Fig. 1. (Color online) (a) A schematic illustration of STE emission. FC, free carrier state; FE, free exciton state; STE, self-trapped exciton state; GS, ground state. Reproduced with permission^[12], Copyright 2020, Nature Publishing Group. (b) Absorption (solid lines) and photoluminescence (dashed lines) spectra for Cs₂AgInCl₆ and Cs₂Ag_0.60Na_0.40InCl₆. (c) Activation energy and PLQY of Cs₂Ag_xNa_1–xInCl₆ powder vs Na content. Reproduced with permission^[9], Copyright 2018, Nature Publishing Group. (d) External quantum efficiency (EQE) of CsPbCl₃:Sm³⁺-based WLED. The inserted pictures are the structure of the device, the transmission electron microscopy (TEM) image of Sm³⁺-doped CsPbCl₃ perovskite quantum dots, and the photo of a working WLED. (e) Emission spectra of Sm³⁺-doped CsPbCl₃ with different doping content under the excitation of 365 nm. (f) PLQYs as a function of Sm³⁺ doping content. (g) EL spectra for the LEDs based on Sm³⁺-doped CsPbCl₃ with different doping content. (d)–(g), reproduced with permission^[10], Copyright 2020, American Chemical Society.

Fig. 2. (Color online) (a) Structure of the perovskite WLED with an active layer composed of α-CsPbI₃ and δ-CsPbI₃. (b) The carrier injection and recombination mechanism for the perovskite WLEDs. (c) Electroluminescence spectra. (d) Current density–voltage (J–V) curve and luminance–voltage (L– V) curve for the perovskite WLEDs. (e) External quantum efficiency and current efficiency of the WLEDs. Reproduced with permission^[11], Copyright 2021, Nature Publishing Group.