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Improving the effectiveness of cancer therapy will require tools that enable more specific cancer targeting and improved tumor visualization. Theranostics have the potential for improving cancer care because of their ability to serve as both diagnostics and therapeutics; however, their diagnostic potential is often limited by tissue-associated light absorption and scattering. Herein, we develop CuInSe 2 @ZnS:Mn quantum dots (QDs) with intrinsic multifunctionality that both enable the accurate localization of small metastases and act as potent tumor ablation agents. By leveraging the growth kinetics of a ZnS shell on a biocompatible CuInSe 2 core, Mn doping, and folic acid functionalization, we produce biocompatible QDs with high near-infrared (NIR)-II fluorescence efficiency up to 31.2%, high contrast on magnetic resonance imaging (MRI), and preferential distribution in 4T1 breast cancer tumors. MRI-enabled contrast of these nanoprobes is sufficient to timely identify small metastases in the lungs, which is critically important for preventing cancer spreading and recurrence. Further, exciting tumor-resident QDs with NIR light produces both fluorescence for tumor visualization through radiative recombination pathways as well as heat and radicals through nonradiative recombination pathways that kill cancer cells and initiate an anticancer immune response, which eliminates tumor and prevents tumor regrowth in 80% of mice.

The impact of strain on the optical properties of semiconductor quantum dots (QDs) is fundamentally important while still awaiting detailed investigation. CdTe/CdS core/shell QDs represent a typical strained system due to the substantial lattice mismatch between CdTe and CdS. To probe the strain-related effects, aqueous CdTe/CdS QDs were synthesized by coating different sized CdTe QD cores with CdS shells upon the thermal decomposition of glutathione as a sulfur source under reflux. The shell growth was carefully monitored by both steady-state absorption and fluorescence spectroscopy and transient fluorescence spectroscopy. In combination with structural analysis, the band alignments as a consequence of the strain were modified based on band deformation potential theory. By further taking account of these strain-induced band shifts, the effective mass approximation (EMA) model was modified to simulate the electronic structure, carrier spatial localization, and electron-hole wave function overlap for comparing with experimentally derived results. In particular, the electron/hole eigen energies were predicted for a range of structures with different CdTe core sizes and different CdS shell thicknesses. The overlap of electron and hole wave functions was further simulated to reveal the impact of strain on the electron-hole recombination kinetics as the electron wave function progressively shifts into the CdS shell region while the hole wave function remains heavily localized in CdTe core upon the shell growth. The excellent agreement between the strain-modified EMA model with the experimental data suggests that strain exhibits remarkable effects on the optical properties of mismatched core/shell QDs by altering the electronic structure of the system.

Light-emitting semiconductor quantum dots (QDs) combined with magnetic resonance imaging contrast agents within a single nanoparticle platform are considered to perform as multimodal imaging probes in biomedical research and related clinical applications. The principles of their rational design are outlined and contemporary synthetic strategies are reviewed (heterocrystalline growth; co-encapsulation or assembly of preformed QDs and magnetic nanoparticles; conjugation of magnetic chelates onto QDs; and doping of QDs with transition metal ions), identifying the strengths and weaknesses of different approaches. Some of the opportunities and benefits that arise through in vivo imaging using these dual-mode probes are highlighted where tumor location and delineation is demonstrated in both MRI and fluorescence modality. Work on the toxicological assessments of QD/magnetic nanoparticles is also reviewed, along with progress in reducing their toxicological side effects for eventual clinical use. The review concludes with an outlook for future biomedical imaging and the identification of key challenges in reaching clinical applications., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In order to advance the development of quantum emitter‐based devices, it is essential to enhance light‐matter interactions through coupling between semiconductor quantum dots with high quality factor resonators. Here, efficient tuning of the emission properties of HgTe quantum dots in the infrared spectral region is demonstrated by coupling them to a plasmonic metasurface that supports bound states in the continuum. The plasmonic metasurface, composed of an array of gold nanobumps, is fabricated using single‐step direct laser printing, opening up new opportunities for creating exclusive 3D plasmonic nanostructures and advanced photonic devices in the infrared region. A 12‐fold enhancement of the photoluminescence in the 900–1700 nm range is observed under optimal coupling conditions. By tuning the geometry of the plasmonic arrays, controllable shaping of the emission spectra is achieved, selectively enhancing specific wavelength ranges across the emission spectrum. The observed enhancement and shaping of the emission are attributed to the Purcell effect, as corroborated by systematic measurements of radiative lifetimes and optical simulations based on the numerical solution of Maxwell's equations. Moreover, coupling of the HgTe photoluminescence to high quality factor modes of the metasurface improves emission directivity, concentrating output within an ≈20° angle. [ABSTRACT FROM AUTHOR]

