Light-emitting diodes (LEDs) based on colloidal semiconductor nanocrystals represent a promising technology for next-generation electroluminescence displays. While ongoing efforts focus on optimizing nanocrystal properties, device performance also critically depends on the LED architecture, particularly the design of interfacial layers. Efficient charge injection and balanced carrier transport toward recombination layers require careful alignment of energy levels between adjacent layers. In this study, we investigate the cooperative role of different hole-transporting (HT) and electron-injecting (EI) polymers in a multilayered all-solution-processed LED structure incorporating CdSe/CdZnS nanoplatelets as deep-red emitters. Three commercially available HT polymers, differing in hole mobility and energy levels, were combined with custom-designed EI polar polymers featuring varied conjugated backbones and tailored highest occupied molecular orbital/lowest unoccupied molecular orbital (HOMO/LUMO) levels. Particular attention is given to the EI/metal interface, whose properties are tuned via phosphonate-functionalized polymer side chains. Device performance is assessed under inert and ambient conditions (without encapsulation) and correlated to the electronic properties of the interfacial layers. Notably, specific HT/EI polymer pairings substantially influence key parameters of fabricated LEDs, enabling either a reduced turn-on voltage down to 1.7 V or enhanced external quantum efficiency up to 7%, depending on the selected combination.

We present a feature-resolved methodology to analyse the photoluminescence dynamics of single emitters using a combination of lifetime, spectral, and photon correlation analyses. By integrating conventional ensemble photon statistics measurements with emission state-resolved, spectrally filtered, and lifetime-gated methods, we uncover emission dynamics that remain hidden in ensemble treatment. We study the fluorescence of single CdSe/CdS core/shell colloidal quantum dots under varying excitation powers. Using feature-resolved analysis, we understand the radiative and non-radiative recombination processes, and estimate quantum parameters. Event-selective analysis provides a versatile toolkit for characterizing emitters, both single and aggregate particles. These methods are broadly applicable to a wide class of photoluminescent emitters, such as nitrogen vacancy centres in nanodiamond, epitaxial quantum dots, and perovskite nanocrystals. The application of these lateral investigation techniques will contribute to the advancement of quantum light source development.

We present experimental and theoretical studies of the time-resolved photoluminescence and its linear polarization of an ensemble of CdSe/CdS colloidal nanoplatelets in the Faraday magnetic fields up to 6 T. The linearly polarized photoluminescence kinetics stems from the excitons resonantly excited with the linearly polarized light pulse and comprises both the structural contribution and the exciton optical alignment effect. The emission from the bright and dark exciton states is distinguished by their different intensity decay timescales with lifetime at cryogenic temperature of about 1 - 2 ns and 100 - 200 ns, respectively. The longitudinal spin relaxation time of the bright exciton was determined to be from 4 to 6 ns depending on the magnetic field. The dark exciton spin relaxation time was estimated to be in the order of 20 to 100 ns. The developed theory for the bright exciton polarization kinetics and the modeling of the data allowed us to conclude that spin dephasing times of the bright as well as of the dark exciton are shorter than 0.3 ns. The origin of such a strong spin relaxation time anisotropy in the ensemble of nanoplatelets is discussed.

Optical alignment and optical orientation of excitons are studied experimentally on an ensemble of core/shell CdSe/CdS colloidal nanoplatelets. Linear and circular polarization of photoluminescence during resonant excitation of excitons is measured at cryogenic temperatures and with magnetic fields applied in the Faraday geometry. The developed theory addresses the optical alignment and optical orientation of excitons in colloidal nanocrystals, taking into account both bright and dark exciton states in the presence of strong electron–hole exchange interaction and the random in-plane orientation of nanoplatelets within the ensemble. Our theoretical analysis of the obtained experimental data allows us to evaluate the exciton fine structure parameters, the g-factors, and the spin lifetimes of the bright and dark excitons. The optical alignment effect enables the identification of the exciton and trion contributions to the emission spectrum, even in the absence of their clear separation in the spectra.

