Rational design and synthesis of narrow-band emitting Eu(II)-based hybrid halides via alkyl thermal cleavage

Organic-inorganic hybrid metal halides have emerged as pivotal luminescent materials for versatile photonic applications. Nevertheless, prevailing chemical design and synthetic strategies of hybrid luminescent halides are constrained by limited compositional engineering and suboptimal phase crystallization. Herein, we propose a universal alkyl thermal cleavage route to design and grow Eu(II)-based hybrid halide crystals. By modulating the alkyl chain length of 25 organic cations, all the as-synthesized halides achieve narrow-band emission with full-width-at-half-maximum (34-52 nm) and tunable colors in the region of blue-cyan-green owing to the highly efficient 5d-4f transition of Eu(II). We further clarify that the tunable emissions are dependent on the combined effect of configuration, average radius, and distortion index of the Eu-X (X = Cl, Br, I) polyhedra. This work provides fundamental insights into the design principle of narrow-band emitting Eu(II)-based hybrid halides and expands the family of hybrid halides as next-generation luminescence materials for emerging photonic applications.