Inorganic Ligand Triggered Transformation from Cs₄PbBr₆ Nanocrystals to Blue-Emitting CsPbBr₃ Nanoplatelets

Abstract

Blue-emitting perovskite nanoplates (NPLs) have been widely investigated for display application. However, the traditional synthetic techniques for high-quality perovskite NPLs are still limited due to their rapid crystallization rate. Here, we developed an inorganic ligand (NOBF4) mediated transformation strategy to obtain blue-emitting CsPbBr3 NPLs. The transformation process was based on the dissolution–recrystallization in a nonpolar environment, involving the dissociation of Cs4PbBr6 NCs to Pb ions, which then reformed PbBr6 4– octahedrons and finally formed two monolayer NPLs with pure blue-emission (line width ∼12 nm). The whole transformation process was clearly detected, and during the process the reorganization of organic ligands tuned by NO+ played a crucial role in the formation of NPLs. This work provides an effective strategy for obtaining pure blue-emitting NPLs and builds a platform for exploring the mechanism for the anisotropic growth of perovskite crystals.

Chemical transformation mechanism for blue-to-green emitting CsPbBr3 nanocrystals

“…The band around 1710 cm −1 was assigned to the CvO stretching vibration of OA. 31 These results indicated that a substantial number of ligands bound to the Cs 4 PbBr 6 NCs surface were effectively eliminated since the nitrite ion in the additive was reactive towards amine species. Unlike the untreated sample, a new emerging peak at 1084 cm −1 , was identified to the BF 4 − anion.…”

“…26,37 This phenomenon of BF 4 − anions adsorption on the surface is common in surface modification of various colloidal nanoparticles, but it was not observed in our previous studies on 2 ML blue-emitting NPLs. 31 Moreover, no signal attributable to NO + was detectable in the region from 2100 to 2200 cm −1 . 26,38 Therefore, we hypothesize that the surface capping properties of the sample treated with more additives were distinct from those reported previously for 2 ML NPLs.…”

“…1h and i), which may be due to the etching effect of the nitrite ion. 26,31 From Fig. 3b and d, it was found that the quantum yield (QY) of the conversion products increases dramatically within four hours and was gradually stabilized at approximately 80%.…”

“…It was worth noting that the multiple strong absorption and emission bands observed in the evolutionary spectra were similar to those from the previous reports, which were identified as the characteristic peaks of the 0D Cs 4 PbBr 6 , Pb-Br intermediates, low-dimensional CsPbBr 3 NPLs (2 ML and 3 ML) and 3D CsPbBr 3 NCs. 31,32 Hence, it is reasonable to speculate that these intermediate processes were closely related to the final precipitation of the brightly green-emitting MHP-NCs. In order to clarify the chemical transformation mechanism for this blue-to-green emitting perovskite analogous, we recorded the time-dependent absorption and photoluminescence (PL) spectra in detail over a long period of time.…”

“…Very recently, we have reported an inorganic ligand (NOBF 4 ) mediated transform-ation strategy from non-luminescent Cs 4 PbBr 6 NCs to the precisely controllable blue-emitting CsPbBr 3 NPLs with a twomonolayer (2 ML) unit cell. 31 This treatment revealed a dynamic dissolution-recrystallization process along with the appearance of deep-blue light (444 nm), where the nitrite ion (NO + ) rendered the intrinsic Cs 4 PbBr 6 NCs unstable by stripping the organic species from their surface. Meanwhile, the NO + -induced acidic environment can protonate OAm into OAm + cations, thus enabling the slow precipitation of the precisely controllable 2 ML CsPbBr 3 NPLs in the non-polar solvent (several hours).…”