Using the Photoluminescence Color Change in Cesium Lead Iodide Nanoparticles to Monitor the Kinetics of an External Organohalide Chemical Reaction by Halide Exchange.

In this work, we demonstrate a photoluminescence-based method to monitor the kinetics of an organohalide reaction by way of detecting released bromide ions at cesium lead halide nanoparticles. Small aliquots of the reaction are added to an assay with known concentrations of CsPbI3, and the resulting Br-to-I halide exchange (HE) results in rapid and sensitive wavelength blueshifts (Δλ) due to CsPbBrxI3-x intermediate concentrations, the wavelengths of which are proportional to concentrations. An assay response factor, C, relates Δλ to Br- concentration as a function of CsPbI3 concentration. The observed kinetics, as well as calculated rate constants, equilibrium, and activation energy of the solvolysis reaction tested correspond closely to synthetic literature values, validating the assay. Factors that influence the sensitivity and performance of the assay, such as CsPbI3 size, morphology, and concentration, are discussed.

Tailoring CsPbBr3 Growth via Non-Polar Solvent Choice and Heating Methods.

This study describes an investigation of the role of non-polar solvents on the growth of cesium lead halide (CsPbX3 X = Br and I) nanoplatelets. We employed two solvents, benzyl ether (BE) and 1-octadecene (ODE), as well as two nucleation and growth mechanisms, one-pot, facilitated by microwave irradiation (MWI)-based heating, and hot-injection, using convection. Using BE and MWI, large mesoscale CsPbBr3 nanoplatelets were produced, whereas use of ODE produced small crystallites. Differences between the products were observed by optical spectroscopies, which showed first band edge absorptions consistent with thicknesses of ∼9 nm [∼15 monolayer (ML)] for the BE-CsPbBr3 and ∼5 nm (∼9 ML) for ODE-CsPbBr3. Both products had orthorhombic crystal structures, with the BE-CsPbBr3 revealing significant preferred orientation diffraction signals consistent with the asymmetric and two-dimensional platelet morphology. The differences in the final morphology were also observed for products formed via hot injection, with BE-CsPbBr3 showing thinner square platelets with thicknesses of ∼2 ML and ODE-CsPbBr3 showing similar morphologies and small crystallite sizes. To understand the role solvent plays in crystal growth, we studied lead plumbate precursor (PbBrn2-n) formation in both solvents, as well as solvent plus ligand solutions. The findings suggest that BE dissolves PbBr2 salts to a higher degree than ODE, and that this BE to precursor affinity persists during growth.