Fig. 1. (a) SEM, (b) EDS mapping, and (c) TEM images of the sample with NdI3. The lattice planes and fast Fourier transform (FFT) images of (d) Cs3Cu2I5 nanoparticles and (e) CsCu2I3 nanorods. (f) XPS analysis of the sample with 9 mol% NdI3, and the respective spectra of (g) Cs 3d, (h) Cu 2p, and (i) I 3d.

Fig. 2. (a) PL spectra of pure Cs3Cu2I5 and CsCu2I3. (b) PL spectra of samples with different concentration of NdI3 under excitation of 316 nm. (c) PLE spectra of emission peaks corresponding to Cs3Cu2I5 and CsCu2I3 of the sample with 9 mol% NdI3. (d) CIE coordinates of the sample with 9 mol% NdI3. (e) XRD diffraction patterns of samples with different concentration of NdI3 compared to the standard XRD patterns of Cs3Cu2I5 and CsCu2I3.

Fig. 3. Crystal structures of (a) Cs3Cu2I5 and (b) CsCu2I3 with optimized lattice parameters from the top.

Fig. 4. (a) PL spectra under excitation wavelength of 320 nm. (b) XRD patterns of the samples with NdI3 added into the CsCu2I3 system with various ratios.

Fig. 5. (a) PL spectra of samples with 9 mol% concentration of NdI3 (PL excitation of 316 nm), TbI3 (PL excitation of 317 nm), PrI3 (PL excitation of 319 nm), and BiI3 (PL excitation of 308 nm). Inset: the precursor solution of NdI3, TbI3, and PrI3 samples. (b) XRD patterns of samples with 9 mol% concentration of NdI3, TbI3, PrI3, and BiI3. (c) CIE coordinates of samples with 9 mol% NdI3 and TbI3. (d)–(g) SEM images of the samples with 9 mol% NdI3, TbI3, PrI3, and BiI3, respectively.