Photoluminescence and Raman Spectra of One-Dimensional Lead-free Perovskite CsCu2I3 Single-Crystal Wires

Lead-free highly luminescent CsCu2I3 perovskite has attracted much attention recently, but agreements on basic optical properties have remained unsettled. By correlating X-ray diffraction with the photoluminescence (PL) of CsCu2I3 single-crystal wires, we first show that blue PL at 420 nm originates from CuI. We then exclude defect states as a source for the broadband emission centered at 570 nm from the lack of defect absorption, PL under sub-bandgap photoexcitation, observations of a linear dependence of PL intensity on excitation laser power, and a strong spectral blueshift under mild hydrostatic pressure. Finally, using a model of the self-trapped exciton and the associated coordinate configuration diagram, we explain pressure evolutions of PL energy, intensity, and lifetime. Single-crystal wires also enable us to obtain polarization-dependent Raman spectra down to 10 cm(-1) and confirm their respective ambient crystal structure of orthorhombic Cmcm and phase transition to Pbnm at similar to 5 GPa.

Automated summary

By correlating X-ray diffraction with photoluminescence (PL) of CsCu2I3 single-crystal wires, this study first identifies the origin of blue PL at 420 nm and excludes defect states as the source for the broadband emission at 570 nm. The pressure evolutions of PL energy, intensity, and lifetime are explained using a model of the self-trapped exciton, and polarization-dependent Raman spectra confirm the crystal structure of CsCu2I3.