Thermally activated delayed fluorescence (TADF) is generally observed in solid-state organic molecules or metalorganic complexes. However, TADF in all-inorganic colloidal nanocrystals (NCs) is rare. Herein, we report the first colloidal synthesis of an air-stable all-inorganic lead-free Cs 2 ZrCl 6 perovskite NCs. The Cs 2 ZrCl 6 NCs exhibit long-lived triplet excited state (138.2 ms), and feature high photoluminescence (PL) quantum efficiency (QY = 60.37 %) due to TADF mechanism. The emission color can be easily tuned from blue to green by synthesizing the mixed-halide Cs 2 ZrBr x Cl 6Àx (0 x 1.5) NCs. Femtosecond transient absorption and temperature dependent PL measurements are performed to clarify the emission mechanism. In addition, Bi 3+ ions are successfully doped into Cs 2 ZrCl 6 NCs, which further extends the PL properties. This work not only develops a new lead-free halide perovskite NCs for potential optoelectronic applications, but also offers unique strategies for developing new inorganic phosphors.

For display applications, it is highly desirable to obtain tunable red/green/blue emission. However, lead‐free perovskite nanocrystals (NCs) generally exhibit broadband emission with poor color purity. Herein, we developed a unique phase transition strategy to engineer the emission color of lead‐free cesium manganese bromides NCs and we can achieve a tunable red/green/blue emission with high color purity in these NCs. Such phase transition can be triggered by isopropanol: from one dimensional (1D) CsMnBr3 NCs (red‐color emission) to zero dimensional (0D) Cs3MnBr5 NCs (green‐color emission). Furthermore, in a humid environment both 1D CsMnBr3 NCs and 0D Cs3MnBr5 NCs can be transformed into 0D Cs2MnBr4⋅2 H2O NCs (blue‐color emission). Cs2MnBr4⋅2 H2O NCs could inversely transform into the mixture of CsMnBr3 and Cs3MnBr5 phase during the thermal annealing dehydration step. Our work highlights the tunable optical properties in single component NCs via phase engineering and provides a new avenue for future endeavors in light‐emitting devices.

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A highly selective two-point separation strategy was designed based on a cross-like all-in-one lab-on-paper analytical device. The stable and cleavable enzyme-coated reduced graphene oxide (rGO)-PdAu probe was fabricated as the signal reporter to enable the visualization and electrochemiluminescence (ECL) dual-mode sensing of Pb. Concretely, the experimental workflow consists of the following process: (i) fabrication of the lab-on-paper device and growth of Au nanoparticles on ECL detection zone, (ii) immobilization of Pb-specific DNAzyme, and (iii) hybridization between DNAzyme and rGO-PdAu-glucose oxidase (GOx) labeled oligonucleotide to form the double-stranded DNA. Upon addition of Pb into the prepared system, the double-helix structure of the DNA was destroyed, resulting in the release of cleaved rGO-PdAu-GOx probe to visualization bar to promote the effective oxidation and color change of 3,3',5,5'-tetramethylbenzidine. As a consequence, the color change can be recognized by naked eye, meanwhile GOx on an uncleaved signal probe can oxidize glucose along with the HO production. As a co-reaction reagent for luminol ECL system, the concentration of HO is proportional to the ECL intensity, which constitutes a new mechanism for colorimetric and ECL dual mode to detect Pb. With the method developed here, the concentration of Pb could be easily determined by the naked eye within a linear range from 5 to 2000 nM, as well as by monitoring the decreased ECL intensity of luminol in a linear range of 0.5-2000 nM. This work not only constructs a simple and versatile platform for on-site visible monitoring of Pb in tap water and river water but also furnishes a strategy for designing a dual-mode sensing toward different heavy metal ions based on specific DNAzyme in the fields of environmental monitoring-related technologies.

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Lead-free halide perovskites have triggered interest in the field of optoelectronics and photocatalysis because of their low toxicity, and tunable optical and charge-carrier properties. From an application point of view, it is desirable to develop stable multifunctional lead-free halide perovskites. We have developed a series of Cs 2 Pt x Sn 1Àx Cl 6 perovskites (0 x 1) with high stability, which show switchable photoluminescence and photocatalytic functions by varying the amount of Pt 4+ substitution. A Cs 2 Pt x Sn 1Àx Cl 6 solid solution with a dominant proportion of Pt 4+ shows broadband photoluminescence with a lifetime on the microsecond timescale. A Cs 2 Pt x Sn 1Àx Cl 6 solid solution with a small amount of Pt 4+ substitution exhibits photocatalytic hydrogen evolution activity. An optical spectroscopy study reveals that the switch between photoluminescence and photocatalysis functions is controlled by sub-band gap states. Our finding provides a new way to develop lead-free multifunctional halide perovskites with high stability.