Reversible control of structural phase transitions and luminescence remains a key challenge in organic-inorganic hybrid metal halides for stimuli-responsive photonic applications. Here, we report two new zero-dimensional (0D) Cd-based metal halides, (DFPD)6CdCl8 and (DFPD)2CdCl4·H2O (DFPD+ = 4,4-difluoropiperidine), in which Sb3+ doping enables distinct emission behaviors governed by coordination geometry. Combined spectroscopic studies and theoretical calculations reveal that Sb3+-doped (DFPD)6CdCl8 exhibits yellow emission with a large Stokes shift arising from triplet self-trapped exciton (3STE) emission, whereas Sb3+-doped (DFPD)2CdCl4·H2O displays excitation-dependent emission due to competing singlet STE (1STE) and 3STE states. This contrast originates from the different Cd-Cl coordination environments (octahedral vs. tetrahedral), which modulate the energy levels and transition dipole moments. Importantly, hydrochloric acid (HCl) and 4,4-difluoropiperidine induce fully reversible interconversion between the two structures, allowing dynamic switching between yellow and deep-orange emission. Based on this reversible luminescence, we further demonstrated applications in dynamic anti-counterfeiting and multilevel information encryption. This work establishes a coordination-structure-driven strategy for programmable emission in 0D hybrid metal halides.

The Ce 3+ -doped metal halides are recognized as ultrafast scintillators due to their allowed 5d→4f radiative transitions, which enable fast decay and high light yield. However, in certain hosts such as Cs 2 ZnCl 4 , Ce 3+ emission is limited by inefficient energy transfer and competitive self-trapped exciton (STE) recombination. Here, we grow a series of centimeter-scale, high-quality Ce 3+ -doped and Ce 3+ –Cu + co-doped Cs 2 ZnCl 4 single crystals with tunable dopant concentrations, and elucidate their carrier relaxation pathways using transient absorption spectroscopy across fs–µs timescales. This Ce 3+ –Cu + co-doping strategy modulates the Ce 3+ 5d energy landscape and facilitates the participation of STEs in radiative recombination. Specifically, co-doping deepens the lowest 5d potential well and promotes Ce 3+ →STE energy transfer. It also redistributes exciton populations between localized and delocalized 5d states and facilitates faster carrier relaxation. As a result, the X-ray excited luminescence intensity is enhanced by nearly an order of magnitude, while the fast γ-ray scintillation decay component is shortened from 4.3 to 2.4 ns. These findings establish a direct link between Ce 3+ 5d dynamics, hot-exciton redistribution, and dopant–host coupling, providing a rational strategy for designing high-efficiency ultrafast scintillators.

A3BX6 perovskites, a family of vacancy-ordered structures, exhibit diverse luminescence behaviors upon photon, electron, and high-energy excitation, primarily originating from intrinsic self-trapped excitons or dopant-induced electronic transitions. Upon B-site cation engineering, ns2 cations tune intrinsic luminescence, whereas transition-metal and rare-earth dopants activate characteristic d–d, d–f, and f–f transitions, enriching A3BX6 optical diversity. The tunable crystal structure and electronic configuration endow A3BX6 perovskites with exceptional versatility for photoluminescence, electroluminescence, and scintillation applications. This review systematically elucidates how B-site chemistry modulates the structure–property–application relationships in this material family. P-block B-site A3BX6 perovskites exhibit high photoluminescence efficiency, broadband emission, and strong ultraviolet absorption, enabling applications in high-sensitivity photodetectors (1.23 × 1012 Jones), information encryption, and white light-emitting diodes. In comparison, rare-earth-based A3BX6 perovskites enable high-efficiency electroluminescent devices, featuring deep-blue light-emitting diode with an external quantum efficiency of 7.9%. Moreover, they exhibit superior scintillation performance, including high x-ray light yield (88,800 ph/MeV), low x-ray detection limit (63 nGy/s), and notable γ-ray response under 137Cs excitation (47,000 ph/MeV; 4.0% energy resolution). These insights highlight the pivotal role of B-site cation engineering in tailoring luminescence mechanisms and enabling multifunctional A3BX6 perovskites for photonic and radiation applications.

