Emergence of multi-peak emission in CsBr-Cs₄PbBr₆-CsPbBr₃ nanocrystals at room temperature

Highly stable and bright emitting CsBr-Cs₄PbBr₆-CsPbBr₃ perovskite nanocrystals were synthesized using chemical route. For nanocrystals formed at higher Cs:Pb (10:1) ratios, multiple peak emission was observed in the UV–visible region (325–550 nm), while at lower Cs:Pb ratios (5:1 to 2.5:1), narrow high-intensity peak (at 522 nm, the signature peak of CsPbBr₃) along with a diminished broad multi-peak emission (325–500 nm) is observed. Blue-emitting nanocrystals were observed at higher Cs:Pb precursor (Pb deficient conditions) ratios. As concentration of Pb increases (Cs:Pb ratio decreases), contribution from broad emission decreases while green emitting 522 nm peak dominates. This broad emission is unique at room temperature for CsBr-Cs₄PbBr₆-CsPbBr₃ mixture of nanocrystals, unlike the single peak narrow emission reported in literature so far for inorganic lead halide perovskites. It is worth mentioning that the CsBr-Cs₄PbBr₆-CsPbBr₃ mixture of nanocrystals is highly stable and hence can be used for various optoelectronic applications.