Chiral organic-inorganic hybrid metal halides are carving out their niche as strong contenders for high-performance circularly polarized luminescence (CPL) emitters, paving the way for innovations like three-dimensional displays and advanced spin-optoelectronics. Recent research has made substantial progress, particularly focusing on the development of red CPL emitters, notorious for their difficulty.
Researchers have succeeded by leveraging the unique electronic properties of trivalent europium ions (Eu3+) coupled with chirality, resulting in the creation of chiral europium-based halides, known as (R/S-3BrMBA)3EuCl6. These innovative materials demonstrate remarkable abilities, including strong red emission with a quantum yield of 59.8% and impressively narrow bandwidths of around 2 nm. The lifetime of this emission reaches approximately 2 milliseconds, alongside a high dissymmetry factor of 1.84 × 10−2, marking them as the brightest chiral red CPL emitters reported to date.
One of the breakthrough aspects of this research is the capability to manipulate the photoluminescence polarization of (R/S-3BrMBA)3EuCl6 using external magnetic fields. This leads to the intriguing observation of positive magneto-photoluminescence effects, which can be significant for various applications.
Published on March 14, 2025, the findings were the result of collaboration among researchers from multiple institutions. The work delineates the synthesis of these chiral Eu-based halides using anti-solvent crystallization techniques, showcasing high phase purity as confirmed through single-crystal X-ray diffraction (SCXRD). The chiral structures crystallize within the orthorhombic Sohncke space group of P212121, demonstrating stability up to approximately 520 K. Notably, these materials also feature optical bandgaps of about 3.37 eV.
The research team observed steady-state photoluminescence (PL) under 465 nm excitation, which produced peaks at 594, 614, 654, and 704 nm. The emission characteristics suggest both strong color purity and high energy efficiency. The findings underline how the 4f-4f electron transitions of europium ions lead to these pronounced emission characteristics. The narrow full width at half maximum (FWHM) of nearly 2 nm at 594 nm is particularly notable, as these transitions are preferred due to their high predictability and resolution.
The Commission International de l’Eclairage (CIE) color coordinates situate (R-3BrMBA)3EuCl6 and (S-3BrMBA)3EuCl6 within the standard red emission region at (0.64, 0.36). Continuous advancements like these are pivotal because high-performance red CPL emitters are fundamental for applications ranging from light-emitting diodes (LEDs) to anticounterfeiting technologies.
The potential of (R/S-3BrMBA)3EuCl6 is bolstered by their large PLQYs of 56.5% and 59.8% for the respective enantiomers, indicating high efficiency primarily derived from radiative recombination, with minimal non-radiative contributions. The calculated figures of merit (FOM) support the advantageous properties of these materials, which have surpassed previous records for similar chiral compounds.
Importantly, beyond their photoluminescent properties, the experiments carried out show unique temperature- and magnetic-field-dependent behaviors. For example, the degree of polarization (DP) increases as temperatures drop, with the behavior set to diverge based on chirality. A constant magnetic field application enhances the photoluminescence polarization effects, reaping benefits from the chirality-induced spin-orbit coupling phenomena.
Interestingly, the researchers noted anomalously positive magneto-photoluminescence, reaching approximately 3% under certain magnetic field strengths at room temperature, which deviates from typical behavior seen in traditional chiral metal halides. This signifies the potential for dynamic control over the emitted light qualities, enabling new possibilities for integration within spintronic applications and enhancing the versatility of these materials.
The study demonstrates how chiral rare-earth halides can offer promising strategies for generating efficient CPL emitters, reflecting substantial advancements toward practical uses within the fields of chiral optoelectronics and next-generation display technologies. With such innovations on the horizon, the development of (R/S-3BrMBA)3EuCl6 could lead to significant impacts on optical technologies, informing the next steps for applications requiring precision and reliability.
Future research will likely explore the integration of these materials within existing optical frameworks and assess their long-term stability and performance under operational conditions. The potential for contributing to both security technologies and advanced display systems positions this work at the forefront of materials science.