@article{Thompson2023,
title = {Red Emission from Copper-Vacancy Color Centers in Zinc Sulfide Colloidal Nanocrystals},
author = {Sarah M. Thompson and Cüneyt Şahin and Shengsong Yang and Michael E. Flatté and Christopher B. Murray and Lee C. Bassett and Cherie R. Kagan},
url = {https://pubs.acs.org/doi/full/10.1021/acsnano.3c00191
https://arxiv.org/abs/2301.04223},
doi = {10.1021/acsnano.3c00191},
year = {2023},
date = {2023-03-09},
journal = {ACS Nano},
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 bio-sensing and opto-electronic 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.},
keywords = {colloidal nanocrystals, color centers, First-principles calculations, impurity doping, Materials Physics, nanocrystals, photoluminescence, quantum dots, transition metals, ZnS},
pubstate = {published},
tppubtype = {article}
}

@article{Patel2022,
title = {Probing the Optical Dynamics of Quantum Emitters in Hexagonal Boron Nitride},
author = {Raj N. Patel and David A. Hopper and Jordan A. Gusdorff and Mark E. Turiansky and Tzu-Yung Huang and Rebecca E. K. Fishman and Benjamin Porat and Chris G. Van de Walle and Lee C. Bassett},
url = {https://journals.aps.org/prxquantum/abstract/10.1103/PRXQuantum.3.030331},
doi = {10.1103/PRXQuantum.3.030331},
year = {2022},
date = {2022-09-01},
journal = {PRX Quantum},
volume = {3},
number = {3},
pages = {030331},
abstract = {Hexagonal boron nitride is a van der Waals material that hosts visible-wavelength quantum emitters at room temperature. However, experimental identification of the quantum emitters’ electronic structure is lacking, and key details of their charge and spin properties remain unknown. Here, we probe the optical dynamics of quantum emitters in hexagonal boron nitride using photon emission correlation spectroscopy. Several quantum emitters exhibit ideal single-photon emission with noise-limited photon antibunching, g(2)(0)=0. The photoluminescence emission lineshapes are consistent with individual vibronic transitions. However, polarization-resolved excitation and emission suggests the role of multiple optical transitions, and photon emission correlation spectroscopy reveals complicated optical dynamics associated with excitation and relaxation through multiple electronic excited states. We compare the experimental results to quantitative optical dynamics simulations, develop electronic structure models that are consistent with the observations, and discuss the results in the context of ab initio theoretical calculations.},
keywords = {2-dimensional systems, color centers, photon emission correlation spectroscopy, photon statistics, point defects, quantum optics, single-photon sources},
pubstate = {published},
tppubtype = {article}
}