Tuning the visible circularly polarized luminescence in highly emissive chiral terbium and europium chlorides

Chiral hybrid metal halides have become increasingly popular due to their high structural tunability and exceptional optoelectronic properties. Incorporating rare-earth (RE) metals into the structural units and inheriting their pure emission characteristics are of great interest and importance. Here, we report two pairs of new isostructural chiral hybrid RE chlorides based on RE metals Tb³⁺ and Eu³⁺, crystallizing in the non-centrosymmetric space group <i>P</i>2₁2₁2₁. The circular dichroism (CD) and circularly polarized luminescence (CPL) spectra of these materials exhibit mirror-like symmetrical shapes, further confirming the polar nature and highly controllable selectivity due to the use of <i>R</i>- or <i>S</i>-methylpiperazinium cations. The CPL emissions have signature sharp signals due to the RE emissions, with dissymmetry factors |<i>g</i>_lum| of ∼4 × 10^-3 for <i>R</i>/<i>S</i>-Tb and ∼6 × 10^-3 for <i>R</i>/<i>S</i>-Eu, respectively. Furthermore, these materials show superior emission properties in the visible region, with a high photoluminescence quantum yield (PLQY) of ∼80% for <i>R</i>/<i>S</i>-Tb and ∼30% for <i>R</i>/<i>S</i>-Eu. In addition, the Tb-Eu alloyed compounds show excitation-dependent tunable CPL in the visible region with green, yellow, or red emission, which can be applied in anti-counterfeiting and information encryption. The highly tunable CPL emission and diversification of chiral RE metal halides in this work offer new routes for chiroptical optoelectronics.