Metal halide perovskites are one of the most investigated semiconductor materials, with the 3D CsPbX₃ structure being renowned for its enhanced optoelectronic performance. Multiple studies are currently attempting to substitute lead with other elements while still retaining the original properties of this material. This effort has led to the fabrication of metal halides of lower dimensionality. Recently, the layered perovskite structures have captured attention for their potential as an emerging class of colloidal semiconductors.

Here we report the colloidal synthesis of the pure Ruddlesden – Popper phase Cs₂CdCl₄:Sb³⁺, using a facile hot injection approach under atmospheric conditions. Through strict adjustment of the synthesis parameters with emphasis on the ligand ratio, we obtained nanoplatelets with a well-defined size and morphology. The particles underwent extensive structural characterization through synchrotron X-ray diffraction, pair distribution function analysis and transmission electron microscopy. Rietveld Refinements assigned a 14/mmm tetragonal space group and confirmed the aforementioned phase. Bright field imaging revealed nanoplatelets with a natural tendency to stack along the ab surface, self-assembling into long chains. Size distribution analysis assigned a length of 22.9 ± 3.8 nm and a thickness of 3.7 ± 0.8 nm, which were consistent with the dimension predictions given by the texture analysis from the x-ray diffraction data [1].

Spectroscopic characterization revealed an intense cyan emission, centered at 510 nm, and with a measured absolute PLQY of 20 ± 5% [1]. The emission is ascribed to the doped Sb³⁺ within the structure and is attributed to an s-p transition that originates from self-trapped excitons from the Sb³⁺ hosts [1][2]. Time-resolved photoluminescence measurements gave a double exponential decay, characterized by a fast (∼1.3 ns) and a long (∼1626 ns) component [1]. The existence of these two components is thought to result from two different recombination routes taking place from the excited Sb³⁺ states. A similar behaviour was previously reported in Sb³⁺ doped double-layered perovskites and is consistent with the findings from the respective bulk phase [2] [3] [4].

This work proves as a confirmation that colloidal synthetic approaches can give access to a new generation of RP phase nanocrystals through halides tuning, metal alloying, the replacement of Cs⁺ by alternative counterions and the introduction of various dopants, such as Bi³⁺ or Mn²⁺.