Solid-state Emitters Research Articles

Extended Conjugation Attenuates the Quenching of Aggregation-Induced Emitters by Photocyclization Pathways.

Herein, we expose how the antagonistic relationship between solid‐state luminescence and photocyclization of oligoaryl alkene chromophores is modulated by the conjugation length of their alkenyl backbones. Heptaaryl cycloheptatriene molecular rotors exhibit aggregation‐induced emission characteristics. We show that their emission is turned off upon breaking the conjugation of the cycloheptatriene by epoxide formation. While this modification is deleterious to photoluminescence, it enables formation of extended polycyclic frameworks by Mallory reactions. We exploit this dichotomy (i) to manipulate emission properties in a controlled manner and (ii) as a synthetic tool to link together pairs of phenyl rings in a specific sequence. This method to alter the tendency of oligoaryl alkenes to undergo photocyclization can inform the design of solid‐state emitters that avoid this quenching mechanism, while also allowing selective cyclization in syntheses of polycyclic aromatic hydrocarbons.

Reversible mechanofluorochromism by simple phenyl and mesitylene appended solid state emitters via crystal to amorphous transitions

Developing a variety of organic compounds with bright solid-state emission is highly advantageous, provided they exhibit stimuli-responsive properties. Such ‘smart’ materials offer a remarkable role in sensing, digital machinery, material science, and the biomedical field. Taking this into account, two phenothiazines (PT) appended vinyl-linked aryl unit (mesitylene/phenyl) two based D–π–A structures have been synthesized. The derivatives have exhibited remarkable luminescence characteristics in a diverse set of solvents due to the twisted intramolecular charge transfer (TICT) state and aggregation-induced emission enhancement properties. Surprisingly, between them, only the mesitylene derivative displays significant and highly reversible mechanofluorochromic (MFC) activity by exhibiting an emission shift from sky blue (467 nm) to cyan (482 nm). The mechanistic insight obtained from P-XRD analysis suggests crystal to amorphous transition causes bathochromic shift upon grinding. SEM analysis reveals two discrete morphologies of the MFC compound in its pristine and ground states. Additionally, DFT and TD-DFT calculations provide insight into their electronic energy levels. Furthermore, results from the electrochemical experiment indicate that they are potential candidates for developing optoelectronic devices.

Converting single photons from an InAs/GaAs quantum dot into the ultraviolet: preservation of second-order correlations

Wavelength conversion at the single-photon level is required to forge a quantum network from distinct quantum devices. Such devices include solid-state emitters of single or entangled photons, as well as network nodes based on atoms or ions. Here we demonstrate the conversion of single photons emitted from a III-V semiconductor quantum dot at 853 nm via sum frequency conversion to the wavelength of the strong transition of Yb+ ions at 370 nm. We measure the second-order correlation function of both the unconverted and the converted photon and show that the single-photon character of the quantum dot emission is preserved during the conversion process.

Coherence in cooperative photon emission from indistinguishable quantum emitters.

Photon-mediated interactions between atoms can arise via coupling to a common electromagnetic mode or by quantum interference. Here, we probe the role of coherence in cooperative emission arising from two distant but indistinguishable solid-state emitters because of path erasure. The primary signature of cooperative emission, the emergence of “bunching” at zero delay in an intensity correlation experiment, is used to characterize the indistinguishability of the emitters, their dephasing, and the degree of correlation in the joint system that can be coherently controlled. In a stark departure from a pair of uncorrelated emitters, in Hong-Ou-Mandel–type interference measurements, we observe photon statistics from a pair of indistinguishable emitters resembling that of a weak coherent state from an attenuated laser. Our experiments establish techniques to control and characterize cooperative behavior between matter qubits using the full quantum optics toolbox, a key step toward realizing large-scale quantum photonic networks.

Nonlinear down-conversion in a single quantum dot

Tailored nanoscale quantum light sources, matching the specific needs of use cases, are crucial building blocks for photonic quantum technologies. Several different approaches to realize solid-state quantum emitters with high performance have been pursued and different concepts for energy tuning have been established. However, the properties of the emitted photons are always defined by the individual quantum emitter and can therefore not be controlled with full flexibility. Here we introduce an all-optical nonlinear method to tailor and control the single photon emission. We demonstrate a laser-controlled down-conversion process from an excited state of a semiconductor quantum three-level system. Based on this concept, we realize energy tuning and polarization control of the single photon emission with a control-laser field. Our results mark an important step towards tailored single photon emission from a photonic quantum system based on quantum optical principles.

