Project W08 combines ultrafast electron diffraction and optical spectroscopy to image atomic-scale lattice dynamics during exciton self-trapping in lead-free double perovskites. Focusing on the coupling between electronic excitation and lattice distortion, it aims to resolve the structural pathway, timescales, and symmetry changes underlying self-trapped exciton formation. By correlating time-resolved structural and electronic measurements, the project establishes principles for controlling exciton localisation, lifetime, and emission efficiency.