Ligand with strong electronegativity induced blue emitting of CsPbBr<sub>3</sub> nanocrystals

Abstract

All-inorganic cesium lead halide (CsPb<i>X</i><sub>3</sub>, <i>X</i> = Cl, Br, I) perovskite nanocrystals (NCs) are promising candidates for the next-generation luminescent materials due to their fascinating physic-optical properties, such as size-tunable optical band gaps, high luminescent quantum yields, and narrow emissive bandwidths. At present, the prepared CsPb<i>X</i><sub>3</sub> NCs are concentrated in the range of green and red. The research of blue CsPb<i>X</i><sub>3</sub> NCs is lacking and these CsPb<i>X</i><sub>3</sub> NCs still suffer problems of low quantum efficiency and poor stability, which limit their application areas. In this paper, 2-acrylamide-2-methyl-propionic sulfonic acid (AMPS) with strong electronegativity is used to prepare CsPb<i>X</i><sub>3</sub> NCs by the thermal injection method. All CsPbBr<sub>3</sub> NCs each have a uniform size, good crystallization, and nanoplate morphology. The CsPbBr<sub>3</sub> NCs each exhibit an optical absorption at 450 nm and a photoluminescence (PL) emission at 462 nm with a full width of half maximum of 20 nm. To further investigate the physical mechanism of the PL shift and explore the effect of AMPS on the transient dynamics of the photocarriers in CsPbBr<sub>3</sub> NCs, we measure the time-resolved PL spectrum and transient absorption spectrum. It can be found that the CsPbBr<sub>3</sub> NCs have only one lifetime of 222 ns, which is one order of magnitude longer than that of the CsPbBr<sub>3</sub> NCs without AMPS. Meanwhile, there is no obvious transient absorption signal. Based on the above experimental results, this blue shift is caused by three reasons. Firstly, AMPS has a strong attraction to the excited electrons, which causes the electrons in the excited state to stay for a long time before returning to the ground state. Because of the relaxation behavior before the radiation transition, the energy released by the radiation transition is larger and the fluorescence wavelength is shorter. Secondly, the prepared CsPbBr<sub>3</sub> NCs have stronger quantum confinement than CsPbBr<sub>3</sub> NCs with cubic block morphology. Finally, AMPS can passivate the surface defects of CsPbBr<sub>3</sub> NCs more effectively. The prepared CsPbBr<sub>3</sub> NCs have less defects, which also causes the PL to be blue-shifted. This study provides not only a method of synthsizing the CsPbBr<sub>3</sub> NCs with blue emitting but also an insight into the surface engineering or physical functionalization of inorganic perovskite NCs.