Ultrafast Charge Dynamics in Trap‐Free and Surface‐Trapping Colloidal Quantum Dots

Smith, Carole; Leontiadou, Marina A.; Page, Robert; O’Brien, Paul; Binks, David J.

doi:10.1002/advs.201500088

Cited by 30 publications

(26 citation statements)

References 42 publications

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“…Here, σ is the absorption cross‐section at the pump wavelength, and

ℏ ω_{pump}

is the pump photon energy. Taking σ as 8 × 10 −19 m 2 and assuming efficient relaxation to the band edge, the average exciton number at threshold is calculated and plotted in Figure b (black). This calculated curve agrees well with the curve for the average exciton number at threshold (blue) inferred using the saturation fit below threshold.…”

Section: Resultsmentioning

confidence: 99%

Gain Spectroscopy of Solution‐Based Semiconductor Nanocrystals in Tunable Optical Microcavities

Patel

Trichet

Coles

et al. 2015

Advanced Optical Materials

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tuned simply by changing their size, such that any emission wavelength in the visible and near infrared of the spectrum can be accessed with a small selection of materials. Several nanocrystal based lasers have now been reported with a variety of device designs. [2][3][4][5][6][7][8][9] Some of these demonstrations have utilized solid fi lms of pure closely packed NQDs [ 3,[5][6][7]9 ] or mixed with titania for better wave-guiding properties. [ 2 ] Others have coated the NQDs onto microtoroids and microspheres to take advantage of the whispering gallery mode structure. [ 4,8 ] Understanding the interplay between the various absorption and emission processes is essential in order to optimize the nanocrystal design. Spectroscopy of the gain produced can be performed using pump-probe techniques [ 10 ] and allows the investigation of exciton relaxation dynamics. However, these rapid transient processes are considerably removed from lasing behavior in the presence of optical feedback and a good understanding of the lasing process is currently lacking.In this paper, we report a convenient method for the direct investigation of the lasing behavior of solution-based NQDs by performing gain spectroscopy enabled via in situ tuning of the cavity feedback wavelength. Tunable cavities and laser emission have been demonstrated by others using various methods. For example, the cavity resonance can be tuned by external heating achieved through either modulating the pump power [ 8 ] or by directly heating the cavity using an electrical heater. [ 11 ] Other methods have utilized strain, [ 12 ] electric-fi eld, [ 13,14 ] or pressure. [ 15 ] However, these methods tend to either have too limited a tuning range for useful spectroscopy, or involve changes to the NQD environment that may themselves modify the gain characteristics, making interpretation of the observed changes in lasing performance diffi cult. By directly tuning the cavity length of a Fabry-Perot style open resonator, we achieve both a wide tuning range and fi ne control limited only by the resolution of the actuator. As a result we are able to observe single mode lasing over a range exceeding 25 nm, and thereby map the spectra for the lasing threshold and differential gain. The NQDs in solution within the cavity experience no change in temperature or stress during tuning and so the changes in lasing performance can be attributed unambiguously to the change in feedback wavelength. From a technological standpoint, our results demonstrate a new approach to widely tunable single mode lasers for chip-scale and low power applications.

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“…Here, σ is the absorption cross‐section at the pump wavelength, and

ℏ ω_{pump}

Section: Resultsmentioning

confidence: 99%

Gain Spectroscopy of Solution‐Based Semiconductor Nanocrystals in Tunable Optical Microcavities

Patel

Trichet

Coles

et al. 2015

Advanced Optical Materials

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“…[69] Ultrafast laser techniques such as transient absorption spectroscopy (TAS) and time-resolved photo luminescence (TRPL) spectroscopy are the well-known tools used to monitor processes such as exciton dynamics, charge/energy transfer, and multiexciton generation phenomena in QDs measurements. [70][71][72][73][74][75][76][77][78] TRPL and TAS can reveal the evolution of excited states in a nanosecond to fs timescale. In TRPL, the time evolution is measured by monitoring emission from the QDs.…”

Section: Tr Spectroscopymentioning

confidence: 99%

Quantum Dots Microstructural Metrology: From Time‐Resolved Spectroscopy to Spatially Resolved Electron Microscopy