A 3 BX 6 perovskites, a family of vacancy-ordered structures, exhibit diverse luminescence behaviors upon photon, electron, and high-energy excitation, primarily originating from intrinsic self-trapped excitons or dopant-induced electronic transitions. Upon B-site cation engineering, ns 2 cations tune intrinsic luminescence, whereas transition-metal and rare-earth dopants activate characteristic d–d, d–f, and f–f transitions, enriching A 3 BX 6 optical diversity. The tunable crystal structure and electronic configuration endow A 3 BX 6 perovskites with exceptional versatility for photoluminescence, electroluminescence, and scintillation applications. This review systematically elucidates how B-site chemistry modulates the structure–property–application relationships in this material family. P-block B-site A 3 BX 6 perovskites exhibit high photoluminescence efficiency, broadband emission, and strong ultraviolet absorption, enabling applications in high-sensitivity photodetectors (1.23 × 10 12 Jones), information encryption, and white light-emitting diodes. In comparison, rare-earth-based A 3 BX 6 perovskites enable high-efficiency electroluminescent devices, featuring deep-blue light-emitting diode with an external quantum efficiency of 7.9%. Moreover, they exhibit superior scintillation performance, including high x-ray light yield (88,800 ph/MeV), low x-ray detection limit (63 nGy/s), and notable γ-ray response under 137 Cs excitation (47,000 ph/MeV; 4.0% energy resolution). These insights highlight the pivotal role of B-site cation engineering in tailoring luminescence mechanisms and enabling multifunctional A 3 BX 6 perovskites for photonic and radiation applications.

Photo-induced dynamics of electronic processes in materials are driven by the coupling between electronic and nuclear degrees of freedom. Here we construct 1D and 2D organic-inorganic tin halides to investigate the functional role of dimensionality to exciton-phonon coupling (EPC) and exciton self-trapping. The results show that the 1D system has strong EPC leading to excitation-independent self-trapped exciton (STE) emission, while the 2D system exhibits over ten times weaker EPC resulting in free exciton emission. By performing femtosecond transient absorption experiments, we directly resolve the room-temperature vibrational wavepackets in the 1D system, some of which propagate along the STE potential energy surface. A combination of wagging and asymmetric stretching motions ( 106 cm-1) in tin iodide is identified as such a mode inducing exciton self-trapping. While no room-temperature wavepackets are observed in the 2D system. These findings uncover the interplay between the dimensionality-dependent EPC and electronic/nuclear dynamics, offering constructive guidance to develop multifunctional organic-inorganic metal halides.

Mn2+-doped nanomaterials are attractive for optoelectronic applications due to their characteristic dopant emission enabled by host-to-dopant energy transfer (ET). However, increasing Mn2+ concentrations typically leads to severe photoluminescence (PL) quenching due to strong Mn2+-Mn2+ interactions and the formation of nonradiative trap states. Here, we demonstrate that this challenge can be overcome in Cd-based perovskite nanocrystals (NCs) by exploiting localized excitons (LEs) coupled to a fast thermodynamic equilibrium with trap states. Ultrafast transient absorption spectroscopy suggests a rapid LE-trap equilibrium (similar to 100 ps) at room temperature. Mn2 + doping further enhances exciton localization and redistributes the exciton population into trap states, which serve as intermediates for Dexter-type energy transfer, accelerating Mn2 + excitation by over an order of magnitude compared to direct energy transfer from LEs. Consequently, efficient and thermally stable Mn2+ emission is achieved at elevated dopant concentrations. The PL quantum yield exceeds that of the undoped NCs by more than 12-fold and retains 70% of its maximum value even at 20% Mn2+ concentration in Cs2CdCl4:Mn2+ NCs.

Halide perovskites exhibit exceptional optoelectronic properties, including strong light absorption and efficient generation of photogenerated charge carriers. However, these advantages are extremely limited in electrocatalytic systems, and their full potential remains largely unexplored. In particular, the underlying mechanisms governing light-assisted electrocatalysis in perovskite materials remain poorly understood. Herein, a Pt-modified Cs2PdBr6 all-inorganic halide perovskite (Cs2PdBr6@Pt-1.5) is designed, which achieves a low overpotential of 11 mV at 10 mA cm(-2) with excellent water stability. Femtosecond transient absorption spectroscopy further demonstrates that the incorporation of Pt increases the population of transient species (<1 ps) and acts as an efficient charge separation channel, thereby promoting charge migration to catalytic active sites and enhancing hydrogen evolution reaction properties. Density functional theory (DFT) calculations reveal that electrons transfer from Cs2PdBr6 to Pt, and Pt-modified Cs2PdBr6 optimizes the adsorption energies of key reaction intermediates, thereby lowering the overpotential for water splitting. These findings highlight the potential of halide perovskites as a stable and efficient platform for light-assisted electrocatalytic water splitting and related energy conversion processes

