Red Emission from Copper-Vacancy Color Centers in Zinc Sulfide Colloidal Nanocrystals

Area of Science:

• Materials Science
• Quantum Information Science
• Solid-State Physics

Background:

• Copper-doped zinc sulfide (ZnS:Cu) exhibits down-conversion luminescence, with visible red, green, and blue emissions (R-Cu, G-Cu, B-Cu).
• Point defects in ZnS:Cu create localized electronic states, enabling sub-bandgap emission and making it suitable for phosphors and quantum information science (single-photon sources, spin qubits).
• Colloidal nanocrystals (NCs) of ZnS:Cu offer tunable properties for biosensing and optoelectronics, serving as ideal hosts for quantum defects.

Purpose of the Study:

• To present a method for synthesizing colloidal ZnS:Cu NCs that primarily emit red light (R-Cu).
• To investigate the origin of R-Cu emission, proposed to stem from the Cu_Zn-V_S complex, a quantum defect.
• To understand the temperature- and time-dependent optical properties and emission dynamics of these R-Cu emitting ZnS:Cu NCs.

Main Methods:

• Synthesis of colloidal ZnS:Cu nanocrystals with a focus on achieving primary R-Cu emission.
• First-principles calculations to confirm the thermodynamic stability and electronic structure of the proposed Cu_Zn-V_S defect.
• Temperature- (19 K to 290 K) and time-dependent optical measurements to analyze luminescence properties and emission dynamics.

Main Results:

• Successful synthesis of colloidal ZnS:Cu NCs exhibiting predominantly R-Cu emission, attributed to the Cu_Zn-V_S complex.
• First-principles calculations validated the stability and electronic structure of the Cu_Zn-V_S defect.
• Observed blueshifting luminescence and an anomalous intensity plateau with increasing temperature, modeled by thermally activated coupling between intrabandgap states.

Conclusions:

• The study provides a controlled synthesis route for R-Cu emitting ZnS:Cu NCs, crucial for quantum defect applications.
• The findings elucidate the emission dynamics of R-Cu, supporting the Cu_Zn-V_S complex as a promising quantum defect in ZnS.
• This work facilitates the development of ZnS-based quantum point defects for quantum information science and related technologies.