Yb3+-mediated energy regulation in an ultralow-phonon Cs2NaLuCl6 double perovskite for optical thermometer and advanced information encryption

The ability to regulate the luminescence in rare earth-activated materials via photo-stimulation plays a pivotal role in non-contact optical thermometer and dynamic information security. However, achieving multimode emissions in simple rare-earth systems through controlled energy transfer remains challenging. Herein, we designed an Er 3+ -activated non-core-shell luminescent material based on the all-inorganic double perovskite Cs 2 NaLuCl 6 with an ultralow phonon energy, enabling high-efficiency and color-tunable emission. Multimodal luminescence is realized via precisely tailored energy migration among Er 3+ ions under diverse excitation wavelengths ( λ ex = 1550, 980, 808, 376 nm). By further introducing Yb 3+ as a sensitizer, the upconversion (UC) intensity and polychromatic emission are significantly enhanced via efficient Er 3+ →Yb 3+ energy transfer under 980 and 376 nm excitation. Additionally, a ratiometric thermometer is developed based on the luminescence intensity ratio (LIR) of the thermally coupled levels (TCLs) in Er 3+ ions, achieving superior relative sensitivity ( S r = 1.12%/K) and resolution (δ T = 1.20 K). Moreover, a high-security encryption/decryption system is constructed by exploiting the tunable luminescence under 376 and 980 nm excitation, enabling multi-wavelength-decoded Chinese Pinyin encoding and ASC-II binary encoding schemes. This work establishes a feasible strategy of precise ion-functionalization in an ultralow-phonon host, demonstrating high-performance capabilities in remote optical thermometry and information encryption, and providing a versatile platform for next-generation photonic applications.