From Dopant to Host: Solution Synthesis and Light-Emitting Applications of Organic-Inorganic Lanthanide-Based Metal Halides

The rich and unique energy level structure arising from 4f n inner shell configuration of trivalent lanthanide ions (Ln 3+ ) renders them highly attractive for light-emitting applications. Currently, research primarily focuses on Ln 3+ doping in either traditional garnets or the recently developed perovskite phosphors. However, there have been few reports on stable phosphors crystallized with pure lanthanide elements. Herein, a universal solution-based route to eight Ln 3+ -based metal halides from the organic-inorganic A 4 LnX 7 family is described, where A + =  4,4-difluoropiperidinium (DFPD + ), Ln 3+ =  Nd 3+ , Eu 3+ , Ho 3+ , Sm 3+ , Tm 3+ , Tb 3+ , Yb 3+ , Er 3+ , and X − =  Cl − , Br − . Visible photoluminescence (PL) is observed from Tb 3+ -, Eu 3+ -, Ho 3+ -, and Sm 3+ -based compounds with Tb and Eu compositions exhibiting high PL quantum yields of 90–100%; Nd 3+ -, Tm 3+ -, Yb 3+ -, and Er 3+ -based crystals show fascinating near-infrared emission. Light-emitting diodes (LEDs) fabricated with (DFPD) 4 TbCl 7 yield characteristic emission of Tb 3+ , representing the first demonstration of electroluminescence from these organic-inorganic Ln 3+ -based metal halides. Moreover, these materials exhibit distinct excitation wavelength-dependent emission after alloying with different Ln 3+ ions, making them interesting for multicolor display and multilevel information encryption applications. It is foreseen that this study will open up the way to a possible design of robust optoelectronic devices based on lanthanide metal halides.