Controlling the Dual-Emission Character of Aryl-Modified o-Carboranes by Intramolecular CH⋅⋅⋅O Interaction Sites.

It is still challenging to realize a dual-emission system, in which two luminescent bands simultaneously appear by photoexcitation, in solid with organic dyes due to the difficulty in regulation of electronic properties in the excited state and concentration quenching. o-Carborane is known to be a versatile platform for constructing solid-state emitters since the sphere boron cluster is favorable for suppressing intermolecular interactions and subsequently concentration quenching. Here, we show solid-state dual-emissive o-carborane derivatives. We prepared 4 types of o-carborane derivatives and found dual-emission behaviors both in solution and solid states. By regulating the rotation at the o-carborane unit with the intramolecular Ccage H⋅⋅⋅O interaction, the dual-emission intensity ratios were changed. Finally, it was demonstrated that the overall photoluminescence spectra can be estimated using the binding energy of intramolecular interactions.

High-fidelity multiphoton-entangled cluster state with solid-state quantum emitters in photonic nanostructures

We propose a complete architecture for deterministic generation of entangled multiphoton states. Our approach utilizes periodic driving of a quantum-dot emitter and an efficient light-matter interface enabled by a photonic crystal waveguide. We assess the quality of the photonic states produced from a real system by including all intrinsic experimental imperfections. Importantly, the protocol is robust against the nuclear spin bath dynamics due to a naturally built-in refocusing method reminiscent to spin echo. We demonstrate the feasibility of producing Greenberger-Horne-Zeilinger and one-dimensional cluster states with fidelities and generation rates exceeding those achieved with conventional ``fusion'' methods in current state-of-the-art experiments. The proposed hardware constitutes a scalable and resource-efficient approach towards implementation of measurement-based quantum computing and quantum communication.

Direct detection of quantum non-Gaussian light from a dispersively coupled single atom

Many applications in quantum communication, sensing and computation need provably quantum non-Gaussian light. Recently such light, witnessed by a negative Wigner function, has been estimated using homodyne tomography from a single atom dispersively coupled to a high-finesse cavity. This opens an investigation of quantum non-Gaussian light for many experiments with atoms and solid-state emitters. However, at their early stage, an atom or emitter in a cavity system with different channels to the environment and additional noise are insufficient to produce negative Wigner functions. Moreover, homodyne detection is frequently challenging for such experiments. We analyse these issues and prove that such cavities can be used to emit quantum non-Gaussian light employing single-photon detection in the Hanbury Brown and Twiss configuration and quantum non-Gaussianity criteria suitable for this measurement. We investigate in detail cases of considerable cavity leakage when the negativity of the Wigner function disappears completely. Advantageously, quantum non-Gaussian light can be still conclusively proven for a large set of the cavity parameters at the cost of overall measurement time, even if noise is present.

Optical charge injection and coherent control of a quantum-dot spin-qubit emitting at telecom wavelengths

Solid-state quantum emitters with manipulable spin-qubits are promising platforms for quantum communication applications. Although such light-matter interfaces could be realized in many systems only a few allow for light emission in the telecom bands necessary for long-distance quantum networks. Here, we propose and implement an optically active solid-state spin-qubit based on a hole confined in a single InAs/GaAs quantum dot grown on an InGaAs metamorphic buffer layer emitting photons in the C-band. We lift the hole spin-degeneracy using an external magnetic field and demonstrate hole injection, initialization, read-out and complete coherent control using picosecond optical pulses. These results showcase a solid-state spin-qubit platform compatible with preexisting optical fiber networks.

Conductive SiO2/HfO2 distributed Bragg reflector achieved by electrical breakdown and its application in GaN-based light emitters

Owing to the excellent optical reflectivity with wavelength tunability, dielectric distributed Bragg reflectors (DBRs) have attracted considerable interest in GaN-based light emitters. Yet, the non-conductive nature of the dielectric DBRs prevents current from passing through, leading to a current crowding effect and hampering dielectric DBRs from unlocking their full potential. In this paper, a conductive dielectric DBR was fabricated utilizing the electrical breakdown (EBD) technique. With the help of optical simulations, excellent optical properties were demonstrated by optimizing the structural designs with a high reflectivity of 98.3% at 450 nm based on 5.5 pairs SiO2/HfO2 DBRs. The outstanding electrical behaviors after the EBD process were verified by current–voltage curves and conductive atomic force microscopy characterization. Moreover, conductive mechanisms of this type of dielectric DBR were elaborated by comparing the EBD behaviors with different metal electrodes, suggesting that metal filaments play an important role in forming the conducting channels. Besides, 450 nm-emission with conductive 5.5 pairs SiO2/HfO2 DBR was successfully prepared, which proves that a conductive DBR can be successfully applied to GaN-based light-emitting devices. The conductive DBR presented in this work contributes to the acceleration of the development of high-power GaN-based solid-state light emitters.

