Near-infrared Spectral Regime Research Articles

Nonlinear Thermoplasmonics in Graphene Nanostructures.

The linear electronic dispersion relation of graphene endows the atomically thin carbon layer with a large intrinsic optical nonlinearity, with regard to both parametric and photothermal processes. While plasmons in graphene nanostructures can further enhance nonlinear optical phenomena, boosting resonances to the technologically relevant mid- and near-infrared (IR) spectral regimes necessitates patterning on ∼10 nm length scales, for which quantum finite-size effects play a crucial role. Here we show that thermoplasmons in narrow graphene nanoribbons can be activated at mid- and near-IR frequencies with moderate absorbed energy density, and furthermore can drive substantial third-harmonic generation and optical Kerr nonlinearities. Our findings suggest that photothermal excitation by ultrashort optical pulses offers a promising approach to enable nonlinear plasmonic phenomena in nanostructured graphene that avoids potentially invasive electrical gating schemes and excessive charge carrier doping levels.

A molecular pyroelectric enabling broadband photo-pyroelectric effect towards self-driven wide spectral photodetection

Broadband spectral photoresponse has shown bright prospects for various optoelectronic devices, while fulfilling high photoactivity beyond the material bandgap is a great challenge. Here, we present a molecular pyroelectric, N-isopropylbenzylaminium trifluoroacetate (N-IBATFA), of which the broadband photo-pyroelectric effects allow for self-driven wide spectral photodetection. As a simple organic binary salt, N-IBATFA possesses a large polarization (~9.5 μC cm−2), high pyroelectric coefficient (~6.9 μC cm−2 K−1) and figures-of-merits (FV = 187.9 × 10−2 cm2 μC−1; FD = 881.5 × 10−5 Pa−0.5) comparable to the state-of-art pyroelectric materials. Particularly, such intriguing attributes endow broadband photo-pyroelectric effect, namely, transient currents covering ultraviolet (UV, 266 nm) to near-infrared (NIR, 1950 nm) spectral regime, which breaks the restriction of its optical absorption and thus allows wide UV-NIR spectral photodetection. Our finding highlights the potential of molecular system as high-performance candidates toward self-powered wide spectral photodetection.

MoSe2/WS2 heterojunction photodiode integrated with a silicon nitride waveguide for near infrared light detection with high responsivity

We demonstrate experimentally the realization and the characterization of a chip-scale integrated photodetector for the near-infrared spectral regime based on the integration of a MoSe2/WS2 heterojunction on top of a silicon nitride waveguide. This configuration achieves high responsivity of ~1 A W−1 at the wavelength of 780 nm (indicating an internal gain mechanism) while suppressing the dark current to the level of ~50 pA, much lower as compared to a reference sample of just MoSe2 without WS2. We have measured the power spectral density of the dark current to be as low as ~1 × 10−12 A Hz−0.5, from which we extract the noise equivalent power (NEP) to be ~1 × 10−12 W Hz−0.5. To demonstrate the usefulness of the device, we use it for the characterization of the transfer function of a microring resonator that is integrated on the same chip as the photodetector. The ability to integrate local photodetectors on a chip and to operate such devices with high performance at the near-infrared regime is expected to play a critical role in future integrated devices in the field of optical communications, quantum photonics, biochemical sensing, and more.

Cylindrical Metalens for Generation and Focusing of Free-Electron Radiation.

Metasurfaces constitute a powerful approach to generate and control light by engineering optical material properties at the subwavelength scale. Recently, this concept was applied to manipulate free-electron radiation phenomena, rendering versatile light sources with unique functionalities. In this Letter, we experimentally demonstrate spectral and angular control over coherent light emission by metasurfaces that interact with free-electrons under grazing incidence. Specifically, we study metalenses based on chirped metagratings that simultaneously emit and shape Smith–Purcell radiation in the visible and near-infrared spectral regime. In good agreement with theory, we observe the far-field signatures of strongly convergent and divergent cylindrical radiation wavefronts using in situ hyperspectral angle-resolved light detection in a scanning electron microscope. Furthermore, we theoretically explore simultaneous control over the polarization and wavefront of Smith–Purcell radiation via a split-ring-resonator metasurface, enabling tunable operation by spatially selective mode excitation at nanometer resolution. Our work highlights the potential of merging metasurfaces with free-electron excitations for versatile and highly tunable radiation sources in wide-ranging spectral regimes.

