Colloidal copper phosphide (Cu 3−x P) nanocrystals are attractive materials because of their ability to support excess delocalized holes, leading to localized surface plasmon resonance (LSPR) absorption in the near-IR. We present a one-pot, colloidal synthesis of Cu 3−x P nanoplatelets from copper halide salts and tris(diethylamino)phosphine [P(NEt 2 ) 3 ] in the presence of oleylamine (OAm) and trioctylamine. Mass spectrometry and nuclear magnetic resonance spectroscopy reveal that the formation of Cu 3−x P is accompanied by an aminophosphonium byproduct, suggesting that Cu 3−x P synthesis proceeds through a mechanism similar to that of other metal phosphide nanocrystals. The in situ copper−phosphorus precursor is identified by mass spectrometry, providing an insight into the prenucleation chemistry that was not possible in other aminophosphine-based metal phosphide syntheses. The final nanocrystal ensemble can be tuned by varying the precursor ratios (OAm/P(NEt 2 ) 3 or P(NEt 2 ) 3 /CuCl), copper halide (CuCl vs CuBr), or temperature, maintaining low polydispersity over a wide parameter space. By modulating the reactivity, the syntheses presented herein can be used to access nanocrystals with lateral sizes of 6.1−23 nm with LSPR energies of 709−861 meV. Overall, this synthesis presents a platform for systematic mechanistic investigations of the chemical processes underlying Cu 3−x P nanocrystal formation. The low polydispersity, size-and LSPR-tunability, and colloidal stability make these nanocrystals promising candidates for further investigations into factors governing the LSPR energy in Cu 3−x P nanomaterials.

EuS and related ferromagnetic semiconductors have long been model materials for spintronic device functionality because of their ability to generate highly spin-polarized electrical currents. Although the low Curie temperature (T C ) of EuS limits practical implementation of such devices, the T C of bulk EuS can be raised by n-doping with trivalent impurity ions such as Gd 3+ . Such doping introduces free conduction-band electrons that strengthen the magnetic exchange, raising T C . In EuS nanostructures, analogous doping has also been explored. Paradoxically, such nanostructures also have a tendency to show native Eu 3+ ″impurities″. It is unclear what impact these impurities or non-native trivalent impurities may have on magnetic ordering. Here, we report spectroscopic, magnetic, and redox-chemical studies aimed at assessing the role of trivalent impurities in the ferromagnetism of colloidal EuS nanocrystals. Combining postsynthetic redox chemistry with optical and electron paramagnetic resonance (EPR) spectroscopic measurements, we show that reduction of native Eu 3+ impurities to Eu 2+ increases the overall magnetization below T C and simultaneously decreases T C by ∼7%, with no evidence of free conduction-band electrons at any stage. The data suggest that some of the newly formed Eu 2+ ions participate in the ferromagnetic ordering despite having a different coordination environment than the Eu 2+ ions of the as-synthesized nanocrystals (e.g., surface vs core Eu 2+ ), and we hypothesize that surface-localized charge compensation and the very negative EuS conduction-band-edge potential prevent n-doping in these nanocrystals. These results demonstrate postsynthetic chemical modulation of the ferromagnetism of colloidal EuS nanocrystals and additionally provide a well-controlled assessment of the contribution of trivalent impurity ions to this magnetism.

The influence of ions of heavy metals Cu 2+ , Pb 2+ , Co 2+ , Ni 2+ , Cd 2+ , Ag + , and ions, which are common components of natural and drinking water (Na + , K + , Ca 2+ , Mg 2+) on the photoluminescence of nanocrystals AgInS 2 with ZnS shell (NCs AgInS 2 /ZnS) was investigated. Experimental data obtained confirm the assumption on the relationship between the level of quenching of NCs AgInS 2 / ZnS photoluminescence under exposure to the heavy metal ions and solubility constant of their sulfides. The concentration of ions Cu 2+ , which caused a statistically significant quenching of NCs AgInS 2 /ZnS photoluminescence, is below their maximum allowable concentration in natural waters. It opens up prospects of NCs AgInS 2 /ZnS for developing methods for environmental monitoring of the copper ions.

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