Effect of Core/Shell Interface on Carrier Dynamics and Optical Gain Properties of Dual-Color Emitting CdSe/CdS Nanocrystals

Pinchetti, Valerio; Meinardi, Francesco; Camellini, Andrea; Sirigu, Gianluca; Christodoulou, Sotirios; Bae, Wan Ki; Donato, Francesco De; Manna, Liberato; Zavelani‐Rossi, M.; Moreels, Iwan; Klimov, Victor I.; Brovelli, Sergio

doi:10.1021/acsnano.6b02635

Cited by 56 publications

(70 citation statements)

References 62 publications

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“…For similar QD architectures, excitation powers of a few 100 μJ/cm 2 give rise to green amplified spontaneous emission. 42 We propose that in our system at excitation powers >200 μJ/cm 2 (see Figure 3a), green stimulated emission by excitons in the shell occurs on a subpicosecond time scale, outpacing exciton transfer into the core. Consequently, at these powers the population of core excitons never reaches inversion and red lasing does not occur.…”

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confidence: 81%

Colloidal-Quantum-Dot Ring Lasers with Active Color Control

et al. 2018

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To improve the photophysical performance of colloidal quantum dots for laser applications, sophisticated core/shell geometries have been developed. Typically, a wider bandgap semiconductor is added as a shell to enhance the gain from the quantum-dot core. This shell is designed to electronically isolate the core, funnel excitons to it, and reduce nonradiative Auger recombination. However, the shell could also potentially provide a secondary source of gain, leading to further versatility in these materials. Here we develop high-quality quantum-dot ring lasers that not only exhibit lasing from both the core and the shell but also the ability to switch between them. We fabricate ring resonators (with quality factors up to ∼2500) consisting only of CdSe/CdS/ZnS core/shell/shell quantum dots using a simple template-stripping process. We then examine lasing as a function of the optical excitation power and ring radius. In resonators with quality factors >1000, excitons in the CdSe cores lead to red lasing with thresholds at ∼25 μJ/cm2. With increasing power, green lasing from the CdS shell emerges (>100 μJ/cm2) and then the red lasing begins to disappear (>250 μJ/cm2). We present a rate-equation model that can explain this color switching as a competition between exciton localization into the core and stimulated emission from excitons in the shell. Moreover, by lowering the quality factor of the cavity we can engineer the device to exhibit only green lasing. The mechanism demonstrated here provides a potential route toward color-switchable quantum-dot lasers.

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confidence: 81%

Colloidal-Quantum-Dot Ring Lasers with Active Color Control

et al. 2018

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“…2020 pure green . On the other hand, dual‐emission colloidal semiconductor nanocrystals are of interest for applications in multimodal imaging, sensing, lighting, and integrated photonics . However, the best EQE of single‐nanocrystal LEDs with dual emission cannot exceed 0.100% .…”

Section: Summary Of Led Performancesmentioning

confidence: 99%

Light‐Emitting Diodes with Cu‐Doped Colloidal Quantum Wells: From Ultrapure Green, Tunable Dual‐Emission to White Light

Liu

Sharma

et al. 2019

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Copper‐doped colloidal quantum wells (Cu‐CQWs) are considered a new class of optoelectronic materials. To date, the electroluminescence (EL) property of Cu‐CQWs has not been revealed. Additionally, it is desirable to achieve ultrapure green, tunable dual‐emission and white light to satisfy the various requirement of display and lighting applications. Herein, light‐emitting diodes (LEDs) based on colloidal Cu‐CQWs are demonstrated. For the 0% Cu‐doped concentration, the LED exhibits Commission Internationale de L'Eclairage 1931 coordinates of (0.103, 0.797) with a narrow EL full‐wavelength at half‐maximum of 12 nm. For the 0.5% Cu‐doped concentration, a dual‐emission LED is realized. Remarkably, the dual emission can be tuned by manipulating the device engineering. Furthermore, at a high doping concentration of 2.4%, a white LED based on CQWs is developed. With the management of doping concentrations, the color tuning (green, dual‐emission to white) is shown. The findings not only show that LEDs with CQWs can exhibit polychromatic emission but also unlock a new direction to develop LEDs by exploiting 2D impurity‐doped CQWs that can be further extended to the application of other impurities (e.g., Mn, Ag).

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“…Furthermore, our compact ratiometric nanostructures exhibit widely separated narrow‐line emission bands, which completely suppresses cross‐readout errors. Specifically, we use so‐called dot‐in‐bulk CdSe/CdS NCs (DiB‐NCs) consisting of a small quantum confined CdSe core (radius ≈1.5 nm) embedded in a bulk‐like CdS shell (thickness ≈8.5 nm). In Figure S1a,b (Supporting Information), we show transmission electron microscopy images of CdSe/CdS NCs during the synthesis at different shell thicknesses (3.5 and 8.5 nm, respectively).…”

Section: Introductionmentioning

confidence: 99%

“…Diffraction patterns collected at different reaction times show that the CdS shell grows in the same zincblende structure of the core for a few layers and then rearranges to the more thermodynamically stable wurtzite structure (Figure S1c, Supporting Information). As a result of their unique internal structure, featuring a sharp, unalloyed, core/shell interface and a 30 meV potential barrier between the core and the shell valence bands ( Figure a), DiB‐NCs exhibit two‐color red and green emission, respectively, from core and shell excitons under low intensity optical excitation (Figure S2, Supporting Information) or electrical pumping . Two‐color light as a result of radiative recombination of excitons localized in different compositional domains of the same heterostructure has been observed also in elongated dot‐in‐rod structures, tetrapods, and spherical core/shell systems …”

Section: Introductionmentioning

confidence: 99%

Two‐Color Emitting Colloidal Nanocrystals as Single‐Particle Ratiometric Probes of Intracellular pH

Bruni

Pedrini

Bossio

et al. 2017

Adv Funct Materials

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Intracellular pH is a key parameter in many biological mechanisms and cell metabolism and is used to detect and monitor cancer formation and brain or heart diseases. pH‐sensing is typically performed by fluorescence microscopy using pH‐responsive dyes. Accuracy is limited by the need for quantifying the absolute emission intensity in living biological samples. An alternative with a higher sensitivity and precision uses probes with a ratiometric response arising from the different pH‐sensitivity of two emission channels of a single emitter. Current ratiometric probes are complex constructs suffering from instability and cross‐readout due to their broad emission spectra. Here, we overcome such limitations using a single‐particle ratiometric pH probe based on dot‐in‐bulk CdSe/CdS nanocrystals (NCs). These nanostructures feature two fully‐separated narrow emissions with different pH sensitivity arising from radiative recombination of core‐ and shell‐localized excitons. The core emission is nearly independent of the pH, whereas the shell luminescence increases in the 3–11 pH range, resulting in a cross‐readout‐free ratiometric response as strong as 600%. In vitro microscopy demonstrates that the ratiometric response in biologic media resembles the precalibralation curve obtained through far‐field titration experiments. The NCs show good biocompatibility, enabling us to monitor in real‐time the pH in living cells.

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Effect of Core/Shell Interface on Carrier Dynamics and Optical Gain Properties of Dual-Color Emitting CdSe/CdS Nanocrystals

Cited by 56 publications

References 62 publications

Colloidal-Quantum-Dot Ring Lasers with Active Color Control

Colloidal-Quantum-Dot Ring Lasers with Active Color Control

Light‐Emitting Diodes with Cu‐Doped Colloidal Quantum Wells: From Ultrapure Green, Tunable Dual‐Emission to White Light

Two‐Color Emitting Colloidal Nanocrystals as Single‐Particle Ratiometric Probes of Intracellular pH

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