Yibo Chen

Applications of stimuli‐responsive metal halides are often constrained by their inherent trade‐off between high response sensitivity and long‐term environmental stability. In this work, by partial incorporation of Cl ⁻ into C ₅ H ₁₁ N ₃ MnBr ₄ (C ₅ H ₁₁ N ₃ ²⁺ = histamine cation), overall structural rigidity and local structural flexibility are successfully integrated within one metal halide, thus leading to the dual optimization of photophysical and responsive performance. The obtained mixed halide, C ₅ H ₁₁ N ₃ MnCl ₃ Br, exhibits markedly improved resistance to both thermal treatment and continuous UV irradiation, as well as a 1.5‐fold increase in photoluminescence quantum yield. Concurrently, the mixed halide exhibits a humidity‐triggered emission color transition from green to red. This transition cannot be reversed unless heated to at least 80°C, demonstrating a unique humidity history memory function, which is highly suitable for humidity contamination monitoring in long‐distance shipping. This work highlights the role of halide ions mixing in activating responsive performance, which has been rarely reported, and provides a new structural regulation strategy to harmonize luminescence efficiency, environmental stability, and stimuli‐responsive functionality in metal halides.

Stimuli-responsive organic-inorganic metal halides hold great promise for emerging information-related applications. In this work, replacing the free halide ion Cl ⁻ with Br ⁻ in C ₅ H ₁₁ N ₃ (MnCl ₃ ·H ₂ O)X (where C ₅ H ₁₁ N ₃ ²⁺ represents histamine cation, X represents free halide ions) converts the non-responsive hybrid C ₅ H ₁₁ N ₃ (MnCl ₃ ·H ₂ O)Cl into a stimuli-responsive C ₅ H ₁₁ N ₃ (MnCl ₃ ·H ₂ O)Br. The latter exhibits reversible photoluminescence color switching between red and green upon thermal or water exposure. Extensive experimental and theoretical analyses reveal that the responsive property primarily stems from weakened hydrogen bonding surrounding H ₂ O molecules after Br ⁻ substitution, which facilitates the initial escape of H ₂ O molecules under heating. Subsequent structural reorganization and coordination transformation then induce the change in photoluminescence. Furthermore, the fabricated halide/polymer luminescent films are demonstrated to be highly applicable in multiple scenarios, such as planar temperature sensing, thermal stamping, and encryption/decryption. This study highlights the crucial yet often overlooked role of free halide ions in metal halides and offers new insights into their structure–property relationships.

Metal halide perovskites with high sensitivity toward external stimuli have been deemed as next‐generation responsive materials. However, realizing high‐level reversibility and stability in the halides is still challenging. This study achieves a rapid and reversible fluorescence response triggered by dynamic water vapor in a hollow‐spheres‐embedded heterostructure, which is composed of 0D Cs ₃ Cu ₂ I ₅ metal halide microcrystals and hollow oxide nanospheres. The fluorescence color of a typical MnO ₂ ─Cs ₃ Cu ₂ I ₅ heterostructure film shifts from blue to yellow within 3 s under dynamic water vapor, a change driven by the phase transition of Cs ₃ Cu ₂ I ₅ to CsCu ₂ I ₃ . The response is reversible upon vapor removal and remains stable over 100 cycles. Notably, the fluorescence of the heterostructure remains well‐preserved after 7 months of ambient storage, demonstrating significantly improved long‐term stability compared to the bare Cs ₃ Cu ₂ I ₅ . This strategy can be extended to alternative metal oxide hollow nanospheres, such as CeO ₂ , yet it is ineffective for solid nanospheres. Several spatial and temporal encryption‐decryption demonstrations with dynamic water vapor as the key are further developed, highlighting the information‐security‐related application potential of the heterostructure. This work not only provides stable and durable stimuli‐responsive metal halides but also contributes a universal structural design strategy to facilitate their development.

Metal halide perovskites are recognized for their solution processability and high luminescent efficiency. Their broad optoelectronic applications are however challenged by their high sensitivity to the environment, a consequence of their ionic nature and low formation energy. Nevertheless, this sensitivity allows for a range of luminescent responses to different stimuli, positioning them as a novel class of responsive materials. This review aims to elucidate the flexible and diverse luminescence responses in metal halide perovskites while highlighting their significance for future information‐related applications. It begins by introducing the working principles of responsive luminescent metal halide perovskites, followed by discussions on their changes in luminescence color, intensity, and lifetime in response to various stimuli, along with further elaboration on their emerging applications in sensing, anti‐counterfeiting, and information encryption. It concludes by summarizing the challenges and providing perspectives on the future development of this exciting field.

Intentional doping plays a pivotal role in customizing metal halides' electronic and optical features. This work manipulates the incorporation and distribution of Mn²⁺ in Cu(I) halide by controlling the elemental steps involved in the growth-doping kinetics as well as investigates the localized lattice and electronic structures in different doping configurations. Complementary experimental and theoretical results demonstrate that a uniform and relatively high Mn²⁺ doping level can be achieved by a step-tailored strategy that encompasses reducing the growth rate of the halide matrix, enhancing the surface adsorption of Mn²⁺, and facilitating the incorporation of the dopants. The optimized doping configuration mitigates severe lattice distortion and decreases the non-radiative transition rate, resulting in explicit dual-band emission and an enhanced photoluminescence quantum yield. This work underscores an effective synthesis strategy to harness the full potential of Mn²⁺-doped metal halides beyond Cu(I)-based ones and also showcases a new working paradigm of separately controlling the doping procedures for obtaining metal halides with customized optical/optoelectronic properties.

Multimode responsive optical materials are garnering ever-increasing attention due to their diverse applications. This work showcases a film assembled with rare-earth-doped CaF₂ hollow nanospheres that exhibit water-vapor-triggered dual-mode optical responses. Upon exposure to flowing water vapor, the film rapidly (less than 1.5 s for a 7.7 μm thickness) transitions to a transparent state and simultaneously undergoes a sharp decrease in the photoluminescence intensity. Both of these changes fully reverse upon water evaporation, demonstrating an impressive reversibility over at least 200 cycles. The water-vapor-induced dual-mode responses are attributed to the altered incident light propagation path stemming from the similar refractive indices between CaF₂ and water, coupled with the water-induced energy loss of the rare-earth ions. The fabrication of encryption patterns displaying separate signals in multiple channels, as well as the demonstration of noncontact sensing for water vapor distribution, underscore the promising application potential of this dual-mode responsive system.