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.