A mixture of N,N,N′-trisubstituted thiourea and cyclic N,N,N′,N′-tetrasubstituted selenourea precursors were used to synthesize three monolayer thick CdS1− xSex nanoplatelets in a single synthetic step. The microstructure of the nanoplatelets could be tuned from homogeneous alloys, to graded alloys to core/crown heterostructures depending on the relative conversion reactivity of the sulfur and selenium precursors. UV-visible absorption and photoluminescence spectroscopy and scanning transmission electron microscopy electron energy loss spectroscopy (STEM-EELS) images demonstrate that the elemental distribution is governed by the relative precursor conversion kinetics. Slow conversion kinetics produced nanoplatelets with larger lateral dimensions, behavior that is characteristic of precursor conversion limited growth kinetics. Across a 10-fold range of reactivity, CdS nanoplatelets have 4× smaller lateral dimensions than CdSe nanoplatelets grown under identical conversion kinetics. The difference in size is consistent with a rate of CdSe growth that is 4× greater than the rate of CdS. The influence of the relative sulfide and selenide growth rates, the duration of the nucleation phase, and the solute composition on the nanoplatelet microstructure are discussed.

Single-emitter plasmonic patch antennas are room-temperature deterministic single-photon sources, which exhibit highly accelerated and directed single-photon emission. However, for efficient operation these structures require 3D nanoscale deterministic control of emitter positioning within the device, which is a demanding task, especially when emitter damage during fabrication is a major concern. To overcome this limitation, the deterministic room-temperature in situ optical lithography protocol uses spatially modulated light to position a plasmonic structure nondestructively on any selected single-emitter with 3D nanoscale control. Herein, the emission statistics of such plasmonic antennas that embed a deterministically positioned single colloidal CdSe/CdS quantum dot, which highlight acceleration and brightness of emission, are analyzed. It is demonstrated that the presented antenna induces a 1000-fold effective increase in the absorption cross-section, and, under high pumping, these antennas show nonlinearly enhanced emission.

Single-emitter plasmonic patch antennas are room-temperature deterministic single-photon sources, which exhibit highly accelerated and directed single-photon emission. However, for efficient operation these structures require 3D nanoscale deterministic control of emitter positioning within the device, which is a demanding task, especially when emitter damage during fabrication is a major concern. To overcome this limitation, the deterministic room-temperature in situ optical lithography protocol uses spatially modulated light to position a plasmonic structure nondestructively on any selected single-emitter with 3D nanoscale control. Herein, the emission statistics of such plasmonic antennas that embed a deterministically positioned single colloidal CdSe/CdS quantum dot, which highlight acceleration and brightness of emission, are analyzed. It is demonstrated that the presented antenna induces a 1000-fold effective increase in the absorption cross-section, and, under high pumping, these antennas show nonlinearly enhanced emission.

We report on the experimental and theoretical studies of optical alignment and optical orientation effects in an ensemble of core/shell CdSe/CdS colloidal nanoplatelets. The dependences of three Stokes parameters on the magnetic field applied in the Faraday geometry are measured under continuous wave resonant excitation of the exciton photoluminescence. Theoretical model is developed to take into account both bright and dark exciton states in the case of strong electron and hole exchange interaction and random in-plane orientation of the nanoplatelets in ensemble. The data analysis allows us to estimate the time and energy parameters of the bright and dark excitons. The optical alignment effect enables identification of the exciton and trion contributions to the photoluminescence spectrum even in the absence of a clear spectral line resolution.

Colloidal semiconductor nanoplatelets exhibit strong quantum confinement for electrons and holes as well as excitons in one dimension, while their in-plane motion is free. Because of the large dielectric contrast between the semiconductor and its ligand environment, the Coulomb interaction between electrons and holes is strongly enhanced. By means of one- and two-photon photoluminescence excitation spectroscopy, we measure the energies of the 1S and 1P exciton states in CdSe nanoplatelets with thicknesses varied from 3 up to 7 monolayers. By comparison with calculations, performed in the effective mass approximation with account of the dielectric enhancement, we evaluate exciton binding energies of 195-315 meV, which is about 20 times greater than that in bulk CdSe. Our calculations of the effective Coulomb potential for very thin nanoplatelets are close to the Rytova-Keldysh model, and the exciton binding energies are comparable with the values reported for monolayer-thick transition metal dichalcogenides.

Colloidal semiconductor nanoplatelets (NPLs) are a subgroup of quantum confined materials that have recently emerged as promising active materials for solution processed light-emitting diodes (LEDs) thanks to their peculiar structural and electronic properties as well as their reduced dimensionality. Nowadays, the conventional structure for NPL-based LEDs makes use of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) as a hole transporting layer (HTL). This is a well-known conjugated conductive polymer because it leads to high LED efficiency, though it has limited stability in air due to its intrinsic acidity and hygroscopicity. Here, we develop a nanocomposite aqueous ink, obtained by blending commercial PEDOT:PSS with water-based, stable and highly concentrated molybdenum disulfide (MoS2) nanosheets, obtained via liquid phase exfoliation (LPE), which is suitable as a HTL for solution processed NPL-based LEDs. We demonstrate that the MoS2 additive effectively works as a performance booster in unpackaged devices, thereby prolonging the lifetime up to 1000 hours under ambient conditions. Moreover, the addition of MoS2 induces a modification of the anode interface properties, including a change in the work function and a significant enhancement of the permittivity of the HTL.

