Promoted Growth and Multiband Emission in Heterostructured Perovskites Through Cs+‐Sublattice Interaction

Abstract Precise control of exciton confinement in metal halide perovskites is critical to the development of high‐performance, stable optoelectronic devices. A significant hurdle is the swift completion of ionic metathesis reactions, often within seconds, making consistent control challenging. Herein, the introduction of different steric hindrances in a Cs+ sublattice within CsYb2F7 is reported, which effectively modulates the reaction rate of Cs+ with lead (Pb2+) and halide ions in solution, extending the synthesis time for perovskite nanostructures to tens of minutes. Importantly, the Cs+ sublattice provides a crystal facet‐dependent preference for perovskite growth and thus exciton confinement, allowing the simultaneous occurrence of up to six emission bands of CsPbBr3. Moreover, the rigid CsYb2F7 nano template offers high activation energy and enhances the stability of the resulting perovskite nanostructures. This methodology provides a versatile approach to synthesizing functional heterostructures. Its robustness is demonstrated by in‐situ growth of perovskite nanostructures on Cs+‐mediated metal‐organic frameworks.

Preparation of CsYb2F7 nanocrystals.CsYb2F7 nanocrystals were synthesized using a modified method with a Cs: Yb: F molar ratio of 1.2:2:7 [S1] .First, an aqueous solution of Yb(CH3COO)3 (0.8 mmol, 4.0 ml) was mixed with oleic acid (4 mL) and 1-octadecene (6 mL) in a round-bottomed flask.The mixture was then heated at 150 °C for 1 hour to remove water.After cooling to 50 °C, a methanol solution of cesium hydroxide (0.48 mmol, 0.96 mL) and ammonium fluoride (2.8 mmol, 7 mL) was added and stirred for 30 minutes at 50 °C, followed by heating at 100 °C for another 30 minutes.Finally, the mixture was heated to 290 °C and kept under nitrogen for 2 hours.After cooling to room temperature, nanocrystals were washed three times with ethanol and redispersed in 4 mL of cyclohexane for CsYb2F7 /CsPbX3 synthesis.
Preparation of CsYb2F7 nanoplates.CsYb2F7 nanoplates were synthesized by the same procedure except for the ratio of Cs:Yb: F being 2:5:8.
Preparation of irregularly shaped CsYb2F7 nanocrystals.CsYb2F7 nanoplates were synthesized by the same procedure but with accelerated heating and cooling.
Synthesis of CsPbBr3 nanomaterials.Cesium lead bromide (CsPbBr3) nanomaterials were synthesized by the hot-injection method [S2] .In the experiment, 0.38 mmol of lead bromide (PbBr2) was dissolved in a mixture of oleic acid (1.0 mL), oleylamine (1.0 mL), and octadecene (15 mL) in a roundbottomed flask.The mixture was heated to 100 °C for 0.5 hours under vacuum to remove moisture and continuously introduced nitrogen gas.The mixture was then increased to 160 °C until the PbBr2 was completely dissolved.A hot solution of cesium oleate (1 mL, 0.1514 M) was quickly injected into the mixture at 180 °C.After 5 seconds, the flask was transferred to an ice bath.CsPbBr3 quantum dots were obtained by centrifugation at 13,000 rpm for 10 minutes and stored in 4 mL of cyclohexane.Mixedhalide perovskite QDs were synthesized by varying the halide composition.
Synthesis of CsYb2F7/CsPbX3 nanostructures.Cesium ytterbium fluoride/cesium lead bromide (CsYb2F7/CsPbX3) nanomaterials were synthesized using a modified hot-injection method [S2] .In the experiment, 0.02-0.36mmol of lead bromide (PbBr2), 1.0 mL of oleic acid (OA), 1.0 mL of oleylamine (OAm), and 10 mL of octadecene (ODE) were added to a three-neck round-bottomed flask.The mixture was heated under vigorous stirring in vacuum to 100 o C for 0.5 hours; then, the moisture residue was removed by purging with nitrogen.The mixture was heated to 180 °C until the PbBr2 was dissolved.A solution of CsYb2F7 nanocrystals in cyclohexane (1.0 mL, 0.1M) was quickly injected and allowed to undergo a 30-min reaction before cooling in an ice-water bath.The resulting solution was transferred to a mixed solvent of octadecene (3.5 mL), oleic acid (0.35 mL), and oleylamine (0.35 mL) and stirred at room temperature for different reaction times (10 seconds, 1 minute, 5 minutes, 10 minutes, 30 minutes, and 1 hour).The resulting samples were centrifuged at 6,000 rpm for 5 minutes, and the supernatant was washed twice with methyl acetate.Finally, the CsYb2F7/CsPbBr3 nanomaterials were obtained by centrifugation at 13,000 rpm for 10 minutes and stored in 4 mL of cyclohexane.Different CsYb2F7/CsPbX3 (X=Cl, Cl/Br, and Br/I) samples were synthesized following the same procedure.