Single Sideband Suppressed Carrier Modulation With Spatiotemporal Metasurfaces at Near-Infrared Spectral Regime

Single sideband suppressed carrier (SSB-SC) modulation enables high efficiency and dispersion-tolerant shifting of light that is of great interest for many optical systems and applications. Herein, the design procedure of a spatiotemporal reflective metasurface is proposed to realize SSB-SC modulation in near-infrared spectral regime. The metasurface consists of a periodic array of plasmonic nanostrips integrated with indium-tin-oxide (ITO) in metal-insulator-metal configuration, wherein two sets of time-varying biasing signals are independently applied to the metasurface for modulating the permittivity of ITO in space and time. The spatiotemporal metasurface features a sawtooth phase profile with linear span over <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$2\pi$</tex-math></inline-formula> and a constant amplitude in time domain, that can be obtained by judicious adjustment of the biasing waveforms. It is established that such spatiotemporal metasurface allows for spurious-free frequency conversion by transforming the incident signal into the first-order up-modulated sideband and suppressing all the undesired mixing products. The normalized conversion efficiency of more than 99% is achieved for the metasurface, while the peak levels of the largest undesired mixing product and the fundamental frequency are reduced down to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-39$</tex-math></inline-formula> dB and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-44$</tex-math></inline-formula> dB, respectively. The proposed spatiotemporal metasurface is exploited for multi-channel and multi-beam scanning via pixelated control over the modulation phase delays assigned to the constituent elements of the spatially-interleaved sub-arrays, rendering a shared-aperture metasurface in space-time. In this case, the crosstalk between the channels with identical operating frequencies is substantially reduced. In addition, spatiotemporal redirection of light based on frequency gradient metasurface is demonstrated, which enables ultrafast, all-angle, and continuous beam-scanning as progressing in time.

Near ultraviolet photonic integrated lasers based on silicon nitride

Low phase noise lasers based on the combination of III–V semiconductors and silicon photonics are well established in the near-infrared spectral regime. Recent advances in the development of low-loss silicon nitride-based photonic integrated resonators have allowed them to outperform bulk external diode and fiber lasers in both phase noise and frequency agility in the 1550 nm-telecommunication window. Here, we demonstrate for the first time a hybrid integrated laser composed of a gallium nitride-based laser diode and a silicon nitride photonic chip-based microresonator operating at record low wavelengths as low as 410 nm in the near-ultraviolet wavelength region suitable for addressing atomic transitions of atoms and ions used in atomic clocks, quantum computing, or for underwater LiDAR. By self-injection locking of the Fabry–Pérot diode laser to a high-Q (0.4 × 106) photonic integrated microresonator, we reduce the optical phase noise at 461 nm by a factor greater than 100×, limited by the device quality factor and back-reflection.

Deep Learning-Assisted Enhanced Fano Resonances in Symmetry-Breaking SOI Metasurface

Metasurfaces analogues of Fano resonances provide a powerful platform for high sensitivity sensing, nonlinear optics, and light manipulation. However, previous Fano-resonant metasurfaces usually are not compatible with silicon complementary metal-oxide semiconductor circuits due to their hybrid material structures and large non-radiative loss. Herein, we theoretically demonstrate a silicon-on-insulator metasurface (SOIM) enhancing Fano resonances by using a tandem neural network design. Multiple Fano resonances with high Q-factor have been observed in the symmetry-breaking SOIM. The Fano-resonant mechanism of the SOIM is analyzed. Additionally, the spectral features of the Fano-resonant SOIM as a function of the symmetry tuning factor of the double silicon nanobars and the environment refractive index are also investigated. The result shows that the Fano-resonant SOIM as a methanol sensor with a sensitivity of 310 nm/RIU can achieve an overall figure of merit of 195 in the near-infrared spectral regime. The designed Fano-resonant SOIM shows enormous potential applications in highly sensitive sensors and light-matter interaction enhancement.