Halide perovskites exhibit exceptional optoelectronic properties, including strong light absorption and efficient generation of photogenerated charge carriers. However, these advantages are extremely limited in electrocatalytic systems, and their full potential remains largely unexplored. In particular, the underlying mechanisms governing light-assisted electrocatalysis in perovskite materials remain poorly understood. Herein, a Pt-modified Cs2PdBr6 all-inorganic halide perovskite (Cs2PdBr6@Pt1.5) is designed, which achieves a low overpotential of 11 mV at 10 mA cm-2 with excellent water stability. Femtosecond transient absorption spectroscopy further demonstrates that the incorporation of Pt increases the population of transient species (<1 ps) and acts as an efficient charge separation channel, thereby promoting charge migration to catalytic active sites and enhancing hydrogen evolution reaction properties. Density functional theory (DFT) calculations reveal that electrons transfer from Cs2PdBr6 to Pt, and Pt-modified Cs2PdBr6 optimizes the adsorption energies of key reaction intermediates, thereby lowering the overpotential for water splitting. These findings highlight the potential of halide perovskites as a stable and efficient platform for light-assisted electrocatalytic water splitting and related energy conversion processes.

Zero-dimensional metal halides have emerged as a versatile platform for the development of light-emitting materials, but achieving tunable or even multicolor emission from a material containing a single type of metal has proven highly challenging. Here, we leverage the "structural tolerance" of recently-developed polymeric metal halides to integrate two distinct coordination units of a single metal into a material, thereby achieving highly tunable optical properties in single-phase metal halides. By manipulating the steric hindrance of polycations, facilely adjustable green, red or bicolor emission can be realized in manganese bromides, which originates from controllable transformation from manganese-bromine tetrahedra into octahedra. This design principle is further extended to polymeric copper halides, wherein broad self-trapped exciton emissions derived from distinct copper-iodine polyhedrons allow the emission colors to be linearly tunable from blue to yellow, encompassing pure white light, by tailoring the composition, excitation wavelength, or temperature. This study opens avenues for facile and precise modulation of the optical properties of metal halides by exploiting the intrinsic coordinative diversity of metal elements.

Near infrared (NIR) fluorescence imaging has received significant attention. However, it remains challenging to develop NIR emitters with a high brightness. Herein, we report a supramolecular approach to formulate NIR fluorescent molecular nanoparticles from cationic NIR fluorophores and cyanostar receptors using their charge-by-charge packing in small-molecule ionic isolation lattices (SMILES). Four types of cationic NIR fluorophores were successfully used to form NIR SMILES nanoparticles. The NIR nanoparticles show fluorescence quantum yields (FQYs) of similar to 1% and are over 60 times brighter than those of single fluorophores. Four different surface capping agents were examined and found to generate stable nanoparticles with slight changes in FQY. Femtosecond transient absorption spectroscopy reveals the low FQY originates from nonradiative decay introduced by interfluorophore coupling. Introduction of inert molecular cations into the SMILES structures raises the FQY to similar to 7%. The NIR SMILES nanoparticles were used for in vivo tumor imaging and are thus promising for bioimaging applications.

DNA-stabilized silver nanoclusters (DNA-AgNCs) have emerged as a promising class of biocompatible fluorophores with tunable emission wavelengths and lifetimes governed by the scaffolding DNA sequence. Unlike conventional organic ligand-protected metal clusters, the structure-photophysical correlation of DNA-AgNCs has not been fully elucidated due to the paucity of crystal structures. To address this, we employ ultrafast transient absorption spectroscopy to unravel the excited-state relaxation processes in three DNA-AgNCs with distinct rod-like and spherical geometries. For the rod-like DNA-AgNC, we observe a nanosecond fluorescent state forming from the Franck-Condon state, followed by the formation of a microsecond-lived state from the nanosecond excited state. For the two DNA-AgNCs with suggested spherical geometries, a microsecond-lived luminescent state is directly formed from the Franck-Condon state on a subpicosecond time scale. These new insights into the relationship between shape and luminescence response will contribute to the photophysical understanding and structural engineering of DNA-AgNCs for specific imaging applications.

