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