Fig. 1. (a) Transmission electron microscopy (TEM), (b) high-resolution TEM (HRTEM) images, and (c) corresponding cesium (Cs), copper (Cu), and chlorine (Cl) elemental mapping images of Cs3Cu2Cl5 NCs. The inset shows selected-area electron diffraction images. (d) TEM, (e) HRTEM images, and (f) Cs, Cu, and Cl elemental mapping of CsCu2Cl3 NCs, respectively. The inset is the corresponding selected-area electron diffraction image.

Fig. 2. (a) XRD patterns of the cesium copper chlorine colloidal perovskite synthesized at 70°C and 120°C, as well as the standard XRD patterns. High-resolution X-ray photoelectron spectroscopy (XPS) spectrum of (b) Cu 2p, (c) Cs 3d, (d) Cl 2p. (e), (f) Crystal structure of 3D CsCu2Cl3 and 0D Cs3Cu2Cl5 NCs, respectively. The pink, bluish, and light-green balls represent the Cs, Cu, and Cl, respectively. (g) Photoluminescence spectra of chlorine colloidal perovskite synthesized at 70°C (CsCu2Cl3) and 120°C (Cs3Cu2Cl5). The inset shows the luminescent photographs of CsCu2Cl3 (top) and Cs3Cu2Cl5 (bottom) films excited under 254 nm UV light.

Fig. 3. Photoluminescence exciton (PLE) spectra of (a) CsCu2Cl3 and (b) Cs3Cu2Cl5. (c) Room-temperature PL decay curves of 0D Cs3Cu2Cl5 and 3D CsCu2Cl3 NCs. PL spectra of (d) CsCu2Cl3 and (e) Cs3Cu2Cl5 NCs excited under different excitation wavelength. (f) Energy level schematic diagram of excited cesium copper chlorine nanocrystals.

Fig. 4. (a), (c) Luminescent spectrum and (b), (d) CIE chromaticity diagram of CsCu2Cl3 and Cs3Cu2Cl5 films excited on a 290 nm UV chip.

Fig. 5. (a) EL spectra of as-fabricated white light-emitting diodes (WLEDs). The insets are the photographs of the emissive WLEDs obtained in the daylight (left) and dark (right). (b) CIE chromaticity diagram of the WLEDs. (c) Pseudocolor plot of the EL spectra of long-time operating WLEDs. (d) Evolution of the normalized luminous efficiency (LE) and CRI values as functions of operating time. (e) CCT of the WLED as a function of the operating time in atmosphere.