Revealing the nature of photoluminescence emission in the metal-halide double perovskite Cs2AgBiBr6

Double perovskite crystals such as Cs2AgBiBr6andnbsp;are expected to overcome the limitation of classic hybrid organicandndash;inorganic perovskite crystals related to the presence of lead and the lack of structural stability. Perovskites are ionic crystals in which the carriers are expected to strongly couple to lattice vibrations. In this work we demonstrate that the photoluminescence (PL) emission in Cs2AgBiBr6andnbsp;is strongly influenced by the strong electronandndash;phonon coupling. Combining photoluminescence excitation (PLE) and Raman spectroscopy we show that the PL emission is related to a color center rather than a band-to-band transition. The broadening and the Stokes shift of the PL emission from Cs2AgBiBr6andnbsp;is well explained using a Franckandndash;Condon model with a Huangandndash;Rhys factor ofandnbsp;Sandnbsp;= 11.7 indicating a strong electronandndash;phonon interaction in this material.