Promise of Lanthanide-Based Perovskite-Inspired Materials: Expanding Horizons in Optoelectronic Applications

Lanthanide-based perovskite-inspired materials, particularly those in the Cs3LnX6 (Ln = Ce, Tb, Gd, etc.) family, have emerged as compelling candidates for next-generation optoelectronic and photonic applications because of their sharp 4f–4f and 5d–4f emissions, high color purity, and excellent thermal stability. Despite these advantages, their integration into electroluminescent (EL) devices remains constrained by low charge-carrier mobility, inefficient carrier injection, and suboptimal light outcoupling. In this Spotlight on Applications article, we provide a comprehensive overview of the crystallographic symmetry, local coordination environments, and electronic structures that govern the optoelectronic properties of Cs3LnX6 compounds. We highlight the photophysical mechanisms underlying their luminescence and examine their multifunctional potential across diverse application domains. We discuss recent advances aimed at overcoming key EL bottlenecks, including interfacial engineering, defect passivation, Ag+ alloying, compositional tuning, and structural reorganization strategies inspired by Li3YX6 analogs. These approaches not only enhance charge transport and light extraction but also open paths for materials design through symmetry-guided electronic tuning. Collectively, this Spotlight establishes fundamental structure–property–function correlations and provides a roadmap toward the development of efficient, stable, and environmentally benign lanthanide-based optoelectronic platforms.