Comparison Of Green Photoluminescence From Cspbbr3 And Cs-4 Pbbr6 Nanocrystals

The bandgap of 0D Cs4PbBr6 is about 3.95 eV (314 nm), however, green fluorescence at around 520 nm is usually observed, resulting in a fierce controversy on photoluminescence (PL) mechanism. Defect state of Cs4PbBr6 and existence of CsPbBr3 impurity are separately proposed to be the source for the green fluorescence. To clarify this argument, the fluorescence from CsPbBr3 and Cs4PbBr6 nanocrystals are comprehensively compared. Assuming the fluorescence from Cs4PbBr6 is caused by impurity of CsPbBr3, the PL properties of Cs4PbBr6 and CsPbBr3 should be quite similar. However, on the contrary, we find there are remarkable divergencies in absorption band edge, excitonic absorption, PL peak position, PL FWHM, PL lifetime, irradiation induced PL variation, PL dependence on excitation power, and excitation power dependent PL lifetime. Therefore, we propose that the green luminescence of Cs4PbBr6 cannot be attributed to the impurity of CsPbBr3. The clarification on this controversy will enhance the fundamental knowledge on perovskites, which will their future applications.