Synthesis of nanorods.Cesium-rare earth-fluoride nanorod hosts were synthesized by a modified hotinjection method.In a typical experiment, Y(CH3CO2)3 (1.0 mL, 0.2 mmol) and Yb(CH3CO2)3 (1.0 mL, 0.2 mmol) were dissolved in a mixture of ODE (6.0 mL) and OA (4.0 mL) in a round-bottomed flask equipped with a temperature sensor.The mixture was stirred at 150 °C for 40 minutes to remove moisture.After cooling to 50 °C, a methanol solution of NH4F (4.0 mL, 1.6 mmol), NaOH (1 mL, 0.5 mmol), and CsOH (1 mL, 0.5 mmol) was added and stirred for 30 minutes.The reaction mixture was then vacuumed at 105 °C for 15 minutes and heated to 290 °C for 2.5 hours under nitrogen.After cooling to room temperature, the resulting nanorods were isolated by washing with ethanol and finally dispersed in 4.0 mL of cyclohexane.The Na: Cs: Y: Yb: F ratio was set at 2.5:2.5:1:1:8.
Synthesis of nanorod composites with different halides.The cesium-rare earth-fluoride nanorod hybrid nanostructures were synthesized by the same injection procedure.In a typical experiment, PbX2 (X=Cl, Br and I, 0.2 mmol), OA (1.0 mL), OAm (1.0 mL), and ODE (10 mL) were added to a two-neck round-bottomed flask.The reaction mixture was heated to 100 °C with vigorous stirring under vacuum for 30 min.Afterward, the flask was purged with N2 and subjected to vacuum again to remove any remaining moisture residue by applying N2 and vacuum several times.The temperature was then increased to 180 °C until the PbX2 precursors were completely dissolved.At this point, a quick injection of the cyclohexane precursor solution (1 mL) was added to the mixture.After 30 min of reaction, the flask was transferred to an ice bath.The composite was obtained by centrifugation at 13000 rpm for 10 minutes, then washed twice with methyl acetate and stored in 4 mL of cyclohexane.
Synthesis of Cs-β-CD-MOFs.A modified methanol vapor diffusion method was used to grow Cs-β-CD-MOFs crystals [S3] .First, β-cyclodextrin (0.1418 g, 0.125 mmol) and CsOH•H2O (0.1894 g, 1 mmol) were dissolved in water (5 mL).This solution was then filtered and placed in a small container, along with 0.5 mL of methanol.The small container was further stored inside a larger container containing 60 mL of methanol.Over a 12-h period at 50 °C, methanol vapor diffused into the water solution, facilitating the growth of Cs-β-CD-MOFs crystals.The resulting crystals were collected by adding a 5 mL methanol solution containing 60 mg of PEG20000 and allowing it to incubate overnight.The obtained products were then washed with ethanol and dichloromethane and dried at 50 °C under vacuum.
The reaction mixture was heated to 100 °C with vigorous stirring.Afterward, the synthesized Cs-β-CD-MOFs were added to the mixture.After 10 min of reaction, a bright Cs-β-CD-MOFs/CsPbBr3 composite was obtained and collected by filtration.

Figure S3 .
Figure S3.Transmission electron microscopy images of the as-prepared CsYb2F7/CsPbBr3 at different reaction times (from 10 s to 1 h), showing a persistent size distribution of about 10 nm in diameter.

Figure S6 .
Figure S6.Raman spectra of host samples and CsYb2F7/CsPbBr3 nanostructures, which were prepared with varying ratios of Cs to Pb, indicating that the hybrid nanostructures exhibit a distinctive Raman peak at approximately 70 cm -1 , similar to that of CsPbBr3 QDs.

Figure
Figure S7.X-ray diffraction patterns of the sub-10 nm nanoplatform and the prepared CsYb2F7/CsPbBr3 composites.

Figure S11 .
Figure S11.TEM images of (A) the cesium-rare earth-fluoride nanorods host and (B) the corresponding CsPbBr3 hybrid nanostructures.

Figure S13 .
Figure S13.X-ray diffraction patterns of the cesium-rare earth-fluoride nanorod platform and the corresponding hybrid nanostructures.

Figure S16 .
Figure S16.The quantum yield of the as-prepared CsYb2F7/CsPbBr3 nanostructures under 365 nm excitation.

Table S2 .
The fitting parameters of Yb-L3 edge EXAFS.