Large Cation Engineering in Organic Antimony Halides for Low‐Loss Active Waveguide

Abstract Active waveguides have attracted growing attention as a basic component of miniaturized and integrated photonic devices. However, most optical waveguide materials suffer from severe self‐absorption, which greatly increases the optical loss. Therefore, developing highly efficient red‐emitting materials with large Stokes shift and negligible self‐absorption is of great interest. Herein, this work proposes a strategy to achieve both large Stokes shifts and high photoluminescence quantum yield (PLQY) in organic metal halide via large cation engineering. Two zero‐dimensional antimony(III) chlorides, (TMA) 2 SbCl 5 and (TMAA) 2 SbCl 5 , are designed and synthesized by screening the ligands with different cationic volumes. Experimental and theoretical results reveal that the large cation can promote the self‐trapped excitons emission and improve stability. Benefiting from the large Stokes shift (291 nm) and high PLQY (98.3%), the as‐prepared (TMAA) 2 SbCl 5 microplate exhibits efficient active waveguide with low loss coefficient of 6.07 × 10 −3 dB µm −1 . This work not only develops a novel active waveguide material, but also provides insights into the role of organic cation, which will provide new inspiration for the exploitation of excellent luminescent metal halides and photonic devices.