2 research outputs found

    Weakening Ligand–Liquid Affinity to Suppress the Desorption of Surface-Passivated Ligands from Perovskite Nanocrystals

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    The interfacial migration of surface-bound ligands highly affects the colloidal stability and optical quality of semiconductor nanocrystals, of which the underlying mechanism is not fully understood. Herein, colloidal CsPbBr3 perovskite nanocrystals (PNCs) with fragile dynamic equilibrium of ligands are taken as the examples to reveal the important role of balancing ligand-solid/solvent affinity in suppressing the desorption of ligands. As a micellar surfactant, glycyrrhizic acid (GA) with bulky hydrophobic and hydrophilic groups exhibits a relatively smaller diffusion coefficient (∼440 μm2/s in methanol) and weaker ligand–liquid affinity than that of conventional alkyl amine and carboxy ligands. Consequently, hydrophilic GA-passivated PNCs (PNCs-GA) show excellent colloidal stability in various polar solvents with dielectric constant ranging from 2.2 to 32.6 and efficient photoluminescence with a quantum yield of 85.3%. Due to the suppressed desorption of GA, the morphological and optical properties of PNCs-GA are well maintained after five rounds purification and two months long-term storage. At last, hydrophilic PNCs-GA are successfully patterned through inkjet- and screen-printing technology. These findings offer deep insights into the interfacial chemistry of colloidal NCs and provide a universal strategy for preparing high-quality hydrophilic PNCs

    Highly Stable K<sub>2</sub>SiF<sub>6</sub>:Mn<sup>4+</sup>@K<sub>2</sub>SiF<sub>6</sub> Composite Phosphor with Narrow Red Emission for White LEDs

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    Poor water resistance and nongreen synthesis remain great challenges for commercial narrow red-emitting phosphor A<sub>2</sub>MF<sub>6</sub>:Mn<sup>4+</sup> (A = alkali metal ion; M = Si, Ge, Ti) for solid-state lighting and display. We develop here a simple and green growth route to synthesize homogeneous red-emitting composite phosphor K<sub>2</sub>SiF<sub>6</sub>:Mn<sup>4+</sup>@K<sub>2</sub>SiF<sub>6</sub> (KSFM@KSF) with excellent water resistance and high efficiency without the usage of toxic and volatile hydrogen fluoride solution. After immersing into water for 6 h, the as-obtained water-resistant products maintain 76% of the original emission intensity, whereas the emission intensity of non-water-resistant ones steeply drops down to 11%. A remarkable result is that after having kept at 85% humidity and at 85 °C for 504 h (21 days), the emission intensity of the as-obtained water-resistant products is at 80–90%, from its initial value, which is 2–3 times higher than 30–40% for the non-water-resistant products. The surface deactivation-enabled growth mechanism for these phosphors was proposed and investigated in detail. We found that nontoxic H<sub>3</sub>PO<sub>4</sub>/H<sub>2</sub>O<sub>2</sub> aqueous solution promotes the releasing and decomposition of the surface [MnF<sub>6</sub>]<sup>2–</sup> ions and the transformation of the KSFM surface to KSF, which finally contributes to the homogeneous KSFM@KSF composite structure. This composite structure strategy was also successfully used to treat KSFM phosphor prepared by other methods. We believe that the results obtained in the present paper will open the pathway for the large-scale environmentally friendly synthesis of the excellent antimoisture narrow red-emitting A<sub>2</sub>MF<sub>6</sub>:Mn<sup>4+</sup> phosphor to be used for white light-emitting diode applications
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