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Zero dimensional perovskite Cs4PbBr6 has attracted considerable attentionrecently not only because of its highly efficient green photoluminescence (PL),but also its two highly debated opposing mechanisms of the luminescence:embedded CsPbBr3 nanocrystals versus intrinsic Br vacancy states. After a briefdiscussion on the root cause of the controversy, we provide sensitive butnon-invasive methods that can not only directly correlate luminescence with theunderlying structure, but also distinguish point defects from embeddednanostructures. We first synthesized both emissive and non-emissive Cs4PbBr6crystals, obtained the complete Raman spectrum of Cs4PbBr6 and assigned allRaman bands based on density functional theory simulations. We then usedcorrelated Raman-PL as a passive structure-property method to identify thedifference between emissive and non-emissive Cs4PbBr6 crystals and revealed theexistence of CsPbBr3 nanocrystals in emissive Cs4PbBr6. We finally employed adiamond anvil cell to probe the response of luminescence centers to hydrostaticpressure. The observations of fast red-shifting, diminishing and eventualdisappearance of both green emission and Raman below Cs4PbBr6 phase transitionpressure of ~3 GPa is compatible with CsPbBr3 nanocrystal inclusions as greenPL emitters and cannot be explained by Br vacancies. The resolution of thislong-lasting controversy paves the way for further device applications of lowdimensional perovskites, and our comprehensive optical technique integratingstructure-property with dynamic pressure response is generic and can be appliedto other emerging optical materials to understand the nature of theirluminescent centers.

Revealing the Origin of Luminescence Center in 0D Cs4PbBr6 Perovskite