Optical Properties Of Quantum Dots Research Articles

III-V nanostructures with different dimensionality on silicon

The possibility of AlGaAs nanowires with GaAs quantum dots and InP nanowires with InAsP quantum dots growth by molecular-beam epitaxy on silicon substrates has been demonstrated. Results of GaAs quantum dots optical properties studies have shown that these objects are sources of single photons. In case of InP nanowires with InAsP quantum dots, the results we obtained indicate that nearly 100% of coherent nanowires can be formed with high optical quality of this system on a silicon surface. The presence of a band with maximum emission intensity near 1.3 μm makes it possible to consider the given system promising for further integration of optical elements on silicon platform with fiber-optic systems. Our work, therefore, opens new prospects for integration of direct bandgap semiconductors and singlephoton sources on silicon platform for various applications in the fields of silicon photonics and quantum information technology.

Low-Cost Synthesis of Silicon Quantum Dots with Near-Unity Internal Quantum Efficiency.

As a cost-effective batch synthesis method, Si quantum dots (QDs) with near-infrared photoluminescence, high quantum yield (>50% in polymer nanocomposite), and near-unity internal quantum efficiency were fabricated from an inexpensive commercial precursor (triethoxysilane, TES), using optimized annealing and etching processes. The optical properties of such QDs are similar to those prepared from state-of-the-art precursors (hydrogen silsesquioxane, HSQ) yet featuring an order of magnitude lower cost. To understand the effect of synthesis parameters on QD optical properties, we conducted a thorough comparison study between common solid precursors: TES, HSQ, and silicon monoxide (SiO), including chemical, structural, and optical characterizations. We found that the structural nonuniformity and abundance of oxide inherent to SiO limited the resultant QD performance, while for TES-derived QDs this drawback can be avoided. The presented low-cost synthetic approach would significantly favor applications requiring high loading of good-quality Si QDs, such as light conversion for photovoltaics.

Coupling between quantum dots and photonic crystal cavities

<p indent="0mm">Cavity quantum electrodynamics studies the interaction between light and matter at the single quanta level, i.e., cavity photons and quantum emitters, which has widespread applications in quantum information processing and optical devices, such as lasers, solar cells and light-emitting diodes. To study cavity quantum electrodynamics, a quantum emitter with excellent quantum properties and a cavity with high quality factor and small mode volume are preferred. The coupling between self-assembled quantum dots and photonic crystal cavities has attracted broad attention due to the advanced semiconductor fabrication techniques and excellent optical properties. Great progress has been made in the last two decades, which provides an efficient quantum interface between light and matter at the near-infrared domain. The self-assembled quantum dots have excellent optical properties, including high brightness, high single photon purity, and high indistinguishability, possessing great advantages in the applications of laser, single-photon source, entangled photon source and quantum bit. On the other hand, photonic crystal cavities have high quality factor and small mode volume, providing strong optical confinement. It can greatly enhance the interaction between light and matter. By coupling to photonic crystal cavities, the optical properties of quantum dots can be strongly modified. For example, in the weak coupling regime, where the coupling strength <italic>g</italic> is smaller than the decay rate of the system, the spontaneous emission rate of quantum dots is enhanced due to the increase of local density of states. The enhancement factor, known as Purcell factor, is proportional to the quality factor and inversely proportional to the mode volume of the cavity. The weak coupling can be used to optimize the performance of optical devices, such as reducing the laser threshold, increasing the efficiency of single-photon source and entangled photon source. In the strong coupling regime, where the coupling strength <italic>g</italic> is larger than the decay rate, the energy shifts back and forth between quantum dots and cavity modes at vacuum Rabi frequency, leading to the formation of exciton-polariton with Rabi splitting about 2<italic>g</italic>. The strong coupling has been widely proposed for the applications in quantum information processing and investigation of nonlinear optical effects at single photon level, such as the realization of quantum logical gate, the operation of qubit, the transfer of quantum states and single-photon blockade. Additionally, photonic crystal structures have a high level of integration. By integrating with waveguides, the coupled system, served as quantum nodes, can be connected to achieve the quantum internet. Besides the traditional photonic crystal cavities, recently a new type of cavity with topological origin has been proposed and demonstrated, providing a more robust platform to investigate cavity quantum electrodynamics and develop optical devices with built-in protection for topological nanophotonic circuitry. In this paper, we review the basic principle and recent progress of the coupling between self-assembled quantum dots and photonic crystal cavities, which show a great opportunity to realize various optical devices with diverse functionalities, providing an ideal platform to realize on-chip photonic circuitry.