Symmetrically Tetra-functionalized Pillar[6]arenes Prepared by Fragment Coupling.

Due to the highly symmetrical structures generated from one-pot syntheses, the partial functionalization of macrocycles is usually beset with low yields and onerous purifications of the target multifunctional macrocycles. To improve this situation, taking pillar[6]arenes as an example, a two-step fragment coupling method has been developed for synthesizing symmetrically tetra-functionalized pillar[6]arenes, namely X-pillar[6]arenes. This method is simple and versatile, which makes hetero-fragment coupling and pre-functionalization available. Nine new macrocycles and a pillar[6]arene-based cage have been prepared. In addition, one of the newly synthesized macrocycles, COOEtEtXP[6], exhibits a strong cyan luminescence in the solid state under irradiation by 365 nm UV light. This emission originates from intramolecular through-space conjugation. Meanwhile, formation of a supramolecular polymer by multiple non-covalent intra/intermolecular interactions helps rigidify the structure and make COOEtEtXP[6] an efficient solid-state emitter. It is believed that this fragment coupling can also be used to realize the multi-functionalization of other macrocycles.

Hybrid device of hexagonal boron nitride nanoflakes with defect centres and a nano-fibre Bragg cavity

Solid-state quantum emitters coupled with a single mode fibre are of interest for photonic and quantum applications. In this context, nanofibre Bragg cavities (NFBCs), which are microcavities fabricated in an optical nanofibre, are promising devices because they can efficiently couple photons emitted from the quantum emitters to the single mode fibre. Recently, we have realized a hybrid device of an NFBC and a single colloidal CdSe/ZnS quantum dot. However, colloidal quantum dots exhibit inherent photo-bleaching. Thus, it is desired to couple an NFBC with hexagonal boron nitride (hBN) as stable quantum emitters. In this work, we realize a hybrid system of an NFBC and ensemble defect centres in hBN nanoflakes. In this experiment, we fabricate NFBCs with a quality factor of 807 and a resonant wavelength at around 573 nm, which matches well with the fluorescent wavelength of the hBN, using helium-focused ion beam (FIB) system. We also develop a manipulation system to place hBN nanoflakes on a cavity region of the NFBCs and realize a hybrid device with an NFBC. By exciting the nanoflakes via an objective lens and collecting the fluorescence through the NFBC, we observe a sharp emission peak at the resonant wavelength of the NFBC.

Rational Design of a New AIE‐Coupled ESIPT‐Based Multi‐chromic State Depended Organo‐luminophore WithTurn‐onEmissive Response to Zn(II) in Aqueous and Solid‐state**

AbstractA newly designed multifunctional AIE‐coupled excited‐state intramolecular proton transfer (ESIPT)‐active asymmetric multichromicfluorophor (MCF) has been synthesized and characterized. From tedious experimental spectroscopic dissection of the photophysical properties ofMCFand two supporting compounds, (3‐benzotriazol‐2‐yl‐2‐hydroxy‐5‐methyl‐benzaldehyde) (R1) and (2‐benzotriazol‐2‐yl‐4‐methyl‐phenol)(R2)with theoretical discussion, it has been established that ESIPT was driven exclusively towards triazole N centre involving a 6‐member H‐bonded network over imine‐N center in both solid state and solution phase. The competition of aggregation enhanced emissive feature and ACQ (aggregation caused quenching) nature ofMCFwere also studied thoroughly in the THF/water mixture. New classes of mechanisms are introduced regarding AIE/ACQ phenomenon, which will eradicate the limitation of designing and development of novel solid state emitters. To the best of our knowledge, this unique feature has never been achieved before. Furthermore, reversible mechanochromic fluorescence behavior upon external grinding and acidochromism nature ofMCFas acid‐base switch has also been observed. In addition,MCFselectively senses Zn2+ion through a colorimetric and fluorescence “turn‐on” route. The actual binding site of Zn2+withMCFhas also been established with the help of spectroscopic studies. The present study will enlighten for a new way to achieve new multifunctional organic luminescent solids.

D–A systems based on oxazolone–coumarin triazoles as solid-state emitters and inhibitors of human cervical cancer cells (HeLa)

D–A systems with solid-state emission and anticancer properties have been synthesized in three steps via the MCR-Click protocol.