Broadband continuous beam-steering with time-modulated metasurfaces in the near-infrared spectral regime

A time-modulated metasurface integrated with indium-tin-oxide (ITO) can dynamically manipulate the scattered light by imparting dispersionless phase discontinuities with 2π span on wavefronts of the generated sidebands. However, maximal frequency conversion efficiency is restricted to a narrow bandwidth at the vicinity of the resonant wavelength due to the dispersive nature of light–matter interactions in such ITO-integrated metasurfaces. Herein, a multiwavelength time-modulated meta-molecule is numerically investigated, which consists of four metal–insulator–metal meta-atoms that are judiciously designed to support four resonant wavelengths at the near-infrared regime. The metasurface platform allows for application of four sets of independent radio-frequency signals to each meta-molecule, which are optimized to excite the output spectra with dominant first-order up-modulated sidebands. Individual modulation of each meta-atom leads to efficient sideband generation at resonant wavelength corresponding to the biased meta-atom. Nevertheless, the conversion efficiency decays rapidly at off-resonant wavelengths. Concurrent modulation of all four meta-atoms within the meta-molecule configuration offers a pathway to simultaneously generate dominant sidebands at all resonant wavelengths while enhancing the frequency conversion efficiency at inter-resonant wavelengths. As the potential application, beam-steering at the up-modulated sideband by both individually and simultaneously biased meta-atoms is demonstrated. It is revealed that simultaneous modulation enables continuous dynamic light deflection over a broad spectrum spanning on 1–1.8 μm, while the steering angle of the wavelengths changes in the range of 34°–85°. Broadband continuous beam-scanning is a non-trivial task that cannot be accomplished by a quasi-static metasurface relying on dispersive resonant phase shift, which hinders simultaneous implementation of linear phase gradients at all incident wavelengths.

Effect of silver iodide (AgI) on structural and optical properties of cobalt doped lead-borate glasses

Materials with distinct optical characteristics are still being explored. Hence, AgI doped cobalt-lead borate glasses of composition [29.7PbO – 0.3CoO – (70-x) B2O3 – xAgI (x = 0.0, 0.25, 0.5 and 1.0 mol%)] were synthesized via conventional melt quenching technique. XRD patterns and SEM micrographs confirmed the prepared glass system's amorphous nature; EDAX elemental analysis was also performed. According to increased density and decreased average boron-boron separation, AgI additives were found to enforce the glassy network's compactness. FT-IR analysis indicates the entry of AgI as a network modifier by converting the tetrahedral (BO4) to trigonal (BO3) units with NBO's ratio growth. The Raman data accords with FT-IR results and provides complementary information around these glasses by detecting additional structural groups. The ellipsometer spectroscopy technique confirmed the ability to control the refractive index of the current glassy system with the AgI addition. The absorption spectra clarified a gradual enhancement of Co3+/Co2+ ions at tetrahedral and/or octahedral sites by AgI additives. Ligand field parameters, such as crystal field intensity (10Dq)and Racah parameters(B&C), were accurately determined. The calculated nephelauxetic ratio (β)indicated a reducing covalent nature among Co2+ ions and the nearby bonds. Calculations of the UV absorption edges showed a clear red-shift by AgI additives with a remarkable gradual reduction of the optical band gap. Besides, the Urbach energy increased, and the metallization criterion varied from 0.394 to 0.391 eV-1, reflecting the semiconductor character of these glasses. The spectral tunability for optical absorption provided here by AgI additives qualifies present glasses as optically active materials for several potential applications in multi-functional optical devices operating in the visible and near-infrared (NIR) spectral regimes.

Influence of La2O3 on the structural, mechanical and optical features of cobalt doped heavy metal borate glasses

The impact of rare-earth oxide (La2O3) on the structural, mechanical and optical properties of cobalt-doped heavy metal borate glassy system is studied. XRD assured the amorphous nature of the prepared samples. The density and average boron-boron separation were found to increase with La2O3 content, thereby enforcing the compactness of the glass network. FT-IR analysis revealed the growth of NBO's ratio due to the gradual conversion of the tetrahedral (BO4) to trigonal (BO3) units with the development of a certain boroxol group (B3O6) fraction. A noticeable enhancement of the elasticity properties, such as the elastic, bulk, and Young's moduli, as well as the microhardness, was confirmed by measuring the ultrasound velocities within prepared samples. The absorption and photoluminescence emission spectra showed a progressive enhancement of Co3+/Co2+ ions in the tetrahedral and/or octahedral positions with La2O3 content. The ligand field strength and Racah parameters were estimated, in which the ionicity nature between Co2+ ions and the nearby ligands is inferred from the nephelauxetic effect. Absorption edge analysis, here performed through Tauc's model, showed a decrease in the band gap and a rise in Urbach energy; the values of each, together with the metallization parameter, reflect the semiconducting character of the prepared samples. The dispersion of the refractive index was determined using the Wemple-DiDomenico single oscillator model and compared to the optical gap energy. Additionally, the nonlinear optical coefficients, here determined within the lower energy spectral range using a third-order nonlinear susceptibility, exhibited progressively increasing value, suggesting a possible integration of the current system in potential nonlinear optical applications. Furthermore, the absorption and photoluminescence spectral tunability here offered through La2O3 additives qualifies the current glasses as optically active materials for many possible applications in multifunctional optical devices operating in visible and near-infrared spectral regimes.

