Fabrication, Optical Property, and White LED Application of Novel Lanthanide‐Based Family Cs2NaLnX6 (X = Cl, Br, I) Perovskite Nanomaterials

Abstract Lead free double perovskites are highly promising optoelectronic materials, but most of them suffer from low photoluminescence quantum yield (PLQY) and poor stability. Herein, a series of lanthanide elements are used to prepare the lead free double perovskite Cs 2 NaLnX 6 (X = Cl, Br, I) nanocrystals (NCs), acting as both the main structural ions and the 4f–4f emission centers. The mechanisms for the broadband emission of Cs 2 NaLnX 6 NCs host are carefully studied based on various spectral results combining ultrafast dynamics detection and first‐principles calculation. The broadband emission of the Cs 2 NaLnX 6 NCs originates from the self‐trapped exciton. The Cs 2 NaLnX 6 NCs show remarkable water stability for more than eight months and favorable temperature and light irradiation stability (500 h). The PLQY for these materials is much higher than most of double perovskite materials, especially for Cs 2 NaEuCl 6 , which can approach to 70%. The white light emission from a single host material Cs 2 NaEuTbCl 6 (Tb:Eu = 25:1) is obtained and applied to a light‐emitting diode device, with a good CIE (Commission International de L'Eclairage) coordinate of (0.334, 0.326) and color rendering index of 91.2. Overall, the characteristics of lanthanide ions endow the super performance of Cs 2 NaLnX 6 NCs, which is obviously an important choice for future optoelectronic devices.