Highly Luminescent and Multifunctional Zero‐Dimensional Cesium Lanthanide Chloride (Cs 3 LnCl 6 ) Colloidal Nanocrystals

Abstract Herein, the synthesis of novel, highly luminescent, and nearly monodisperse zero‐dimensional (0D) cesium lanthanide chloride (Cs 3 LnCl 6 ; Ln = Y, Ce, Gd, Er, Tm, Yb) colloidal nanocrystals (NCs) is reported for the first time. The Cs 3 LnCl 6 NCs are synthesized using a heating‐up method and exhibit highly uniform size and shape. The monoclinic‐phase Cs 3 LnCl 6 NCs contain completely isolated [LnCl 6 ] 3− octahedral units, resulting in 0D ternary metal halide structures. Therefore, these NCs exhibit deep‐blue photoluminescence under ultraviolet excitation, and this photoluminescence can be tuned by changing the lanthanide cations within the [LnCl 6 ] 3− octahedral units. High photoluminescence quantum yields of up to 60% and 90% are observed for the Cs 3 YbCl 6 and Cs 3 YCl 6 NCs, respectively, at room temperature and under ambient conditions. The Cs 3 LnCl 6 NCs exhibit characteristic optical and magnetic properties owing to the f‐orbitals of the lanthanide elements. For example, near‐infrared‐to‐visible upconversion luminescence appears when Cs 3 LnCl 6 NCs are doped with Er 3+ and Yb 3+ ions. In addition, the Cs 3 GdCl 6 NCs demonstrate paramagnetic properties owing to the unpaired electrons within the f‐orbitals of the trivalent gadolinium ions. This study provides guidance for the rational design and synthesis of novel lanthanide‐based 0D metal halide NCs, which can potentially be used as highly efficient, multifunctional NC emitters.