Given the ubiquitous examples of semiconductor nanorods synthesis, CuInS2‐based anisotropic heterostructures still lag behind in terms of shape/optical properties control. Here, core/shell CuInS2/CdS dot‐in‐rod nanoheterostructures which exhibit high degree of the morphology control, and a strong emission in the near‐infrared range of 700–900 nm, are realized. The authors made use of the seeded growth approach utilizing wurtzite CuInS2 quantum dots as seeds, which allows for tuning the dimension of the resulting core/shell nanorods, including the core size and the shell thickness. Time‐dependent photoluminescence studies reveal slowing down of the recombination rate with increasing thickness of the shell, which is characteristic for the quasi‐type II heterostructure. Alloying of the CuInS2 cores with Zn does not perturb the shell growth process, but enables improvement of the photoluminescence quantum yield of the resulting core/shell CuInZnS2/CdS nanorods to 45%, as compared to ≈30% for CuInS2/CdS nanorods. [ABSTRACT FROM AUTHOR]

Narrow bandgap semiconductor‐based photodetectors often suffer from high room‐temperature noise and are therefore operated at low temperatures. Here, a hybrid poly(3‐hexylthiophene) (P3HT): HgTe quantum dot (QD) phototransistor is reported, which exhibits high sensitivity and fast photodetection up to 2400 nm wavelength range at room temperature. The active layer of the phototransistor consists of HgTe QDs well dispersed in a P3HT matrix. Fourier‐transform infrared spectra confirm that chemical grafting between P3HT and HgTe QDs is realized after undergoing prolonged coblend stirring and a ligand exchange process. Thanks to the shifting of the charge transport into the P3HT and the partial passivation of the surface traps of HgTe QDs in the blend, the P3HT: HgTe QD hybrid phototransistor shows significantly improved gate‐voltage tuning, 15 times faster response, and ≈80% reduction in the noise level compared to a pristine HgTe QD control device. More than 1011 Jones specific detectivity (estimated from the noise spectral density measured at 1 kHz) is achieved at room temperature, and the response time (measured at 22 mW cm−2 illumination intensity) of the device is less than 1.5 µs. That is comparable to commercial epitaxially grown IR photodetectors operated in the same wavelength range. [ABSTRACT FROM AUTHOR]

An H2O2‐assisted top‐down approach is used to synthesize brightly luminescent, color‐tunable sulfur quantum dots (SQDs), with a photoluminescence quantum yield of up to 23 %. The formation of SQDs involves dissolution of bulk sulfur powder into small particles in an alkaline environment in the presence of polyethylene glycol, followed by H2O2‐assisted etching of polysulfide species, which has the advantage of the passivation of surface states. This synthetic strategy allows us to simultaneously control the final size of SQDs, to tune their emission color, and to improve their emission quantum yield by eliminating surface traps. Down‐conversion white light emitting diodes were also fabricated using blue emissive SQDs and orange emissive copper nanoclusters, with CIE color coordinates of (0.33, 0.32) and a high color rendering index of 91. The water‐soluble, highly luminescent SQDs are promising luminescent materials that can be produced from abundant precursor materials. [ABSTRACT FROM AUTHOR]

Quantum confined semiconductor nanoparticles, such as colloidal quantum dots, nanorods and nanoplatelets have broad extended absorption spectra at energies above their bandgaps. This means that they can absorb light at high photon energies leading to the formation of hot excitons with finite excited state lifetimes. During their existence, the hot electron and hole that comprise the exciton may start to cool as they relax to the band edge by phonon mediated or Auger cooling processes or a combination of these. Alongside these cooling processes, there is the possibility that the hot exciton may split into two or more lower energy excitons in what is termed carrier multiplication (CM). The fission of the hot exciton to form lower energy multiexcitons is in direct competition with the cooling processes, with the timescales for multiplication and cooling often overlapping strongly in many materials. Once CM has been achieved, the next challenge is to preserve the multiexcitons long enough to make use of the bonus carriers in the face of another competing process, non-radiative Auger recombination. However, it has been found that Auger recombination and the several possible cooling processes can be manipulated and usefully suppressed or retarded by engineering the nanoparticle shape, size or composition and by the use of heterostructures, along with different choices of surface treatments. This review surveys some of the work that has led to an understanding of the rich carrier dynamics in semiconductor nanoparticles, and that has started to guide materials researchers to nanostructures that can tilt the balance in favour of efficient CM with sustained multiexciton lifetimes. [ABSTRACT FROM AUTHOR]