The role of indium carboxylate precursors in the synthesis of monodisperse InP quantum dots was investigated. The reaction between acid-free indium palmitate and tris(trimethylsilyl)phosphine (P(TMS)3) was monitored by using high-temperature 31P NMR, indicating the presence of a single molecular phosphorus species throughout the duration of the reaction. The addition of varying amounts of carboxylic acid and its effects on both the reaction kinetics and the optical properties of InP QDs were studied. In the presence of acid, rapid protonation of P(TMS)3 led to the formation of a mixture of four HxP(TMS)3-x species, resulting in the poorer controlled formation of InP nanocrystals. Upon deposition of a gradated ZnSeS shell on the synthesized InP core, luminescent quantum dots were obtained (QY 67%; PL: FWHM 40 nm).

Lead halide perovskite nanocrystals (LHP NCs) exhibit remarkable optical and optoelectronic properties but greatly suffer from poor stability in standard ambient and in-use conditions. These stability issues hinder their utilization in many technological applications and their integration within industrial processes. Herein, we report a polymeric nanoencapsulation method of these NCs based on a spray-drying process, with the aim of using them as light downconverting materials in LED devices. CsPbBr3 NCs were encapsulated in acrylate-based polymers to form NC/polymer nanocomposite beads, with an average diameter lower than 500 nm. Structural and optical characterizations demonstrated good preservation of the NC properties after spray drying despite quite harsh process conditions. Specific acrylate-based polymers were selected in order to match native surface ligands from our NCs. This was necessary to obtain an effective encapsulation within the beads. To evaluate the photostability of encapsulated NCs under in-use conditions, bare NCs and encapsulated NCs were deposited on the chip of a blue LED downconverter to compare their luminescence stability. We observed that under continuous blue photon excitation, the NC/polymer nanocomposite beads exhibit much better resistance to photobleaching compared to bare NCs.

The surface of nominally diamagnetic colloidal CdSe nanoplatelets can demonstrate paramagnetic behaviour owing to the uncompensated spins of dangling bonds, as we reveal here by optical spectroscopy in high magnetic fields up to 15 T using the exciton spin as a probe of the surface magnetism. The strongly nonlinear magnetic field dependence of the circular polarization of the exciton emission is determined by the magnetization of the dangling-bond spins (DBSs), the exciton spin polarization as well as the spin-dependent recombination of dark excitons. The sign of the exciton–DBS exchange interaction depends on the nanoplatelet growth conditions. The surface of CdSe nanoplatelets can exhibit a paramagnetic behaviour that influences the polarization properties of the optical emission.

Micro-ring resonators made of titanium dioxide were decorated with local light sources comprising CdSe/CdS colloidal quantum dot aggregates. The active micro-resonators are operated to achieve efficient evanescent excitation of nearby co-planar integrated waveguides. Coupled-mode analysis and numerical simulations are used to capture the dynamic of the optical interaction between locally activated resonators and integrated waveguides. In this context, we exemplify the key role of resonator intrinsic loss. Next, we show that locally activated or bus-waveguide excited resonators are in optimum waveguide interaction for the same so-called critical coupling condition, although the physical origin of this property is different for each configuration. More importantly, we found that a locally activated resonator is a fabrication imperfection tolerant configuration for the coupling light of local sources into waveguides. This remarkable property originates from the opposite change of the power cycling into the resonator and the waveguide coupling efficiency as a function of the resonator-waveguide separation gap. By operating an 8-μm-radius ring resonator with loaded quality factors around Q = 2100, we experimentally demonstrate a 5.5-dB enhancement of the power coupled into the output waveguide compared to a direct local source waveguide excitation.

