Fig. 1. Schematic of metal halide perovskite ABX₃ structure

Fig. 2. Photographs and PL spectra of APbX₃ perovskite QDs under UV-lamp, where A=MA, Cs, or FA, and X=Cl, Br, or I^[31]

Fig. 3. Spectra. (a) PL spectra of Li⁺-doped MAPbI₃ films^[35]; (b) absorption and PL spectra of Rb⁺-doped CsPbBr₃ QDs^[40]; (c) absorption and PL spectra of Na⁺-doped CsPbBr₃ QDs^[36]; (d) absorption and PL spectra of K⁺-doped CsPbCl₃ QDs^[38]

Fig. 4. TEM images of CsPb_xMn_1－xCl₃ QDs and PL emission spectra^[49]_. (a)‒(d) Molar ratios of Pb to Mn are 1∶1.25, 1∶2.5, 1∶5, and 1∶10, respectively; (e)‒(f) absorption and PL spectra

Fig. 5. Energy level diagram of Mn²⁺-doped CsPbX₃ QDs^[52]

Fig. 6. CsPb_1－xSn_xBr₃ perovskite QDs synthesized with solution re-precipitation^[58]. (a) Photographs of CsPb_1－xSn_xBr₃ perovskite QDs under 365 nm UV illumination; (b)‒(c) absorption and PL spectra of CsPb_1－xSn_xBr₃ perovskite QDs with different Sn²⁺-doping concentrations

Fig. 7. Cs₂SnI₆ perovskite nanocrystals^[62]. (a) Morphology schematics of synthesized Cs₂SnI₆ perovskite nanocrystals and their photographs; (b)‒(f) Cs₂SnI₆ perovskite nanocrystals with different shapes

Fig. 8. Optical properties of CsPbX₂ perovskite doped with divalent metal ions. (a)‒(c) PL and absorption spectra and PL decay traces of CsPbCl₃ QDs and Ni²⁺-doped CsPbCl₃ QDs under UV (365 nm) illumination, and PL decay trace of Ni²⁺-doped CsPbCl₃ QDs (doping concentration of 11.9%), showing a fast and a slow component^[66]; (d)‒(f) photos, PLQY, and XRD of undoped and Sr²⁺-doped CsPbI₃ QDs under UV-light (365 nm) irradiation, the doping concentration(molar fraction) of SrI₂ is 0%, 40%, and 60%^[71]; (g)‒(i) absorption and PL spectra, PL peak,PLQY and decay curves of CsPbI₃ QDs and CsPb_1－xZn_xI₃ QDs^[73]

Fig. 9. Photoelectric properties of Bi³⁺ doped perovskite. (a)‒(d) Unit cell structures and absorption and PL spectra of Cs₃Bi₂X₉ perovskite QDs^[78]; (e)‒(f) crystal structures of δ-CsPbI₃ and α-CsPbI₃, respectively, and surface morphologies and illumination picture of CsPb_1－xBi_xI₃ (0≤x<0.1) perovskites^[80]

Fig. 10. Optical properties of rare earth ion (RE³⁺) doped perovskite materials. (a)‒(c) Absorption and emission spectra of CsPbCl_xBr_3－x and CsPbCl_xBr_3－x QDs doped with different lanthanide ions; (d) schematic of energy transfer mechanism in the Yb³⁺, Ce³⁺ co-doped CsPbCl_1.5Br_1.5 QDs