Synthesis and Characterization of Zintl-Phase BaCd₂P₂ Quantum Dots for Optoelectronic Applications

We demonstrate the growth of size-controlled, high optical quality Zintl-phase BaCd₂P₂ colloidal quantum dots (QDs), an emerging semiconductor absorbing/emitting in the red and predicted to have favorable defect chemistry. The QDs are grown via hot injection of a phosphorus precursor into a solution of solubilized Ba and Cd precursors. The absorbance and photoluminescence (PL) are tunable via growth temperature and show a bandgap ranging from 1.47 to 1.81 eV, depending on the size, which ranges from 3 to 9 nm based on electron microscopy. Selected area electron diffraction is used to determine that the BaCd₂P₂ QDs crystallize in the P3̅m1 space group, same as the bulk material. Raman spectroscopy, powder X-ray diffraction, and X-ray fluorescence studies further confirm that BaCd₂P₂ QDs match those of the crystalline phase bulk material. The high optoelectronic quality is assessed by quantification of long-lived photoexcited carriers (∼160 ns average weighting), as determined by time-resolved PL spectroscopy, and bright red visible emission (∼21% PL quantum yield) despite no complex surface passivation. Furthermore, a demonstration of thin-film fabrication is shown via a solid state ligand exchange protocol. This synthetic protocol enables researchers to explore and utilize BaCd₂P₂ Zintl-phase QDs, as well as adjacent compositions, for a variety of optoelectronic applications enabled by their semiconducting properties.