The development of the research into the synthesis and optoelectronic applications of HgTe and related quantum dots (QDs) is reviewed, from the early days when it was felt that it might be a useful replacement for rare earths in telecom optical amplifiers, through to its more recent and broader appeal as an IR photodetector technology. Appropriately the early investigation of the material sprang from a contact with Prof. Horst Weller and his group at Hamburg University. Though the problem of Auger recombination meant that it was not so easy to make telecom amplifiers and lasers as many had hoped, it has proved to have an extraordinarily broad bandgap tuning range and just recently this has resulted in the demonstration of photodetectors in the mid- to long-IR region operating at up to 12 μm wavelength. This impressive flexibility has led to interest in HgTe QDs and optoelectronic devices based on them to be as strong as ever and growing as the prospects for commercialization improve with every narrowing in the gap between the performance of present day epitaxial devices and QD-based technology. In a further satisfying and well timed twist, Prof. Weller's 60th year has seen preliminary reports of extended gain lifetime in `doped' HgTe QDs which may yet lead to a completing of the circle with the distinct possibility of electrically driven telecom wavelength lasers and amplifiers in the coming years. This review follows the development of the several synthetic methods to grow colloidal HgTe QDs, and their deployment in optoelectronic devices to the present. [ABSTRACT FROM AUTHOR]

In a line with most recent trends in developing non-toxic fluorescent nanomaterials, we combined blue emissive carbon dots with green and red emissive zinc copper indium sulfide (ZCIS) core/shell quantum dots (QDs) to achieve white light-emitting diodes (WLEDs) with a high color rendering index of 93. This indicates that ZCIS QDs, with their broad emission bands, can be employed to effectively make up the emission of carbon dots in the yellow and red regions to produce WLEDs in the wide region of color temperature by tuning the volume ratio of these constituting luminophores. Their electroluminescence characteristics including color rendering index, Commission Internationale de l'Eclairage (CIE) color coordinates, and color temperatures were evaluated as a function of forward current. The CIE-1931 chromaticity coordinates of the as-prepared WLEDs, exhibiting good stability, were slightly shifted from (0.321, 0.312) at 10mA to (0.351, 0.322) at 30 mA, which was mainly caused by the different thermal quenching coefficients of carbon dots and ZCIS QDs. [ABSTRACT FROM AUTHOR]

The ability to detect near-infrared and mid-infrared radiation has spawned great interest in colloidal HgTe quantum dots (QDs). In contrast to the studies focused on extending the spectral range of HgTe QD devices, the temporal response, another figure of merit for photodetectors, is rarely investigated. In this work, a single layer, aqueous HgTe QD based photoconductor structure with very fast temporal response (up to 1 MHz 3 dB bandwidth) is demonstrated. The device is fabricated using a simple spray-coating process and shows excellent stability in ambient conditions. The origin of the remarkably fast time response is investigated by combining light intensity-dependent transient photocurrent, temperature-dependent photocurrent, and field-effect transistor (FET) measurements. The charge carrier mobility, as well as the energy levels and carrier lifetimes associated with the trap states in the QDs, are identified. The results suggest that the temporal response is dominated by a fast bimolecular recombination process under high light intensity and by a trap-mediated recombination process at low light intensity. Interestingly, it was found that the gain and time response of aqueous HgTe QD-based photoconductors can be tuned by controlling the QD size and surface chemistry, which provides a versatile approach to optimize the photodetectors with selectable sensitivity and operation bandwidth. [ABSTRACT FROM AUTHOR]

Among materials produced as colloidal quantum dots (CQDs), HgTe has a special status being the only material covering the whole infrared range from the visible to the THz (0.7–100 µm). This unique property resulting from its electronic structure, combined with an air stability and a capacity for charge conduction has generated consistent and massive efforts to produce and improve HgTe CQDs over the past two decades. Meanwhile, HgTe CQDs offer an infrared platform more advanced than any other colloidal alternatives in the mid‐wave infrared regarding their integration into advanced photonic and optoelectronic applications. Here, the latest developments of HgTe CQDs relative to the material's growth, electron structure modelling, its integration into photonic structures and its transfer as the active material from single element devices toward complex sensors and infrared imagers are reviewed. Finally, a discussion about the potential of this material for industry, rising new challenges beyond economical and production considerations at low technological readiness level, relative to the material and device design, is also included. [ABSTRACT FROM AUTHOR]

Examines the formation of hybrid CdTe/HgTe quantum dots using an aqueous colloidal growth technique. Fluorescence; Quantum efficiency; Potential as an optical amplifier medium; Optical amplification in a dilute aqueous suspension of quantum dots.

