Impact of acid–amine equilibrium for triggering the formation of CsPbBr3 platelets and subsequent long-range self-assembly as a function of acid concentration is reported. The study was performed by treating Cs precursor followed by oleic acid to the ongoing process of L2PbBr4 layered perovskites formation at room temperature, and this led to the thinnest possible platelets of CsPbBr3 with one atomic layer of Cs insertion. These platelets form self-assembly in the micrometer range, and this ordering was tuned as a function of oleic acid concentration and reaction time. With evidence obtained from in situ live monitoring by optical microscopy of these assemblies during the ongoing reaction in solution and analyzing the collected samples ex situ by electron microscopy, it was established that these long-range 1D organizations of platelets took place in solution. Details of the insights of the formation, self-assembly, and impact of different reaction parameters in the formation of these platelets are investigated and reported in this Letter.

A self-digestive process leading to strong blue-emitting nearly monodisperse CsPbBr3 quantum rods in wide-area 2D self-assembly is reported. These are facilitated by aging the presynthesized ultrathin CsPbBr3 nanowires dispersed in appropriate solvent. The time frame was unusual, and the reaction continued for 3–5 days to observe such intriguing patterns. Interfering species such as unreacted precursors, amines, or acids were intentionally minimized with repeated purification for triggering this self-digestive process, which led to the quantum-confined nanorods. Carrying out this reaction in different solvents and in the presence of various additives, the reaction mechanism for such a slow process is established. These nanorods and their large-area self-assembly remained unique in perovskite nanostructures, and the chemistry of the slow process also provided new fundamental insights of the crystallization process of nanorods and their self-assembly.

We have reported earlier that silica nanodisks are formed by the reverse micelle solÀgel (RMSG) method, from ternary Aerosol OT (AOT)/nheptane/water mixtures. These nanodisks are formed from the ternary mixtures with higher water contents and containing a significant concentration of FeCl 3 . Such mixtures undergo a phase separation. The present work seeks to identify the origin of these nanodisks. They are found to be produced from the lower, water-rich layer and not from the upper, oil-rich layer or from the interfacial region. Further, upon increasing the water content by a factor of 10, the phase separation is achieved in the absence of the salt as well. In the next step, the naodisks are observed to form from concentrated aqueous AOT solutions, with no involvement of organic solvents. Polarized optical microscopy and infrared studies reveal the occurrence of lamellar AOT micelles in these media. These micelles act as the templates for the nanodisks. This phenomenon paves the way for the soft chemical preparation of nanodisks in the aqueous phase, without the need of using salt or organic solvents.

Postsynthesis halide treatment can brighten perovskite nanocrystals. While this has been recently explored for undoped nanocrystals having only the exciton emission, herein, the impact of halide-enriched and -deficient environments was studied for dual-emitting Mn­(II)-doped CsPbBr3 nanorods. This was performed by adopting a self-regulated approach where the nanorod solution reversibly switched the color brightness from blue to orange and vice versa by dilution and evaporation, respectively. With control experiments, it was established that the color switching was not due to a change in the rate of the exciton energy transfer from host to dopant energy states; rather, it was related to self-regulated fulfilling and again creating halide vacancies observed with variation of nanorod concentration. Being that the halide vacancy was established as one of the key factors for controlling the brightness of these nanocrystals, this reversible switching in doped CsPbBr3 adds new fundamental insight into controlling the photoluminescence of these emerging nanocrystals.

Attenuated total reflection infrared (ATR-IR) spectroscopy is used to study the adsorption of gold and silver nanoparticles and the layer-by-layer (LBL) growth of polyelectrolyte multilayers on a Ge ATR crystal. The Ge ATR crystal is first functionalized using positively charged polyelectrolyte poly(allylamine hydrochloride) (PAH). Then citrate-stabilized gold or silver nanoparticles are adsorbed onto the modified Ge ATR crystal. When gold or silver nanoparticles are adsorbed, a drastic increase of the water signal is observed which is attributed to an enhanced absorption of IR radiation near the nanoparticles. This enhancement was much larger for the silver nanoparticles (SNP). On top of the nanoparticles multilayers of oppositely charged polyelectrolytes PAH and poly(sodium 4-styrenesulfonate) (PSS) were deposited, which allowed to study the enhancement of the IR signals as a function of the distance from the nanoparticles. Furthermore, adsorption of a thiol, N-acetyl-L-cysteine, on the nanoparticles confirmed the enhancement. In the case of SNP an absorbance signal of about 15% was observed, which is a factor of about 40 times larger compared to typical signals measure without nanoparticles.