Hasna

Hou

Welland

2020

Part & Part Syst Charact

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Quantum dots (QDs) have gained broad acceptance, applicability, and much interest in current semiconductor technology due to their unique optical and electrical properties. [1,2] QDs are semiconductors with size between 3 and 20 nm where electron and hole wave functions are highly confined. [3] The dimension should be comparable to the Bohr exciton radius of the material, and that leads to discrete energy levels in QD. QDs are attracted by their unique atomiclike narrow emission that can be tuned easily by controlling their size, structure, and composition. [4-6] The optical and electrical properties of QDs are better than organic fluorophores. For instance, QD has high quantum efficiency, excellent color gamut, narrow emission bandwidths, broad color tunability, high photostability, and high air stability. [7] These excellent properties make QD a potential candidate for applications in various fields such as optoelectronics, sensing, and imaging. [1,8-10] QDs are typically composed of group II-VI, III-V, and IV-VI compound semiconductors such as CdS, CdSe, PbS, ZnS, InAs, and ZnInS. [11-16] Because of minimal particle diameter, QDs have a high surface-to-volume ratio, and these surface trap states act as centers for nonradiative transitions that diminish the performance of QDs. This can be overcome by the growth of inorganic shells such as ZnS, CdTe, and CdSe. Various core-shell QDs such as CdSe/ZnS,

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“…The phosphorescence of iridium(III) complexes is quenched by the intracellular O 2 , which is restored through two-electron bioreduction in a hypoxic environment. Wen et al27 synthesized an oxygen-sensitive complex, with iridium covalently attached to mesoporous silica-coated and core-shell upconverted nanoparticles (UCNPs), denoted as core-shell UCNPs@mSiO 2 -Ir, to monitor O 2 concentrations as indicated by the increase or decrease in through luminescence. The up-conversion channel of iridium can emit 600 nm oxygen-quenchable phosphorescence after absorbing 980 nm near-infrared (NIR) light, which is converted from the energy of UCNPs, and hence, can exhibit relatively deep tumor penetration compared with non-NIR light excitation.…”

Section: Hypoxia-active Nanoparticles For Imagingmentioning

confidence: 99%

<p>Hypoxia-active nanoparticles used in tumor theranostic</p>

Wang¹,

Shang²,

Niu³

et al. 2019

IJN

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Hypoxia is a hallmark of malignant tumors and often correlates with increasing tumor aggressiveness and poor treatment outcomes. Therefore, early diagnosis and effective killing of hypoxic tumor cells are crucial for successful tumor control. There has been a surge of interdisciplinary research aimed at developing functional molecules and nanomaterials that can be used to noninvasively image and efficiently treat hypoxic tumors. These mainly include hypoxia-active nanoparticles, anti-hypoxia agents, and agents that target biomarkers of tumor hypoxia. Hypoxia-active nanoparticles have been intensively investigated and have demonstrated advanced effects on targeting tumor hypoxia. In this review, we present an overview of the reports published to date on hypoxia-activated prodrugs and their nanoparticle forms used in tumor-targeted therapy. Hypoxia-responsive nanoparticles are inactive during blood circulation and normal physiological conditions but are activated by hypoxia once they extravasate into the hypoxic tumor microenvironment. Their use can enhance the efficiency of tumor chemotherapy, radiotherapy, fluorescence and photoacoustic intensity, and other imaging and therapeutic strategies. By targeting the broad habitats of tumors, rather than tumor-specific receptors, this strategy has the potential to overcome the problem of tumor heterogeneity and could be used to design diagnostic and therapeutic nanoparticles for a broad range of solid tumors.

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Ultrafast Charge Dynamics in Trap‐Free and Surface‐Trapping Colloidal Quantum Dots

Cited by 30 publications

References 42 publications

Gain Spectroscopy of Solution‐Based Semiconductor Nanocrystals in Tunable Optical Microcavities

Gain Spectroscopy of Solution‐Based Semiconductor Nanocrystals in Tunable Optical Microcavities

Quantum Dots Microstructural Metrology: From Time‐Resolved Spectroscopy to Spatially Resolved Electron Microscopy

<p>Hypoxia-active nanoparticles used in tumor theranostic</p>

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