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.
elements to replace lead due to the high toxicity. Lead-free halide perovskite NCs have recently received increasing attention for their low toxicity, high stability, and chemical diversity. [3-8] The most direct way is usually isovalent substitution of Pb 2+ with Sn 2+. [3] Unfortunately, lead-free CsSnX 3 (X = Cl, Br, and I) NCs is extremely unstable because of the easy oxidation of Sn 2+ into Sn 4+ in air. [3] Subsequently, A 3 M ' 2 X 9-type layer perovskite, A 2 MM ' X 6-type, and A 2 BX 6-type double perovskite (where A denotes alkali-metal ions; M, M' and B denotes monovalent-, trivalent-, and tetravalent-cations; X denotes halogen ions) with high stability have been reported. [9-20] However, optoelectronic devices based on these lead-free perovskite NCs have made limited progress. Such as, photodetectors based on lead-free perovskite NCs exhibited low responsivity (typically <1 A W −1). [17,18] This is mainly due to the low crystallinity, prominent charge-carrier trapping, and short charge-carrier lifetimes of these NCs. In this paper, we report, for the first time, the colloidal synthesis of a series of trigonal (R3̅ m) vacancy-ordered quadrupleperovskite NCs, i.e., Cs 4 CdSb 2 Cl 12 , Cs 4 MnSb 2 Cl 12 , Cs 4 CdBi 2 Cl 12 , and Cs 4 MnBi 2 Cl 12. The photoluminescence quantum yield (PLQY) can be enhanced by 96-fold while the PL lifetime can be enhanced by 77-fold in Cs 4 MnBi 2 Cl 12 NCs through metal alloying. Studies of the charge-carrier dynamics including temperature-dependent PL and femtosecond (fs) transient absorption (TA) measurements were performed to clarify the mechanism of the PL enhancement, which is due to the elimination of the charge-carrier trapping process and increased crystallinity. Besides, the PL-peak position can be tuned continuously from 590 to 640 nm by changing the MnCl bond distance via metal alloying. Finally, we fabricate photodetectors based on quadruple-perovskite NCs, which exhibit high responsivity (0.98 × 10 4 A W −1) and an EQE of 3 × 10 6 %. The responsivity is much higher than previous reported photodetectors base on lead-free perovskite NCs. These results show that quadruple-perovskite NCs open new possibilities for optoelectronic applications. The colloidal synthesis of halide quadruple-perovskite NCs was performed using a modified hot-injection method-for details see the Experimental Section. [14] As shown in Figure 1a,b, replacing M in A 2 MM'X 6 with one M'' (M'' denotes a +2 cation) The colloidal synthesis of a new type of lead-free halide quadruple-perovskite nanocrystals (NCs) is reported. The photoluminescence quantum yield and charge-carrier lifetime of quadruple-perovskite NCs can be enhanced by 96 and 77-fold, respectively, via metal alloying. Study of charge-carrier dynamics provide solid demonstrate that the PL enhancement is due to the elimination of ultrafast (1.4 ps) charge-carrier trapping processes in the alloyed NCs. Thanks to the high crystallinity, low trap-state density, and long carrier lifetime (193.4 μs), the alloyed quadruple-perovskite N...
Single-component emitters with stable and bright warm white-light emission are highly desirable for high-efficacy warm white light-emitting diodes (warm-WLEDs), however, materials with such luminescence properties are extremely rare. Lowdimensional lead (Pb) halide perovskites can achieve warm white photoluminescence (PL), yet they suffer from low stability and PL quantum yield (PLQY). While Pb-free air-stable perovskites such as Cs 2 AgInCl 6 emit desirable warm white light, sophisticated doping strategies are typically required to increase their PL intensity. Moreover, the use of rare metal-bearing compounds along with the typically required vacuum-based thin-film processing may greatly increase their production cost. Herein, organic-inorganic hybrid cuprous (Cu + )-based metal halide MA 2 CuCl 3 (MA = CH 3 NH 3 + ) that meets the requirements of i) nontoxicity, ii) high PLQY, and iii) dopant-free is presented. Both single crystals and thin films of MA 2 CuCl 3 can be facilely prepared by a low-cost solution method, which demonstrate bright warm white-light emission with intrinsically high PLQYs of 90-97%. Prototype electroluminescence devices and down-conversion LEDs are fabricated with MA 2 CuCl 3 thin films and single crystals, respectively, which show bright luminescence with decent efficiencies and operational stability. These findings suggest that MA 2 CuCl 3 has a great potential for the single-component indoor lighting and display applications.
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