We investigate the charge separation dynamics provided by carrier surface trapping in CdSe/CdS core/shell nanoplatelets by means of a three-laser-beam pump-orientation-probe technique, detecting the electron spin coherence at room temperature. Signals with two Larmor precession frequencies are found, which strongly differ in their dynamical characteristics and dependencies on pump power and shell thickness. The electron trapping process occurs on a time scale of about 10 ns, and the charge separation induced thereby has a long lifetime of up to hundreds of microseconds. On the other hand, the hole trapping requires times from subpicoseconds to hundreds of picoseconds, and the induced charge separation has a lifetime of a few nanoseconds. With increasing CdS shell thickness the hole trapping vanishes, while the electron trapping is still detectable. These findings have important implications for understanding the photophysical processes of nanoplatelets and other colloidal nanostructures.

Colloidal semiconductor nanocrystals (NCs) and, recently, nanoplatelets (NPLs), owing to their efficient and narrow-band luminescence, are considered as frontier materials for light-emitting diode (LED) technology. NC-LEDs typically incorporate interfacial layers as charge regulators to ensure charge balancing and high performance. In this Letter, we show the prolongation of the lifetime of multilayer solution-processed NC-LEDs by combining a self-doped conductive conjugated polyelectrolyte and exfoliated molybdenum disulfide (MoS2) flakes as an alternative to PEDOT:PSS. The ink features a neutral pH and a tunable hydrophobicity that mainly results in a remarkable stability of LEDs, using CdSe/CdZnS NPLs.

The low-temperature emission spectrum of CdSe colloidal nanoplatelets (NPLs) consists of two narrow lines. The high-energy line stems from the recombination of neutral excitons. The origin of the low-energy line is currently debated. We experimentally study the spectral shift, emission dynamics, and spin polarization of both lines at low temperatures down to 1.5 K and in high magnetic fields up to 60 T and show that the low-energy line originates from the recombination of negatively charged excitons (trions). This assignment is confirmed by the NPL photocharging dynamics and associated variations in the spectrum. We show that the negatively charged excitons are considerably less sensitive to the presence of surface spins than the neutral excitons. The trion binding energy in three-monolayer-thick NPLs is as large as 30 meV, which is 4 times larger than its value in the two-dimensional limit of a conventional CdSe quantum well confined between semiconductor barriers. A considerable part of this enhancement is gained by the dielectric enhancement effect, which is due to the small dielectric constant of the environment surrounding the NPLs.

Plasmonic antennas are attractive optical structures for many applications in nano and quantum technologies. By providing enhanced interaction between a nanoemitter and light, they efficiently accelerate and direct spontaneous emission. One challenge, however, is the precise nanoscale positioning of the emitter in the structure. Here we present a laser etching protocol that deterministically positions a single colloidal CdSe/CdS core/shell quantum dot emitter inside a subwavelength plasmonic patch antenna with three-dimensional nanoscale control. By exploiting the properties of metal-insulator-metal structures at the nanoscale, the fabricated single emitter antenna exhibits an extremely high Purcell factor (>72) and brightness enhancement by a factor of 70. Due to the unprecedented quenching of Auger processes and the strong acceleration of multiexciton emission, more than 4 photons per pulse can be emitted by a single quantum dot. Our technology permits the fabrication of bright room-temperature single-emitter sources emitting either multiple or single photons.

Efficient coupling of nanoemitters to photonic or plasmonic structures requires spatial and spectral matching and the control of the orientation of the emitting dipoles. Whereas spectral matching can be easily obtained in plasmonics and whereas several strategies aim to achieve control of the emitter location inside nanostructures, the control of orientation still remains a challenge Nevertheless depending of the emitting dipole orientation, the light matter interaction between can switch from a quasi nul value to a large interaction with plenty of positive outcomes on the emission characteristics (emission diagram, brightness, dynamics...). Therefore, many experiments try to face this major problem by statistics. They rely on the realization of numerous samples, in order to be able to statistically get a well aligned dipole to realize an efficient coupling to a nanostructure. In order to avoid these statistical trials, the knowledge of the nature of the emitter and its orientation is crucial for a deterministically approach for nanolithography. We have developed a method relying on the combination of polarimetric measurement and emission diagram which gives fine information both on the emitting dipolar transition involved and on the dipolar orientation. In this talk, we first demonstrate that single rectangular colloidal CdSe/CdS nanoplatetelets present polarized emission due to dielectric effect correlated to their rectangular shape anisotropy. We then illustrate the that with cubic nanoplatelets, the achievement of vertical emitting dipoles, optimally coupled to plasmonic surfaces, can be obtained with a good probability. We will then present how such a protocol can be implemented in in-situ deterministic realization of antennas.