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.
Triplet exciton‐based long‐lived phosphorescence is severely limited by the thermal quenching at high temperature. Herein, we propose a novel strategy based on the energy transfer from triplet self‐trapped excitons to Mn2+ dopants in solution‐processed perovskite CsCdCl3. It is found the Mn2+ doped hexagonal phase CsCdCl3 could simultaneously exhibit high emission efficiency (81.5 %) and long afterglow duration time (150 s). Besides, the afterglow emission exhibits anti‐thermal quenching from 300 to 400 K. In‐depth charge‐carrier dynamics studies and density functional theory (DFT) calculation provide unambiguous evidence that carrier detrapping from trap states (mainly induced by Cl vacancy) to localized emission centers ([MnCl6]4−) is responsible for the afterglow emission with anti‐thermal quenching. Enlightened by the present results, we demonstrate the application of the developed materials for optical storage and logic operation applications.
Vacancy‐ordered perovskite nanocrystals (NCs) have recently attracted much interest owing to their unique structure and optical properties; however, regulating self‐trapped excitons (STEs) in vacancy‐ordered perovskite NCs to exhibit tunable multicolor emission is still challenging because of the highly localized charge distribution and strong carrier‐phonon coupling. Herein, the first colloidal synthesis of lead‐free vacancy‐ordered Cs2HfCl6 perovskite NCs by a hot‐injection method using hafnium acetylacetonate as metal precursors is reported. The passivation strategy of sub‐bandgap trap states inside Cs2HfCl6 NCs is proposed by doping Sb3+. X‐ray photoelectron spectroscopy (XPS) measurements verify that the passivation of sub‐bandgap trap states may be attributed to the enhanced chemical interaction between the Hf4+ cations and Cl– anions. Simultaneously, the introduction of Sb3+ ions yields a bright orange emission. Employing lanthanide acetylacetonate compounds, four lanthanide ions including Pr3+, Eu3+, Tb3+, and Ho3+ are doped into the Cs2HfCl6 NCs, which achieves tunable multicolor emissions (from blue to green to pink) through the energy transfer from STEs to lanthanide ions. This investigation not only develops a novel vacancy‐ordered perovskite NCs, but also provides effective strategies for tuning the optical properties of lead‐free vacancy‐ordered perovskite NCs.
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