All-inorganic cesium lead halides (CsPbX₃, X=Cl, Br, I) nanocrystals (NCs) have drawn great attentions due to their intriguing optoelectronic properties such as large absorption coefficient, high photoluminescence (PL) quantum yield (QY), narrow emission band, and tunable bandgap.

Great efforts have been devoted to the controlled synthesis, luminescence mechanism and applications of CsPbX₃ NCs. Previous studies mainly focused on the visible spectral region, and there haven't been any studies on ultraviolet (UV)-emitting all-inorganic halide perovskites.

In a study published in Angewandte Chemie International Edition, a research group led by Prof. CHEN Xueyuan from Fujian Institute of Research on the Structure of Matter (FJIRSM) of he Chinese Academy of Sciences proposed a unique strategy for designing UV-emitting luminescent all-inorganic halide perovskites by engineering the bandgap and surface structure of CsPbCl₃ NCs. 

The PL emission of CsPbCl₃ NCs can be manipulated to the UV region with an emission peak at 381 nm by doping with Cd²⁺ without altering their morphology and crystal structure. The PL intensity of CsPbCl₃:Cd²⁺ NCs can be increased by 19.5 times upon treatment with CdCl₂. Correspondingly, their PLQY was remarkably enhanced from 0.9% up to 60.5% by virtue of the surface passivation with CdCl₂. 

Meanwhile, the photostability was markedly improved. Upon continuous excitation with a 330-nm lamp (8 W), the pristine CsPbCl₃:Cd²⁺ NCs exhibited negligible PLQY (< 0.1%) after seven days. By contrast, the PLQY of the surface passivated CsPbCl₃:Cd²⁺ NCs remained 50.5%.

Furthermore, by means of PL decays, femtosecond transient absorption analysis, and first-principle calculations, the researchers together with Prof. DENG Shuiquan from FJIRSM, unveiled the PL enhancement mechanism. They demonstrated that the PL enhancement may be caused by the significant reduction of surface defects like chloride vacancy (VCl), which may cause deleterious nonradiative recombination. 

This study provides a general approach for the design of highly efficient UV luminescent halide perovskite NCs, opening up a new avenue for the exploitation of high-performance optoelectronic devices towards versatile applications such as lasers and LED devices.

Schematic illustration for engineering the bandgap and surface structure of CsPbCl₃ NCs to achieve highly efficient UV luminescence (Image by Prof. CHEN’s group)