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

Abstract

Copper-doped zinc sulfide (ZnS:Cu) exhibits down-conversion luminescence in the UV, visible, and IR regions of the electromagnetic spectrum; the visible red, green, and blue emission is referred to as R-Cu, G-Cu, and B-Cu, respectively. The sub-bandgap emission arises from optical transitions between localized electronic states created by point defects, making ZnS:Cu a prolific phosphor material and an intriguing candidate material for quantum information science, where point defects excel as single-photon sources and spin qubits. Colloidal nanocrystals (NCs) of ZnS:Cu are particularly interesting as hosts for the creation, isolation, and measurement of quantum defects, since their size, composition, and surface chemistry can be precisely tailored for biosensing and optoelectronic applications. Here, we present a method for synthesizing colloidal ZnS:Cu NCs that emit primarily R-Cu, which has been proposed to arise from the CuZn-VS complex, an impurity-vacancy point defect structure analogous to well-known quantum defects in other materials that produce favorable optical and spin dynamics. First-principles calculations confirm the thermodynamic stability and electronic structure of CuZn-VS. Temperature- and time-dependent optical properties of ZnS:Cu NCs show blueshifting luminescence and an anomalous plateau in the intensity dependence as temperature is increased from 19 K to 290 K, for which we propose an empirical dynamical model based on thermally activated coupling between two manifolds of states inside the ZnS bandgap. Understanding of R-Cu emission dynamics, combined with a controlled synthesis method for obtaining R-Cu centers in colloidal NC hosts, will greatly facilitate the development of CuZn-VS and related complexes as quantum point defects in ZnS.

Molecular insight into intrinsic-trap-mediated emission from atomically precise copper-based chalcogenide models

“…NTO is an occasional phenomenon, which has been observed previously in defect emission. 36 It is generally been explained by thermally activated carrier transfer from lower- to higher-energy emissive electron traps. Fig.…”

Moisture-Induced Degradation of Quantum-Sized Semiconductor Nanocrystals through Amorphous Intermediates

“…A mechanistic understanding of the degradation of semiconductor nanocrystals, with focusing on structure transformation pathways during nanocrystal deformation, can facilitate the design and synthesis of highly stable nanocrystals with robust structures. In addition, it is important to investigate structural deformation of nanocrystals in atomic-scale spatial resolution because minor variations in their atomic arrangements can significantly change their properties. − However, previous studies have typically focused on studying changes in the photophysical properties of semiconductor nanocrystals during the degradation process without tracing the real-time structural changes. , …”