Chiral europium halides with high-performance magnetic field tunable red circularly polarized luminescence at room temperature

Chiral organic-inorganic hybrid metal halides as promising circularly polarized luminescence (CPL) emitter candidates hold great potential for high-definition displays and future spin-optoelectronics. The recent challenge lies primarily in developing high-performance red CPL emitters. Here, coupling the f-f transition characteristics of trivalent europium ions (Eu³⁺) with chirality, we construct the chiral Eu-based halides, (R/S-3BrMBA)₃EuCl₆, which exhibit strong and predictable red emission with large photoluminescence quantum yield (59.8%), narrow bandwidth (≈2 nm), long lifetime (≈2 ms), together with large dissymmetry factor |g_lum| of 1.84 × 10^-2. Compared with the previously reported chiral metal halides, these chiral Eu-based halides show the highest red CPL brightness. Furthermore, the degree of photoluminescence polarization in (R/S-3BrMBA)₃EuCl₆ can be manipulated by the external magnetic field. Particularly, benefiting from the field-generated Zeeman splitting and spin mixing at exciton states, an anomalously positive magneto-photoluminescence was observed at room temperature. This work provides an efficient strategy for constructing both high-performance and pure-red CPL emitters. It also opens the door for chiral rare-earth halides toward chiral optoelectronic and spintronic applications.