Low-dimensional organic-inorganic hybrid metal halides (HMH) have attracted widespread attention due to their tunable chemical composition and exceptional optoelectronic properties. However, there are only limited numbers of reports about lanthanide elements-based metal halides. Herein, we synthesize a zero-dimensional (0D) metal halide, (DFPD)(4)TbCl7 (DFPD = 4,4-difluoropiperidinium), which exhibits intrinsic emission from the lanthanide ion (Tb3+). Interestingly, by doping a small amount of Sb3+, an additional emission peak emerged at 625 nm. Apart from the dual band photoluminescence (PL), the photoluminescence quantum yield (PLQY) is increased from similar to 40% to near unity (99.6%) after doping (DFPD)(4)TbCl7 HMH with Sb3+. To reveal the enhanced PLQY and dual band emission in (DFPD)(4)TbCl7:Sb3+, we carried out temperature-dependent PL measurements and density functional theory (DFT) calculation. We found the observed dual-band emission originated from intrinsic emission of Tb and self-trapped exciton (STEs) emission, which is introduced by the [SbCl6](3-) octahedron. The extra radiative channel introduced by STEs contributes to the enhanced PLQY. Taking advantage of the efficient PL and high stability of (DFPD)(4)TbCl7:Sb3+, we fabricated a stable white-light-emitting diode with a color rendering index of 93. Furthermore, the temperature-dependent PL of (DFPD)(4)TbCl7:Sb3+ ensures its application as active material for optical thermometry. Our work provides a new strategy for developing lanthanide-based HMH with high performance for light emitting applications.

In this manuscript, we create a new hetero dyad consisting of two electron acceptors with nearly isoenergetic HOMO and LUMO levels, namely perylene diimide (PDI) and aza dioxa triangulenium (ADOTA). This dyad system displays an unusual and reversible excited state electron transfer process. Upon excitation, the dyad shows complete energy transfer from the locally excited PDI to the ADOTA moiety in ∼1 ps, followed by photoinduced electron transfer (PET), forming oxidized PDI and reduced ADOTA. While this PET process is fast (k PET≈ 150 ps), the reversibility establishes an equilibrium between fluorescent locally excited ADOTA and the dark charge shifted PET state. We investigate the formation of and decay from this unusual reversible excited state electron transfer system by fs transient absorption and time-resolved fluorescence spectroscopy in different solvent mixtures because the solvent modulates the deactivation rate of the PET state. Electrochemistry confirms that both the local HOMOs and LUMOs of PDI and ADOTA are nearly isoenergetic but can be shifted by solvent polarity, which elucidates the reason for the unusual reversible electron transfer process and its sensitivity to the solvent. We further investigate near degeneracy of the LUMOs through spectroscopy of the chemically reduced dyad. We find that there is an equilibrium between the reduction of the cationic ADOTA to a neutral dyad, which is favored in DCM. However, in DMF, we find reduction of the PDI leads to formation of the zwitterionic dyad.

Metasurfaces supporting bound states in the continuum (BIC) can be leveraged as lasing platforms, offering ultra-compact and highly coherent light sources. Although designs using low-index polymers that do not require etching have been demonstrated and shown to possess remarkably high quality factors for free-space radiation, these have been so far limited to passive designs. Here, we report on highly coherent BIC-based lasing, emerging from etch-free metasurfaces that are directly patterned onto organic supramolecular materials consisting of small-molecule, ionic isolation lattices (SMILES). We observe highly directional lasing with a divergence angle of 0.2°, linewidth of 0.04 nm — limited by the spectral resolution of our measurement setup — and a temporal coherence of 20.4 ± 2.4 ps. The reported performance is a direct consequence of the combination of high-quality metasurface designs with the intrinsic uniformity and stability of SMILES, offering a strategy to realize active metasurfaces and organic molecular lasers, superior to alternative approaches based on solution-processable materials. Etch-free metasurfaces supporting bound states in the continuum have been used for lasing, although only as passive devices. Here, authors demonstrate highly coherent lasing from an active etch-free metasurface, showing a divergence angle of 0.2⁰, a linewidth of 0.04 nm and coherence time of 20.4 ps.

Metal halide perovskites (MHPs) with stimuli-responsive photoluminescence (PL) have attracted widespread attention for their application in optical encryption. However, existing metal halide perovskites typically exhibit a monochromatic PL emission and response to a single stimulus. As a result, they show limited encryption security. Therefore, it is crucial to develop a strategy to transition from single-stimulus responsive materials to multistimuli responsive ones. Herein, for the first time, we reported a strategy through cation alloying to form Cs x Rb2-x MnBr4(H2O)2 with multistimuli responsive PL. A continuous PL color change of Cs x Rb2-x MnBr4(H2O)2 was achieved from nonluminous, red and green light emissions with temperature, which is attributed to the chemical transformation from Cs x Rb2-x MnBr4(H2O)2 to Rb2MnBr4, RbMnBr3, Rb3MnBr5, and Cs3MnBr5. More importantly, Cs+ alloying can enable the chemical transformation from Cs x Rb2-x MnBr4(H2O)2 to RbMnBr3, Cs3MnBr5, and Rb3MnBr5 in isopropanol accompanied by PL change from red to green. Furthermore, such a chemical transformation of Cs x Rb2-x MnBr4(H2O)2 can also be triggered by water. These results highlight Cs alloying as a unique strategy to expand the multistimuli responsive PL modes of MHPs. Our findings present a straightforward approach for designing multistimuli responsive materials with potential applications in information storage, anticounterfeit labeling, and information security.

