Luminescence upconversion in colloidal double quantum dots

ConspectusPairs of coupled quantum dots with controlled coupling between the two potential wells serve as an extremely rich system, exhibiting a plethora of optical phenomena that do not exist in each of the isolated constituent dots. Over the past decade, coupled quantum systems have been under extensive study in the context of epitaxially grown quantum dots (QDs), but only a handful of examples have been reported with colloidal QDs. This is mostly due to the difficulties in controllably growing nanoparticles that encapsulate within them two dots separated by an energetic barrier via colloidal synthesis methods. Recent advances in colloidal synthesis methods have enabled the first clear demonstrations of colloidal double quantum dots and allowed for the first exploratory studies into their optical properties. Nevertheless, colloidal double QDs can offer an extended level of structural manipulation that allows not only for a broader range of materials to be used as compared with epitaxially grown counterparts but also for more complex control over the coupling mechanisms and coupling strength between two spatially separated quantum dots.The photophysics of these nanostructures is governed by the balance between two coupling mechanisms. The first is via dipole–dipole interactions between the two constituent components, leading to energy transfer between them. The second is associated with overlap of excited carrier wave functions, leading to charge transfer and multicarrier interactions between the two components. The magnitude of the coupling between the two subcomponents is determined by the detailed potential landscape within the nanocrystals (NCs).One of the hallmarks of double QDs is the observation of dual-color emission from a single nanoparticle, which allows for detailed spectroscopy of their properties down to the single particle level. Furthermore, rational design of the two coupled subsystems enables one to tune the emission statistics from single photon emission to classical emission. Dual emission also provides these NCs with more advanced functionalities than the isolated components. The ability to better tailor the emission spectrum can be advantageous for color designed LEDs in lighting and display applications. The different response of the two emission colors to external stimuli enables ratiometric sensing. Control over hot carrier dynamics within such structures allows for photoluminescence upconversion.This Account first provides a description of the main hurdles toward the synthesis of colloidal double QDs and an overview of the growing library of synthetic pathways toward constructing them. The main discoveries regarding their photophysical properties are then described in detail, followed by an overview of potential applications taking advantage of the double-dot structure. Finally, a perspective and outlook for their future development is provided.

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“…43 We used CdSe doped with only one or a few Te atoms as seeds for the growth of CdS rods by hot injection. 4,15 …”

Section: Synthesis Of Colloidal Double Quantum Dotsmentioning

confidence: 99%

“…The PbSe NIR emission lifetime, depicted in blue in the inset, is fitted by a single exponential of 2.1 ± 0.1 μs (dashed pink). Panels a and b adapted with permission from ref (15), copyright 2013 Macmillan Publishers Limited. Panels c–f adapted with permission from ref (16).…”

Section: Photoluminescence Upconversionmentioning

confidence: 99%

Colloidal Double Quantum Dots

et al. 2016

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“…These challenges associated with DHNR growth, thus far, have not been addressed using solution chemistry, but the ability to epitaxially grow two distinct materials around a nanocrystal should in general lead to a whole new subclass of complex nanomaterials with multiple functionalities. Photocatalytic activity and luminescence upconversion enabled by metal 33 and a semiconductor of different composition 34 grown at the tip of a dot-in-a-rod structure, respectively, demonstrate promise in such directions of materials synthesis. Multiple compositions in nanorod heterostructures or hybrid structures may lead to additional opportunities such as unique means of assembly 35 .…”

Section: Challenges In Synthesismentioning

confidence: 99%

Double-heterojunction nanorods

et al. 2014

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As semiconductor heterostructures play critical roles in today's electronics and optoelectronics, the introduction of active heterojunctions can impart new and improved capabilities that will enable the use of solution-processable colloidal quantum dots in future devices. Such heterojunctions incorporated into colloidal nanorods may be especially promising, since the inherent shape anisotropy can provide additional benefits of directionality and accessibility in band structure engineering and assembly. Here we develop doubleheterojunction nanorods where two distinct semiconductor materials with type II staggered band offset are both in contact with one smaller band gap material. The double heterojunction can provide independent control over the electron and hole injection/ extraction processes while maintaining high photoluminescence yields. Light-emitting diodes utilizing double-heterojunction nanorods as the electroluminescent layer are demonstrated with low threshold voltage, narrow bandwidth and high efficiencies.

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“…Similar to the case where the carriers excited above band gap by linear absorption can result in normal photoluminescence, the carriers excited by the nonlinear process also can result in photoluminescence, the upconversion photoluminescence (UCPL) [12][13][14][15]. In case of UCPL the emitted photon can have larger energy than the input photon.…”

Section: Introductionmentioning

confidence: 99%