Fig. 1

The crystal structure and phase purities of 2D RPs. a The crystal structure of N = 4 with a unit cell enclosed by the green rectangle. The directions of the pump and probe beams with respect to the crystal orientation are illustrated on the top. b Characteristic X-ray diffraction peaks of the single-crystal flakes (N = 1–6) obtained from θ–2θ scans. c Photoluminescence spectra of the 2D RPs