Efficient emission based on the triplet STEs and the energy transition process (Image by CONG Muyu and YANG Bin)

They synthesized lead-free double perovskite NCs with varying sizes. The optical results indicated that the size had negligible influence on the absorption and PL peak position, while which mainly affected the PL quantum yield (PLQY). They further modified the Sb doping content, and obtained the NCs with bright green emission, whose PLQY was as high as 95%.

They also studied the dynamics of triplet STEs in double perovskite NCs via the measurements such as time-resolution PL (TR-PL), femtosecond transient absorption (TA), and magneto-optical spectroscopic measurement.

Furthermore, they achieved the triplet STEs mediated efficient energy transfer to dopants by alloying with Mn²⁺, and they formed the efficient white-emission with high PLQY of 87%. In addition, they formulated simple LEDs based the Mn²⁺ alloy NCs.

"This work may boost the understanding of STEs in double perovskites and promote its development in illumination-related applications," said Prof. HAN.

This work was supported by the National Natural Science Foundation of China, the National Key Research and Development Program of China, and the Science Challenging Program. (Text by CONG Muyu and YANG Bin)