Bright magnetic dipole radiation from two-dimensional lead-halide perovskites

Layered Lead Iodide of [Methylhydrazinium]2PbI4 with a Reduced Band Gap: Thermochromic Luminescence and Switchable Dielectric Properties Triggered by Structural Phase Transitions

“…Additional redshifted bands have been observed for many A 2 PbI 4 compounds, and they were usually attributed to bound excitons, 28,34 phonon replicas of the FE, 33 and out-of-planeoriented magnetic dipole transition. 80 Bound excitons were found red-shifted at RT by around 32 nm for cystamine lead iodide and 30 nm for PEA 2 PbI 4 . 28,34 Furthermore, study of PEA 2 PbI 4 revealed significant blue shift of the BE PL on cooling.…”

“…33 In the case of butylammonium lead iodide, the band red-shifted by 20 nm was attributed to the out-of-planeoriented magnetic dipole transition. 80 The strong decrease of the separation between P1 and P2 bands in MHy 2 PbI 4 is not consistent with phonon replica, but such behavior as well as significantly larger width of the P2 band could indicate that this emission comes from BE states. PL quantum yield (PLQY) of MHy 2 PbI 4 reaches 0.8% at RT.…”

“…33 The same decay times were also reported for the FE and red-shifted band in butylammonium lead iodide attributed to out-of-plane-oriented magnetic dipole transition (0.296 ns). 80 Thus, decay times of MHy 2 PbI 4 are consistent with assignment of the P2 band to weakly bound exciton. With increasing temperature, the decay times of both emissions in MHy 2 PbI 4 increase to 0.70 ns, i.e., they are significantly longer than the lifetimes of 3AMPPbI 4, 4AMPPbI 4 , and PEA 2 PbI 4 (0.08, 0.04, and 0.17 ns, respectively).…”