Effect of Micelle Encapsulation on Toxicity of CdSe/ZnS and Mn-Doped ZnSe Quantum Dots

The optical properties of quantum dots (QD) make them excellent candidates for bioimaging, biosensing, and therapeutic applications. However, conventional QDs are comprised of heavy metals (e.g., cadmium) that pose toxicity challenges in biological systems. Synthesising QDs without heavy metals or introducing thick surface coatings, e.g., by encapsulation in micelles, can reduce toxicity. Here, we examined the toxicity of micelle encapsulated tetrapod-shaped Mn-doped ZnSe QDs, comparing them to 3-mercaptopropionic acid (MPA)-capped Mn-doped ZnSe QDs prepared by ligand exchange and commercial CdSe/ZnS QD systems that were either capped with MPA or encapsulated in micelles. HepG2 cell treatment with MPA-coated CdSe/ZnS QDs resulted in a dose-dependent reduction of viability (MTT assay, treatment at 0–25 μg/mL). Surprisingly, no reactive oxygen species (ROS) or apoptotic signaling was observed, despite evidence of apoptotic behavior in flow cytometry. CdSe/ZnS QD micelles showed minimal toxicity at doses up to 25 μg/mL, suggesting that thicker protective polymer layers reduce cytotoxicity. Despite their shape, neither MPA- nor micelle-coated Mn-doped ZnSe QDs displayed a statistically significant toxicity response over the doses investigated, suggesting these materials as good candidates for bioimaging applications.

The effect of nanorod on the nonlinear optical properties of quantum dot in a hybrid structure: under a quasistatic approximation

In a hybrid structure consisting of a nanorod and a core/shell quantum dot, the interparticle interactions of elements and the effect of the optical response of nanorod on the third-order nonlinear optical response of quantum dot are investigated. The effective parameters in these interactions such as the enhancement factors, type of structural configuration, dimensional ratio, type of background medium, quantum dot size and interparticle distance are studied in the structure for engineering the system to an optimum response. The enhancement factors of field due to the presence of nanorod are obtained in the site of quantum dot, followed by the third-order optical nonlinear response quantum dot is calculated by using the local field theory. It is seen for the situation where quantum dot is perpendicular to the axis of nanorod, the interparticle interactions and enhancement factors have maximum amount at a given aspect ratio of nanorod (about 2.5), depending on the type of surrounding environment. Therefore, the nanorod can produce great nonlinearities atthe quantum dot compared to the spherical nanoparticle into the hybrid structure . As well, it is found that the larger sizes of quantum dot and less interparticle distances cause to the stronger coupling and thereby larger optical nonlinearity in the quantum dot.

Safe Synthesis of InP Quantum Dots for Biological Applications

Semiconductor nanocrystals (also known as quantum dots) have been extensively studied because of their unique optical properties which makes them promising candidates for bio imaging and bio sensing. II-VI semiconductor quantum dots are commonly used in biomedical applications because of their near unit quantum yields and narrow emission profiles. Despite these advantages, II-VI semiconductor nanocrystals contain toxic metals. As a result, III-V semiconductor nanocrystals such as InP are promising replacements for cadmium-based semiconductor nanocrystals. However, the synthesis of bright InP quantum dots with narrow size distribution is challenging mainly due to the use of overly reactive phosphorus precursors like tris(trimethylsilyl) phosphine (TMS)3P. This reagent is also highly flammable. We employed less pyrophoric sterically encumbered tris(triethylsilyl) phosphine and tris(tributylsilyl) phosphine for the synthesis and observed that quantum yield and the emission color saturation (fwhm) of InP nanocrystals are improved compared to those prepared with (TMS)3P, but not up to the levels realized with CdSe. HF treatment is often employed as a post-synthetic treatment to improve the optical properties of quantum dots. We demonstrate that ammonium bifluoride is a safer alternative to extremely hazardous HF. Ammonium bifluoride etched InP core dots were further passivated to create InP/ZnSeS core-shell quantum dots that were later water-solubilized and functionalized for biological applications. Figure 1

