Room-Temperature Quantum Emission from Cu-V Defects in ZnS:Cu Colloidal Nanocrystals.

We report room-temperature observations of Cu-V quantum emitters in individual ZnS:Cu nanocrystals (NCs). Using time-gated imaging, we isolate the distinct ∼3-μs-long, red photoluminescence (PL) emission of Cu-V defects, enabling their precise identification and statistical characterization. The emitters exhibit distinct blinking and photon antibunching, consistent with individual NCs containing two to four Cu-V defects. The quantum emitters' PL spectra show a pronounced blue shift compared to NC dispersions, likely due to photochemical and charging effects. Emission polarization measurements of quantum emitters are consistent with a σ-character optical dipole transition and the symmetry of the Cu-V defect. These observations motivate further investigation of Cu-V defects in ZnS NCs for use in quantum technologies.