Low-dimensional halide perovskites have recently attracted considerable attention as promising candidates for single-component white light-emitting diodes (WLEDs). However, it remains challenging to achieve highly efficient white light emission in 2D systems. Herein, white light emitting Cu+/Mn2+ codoped 2D (PPDA)CdCl4 perovskites are synthesized via a facile fabrication method. The host is weakly emissive. However, Cu+ and Mn2+ doping can lead to strong green and orange-red emission, respectively. Spectroscopic characterizations show that there are two independent emission centers, the Cu+-induced extrinsic self-trapped exciton (STE), which leads to the green emission, and the isolated Mn2+ ion which results in orange-red emission via the inherent 4T1(G)→6A1(S) transition. Interestingly, by optimizing the ratio of Cu+ and Mn2+, the codoped sample can exhibit tunable white light emission with variable correlated color temperatures and high photoluminescence quantum yields of 45.2%-51.1%. In addition, the codoped samples can also exhibit interesting excitation-dependent emission properties. This work opens up new opportunities for the development of high-performance 2D perovskite luminescent materials.

Fluorescent off-on probes based on a modular design where an analyte sensitive PET moiety is attached to a fluorophore are extremely successful. Here we report a new modular fluorescence probe design switched by dynamic quenching due to proton coupled electron transfer (PCET) mediated by collision with weak bases in solution. The fluorescence lifetime of this probe directly reports on the rate of deprotonation by the weak bases in the solution. We investigate the probe design, mechanism of response, and sensitivity to various abundant weak bases/metabolites including acetate, glutamate, phosphate, valine, and amines. We find that this modular PCET based probe design, in contrast to traditional PET probes, can work efficiently with a fluorescence lifetime readout providing a calibration free probe for weak bases. Upon further development we envision such dynamic PCET probes as sensitive tools for studies of cellular buffer systems and metabolite pools.

Tunable broad-spectrum luminescent materials covering the ultraviolet (UV), visible, and near infrared (NIR) regions are essential for next-generation optoelectronic technologies. However, conventional systems are often limited by inefficient UV emission and the inability to integrate multiple spectral components within a single material. Here, a design strategy that combines ns2-ion with controlled lattice distortion is introduced to overcome these challenges. Using 4,4-difluoropiperidine (DFPD) as the organic cation, a family of hybrid metal halide phosphors, [(DFPD)2MCl4·H2O, M = Cd/Zn] doped with different ns2 ion (Sn2+, Pb2+, Sb3+, Bi3+, and Te4+) is synthesized. It is revealed that reduced lattice distortion correlates with enhanced photoluminescence quantum yield (PLQY), enabling broadband self-trapped exciton emission spanning the UV-vis-NIR range within a single host matrix. Leveraging the highly efficient UV emission of 2% Pb-doped (DFPD)2CdCl4·H2O (PLQY: 93%), a high-performance white light emitter with a color rendering index of 92.9 and a correlated color temperature of 6087 K is demonstrated. The materials further exhibit promising functionality in NIR imaging and multi-level anti-counterfeiting. This work elucidates the interplay between lattice distortion and exciton dynamics in Cd/Zn-based hybrid metal halides, providing fundamental insights into their photophysics and establishing a versatile strategy for designing next-generation broadband multifunctional optoelectronic materials.

We investigate the excited-state intramolecular proton transfer (ESIPT) process and luminescence mechanism of a 2-(2 '-hydroxyphenyl)imidazo[1,2-a]pyridine derivative (HIP-Br) in dichloromethane (DCM) and dimethyl sulfoxide (DMSO) using both implicit and explicit solvation models. Computational results reveal that the ESIPT process of HIP-Br proceeds efficiently in DCM regardless of the solvation model. In contrast, in DMSO, the ESIPT process is suppressed under the explicit solvation model due to the formation of intermolecular hydrogen bonds between HIP-Br and DMSO molecules, which disrupt the intramolecular hydrogen bond. This study underscores the importance of considering explicit solute-solvent interactions when modeling excited-state processes in hydrogen-bonding solvents.