Stanford Advisors

All Publications

  • A room-temperature polarization-sensitive CMOS terahertz camera based on quantum-dot-enhanced terahertz-to-visible photon upconversion. Nature nanotechnology Shi, J., Yoo, D., Vidal-Codina, F., Baik, C. W., Cho, K. S., Nguyen, N. C., Utzat, H., Han, J., Lindenberg, A. M., Bulović, V., Bawendi, M. G., Peraire, J., Oh, S. H., Nelson, K. A. 2022


    Detection of terahertz (THz) radiation has many potential applications, but presently available detectors are limited in many aspects of their performance, including sensitivity, speed, bandwidth and operating temperature. Most do not allow the characterization of THz polarization states. Recent observation of THz-driven luminescence in quantum dots offers a possible detection mechanism via field-driven interdot charge transfer. We demonstrate a room-temperature complementary metal-oxide-semiconductor THz camera and polarimeter based on quantum-dot-enhanced THz-to-visible upconversion mechanism with optimized luminophore geometries and fabrication designs. Besides broadband and fast responses, the nanoslit-based sensor can detect THz pulses with peak fields as low as 10 kV cm-1. A related coaxial nanoaperture-type device shows a to-date-unexplored capability to simultaneously record the THz polarization state and field strength with similar sensitivity.

    View details for DOI 10.1038/s41565-022-01243-9

    View details for PubMedID 36329270

  • Terahertz Field-Induced Reemergence of Quenched Photoluminescence in Quantum Dots NANO LETTERS Shi, J., Gao, F. Y., Zhang, Z., Utzat, H., Barotov, U., Farahvash, A., Han, J., Deschamps, J., Baik, C., Cho, K., Bulovic, V., Willard, A. P., Baldini, E., Gedik, N., Bawendi, M. G., Nelson, K. A. 2022; 22 (4): 1718-1725


    The continuous and concerted development of colloidal quantum dot light-emitting diodes over the past two decades has established them as a bedrock technology for the next generation of displays. However, a fundamental issue that limits the performance of these devices is the quenching of photoluminescence due to excess charges from conductive charge transport layers. Although device designs have leveraged various workarounds, doing so often comes at the cost of limiting efficient charge injection. Here we demonstrate that high-field terahertz (THz) pulses can dramatically brighten quenched QDs on metallic surfaces, an effect that persists for minutes after THz irradiation. This phenomenon is attributed to the ability of the THz field to remove excess charges, thereby reducing trion and nonradiative Auger recombination. Our findings show that THz technologies can be used to suppress and control such undesired nonradiative decay, potentially in a variety of luminescent materials for future device applications.

    View details for DOI 10.1021/acs.nanolett.1c04873

    View details for Web of Science ID 000776700100035

    View details for PubMedID 35142222

  • All-optical fluorescence blinking control in quantum dots with ultrafast mid-infrared pulses. Nature nanotechnology Shi, J., Sun, W., Utzat, H., Farahvash, A., Gao, F. Y., Zhang, Z., Barotov, U., Willard, A. P., Nelson, K. A., Bawendi, M. G. 2021


    Photoluminescence intermittency is a ubiquitous phenomenon, reducing the temporal emission intensity stability of single colloidal quantum dots (QDs) and the emission quantum yield of their ensembles. Despite efforts to achieve blinking reduction by chemical engineering of the QD architecture and its environment, blinking still poses barriers to the application of QDs, particularly in single-particle tracking in biology or in single-photon sources. Here, we demonstrate a deterministic all-optical suppression of QD blinking using a compound technique of visible and mid-infrared excitation. We show that moderate-field ultrafast mid-infrared pulses (5.5mum, 150fs) can switch the emission from a charged, low quantum yield grey trion state to the bright exciton state in CdSe/CdS core-shell QDs, resulting in a significant reduction of the QD intensity flicker. Quantum-tunnelling simulations suggest that the mid-infrared fields remove the excess charge from trions with reduced emission quantum yield to restore higher brightness exciton emission. Our approach can be integrated with existing single-particle tracking or super-resolution microscopy techniques without any modification to the sample and translates to other emitters presenting charging-induced photoluminescence intermittencies, such as single-photon emissive defects in diamond and two-dimensional materials.

    View details for DOI 10.1038/s41565-021-01016-w

    View details for PubMedID 34811550

  • Room Temperature Terahertz Electroabsorption Modulation by Excitons in Monolayer Transition Metal Dichalcogenides NANO LETTERS Shi, J., Baldini, E., Latini, S., Sato, S. A., Zhang, Y., Pein, B. C., Shen, P., Kong, J., Rubio, A., Gedik, N., Nelson, K. A. 2020; 20 (7): 5214-5220


    The interaction between off-resonant laser pulses and excitons in monolayer transition metal dichalcogenides is attracting increasing interest as a route for the valley-selective coherent control of the exciton properties. Here, we extend the classification of the known off-resonant phenomena by unveiling the impact of a strong THz field on the excitonic resonances of monolayer MoS2. We observe that the THz pump pulse causes a selective modification of the coherence lifetime of the excitons, while keeping their oscillator strength and peak energy unchanged. We rationalize these results theoretically by invoking a hitherto unobserved manifestation of the Franz-Keldysh effect on an exciton resonance. As the modulation depth of the optical absorption reaches values as large as 0.05 dB/nm at room temperature, our findings open the way to the use of semiconducting transition metal dichalcogenides as compact and efficient platforms for high-speed electroabsorption devices.

    View details for DOI 10.1021/acs.nanolett.0c01134

    View details for Web of Science ID 000548893200068

    View details for PubMedID 32539410