Lead halide perovskite materials have attracted significant attention in the context of photovoltaics and other optoelectronic applications, and recently, research efforts have been directed to nanostructured lead halide perovskites. Collodial nanocrystals (NCs) of cesium lead halides (CsPbX3, X = Cl, Br, I) exhibit bright photoluminescence, with emission tunable over the entire visible spectral region. However, previous studies on CsPbX3 NCs did not address key aspects of their chemistry and photophysics such as surface chemistry and quantitative light absorption. Here, we elaborate on the synthesis of CsPbBr3 NCs and their surface chemistry. In addition, the intrinsic absorption coefficient was determined experimentally by combining elemental analysis with accurate optical absorption measurements. (1)H solution nuclear magnetic resonance spectroscopy was used to characterize sample purity, elucidate the surface chemistry, and evaluate the influence of purification methods on the surface composition. We find that ligand binding to the NC surface is highly dynamic, and therefore, ligands are easily lost during the isolation and purification procedures. However, when a small amount of both oleic acid and oleylamine is added, the NCs can be purified, maintaining optical, colloidal, and material integrity. In addition, we find that a high amine content in the ligand shell increases the quantum yield due to the improved binding of the carboxylic acid.

ABSTRACT:We present synthesis protocols, based on indium halide and aminophosphine precusors, that allow for the economic, up-scaled production of InP Quantum Dots (QDs). The reactions attain a close to full yield conversion -with respect to the indium precursor -and we demonstrate that size tuning at full chemical yield is possible by straightforward adaptations of the reaction mixture. In addition, we present ZnS and ZnSe shell growth procedures that lead to InP/ZnS and InP/ZnSe core/shell QDs that emit from 510 nm to 630 nm with an emission linewidth between 46 nm and 63 nm. This synthetic method is an important step towards performing Cd-free QDs, and it could help the transfer of colloidal QDs from the academic field to product applications.Colloidal QDs have rapidly evolved from a lab-scale invention of academic interest to new, useful building blocks widely applied in various fields of nanoscience and technology research.1 This is mainly due to high precision, synthetic schemes developed for cadmium chalcogenide QDs, 2 which have made available monodisperse QD ensembles that preserve the unique, size-tunable optoelectronic properties of individual QDs. The restrictions several countries have imposed on the use of cadmium however question the long term feasibility of product applications relying on cadmium-chalcogenide based QDs, hence the quest for Cd-free alternatives.3 This search has mainly focused on CuInS2 and InP where, similar to CdSe, size quantization enables the bandgap transition to be tuned across most of the visible spectrum. Especially InP QDs combine a reduced toxicity with emission characteristics close to those of CdSe-based QDs. 4 The strategies developed to produce colloidal InP QDs can be roughly divided in two groups. The first group includes high reactivity P(-III) precursors such as tris(trimethylsilyl)phosphine [(TMS)3P] 5-7 or phosphine [PH3], 8 and the second group utilizes lower reactivity P(0) and P(+III) precursors such as trioctylphosphine (TOP), 9 P4, 10 or PCl3. 11 Based on size dispersion -a key parameter to be minimized for most QD-based applications -P(-III) precursors give the best results. In particular, (TMS)3P has been the most commonly used phosphorous precursor, where optimized protocols yield emission lines with a full width at half maximum (FWHM) of 40-60 nm.12 Unfortunately, (TMS)3P is a costly and pyrophoric precursor that tends to decompose and forms lethally toxic PH3 in contact with air. This renders upscaled (TMS)3P-based InP production elusive and may explain why InP QDs are far less studied than CdSe QDs. Opposite from the high reactivity P(-III) precursors, protocols to synthesize InP QDs with low reactivity precursors yield QDs with too large a size-dispersion for most of the potential applications.Recently, an innovative and potentially efficient alternative to make InP QDs has been published by Song et al.. 13 These authors use tris(dimethylamino)phosphine [(DMA)3P] as a phosphorous precursor, which can be classified as a low-reactive P(+III) precurso...

Nanocrystal-ligand interactions and ligand exchange processes are usually described by a uniform distribution of equal binding sites. Here, we analyze this assumption by a quantitative study of the displacement of Z-type cadmium oleate ligands from CdSe nanocrystals by addition of L-type ligands. First, we determined the stoichiometry of the displacement reaction by analyzing the equilibrium upon dilution using solution nuclear magnetic resonance spectroscopy. We found that 1 equivalent of tetramethylethylene-1,2-diamine (TMEDA) or two equivalents of n-butylamine or benzylamine bind the displaced cadmium oleate. We only reached a comprehensive description of the displacement isotherm by including two types of