Design and parametric simulation of triangle nano-particle structures for the visible and near-infrared frequencies

In this paper, the cross bow-tie nano-antenna (CBNA) with dimensions around wavelength of incident light is designed and simulated, with an emphasis on absorption cross section, absorption and reflection coefficients, as well as the electric field enhancement, in the visible and near-infrared spectral regime. The optical properties of the proposed nano-antenna have been investigated in details based on its geometric parameters and material type (for patch, substrate and the medium surrounding the antenna). Then the array of unit cell of proposed CBNA has been performed. The spectral response of the nano-antenna can be adjusted by geometric parameters, which provides control over the spatial resonance position and electric field enhancement amplitude. The CBNA with due to symmetric shape along the antenna’s length and width, is less sensitive to incident light polarization. Since the polarization of incident light is not selective and this nano-structure can enhance the incident light in both directions x and y, so it will useful for optical energy harvesting. In order to determine the resonance properties of CBNA, computer simulation technology (CST) microwave studio(© 1998–2018 CST.), as a three-dimensional electromagnetic field solver based on finite integration technique (FIT), is used for simulations. Commercial software, FDTD (finite difference time domain) Solutions(© 2013–2017 Lumerical Inc.), available from Lumerical corporation, is also used to calculate the amount of absorption, reflection and transmission coefficients of the CBNA.

Information Transfer by Near-Infrared Surface-Plasmon-Polariton Waves on Silver/Silicon Interfaces

Electronic interconnections restrict the operating speed of microelectronic chips as semiconductor devices shrink. As surface-plasmon-polariton (SPP) waves are localized, signal delay and crosstalk may be reduced by the use of optical interconnections based on SPP waves. With this motivation, time-domain Maxwell equations were numerically solved to investigate the transport of information by an amplitude-modulated carrier SPP wave guided by a planar silicon/silver interface in the near-infrared spectral regime. The critical-point model was used for the permittivity of silicon and the Drude model for that of silver. The signal can travel long distances without significant loss of fidelity, as quantified by the Pearson and concordance correlation coefficients. The signal is partially reflected and partially transmitted without significant loss of fidelity, when silicon is terminated by air; however, no transmission occurs when silicon is terminated by silver. The fidelity of the transmitted signal in the forward direction rises when both silicon and silver are terminated by air. Thus, signals can possibly be transferred by SPP waves over several tens of micrometers in microelectronic chips.

Discovery and analysis of a ULX nebula in NGC 3521

ABSTRACT We present Very Large Telescope/X-shooter and Chandra X-ray observatory/ACIS observations of the ULX [SST2011] J110545.62 + 000016.2 in the galaxy NGC 3521. The source identified as a candidate near-infrared counterpart to the ULX in our previous study shows an emission line spectrum of numerous recombination and forbidden lines in the visible and near-infrared spectral regime. The emission from the candidate counterpart is spatially extended (∼34 pc) and appears to be connected with an adjacent H ii region, located ∼138 pc to the NE. The measured velocities of the emission lines confirm that both the candidate counterpart and H ii region reside in NGC 3521. The intensity ratios of the emission lines from the ULX counterpart show that the line emission originates from the combined effect of shock and photoionization of low metallicity (12 + log (O/H) = 8.19 ± 0.11) gas. Unfortunately, there is no identifiable spectral signature directly related to the photosphere of the mass-donor star in our spectrum. From the archival Chandra data, we derive the X-ray luminosity of the source in the 0.3–7 keV range to be (1.9 ± 0.8) × 1040 er g cm−2 s−1, almost a factor of four higher than what is previously reported.

