Air‐Stable, Near‐ to Mid‐Infrared Emitting Solids of PbTe/CdTe Core–Shell Colloidal quantum dots

Proteşescu, Loredana; Zünd, Tanja; Bodnarchuk, Maryna I.; Kovalenko, Maksym V.

doi:10.1002/cphc.201501008

Cited by 19 publications

(10 citation statements)

References 60 publications

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“…As well as with the large variation in size and composition of the QDs shown here, these MIR absorption features have also been reported in various forms of SnTe QDs that are both Sn deficient and Sn rich which strongly suggests that the feature is a result of Sn-related surface chemistry rather than an LSPR or intraband state. The PbTe QDs showed no such MIR absorption, but were prepared with the same organic ligands, discounting the oleic acid terminal group as the cause of the static absorption feature. It is well established that any unpassivated surface Sn sites of SnTe are quick to oxidize .…”

Section: Resultsmentioning

confidence: 99%

Room Temperature Mid-IR Detection through Localized Surface Vibrational States of SnTe Nanocrystals

Cryer

Halpert

2018

ACS Sens.

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Quantum dots (QDs) are now well established as promising materials for room temperature mid-infrared (MIR) detection beyond 3 μm.Here, we have replaced commonly reported mercury based quantum dots with less toxic SnTe and PbSnTe. Inverse MIR detection at room temperature is demonstrated with planar, solution, and air-processed PbSnTe and SnTe QD devices. The detection mechanism is shown to be mediated by an interaction between MIR radiation and the vibrational stretches of adsorbed hydroxyl species. Devices are shown to possess mA/W responsivity via a reduction in conductance due to MIR irradiation and, unlike classic MIR photoconductors, are unaffected by visible wavelengths. As such, these devices offer the possibility of MIR thermal imaging that has an intrinsic solution to the blinding caused by higher energy light sources.

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Section: Resultsmentioning

confidence: 99%

Room Temperature Mid-IR Detection through Localized Surface Vibrational States of SnTe Nanocrystals

Cryer

Halpert

2018

ACS Sens.

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“…These QDs showed strong degradation in emission intensity with exposure to an ambient atmosphere, argued to be a result of photo-oxidation effects. More recently, core-shell colloidal QDs of PbTe/CdTe have demonstrated mid-IR emission at 3 μm wavelengths, with little to no degradation in emission with exposure to atmosphere, which is presumably the result of the protective shell surrounding the PbTe QD core [274]. Core-shell QDs in the HgSe/CdS material system have also demonstrated emission out to 5 μm [275].…”

Section: Alternative Materials Quantum Dot and Nanocrystal Emittersmentioning

confidence: 99%

Next-generation mid-infrared sources

Jung

Bank

Lee

et al. 2017

J. Opt.

145

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The mid-infrared (mid-IR) is a wavelength range with a variety of technologically vital applications in molecular sensing, security and defense, energy conservation, and potentially in free-space communication. The recent development and rapid commercialization of new coherent mid-infrared sources have spurred significant interest in the development of mid-infrared optical systems for the above applications. However, optical systems designers still do not have the extensive optical infrastructure available to them that exists at shorter wavelengths (for instance, in the visible and near-IR/telecom wavelengths). Even in the field of optoelectronic sources, which has largely driven the growing interest in the mid-infrared, the inherent limitations of state-of-the-art sources and the gaps in spectral coverage offer opportunities for the development of new classes of lasers, light emitting diodes and emitters for a range of potential applications. In this topical review, we will first present an overview of the current state-of-the-art mid-IR sources, in particular thermal emitters, which have long been utilized, and the relatively new quantum-and interband-cascade lasers, as well as the applications served by these sources. Subsequently, we will discuss potential midinfrared applications and wavelength ranges which are poorly served by the current stable of mid-IR sources, with an emphasis on understanding the fundamental limitations of the current source technology. The bulk of the manuscript will then explore both past and recent developments in midinfrared source technology, including narrow bandgap quantum well lasers, type-I and type-II quantum dot materials, type-II superlattices, highly mismatched alloys, lead-salts and transitionmetal-doped II-VI materials. We will discuss both the advantages and limitations of each of the above material systems, as well as the potential new applications which they might serve. All in all, this topical review does not aim to provide a survey of the current state of the art for mid-IR sources, but instead looks primarily to provide a picture of potential next-generation optical and optoelectronic materials systems for mid-IR light generation.