Graphene plasmonic coupling with intersubband radiation of truncated pyramidal-shaped InAs/GaAs quantum dots

It is well known that the intersubband radiation of InAs/GaAs quantum dots (QDs) falls in the terahertz/far-infrared spectral region. If these so-called atom-like systems are placed in the vicinity of graphene, their radiation can be coupled with plasmonic modes of graphene. As the graphene plasmons tightly concentrate the electromagnetic waves in the small zones, beyond the diffraction limit, the optical properties of QDs can then be enhanced by the so-called Purcell effect if frequency tuning and mode overlapping are well performed. Owing to this idea, in this work, we report on the enhancement of linear and third-order optical susceptibilities of truncated pyramidal-shaped InAs/GaAs QDs with use of graphene plasmonics. Graphene flakes in various configurations were located inside the QDs, and their transition dipole moments (TDMs) were calculated. Our results show 120-fold enhancement in TDM with optimization on the flakes’ and QDs’ geometries. Consequently, the linear and nonlinear optical susceptibilities of QDs are enhanced noticeably. Precisely, the linear and third-order susceptibilities of QDs with base length of 25 nm and height of 3 nm were enhanced enormously up to 1.18 × 10 5 and 1.4 × 10 10 times, respectively. This passive method is promising for enhancing the performance of QD-based optoelectronic devices such as lasers, LEDs, sensors, and so on.

Giant enhancement of optical nonlinearity in two-dimensional materials by multiphoton-excitation resonance energy transfer from quantum dots

Colloidal quantum dots are promising photoactive materials that enable plentiful photonic and optoelectronic applications ranging from lasers, displays and photodetectors to solar cells1,2,3,4,5,6,7,8,9. However, these applications mainly utilize the linear optical properties of quantum dots, and their great potential in the broad nonlinear optical regime is still waiting for full exploration10,11,12. Here, we demonstrate that a simple coating of a sub-200-nm-thick quantum dot film on two-dimensional materials can significantly enhance their nonlinear optical responses (second, third and fourth harmonic generation) by more than three orders of magnitude. Systematic experimental results indicate that this enhancement is driven by a non-trivial mechanism of multiphoton-excitation resonance energy transfer, where the quantum dots directly deliver their strongly absorbed multiphoton energy to the adjacent two-dimensional materials by a remote dipole–dipole coupling. Our findings could expand the applications of quantum dots in many exciting areas beyond linear optics, such as nonlinear optical signal processing, multiphoton imaging and ultracompact nonlinear optical elements.

Nanocrystal Quantum Dots: From Discovery to Modern Development.

This review traces nanocrystal quantum dot (QD) research from the early discoveries to the present day and into the future. We describe the extensive body of theoretical and experimental knowledge that comprises the modern science of QDs. Indeed, the spatial confinement of electrons, holes, and excitons in nanocrystals, coupled with the ability of modern chemical synthesis to make complex designed structures, is today enabling multiple applications of QD size-tunable electronic and optical properties.

Lasing emission from Tin disulfide quantum dots

Lasing emission is a good way to exhibit the excellent optical properties of quantum dots (QDs). In this paper, we synthesize the Tin disulfide (SnS2) QDs by a facile method of sonication. In a Fabry–Perot laser cavity, the lasing emission at ~500 nm is realized by the SnS2 QDs with an excitation threshold value of 19.3 kW/cm2. The results show that the SnS2 QDs have a promising application as laser gain medium.

