Europium doping effects on the properties of CsPbBr ₃ nanocrystals: <i>in situ vs. ex situ</i> synthetic path analysis

Cesium lead bromide (CsPbBr₃) nanocrystals (NCs), a class of metal halide perovskites (MHPs), exhibit remarkable optoelectronic properties, making them attractive for applications such as photovoltaics and radiation detection. However, CsPbBr₃ NCs suffer from poor luminescence efficiency and short service life, which presents significant challenges. Doping with rare-earth elements like europium (Eu) offers a promising strategy to enhance their performance due to Eu's unique electronic structure. This study analytically compares the effects of <i>in situ</i> and <i>ex situ</i> Eu doping on the structural, optical, and photocatalytic properties of CsPbBr₃ NCs. <i>In situ</i> doping was performed by adding Eu during NC synthesis <i>via</i> a hot-injection method, while <i>ex situ</i> doping involved post-synthetic treatment using sonication. Comprehensive characterization, by TEM, XRD, XPS, ICP-MS, and UV-Vis, and evaluation of their photoluminescence and photocatalytic activity revealed that Eu incorporation strongly depends on the doping method. <i>In situ</i> Eu doping, particularly at 5 wt%, led to effective lattice incorporation, enhancing the optical emission and photocatalytic performance. In contrast, <i>ex situ</i> Eu primarily localized on the NC surface, resulting in limited property improvements. These findings underscore the importance of the doping strategy in tailoring perovskite NC functionality for advanced optoelectronic and photocatalytic applications.