Efficient Deep-Blue Light-Emitting 2D (100)-Oriented Perovskites and Spectral Broadening by Exciton Self-Trapping for White-light Emissions

Efficient narrow deep-blue and broadband emissions in layered 2D organic–inorganic hybrid metal halide perovskites (MHPs) are attracting more attention and need further study. In this work, two (100)-oriented 2D organic-inorganic hybrid MHPs of (TFI)₂PbBr₄ and (TFI)₂PbCl₄·H₂O (TFI = 4-(trifluoromethyl)-1H-imidazole) with efficient deep-blue and bluish-white emissions are synthesized and the photoluminescence quantum yields (PLQYs) reached up to 81.21% and 20.23%, respectively. As both intrinsic lattice distortions of two crystals with similar crystal structure are almost negligible, they have theoretical deep-blue emissions empirically. However, the halogen substitution of chlorine (Cl) by bromine (Br) broadened the deep-blue photoluminescence to a bluish-white area. Here, the spectral broadening phenomenon is discussed in detail. The (TFI)₂PbBr₄ film shows a narrow emission with a 16 nm full width at half maximum (FWHM) peaking at 435 nm upon excitation, and an ultraviolet-pumped light-emitting diode (LED) prepared by bluish-white (TFI)₂PbCl₄·H₂O phosphor shows a color rendering index (CRI) of ≈93 and a related color temperature (CCT) of 4162K, indicating their potential applications in deep-blue and white LEDs, respectively.