All‐Inorganic CsCu₂I₃ Single Crystal with High‐PLQY (≈15.7%) Intrinsic White‐Light Emission via Strongly Localized 1D Excitonic Recombination

Abstract

In order to achieve a high quantum efficiency, doping crystals with appropriate elements such as sodium cations (ref. [8]) to reduce electronic dimension is a useful method. [5,8] However, doping also tends to cause nonradiation recombination loss. [13] Therefore, a reliable and promising way is to synthesize high-quality inorganic metal halide single crystal (SC) with natural lowdimensional structure to realize stable and high quantum efficiency white-light illumination application.In this work, we successfully synthesized 1D CsCu 2 I 3 SC by replacing toxic Pb with eco-friendly and abundant Cu, and organic molecules with large-radius Cs. [12,13] The "one dimension" we noted here is localized dimension of electron. [14] Through density functional theory (DFT) calculation, in 1D CsCu 2 I 3 SC, [Cu 2 I 3 ] − octahedra contributes most electronic states, and Cs + only forms a 1D electronic structure with isolated [Cu 2 I 3 ] − in 2D direction. Therefore, CsCu 2 I 3 SC obtains a high photoluminescence quantum yield (PLQY ≈15.7%) of the IWE at room temperature. [2] We also calculated that the crystal has a high radiation recombination rate which is owning to the 1D localized electronic structure, and this rate is the key to its high PLQY. [15,16] Under a strong injection and atmospheric environment, the PL intensity of all-inorganic CsCu 2 I 3 SC only decays about 5% after 750 min ( Figure S5, Supporting Information). This excellent stability demonstrates that the all-inorganic CsCu 2 I 3 SC possesses a great prospect in high-efficiency lighting applications.High-quality CsCu 2 I 3 SCs were synthesized by antisolvent infiltration method. [17,18] Cesium iodide and cuprous (I) iodide in certain ratio were dissolved in dimethyl formamide (DMF)dimethyl sulfoxide (DMSO) (4:1) to obtain a saturated solution. Then, methanol (antisolvent) was slowly dropped into the saturated solution to form a white precipitate (the white precipitate quickly dissolved again) until it no longer dissolved. The solution was filtered and then placed in a beaker with methanol atmosphere to grow crystals. Several days later, centimeter-scale high-quality CsCu 2 I 3 SCs were obtained (refer to the Supporting information and the Experimental Section for more details). Figure 1a shows an optical image of a rod-shaped CsCu 2 I 3 SCs excited by ultraviolet light. The SC has a size of about 10 mm × 1.5 mm, being colorless and transparent at room temperature but having strong white-light emission under ultraviolet light. Crystal structure of the CsCu 2 I 3 SC was obtained through single-crystal X-ray diffraction (SCXRD) test (Figure 1b,c), which belongs to orthorhombic system. The 1D Energy-saving white lighting from the efficient intrinsic emission of semiconductors is considered as a next-generation lighting source. Currently, white-light emission can be composited with a blue light-emitting diode and yellow phosphor. However, this solution has an inevitable light loss, which makes the improvement of the energy utilization efficiency more difficult. T...

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