Tuning Glass Formation in Hybrid Crystals with Alkali Metal Crown Ether Cations for Nonlinear Optical Glass-Ceramic

Organic-inorganic hybrid glasses represent an emerging class of functional optoelectronic materials with excellent processability, yet face the challenge in ensuring melting prior to decomposition of crystalline precursors. Here, by encapsulating a series of alkali metal and ammonium ions within 18-crown-6 cavities, we present five polar hybrid crystals formulated as (A18C6)[Cu2(SCN)3] (A = Na, K, NH4, Rb, Cs) and detailly evaluated their thermal stability and glass-forming ability. Among them, 2 (A = K) exhibits the closest size match, affording the highest decomposition temperature (195.3 °C) and enabling a reversible crystal-liquid-glass-crystal transition. The resulting glass-ceramic retains phase-matchable second-harmonic generation activity with 0.56 times that of its crystalline counterpart and 0.39 times that of KDP. This work pioneers a practical platform with supramolecular cation encapsulation to design melt-processable hybrid materials for advanced optoelectronic devices.