Quantum mechanics

Chemical physics

Materials science

Stokes shift

Excitation

Phonon

Perovskite (structure)

Photoluminescence

Inorganic chemistry

Metal halides

Iodide

Band gap

Physics

Exciton

Luminescence

Condensed matter physics

Crystallography

Chemistry

Optoelectronics

Halide

Nature Communications

Two-dimensional metal halide perovskites of Ruddlesden–Popper type have recently moved into the centre of attention of perovskite research due to their potential for light generation and for stabilisation of their 3D counterparts. It has become widespread in the field to attribute broad luminescence with a large Stokes shift to self-trapped excitons, forming due to strong carrier–phonon interactions in these compounds. Contrarily, by investigating the behaviour of two types of lead-iodide based single crystals, we here highlight the extrinsic origin of their broad band emission. As shown by below-gap excitation, in-gap states in the crystal bulk are responsible for the broad emission. With this insight, we further the understanding of the emission properties of low-dimensional perovskites and question the generality of the attribution of broad band emission in metal halide perovskite and related compounds to self-trapped excitons.

Extrinsic nature of the broad photoluminescence in lead iodide-based Ruddlesden–Popper perovskites