Photon and Phonon Coherence to Enhance Photoluminescence by Magnetic Polarons in Mn-Doped Rb3Cd2Cl7 Perovskites

All-inorganic metal halide perovskite semiconductors have great potentials in lighting applications, but the effect of excitonic magnetic polarons (EMPs) in the transition metal (TM) ion-doped halide perovskites on their luminescence processes has not been extensively understood. Here, we have synthesized Mn2+-doped Rb3Cd2Cl7 perovskite powders with different doping amounts by a hydrothermal method. After Mn­(II) is doped, Rb3Cd2Cl7 gives strong emission, though the Rb3Cd2Cl7 powder itself does not emit light. This emission originates from the intrinsic self-trapped exciton (STE) formation enhanced by the ferromagnetic Mn–Mn pair with spin–spin coupling, that is, the magnetic polaron whose astonishing luminescence at 587 nm has a quantum yield up to 147%. Some shallow trapped centers below the conduction band out of high d levels by localized EMPs after photoexcitation are proven to add to this luminescence process. The thermoluminescence phenomenon with rising temperature proves that these shallow trapped carriers are present with phonon and multiphonon notation, and their efficient transfer to the conduction band and the STE state occurs via the electron–phonon coupling during photoexcitation. This compound provides a new way for TM-doped perovskite material design and applications for magneto-optical and display technology.