A surface engineering strategy aimed at improving the stability of CsPbI3 perovskite quantum dots (QDs) both in solution and as films is demonstrated, by performing partial ligand exchange with a short chain ligand, 2‐aminoethanethiol (AET), in place of the original long chain ligands, oleic acid (OA) and oleylamine (OAm), used in synthesis. This results in the formation of a compact ligand barrier around the particles, which prevents penetration of water molecules and thus degradation of the films and, in addition, at the same time improves carrier mobility. Moreover, the AET ligand can passivate surface traps of the QDs, leading to an enhanced photoluminescence (PL) efficiency. As a result, AET‐CsPbI3 QDs maintain their optical performance both in solution and as films, retaining more than 95% of the initial PL intensity in water after 1 h, and under ultraviolet irradiation for 2 h. Photodetectors based on the AET‐CsPbI3 QD films exhibit remarkable performance, such as high photoresponsivity (105 mA W−1) and detectivity (5 × 1013 Jones at 450 nm and 3 × 1013 Jones at 700 nm) without an external bias. The photodetectors also show excellent stability, retaining more than 95% of the initial responsivity in ambient air for 40 h without any encapsulation. [ABSTRACT FROM AUTHOR]

Ultrafast transient absorption spectroscopy is used to investigate sub-nanosecond exciton dynamics in Cd x Hg (1 − x ) Te alloy colloidal quantum dots. A bleach was observed at the band gap due to state-filling, the mono-exponential decay of which had a characteristic lifetime of 91 ± 1 ps and was attributed to biexciton recombination; no evidence of surface-related trapping was observed. The rise time of the bleach, which is determined by the rate at which hot electrons cool to the band-edge, ranged between 1 and 5 ps depending on the pump photon energy. Measuring the magnitude of the bleach decay for different pump fluences and wavelengths allowed the quantum yield of multiple exciton generation to be determined, and was 115 ± 1% for pump photons with energy equivalent to 2.6 times the band gap. [ABSTRACT FROM AUTHOR]

Solution processed colloidal semiconductor quantum dots offer a high potential for decreasing costs and expanding versatility of many electronic and optoelectronic devices. Initially used as a research tool to study charge carrier mobilities in closely packed quantum dot thin films, field effect transistors with quantum dots as the active layer have recently experienced a breakthrough in performance (achievement of mobilities higher than 30cm2 V−1 s−1) as a result of a proper choice of surface ligands and/or improved chemical treatment of the nanoparticle films during device processing. Here we review these innovative developments and the continuing work that may soon lead to commercial grade electronic components. [ABSTRACT FROM AUTHOR]

A computer controlled, automated synthesis method has been used to grow HgTe quantum dots (QDs) entirely at room temperature, using an aprotic solvent, dimethyl sulfoxide. The growth is carried out with small iterative additions of the Te precursor, which allows frequent sampling of the products to assess the growth trajectory in terms of the relationship between the QD concentration and QD diameters as the reaction proceeds. As such, this approach is a useful tool to develop a detailed understanding of the growth process and to work toward optimizing the reaction conditions in terms of the quality of the resulting QDs. HgTe QDs with emission spectra ranging up to 3000 nm and with photoluminescence quantum yields of up to 17% at 2070 nm have been produced by this method. Although coupling of the exciton to ligand vibrations is inevitable in this energy range, attention to the growth conditions and QD quality can influence the detailed coupling mechanisms, with fewer carrier traps reducing the extent of polaron mediated coupling. The influence of reaction conditions such as ligand-to-cation ratios and rate of Te precursor addition upon the onset of QD aggregation has been also examined. The method is readily up-scalable and has been employed to produce HgTe QD materials for infrared photodetectors. [ABSTRACT FROM AUTHOR]

Fabrication of DNA/Quantum Dot (QD) complexes making use of electrostatic adsorption forces has advantages of the cost-efficiency and simplicity. To obtain aggregation-free complexes, high molecular weight polymers or the purposefully designed ligands are commonly employed as a bridge between DNA and QDs, which limits their applications in practice. In this work, DNA/QDs complexes were obtained using electrostatic adsorption between cysteamine stabilized CdTe QDs and self-assembled DNA nanocages. Zeta potential, dynamic light scattering and gel electrophoresis measurements demonstrated their aggregation-free state, different from the cases where single-stranded and double-stranded DNAs were used. The appearance of aggregation-free complexes in the case of DNA nanocages was ascribed to their 3D rigid structure. Förster resonance energy transfer (FRET) was demonstrated for the complexes of Cy3 labeled DNA nanocages and QDs, pointing out on the close proximity of these building blocks. [ABSTRACT FROM AUTHOR]