Transparent Conductive Oxides and Their Applications in Near Infrared Plasmonics

Transparent conductive oxides (TCOs) have been widely used as an important component of optoelectronic devices. They are required to exhibit high performance in both visible‐range transparency and electronic conductivity simultaneously. In near infrared (NIR) wavelength, these highly doped semiconductor oxide materials exhibit a drop in their real part of dielectric permittivity from positive to negative. In other words, the epsilon‐near‐zero (ENZ) frequency of TCO is located in NIR spectral regime. On the other hand, the imaginary part of the permittivity is relatively low which implies less optical loss when compared to noble metals. This “metal‐like” permittivity dispersion characteristic of TCOs means their capability to support surface plasmons (SPs) in the NIR regime. In this paper, a summary of various physical parameters of commonly used TCOs such as ITO, AZO, and FTO, etc., is given. These parameters include carrier density, carrier mobility, plasma frequency, and ENZ wavelength. The difference among these parameters determines their diverse performance in infrared range. In this paper, the important role of TCOs for applications in the NIR/IR wavelength ranges are reinforced, as they are demonstrated in the visible range.

Role of temperature in de-mixing absorbance spectra composed of compound electrolyte solutions.

This work is focused on the role of temperature in the de-mixing of absorbance spectra measured in mixed aqueous Na2SO4 and NaNO3 solutions. First, the influence of temperature on the absorbance spectrum of demineralized water was determined. Second, the absorbance spectra of five separate electrolytes (NaNO2, NaNO3, CaCl2, K2CO3, and NaOH) at three temperatures (4°C, 25°C, and 50°C) for concentrations ranging from 0.0625M to 0.5M were examined. These five electrolytes show similar temperature dependencies. Finally, absorbance spectra of mixed solutions were investigated at temperatures of 5°C, 15°C, 25°C, 35°C, and 45°C for concentrations ranging from 0.0625M to 0.5M per electrolyte in the mixture. The spectral window from 650 to 1100nm was utilized to observe the ionic and temperature influences on the vibrational modes of the OH bond in the solvent molecules. The effects of dissolving Na2SO4 and NaNO3 are nonlinearly cumulative at lower temperatures indicating extended alteration of the water structure beyond the first hydration shell. A similar trend was observed for a mixture of Na2CO3 and NaCl. Furthermore, it was found that higher temperatures are better for recovering the separate component absorption signatures of an electrolyte mixture. The near-infrared spectral regime is well suited for integrated sensing, and therefore these results can help in designing an integrated sensor to identify inorganic species in water.

Tunable optical switching in the near-infrared spectral regime by employing plasmonic nanoantennas containing phase change materials

We propose the design of switchable plasmonic nanoantennas (SPNs) that can be employed for optical switching in the near-infrared regime. The proposed SPNs consist of nanoantenna structures made up of a plasmonic metal (gold) such that these nanoantennas are filled with a switchable material (vanadium dioxide). We compare the results of these SPNs with inverted SPN structures that consist of gold nanoantenna structures surrounded by a layer of vanadium dioxide (VO2) on their outer surface. These nanoantennas demonstrate switching of electric-field intensity enhancement (EFIE) between two states (On and Off states), which can be induced thermally, optically or electrically. The On and Off states of the nanoantennas correspond to the metallic and semiconductor states, respectively of the VO2 film inside or around the nanoantennas, as the VO2 film exhibits phase transition from its semiconductor state to the metallic state upon application of thermal, optical, or electrical energy. We employ finite-difference time-domain (FDTD) simulations to demonstrate switching in the EFIE for four different SPN geometries - nanorod-dipole, bowtie, planar trapezoidal toothed log-periodic, and rod-disk - and compare their near-field distributions for the On and Off states of the SPNs. We also demonstrate that the resonance wavelength of the EFIE spectra gets substantially modified when these SPNs switch between the two states.