Linear and nonlinear optical properties in spherical quantum dots: Inversely quadratic Hellmann potential

The aims of the reported work are to provide new insights into the quantum dot optical properties confined in an inverse of a quadratic Hellmann potential. The Schrödinger equation is solved using the Nikiforov-Uvarov (NU) method, in order to obtain the analytical expressions of the eigenenergies and the eigenfunctions. The linear together with the third-order nonlinear changes in absorption coefficients and refractive index are investigated using the density matrix formalism. The absorption coefficients and the refractive index changes are strong related to the structure parameters and the optical intensity.

Excited-State Properties of Defected Halide Perovskite Quantum Dots: Insights from Computation.

CsPbBr3 quantum dots (QDs) have been recently suggested for their application as bright green light-emitting diodes (LEDs); however, their optical properties are yet to be fully understood and characterized. In this work, we utilize time-dependent density functional theory to analyze the ground and excited states of the CsPbBr3 clusters in the presence of various low formation energy vacancy defects. Our study finds that the QD perovskites retain their defect tolerance with limited perturbance to the simulated UV-vis spectra. The exception to this general trend is that Br vacancies must be avoided, as they cause molecular orbital localization, resulting in trap states and lower LED performance. Blinking will likely still plague CsPbBr3 QDs, given that the charged defects critically perturb the spectra via red-shifting and lower absorbance. Our study provides insight into the tunability of CsPbBr3 QDs optical properties by understanding the nature of the electronic excitations and guiding improved development for high-performance LEDs.

Effect of magnetic field on energy states and optical properties of quantum dots and quantum antidots

In this study, the effect of magnetic field on electronic spectra and optical properties of spherical quantum dot (QD) and quantum anti-dot (QAD) are investigated. The energies and corresponding wave functions are calculated by using the finite difference method and oscillator strengths are obtained based on the dipole approximation approach. Based on perturbation theory, our theoretical results are presented and it will be shown clearly how the magnetic field affects energy levels and intersubband transitions. In the following, our numerical results based on a comparative perspective for both QD and QAD models are given. Our results indicate that in the presence of magnetic field, changes on energy levels and optical properties of QD and QAD are considerably different. In addition, we study the effect of change in core and shell dimensions in the presence of magnetic field on the energy states and oscillator strengths of both nanostructures.

Effect of Fe-=SUB=-3-=/SUB=-O-=SUB=-4-=/SUB=- nanoparticle concentration on the luminescence of AgInS-=SUB=-2-=/SUB=-/ZnS in hybrid complex CaCO-=SUB=-3-=/SUB=--Fe-=SUB=-3-=/SUB=-O-=SUB=-4-=/SUB=-@AgInS-=SUB=-2-=/SUB=-/ZnS-=SUP=-*-=/SUP=-

In this paper, we studied the properties of a multifunctional system, in which the luminescent and magnetic properties are combined. The calcium carbonate microspheres are used as porous matrices for complexes combining luminescence properties of AgInS2/ZnS quantum dots and magnetic properties of Fe3O4 nanoparticles. The study investigates the effect of magnetic nanoparticles concentration on optical properties of quantum dots in CaCO3-Fe3O4@AgInS2/ZnS complexes. It is shown that applying calcium carbonate microspheres as a matrix permits to reduce quenching of the quantum dots luminescence. Keywords: hybrid system; ternary quantum dots; magnetic nanoparticles; iron oxide; calcium carbonate microspheres.

Emission and Decay Lifetime Tunability in Less-Toxic Quaternary ZnCuInS Quantum Dots

Due to the increasing need for the use of safer nanomaterials in the electronic and optoelectronic sectors, there is a growing emphasis on the development of less-toxic quantum dots (QD) as replacements for traditional cadmium or lead-based QD technologies. Although the ternary Cu-In-S (CIS) QDs have gained prominence due to their advantageous optical properties and unique tunability, their intrinsically defective structures present some drawbacks for device applications. A one-pot, high-throughput process was developed to synthesize quaternary Zn-Cu-In-S (ZCIS) QDs, which show higher structural crystallinity and lattice stability. Stoichiometric variation was explored to determine its impact on QD optical and structural properties. It was found that the trial-cationic structure of the quaternary ZCIS QDs allowed further variation and flexibility of QD properties. Induction of Cu deficiency via In- or Zn-excess precursor ratios improved photoluminescence (PL) intensity and structural stability. ZnS overcoating was investigated, but it was found that the Zn-containing ZCIS cores, which are more stable than core CIS QDs, benefitted only minimally from Zn-passivation. The highly emissive quaternary QDs produced through this scalable synthesis procedure are widely tunable and functionalizable, capable of emission from 564-650 nm, and with a high lifetime up to 159 ns, making them more suitable for a variety of device applications.

