Excitation-Wavelength-Dependent Emission of Congruently Melting Iodocuprate Hybrid Materials

In the context of the emergence of metal halide perovskites for optoelectronic materials, the lead-free and earth-abundant copper(I)-based halide hybrids are of high interest. Here, we report on two iodocuprate hybrids (HO₂C(CH₂)_{n -1}NH₃)CuI₂ (n = 3, 4) exhibiting excitation-wavelength-dependent emission. The thermodynamically stable n = 4 compound (2D-C4) is based on a rare 2D iodocuprate network, while a more common 1D network of edge-sharing tetrahedra is found both in the n = 3 compound (1D-C3) and in the metastable n = 4 (1D-C4) hybrid. Depending on the excitation wavelength, 2D-C4 and 1D-C3 hybrids exhibit yellow emission, red emission, or white light emission-resulting from the emission of both components,-while 1D-C4 does not emit in the red region. The description of the electronic structure based on density functional theory (DFT) indicates two different origins for the emissions of 2D-C4 and 1D-C3, in particular from iodide vacancies (red emission), which involve mid-gap states. The emission of 2D-C4 can also be modulated from red to yellow depending on applied pressure. 2D-C4 also has an exceptionally low congruent melting temperature of 110 °C, allowing the solvent-free preparation of thin films. Finally, phosphor-converted-LED based on 2D-C4 have been prepared, showing that either pink or nearly white emission is produced.