Ultra-broadband enhancement of nonlinear optical processes from randomly patterned super absorbing metasurfaces

Broadband light trapping and field localization is highly desired in enhanced light-matter interaction, especially in harmonic generations. However, due to the limited resonant bandwidth, most periodic plasmonic nanostructures cannot cover both fundamental excitation wavelength and harmonic generation wavelength simultaneously. Therefore, most previously reported plasmonic nonlinear optical processes are low in conversion efficiency. Here, we report a strong enhancement of second harmonic generation based on a three-layered super absorbing metasurface structure consisting of a dielectric spacer layer sandwiched by an array of random metallic nanoantennas and a metal ground plate. Intriguingly, the strong light trapping band (e.g. >80%) was realized throughout the entire visible to near-infrared spectral regime (i.e., from 435 nm to 1100 nm), enabling plasmonically enhanced surface harmonic generation and frequency mixing across a broad range of excitation wavelengths, which cannot be achieved with narrow band periodic plasmonic structures. By introducing hybrid random antenna arrays with small metallic nanoparticles and ultra-thin nonlinear optical films (e.g. TiO2) into the nanogaps, the nonlinear optical process can be further enhanced. This broadband light-trapping metastructure shows its potential as a building block for emerging nonlinear optical meta-atoms.

Radiation effects on GaAs/AlGaAs core/shell ensemble nanowires and nanowire infrared photodetectors

With the recent advances in nanowire (NW) growth and fabrication, there has been rapid development and application of GaAs NWs in optoelectronics. It is also of importance to study the radiation tolerance of optoelectronic nano-devices for atomic energy and space-based applications. Here, photoluminescence (PL) and time-resolved photoluminescence measurements were carried out on GaAs/AlGaAs core/shell NWs at room temperature before and after 1 MeV proton irradiation with fluences ranging from 1.0 × 1012–3.0 × 1013 cm−2. It is found that the GaAs/AlGaAs core/shell NWs with smaller diameter show much less PL degradation compared with the ones with larger diameters. The increased radiation hardness is mainly attributed to the improvement of a room temperature dynamic-annealing mechanism near the surface of the NWs. We also found that the minority carrier lifetime is closely related to both the PL intensity and defect density induced by irradiation. Finally, GaAs/AlGaAs ensemble NW photodetectors operating in the near-infrared spectral regime have been demonstrated. The influence of proton irradiation on light and dark current characteristics also indicates that NW structures are a good potential candidate for radiation harsh-environment applications.

Errata: Enhancement of light absorption efficiency of amorphous-silicon thin-film tandem solar cell due to multiple surface-plasmon-polariton waves in the near-infrared spectral regime

The reflectances of a thin-film solar cell were computed, using the rigorous coupled-wave approach, as functions of the angle of incidence and the free-space wavelength for illumination by linearly polarized plane waves. A tandem solar cell made of amorphous-silicon alloys was considered. The metallic back-reflector was taken to be periodically corrugated. Both the simple and the compound periodic corrugations of the metallic back-reflector (surface-relief gratings) were investigated. Low-reflectance bands in the reflectance spectrums were correlated with the solutions of the underlying canonical boundary-value problem to delineate the excitation of multiple surface-plasmon-polariton (SPP) waves. For the standard AM1.5 solar irradiance spectrum, we found that the light absorption efficiency in the near-infrared spectral regime can be increased up to 100% when multiple SPP waves of both linear polarization states are excited.

Competition between Auger Recombination and Hot‐Carrier Trapping in PL Intensity Fluctuations of Type II Nanocrystals

Performing time-tagged, time-correlated, single-photon-counting studies on individual colloidal nanocrystal quantum dots (NQDs), the evolution of photoluminescence (PL) intensity-fluctuation behaviors in near-infrared (NIR) emitting type II, InP/CdS core-shell NQDs is investigated as a function of shell thickness. It is observed that Auger recombination and hot-carrier trapping compete in defining the PL intensity-fluctuation behavior for NQDs with thin shells, whereas the role of hot-carrier trapping dominates for NQDs with thick shells. These studies further reveal the distinct ramifications of altering either the excitation fluence or repetition rate. Specifically, an increase in laser pump fluence results in the creation of additional hot-carrier traps. Alternately, higher repetition rates cause a saturation in hot-carrier traps, thus activating Auger-related PL fluctuations. Furthermore, it is shown that Auger recombination of negatively charged excitons is suppressed more strongly than that of positively charged excitons because of the asymmetry in the electron-hole confinement in type II NQDs. Thus, this study provides new understanding of how both NQD structure (shell thickness and carrier-separation characteristics) and excitation conditions can be used to tune the PL stability, with important implications for room-temperature single-photon generation. Specifically, the first non-blinking NQD capable of single-photon emission in the near-infrared spectral regime is described.