Synthesis and characterization of oleic acid stabilized CdTe quantum dots and their properties as luminescence quencher of a pyridine pendented rod-coil homopolymer

Abstract We report a facile one-step non aqueous synthesis of oleic acid stabilized cadmium telluride (CdTe) quantum dots (QDs) with an average diameter of 3 nm to 4 nm by hot injection method. The synthesized oleic acid capped QDs observed by TEM were nearly spherical. The optical properties of QDs were characterized by UV-Vis absorption spectra and photoluminescence (PL) spectra. The structures of QDs and their surface passivation were further verified using transmission electron microscope (TEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The quenching effect of the CdTe QD was explored by addition of CdTe nanocrystals into a solution of rod-coil homopolymer (poly[10-(6-(9,9-diethyl-7-(pyridin-4- yl)-9H-fluoren-2-yl)naphthalen-2-yloxy) decyl methacrylate]) (PFNA) having pendent pyridine. The gradual addition of quantum dots to the solution of PFNA quenched the PL spectra of PFNA. This may be used to explore the coordination ability of pyridine containing homopolymer with CdTe quantum dots.

Strong photocharging effect in CsPbBr3 nanocrystal films

In this study, a strong photocharging effect has been detected by a spectroscopic study of colloidal CsPbBr3 quantum dot film. Photocharging induces the formation of charged excitons, even with the application of a very low excitation laser power. Thus, it can introduce a drastic problem on the optical properties of quantum dots when the charges are involved. The charge exciton then can absorb another photon from the next laser pulse, leading to a trion state. The presence of the trion state was proven by studying its behavior against three effects, namely laser power, electric field (EF) and temperature (T) dependence. The trion area of the peak increases linearly with the increasing of the laser power, which we consider to be an indication of the influence of a strong photocharging effect, suggesting that long-lived charges can be kept trapped in quantum dots (QDs). It was also found the trion is affected by an external electric field, due to the weak Stark effect. It is more sensitive than the excitonic state to the electric field due to the presence of electron–electron repulsion forces. A red-shift behavior was observed when heating the sample above 180 K, which is a strong evidence of the presence of a trapping state.

Tuning the Optical Properties of Quantum Dots to Increase the Efficiency of Solar Cells

Tuning the Optical Properties of Quantum Dots to Increase the Efficiency of Solar Cells

Electronic and Optical Properties of Quantum Dot Surrounded by Doped Cylindrical Nanowire

Electronic and Optical Properties of Quantum Dot Surrounded by Doped Cylindrical Nanowire

Study on fluorescence properties and stability of Cu2+-Substituted CsPbBr3 perovskite quantum dots

The toxicity and stability of all-inorganic perovskite quantum dots are major challenge to be addressed in its commercialization process. Here, the toxicity of lead is reduced while improving the optical properties of quantum dots via replacing Pb2+ ions in CsPbBr3 perovskites quantum dots with low-toxicity and cost-effectiveness Cu2+ cations. The PL emission and absorption peaks of quantum dots appear blue shift due to lattice shrinkage caused by copper ion doping. At the same time, we also observed that with the increase of Cu2+ doping concentration, the fluorescence lifetime of quantum dots decreased from 40.66 ns to 8.23 ns. Next, the slim CsPbBr3:Cu@SiO2 core-shell QDs were synthesized via a simply one-step synthesis method. Compared with the original CsPbBr3:Cu QDs, the stability of the quantum dots after coated has been significantly improved. Benefiting from this effective cladding strategy, these CsPbBr3:Cu@SiO2 can be well used for manufacturing high-performance perovskite LEDs.