Revealing the Origin of Luminescence Center in 0D Cs₄PbBr₆ Perovskite

Abstract

0D perovskite Cs4PbBr6 has attracted considerable attention recently because of its highly efficient green photoluminescence (PL) and highly debated opposing mechanisms: embedded CsPbBr3 nanocrystals versus intrinsic Br vacancy states. Here we provide sensitive but noninvasive methods that can not only directly correlate luminescence with the underlying structure, but also distinguish point defects from embedded nanostructures. We first use correlated Raman-PL as a passive structure–property method to identify the difference between emissive and nonemissive Cs4PbBr6 crystals and reveal the existence of CsPbBr3 nanocrystals in emissive Cs4PbBr6. We then employ a diamond anvil cell to probe the response of luminescence centers to hydrostatic pressure. The observations of fast red-shifting, diminishing, and eventual disappearance of both green emission and Raman exclude Br vacancies as possible luminescent centers. The resolution of this long-lasting controversy paves the way for further device applications of low dimensional perovskites, and our techniques are applied to other emerging materials.