Cherie R Kagan Research Group

@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://arxiv.org/abs/2301.04223},

year  = {2023},

date = {2023-01-13},

urldate = {2023-01-13},

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 Cu_{Zn}-V_{S} 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 Cu_{Zn}-V_{S}. Temperature- and time-dependent optical properties of ZnS:Cu NCs show blueshifting luminescence and a non-monotonic 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 Cu_{Zn}-V_{S} and related complexes as quantum point defects in ZnS.},

keywords = {},

pubstate = {forthcoming},

tppubtype = {article}

}

@article{Neuhaus2023,

title = {Frequency Stabilization and Optically Tunable Lasing in Colloidal Quantum Dot Superparticles},

author = {Steven J. Neuhaus and Emanuele Marino and Christopher B. Murray and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/full/10.1021/acs.nanolett.2c04498},

doi = {10.1021/acs.nanolett.2c04498},

year  = {2023},

date = {2023-01-05},

urldate = {2023-01-05},

journal = {Nano Letters},

volume = {23},

issue = {2},

pages = {645–651},

abstract = {Self-assembled superparticles composed of colloidal quantum dots establish microsphere cavities that support optically pumped lasing from whispering gallery modes. Here, we report on the time- and excitation fluence-dependent lasing properties of CdSe/CdS quantum dot superparticles. Spectra collected under constant photoexcitation reveal that the lasing modes are not temporally stable but instead blue-shift by more than 30 meV over 15 min. To counter this effect, we establish a high-fluence light-soaking protocol that reduces this blue-shift by more than an order of magnitude to 1.7 ± 0.5 meV, with champion superparticles displaying mode blue-shifts of <0.5 meV. Increasing the pump fluence allows for optically controlled, reversible, color-tunable red-to-green lasing. Combining these two paradigms suggests that quantum dot superparticles could serve in applications as low-cost, robust, solution-processable, tunable microlasers.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Parra2022,

title = {Large Exciton Polaron Formation in 2D Hybrid Perovskites via Time-Resolved Photoluminescence},

author = {Sebastian Hurtado Parra and Daniel B. Straus and Bryan T. Fichera and Natasha Iotov and Cherie R. Kagan and James M. Kikkawa},

url = {https://pubs.acs.org/doi/full/10.1021/acsnano.2c09256},

doi = {10.1021/acsnano.2c09256},

year  = {2022},

date = {2022-12-15},

journal = {ACS Nano},

volume = {16},

issue = {12},

pages = {21259–21265},

abstract = {We find evidence for the formation and relaxation of large exciton polarons in 2D organic–inorganic hybrid perovskites. Using ps-scale time-resolved photoluminescence within the phenethylammonium lead iodide family of compounds, we identify a red shifting of emission that we associate with exciton polaron formation time scales of 3–10 ps. Atomic substitutions of the phenethylammonium cation allow local control over the structure of the inorganic lattice, and we show that the structural differences among materials strongly influence the exciton polaron relaxation process, revealing a polaron binding energy that grows larger (up to 15 meV) in more strongly distorted compounds.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Nguyen2022,

title = {Deterministic Quantum Light Arrays from Giant Silica-Shelled Quantum Dots},

author = {Hao A. Nguyen and David Sharp and Johannes E. Fröch, and Yi-Yu Cai and Shenwei Wu and Madison Monahan and Christopher Munley and Arnab Manna and Arka Majumdar and Cherie R. Kagan and Brandi M. Cossairt*},

url = {https://pubs.acs.org/doi/full/10.1021/acsami.2c18475},

doi = {10.1021/acsami.2c18475},

year  = {2022},

date = {2022-12-12},

urldate = {2022-12-12},

journal = {ACS Applied Materials & Interfaces},

volume = {15},

issue = {3},

pages = {4294–4302},

abstract = {Colloidal quantum dots (QDs) are promising candidates for single-photon sources with applications in photonic quantum information technologies. Developing practical photonic quantum devices with colloidal materials, however, requires scalable deterministic placement of stable single QD emitters. In this work, we describe a method to exploit QD size to facilitate deterministic positioning of single QDs into large arrays while maintaining their photostability and single-photon emission properties. CdSe/CdS core/shell QDs were encapsulated in silica to both increase their physical size without perturbing their quantum-confined emission and enhance their photostability. These giant QDs were then precisely positioned into ordered arrays using template-assisted self-assembly with a 75% yield for single QDs. We show that the QDs before and after assembly exhibit antibunching behavior at room temperature and their optical properties are retained after an extended period of time. Together, this bottom-up synthetic approach via silica shelling and the robust template-assisted self-assembly offer a unique strategy to produce scalable quantum photonics platforms using colloidal QDs as single-photon emitters.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Zhao2022,

title = {Engineering the Surface Chemistry of Colloidal InP Quantum Dots for Charge Transport},

author = {Tianshuo Zhao and Qinghua Zhao and Jaeyoung Lee and Shengsong Yang and Han Wang and Ming-Yuan Chuang and Yulian He and Sarah M. Thompson and Guannan Liu and Nuri Oh and Christopher B. Murray and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/full/10.1021/acs.chemmater.2c01840},

doi = {10.1021/acs.chemmater.2c01840},

year  = {2022},

date = {2022-09-07},

urldate = {2022-09-07},

journal = {Chemistry of Materials},

volume = {34},

issue = {18},

pages = {8306–8315},

abstract = {Colloidal InP quantum dots (QDs) have emerged as potential candidates for constructing nontoxic QD-based optoelectronic devices. However, charge transport in InP QD thin-film assemblies has been limitedly explored. Herein, we report the synthesis of ∼8 nm edge length (∼6.5 nm in height), tetrahedral InP QDs and study charge transport in thin films using the platform of the field-effect transistor (FET). We design a hybrid ligand-exchange strategy that combines solution-based exchange with S2– and solid-state exchange with N3– to enhance interdot coupling and control the n-doping of InP QD films. Further modifying the QD surface with thin, thermally evaporated Se overlayers yields FETs with an average electron mobility of 0.45 cm2 V–1 s–1, ∼10 times that of previously reported devices, and a higher on–off current ratio of 103–104. Analytical measurements suggest lower trap-state densities and longer carrier lifetimes in the Se-modified InP QD films, giving rise to a four-time longer carrier diffusion length.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}