Dual-band white light emission and temperature-dependent luminescence of Sn2+ in the metastable structure of Cs2CaCl4(H2O)2†

The quest for novel luminescent materials with tunable color emission and temperature-sensing capabilities remains a vibrant field of research, particularly for applications in solid-state lighting and security features. The as-synthesized rod-like crystal Cs₂CaCl₄(H₂O)₂:Sn²⁺ (R-CCCH:Sn²⁺) exhibits dual-band white light emission characterized at 415 nm and 540 nm, which correspond to the singlet state and triplet state transitions of Sn²⁺, respectively. Upon heating from 298 to 428 K, an anomalous enhancement in the intensity of the 415 nm emission in R-CCCH:Sn²⁺ was observed while its 540 nm emission underwent significant thermal quenching. The observation of the temperature-dependent photoluminescence (PL) indicates that R-CCCH:Sn²⁺ exists in a metastable state. Upon calcination at 428 K for 20 min, R-CCCH:Sn²⁺ changed to the stable state particle-like crystal Cs₂CaCl₄(H₂O)₂:Sn²⁺ (P-CCCH:Sn²⁺), exhibiting STEs of the CCCH matrix and the ³P₁ → ¹S₀ transition of Sn²⁺. The significance of this work lies in the discovery of the metastable state in CCCH and the manipulation of Sn²⁺ to emit both singlet and triplet transitions, leading to white light emission.