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“…Here we suggest that the absorption feature is the result of an adsorbed hydroxyl group on the oxidised QD surface of Sn containing QDs, a well understood feature reported many times previously [237,[243][244][245][246]. This oxidation occurs at poorly passivated regions of the QD surface from trace oxygen introduced during the synthesis or during processing [242,247]. absorbance below 1000 cm −1 .…”

Section: Absorbance Featuressupporting

confidence: 65%

“…This strongly implies that the feature is a result of Sn-related surface chemistry rather than an LSPR or intraband state. The PbTe QDs showed no such MIR absorption [242], but were prepared with the same organic ligands, discounting the oleic acid terminal group as the cause of the static absorption feature. It is well established, and shown again here with the XPS measurements, that any unpassivated surface Sn sites of SnTe are quick to oxidise [238].…”

Section: Absorbance Featuresmentioning

confidence: 99%

Device Applications of Solution Processed MIR Semiconductor Nanocrystal Thin Films

Cryer¹

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<p>Colloidal semiconductor nanocrystals (NCs) with bandgaps less than 1 eV allow the development of mid wave infrared (MIR) sensitive detectors that exploit the benefits of colloidal materials, primarily bandgap selection and solution deposition. Additionally, the electrical behaviour of these films can be examined for characteristics that can increase the functionality of NC based detectors. The production of devices that are designed to be competitive as ultra-low-cost, room temperature MIR detectors, operating with photonic, rather than thermal detection is detailed. The evolution of the colloidal synthesis, spray deposition methods, substrate materials and post deposition treatments used here lead to highly robust and high performing devices. These devices demonstrate a “colour” sensitivity down to 300 nm in the MIR (≈10 % of scale), with superior responsivities for this class of device, up to 0.9 AW⁻¹, and competitive specific detectivity up to 8 × 10⁹ Jones at 200 Hz and 300 K. Furthermore, these devices utilise a cheap and robust substrate material that allows operation after deformation up to 45 ° without degradation over many cycles. These devices offer a template for ultra-low-cost MIR detectors with performance that rivals microbolometers but with better measurement speed and spectral sensitivity. As such these devices showcase the key advantages of using colloidal NCs in MIR applications. Planar and fully air processed thin film devices that demonstrate photo-induced memristive behaviour and can be used as a transistors, photode-tectors or memory devices are investigated. Following long term (60 h) air exposure, unpackaged NC films develop reliable memristive characteristics in tandem with temperature, gate and photoresponse. On/off ratios of more than 50 are achieved and the devices show long term stability, producing repeatable metrics over days of measurement. The on/off behaviour is shown to be dependent on previous charge flow and carrier density, implying memristive rather than switching behaviour. These observations are described within a long term trap filling model. This work represents an advance in the integration of NC films into electronic devices, which may lead to the development of multi-functional electronic components. Building on the previous work the steps taken to move from a planar device, that works well in controlled conditions, to a multi-pixel sensor that can demonstrate MIR video imaging at room temperature in a noisy environment are shown. This is achieved with a 15 pixel detector that consists only of a polymer substrate and solution patterned NC pixels. This device can detect a 373 K object with the device at 298 K in a noisy environment. This performance is enabled by photogain at 5 V bias that reaches a maximum External Quantum Efficiency (EQE) of 1940 ± 290 % for a pixel with a 3.3 µm bandgap. Through the use of four separate bandgaps it is shown that “multicolour” thermal imaging systems can deliver another layer of information, on top of intensity, to the user. The behaviour of the system is examined under use and it is shown that the photoconductive device behaves as expected with regards to bias, and that trap enabled gain is sensitive to total incident flux, more than the spectral energy distribution of the target. Finally, it is shown that solution patterned QD fabrication methods can deliver electrical reproducibility between pixels that is sufficient to allow an imaging plane of multiple pixels. The somewhat neglected tin chalcogenide semiconductor nanocrystals are investigated and inverse MIR detection at room temperature is demonstrated with planar, solution and airprocessed PbSnTe and SnTe QD devices. The detection mechanism is shown to be mediated by an interaction between MIR radiation and the vibrational stretches of adsorbed hydroxyl species at the oxdised NC surface. Devices are shown to possess mAW⁻¹ responsivity via a reduction in film conductance due to MIR radiation and, unlike classic MIR photoconductors, are unaffected by visible wavelengths. As such these devices offer the possibility of MIR thermal imaging that has an intrinsic solution to the blinding caused by higher energy light sources. In summary, it is shown that semiconductor NCs with an all ambient fully solution processed deposition and ligand exchange procedure can be used to create simple, robust and cheap devices that are beginning to demonstrate metrics on par with current commercial thermal detector systems. It is also shown that these devices can under certain circumstances demonstrate novel behaviours that offer the prospects of enhanced or novel functionality.</p>

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Air‐Stable, Near‐ to Mid‐Infrared Emitting Solids of PbTe/CdTe Core–Shell Colloidal quantum dots

Cited by 19 publications

References 60 publications

Room Temperature Mid-IR Detection through Localized Surface Vibrational States of SnTe Nanocrystals

Room Temperature Mid-IR Detection through Localized Surface Vibrational States of SnTe Nanocrystals

Next-generation mid-infrared sources

Device Applications of Solution Processed MIR Semiconductor Nanocrystal Thin Films

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