Quantum emitters and detectors based on 2D van der Waals materials.

Light plays an essential role in our world, with several technologies relying on it. Photons will also play an important role in the emerging quantum technologies, which are primed to have a transformative effect on our society. The development of single-photon sources and ultra-sensitive photon detectors is crucial. Solid-state emitters are being heavily pursued for developing truly single-photon sources for scalable technology. On the detectors' side, the main challenge lies in inventing sensitive detectors operating at sub-optical frequencies. This review highlights the promising research being conducted for the development of quantum emitters and detectors based on two-dimensional van der Waals (2D-vdW) materials. Several 2D-vdW materials, from canonical graphene to transition metal dichalcogenides and their heterostructures, have generated a lot of excitement due to their tunable emission and detection properties. The recent developments in the creation, fabrication and control of quantum emitters hosted by 2D-vdW materials and their potential applications in integrated photonic devices are discussed. Furthermore, the progress in enhancing the photon-counting potential of 2D material-based detectors, viz. 2D photodetectors, bolometers and superconducting single-photon detectors functioning at various wavelengths is also reported.

Fluorescent Organic Lewis-Pair Nanoparticles: Excited-State Intramolecular Proton Transfer Molecule 2-(2'-Hydroxyphenyl)benzothiazole Undergoes GSIPT Reactions To Be a Solid-State Nanoemitter.

The excited-state intramolecular proton transfer (ESIPT) reaction, one of the fundamental photochemical processes, is known to occur in 2-(2'-hydroxyphenyl)benzothiazole (HBT), showing an enol-to-keto phototautomerization. In this article, Lewis-pair adduct formation is demonstrated between HBT (Lewis base) and diphenylborinic anhydride (DPBA; Lewis acid), in which the proton transfer occurs in the ground state to form the keto tautomer of HBT. The HBT/DPBA Lewis-pair adduct exhibits strong pale-blue fluorescence at 480 nm in dichloroethane. Additionally, organic Lewis-pair nanoparticles of HBT/DPBA are successfully synthesized on the basis of a reprecipitation protocol in which HBT in conjunction with DPBA dissolved in acetone was rapidly injected into water under ultrasonication. DPBA here also acts as a stabilizing or protecting agent to form spherical nanoparticles with well dispersion. The nanoparticles also exhibit strong keto-type emission centered at 490 nm, changing the emission color to bluish-green. Quantum chemical calculations find the sole formation of the keto tautomer of HBT counterpart in the Lewis pair. Importantly, the present synthesis methodology based on Lewis acid-base chemistry does not require complicated operations to organically synthesize solid-state emitters and thus will play a key role in simply controlling the emission behavior for the new type of organic nanoparticles.

Remote excitation between quantum emitters mediated by an optical Fano resonance

Remote coupling between quantum emitters is of great importance for constructing quantum networks. Conventionally, this can be achieved via photon exchange by incorporating the quantum emitters in a waveguide or a large cavity. However, such photonic structures suffer from low quality-factors or large mode volumes, limiting the efficiency of light–matter interaction. Here, we demonstrate remote coupling between two site-controlled semiconductor quantum dot emitters mediated by an optical Fano resonance induced by coupling cavity modes via a continuum waveguide state. Unlike ordinary coupled modes, the Fano mode offers both a spatially extended field and a high local density of optical states at the emitters, enhancing light–matter interaction. This coupling scheme allows the demonstration of mutual excitation between two quantum dots separated in space by > 17 wavelengths. Our approach holds promise for achieving long-distance interaction without compromising interaction efficiency, which is essential for scaling up on-chip integration of quantum networks based on solid-state quantum emitters.

Band-edge emission enhancement in sputtered ZnO thin films with ultraviolet surface lattice resonances

Metallic nanostructures acting as optical nanoantennas can significantly enhance the photoluminescence (PL) of nearby emitters. Albeit luminescence enhancement factors of several orders of magnitude have been reported for quantum dots or molecules, in the case of bulk emitters, the magnitude of the plasmonic enhancement is strongly hindered by the weak spatial overlap between the active medium and the electromagnetic modes of the nanoantenna. Here, we propose a solid-state ultraviolet emitter based on a thin film of zinc oxide (ZnO) coupled with an array of aluminum (Al) nanoparticles. The Al nanorod array is designed to sustain surface lattice resonances (SLRs) in the near ultraviolet, which are hybrid modes exhibiting a Fano-like lineshape with narrowed linewidth relatively to the non-hybridized plasmonic modes. By changing both the period of the array and the dimensions of the nanorods, the generated SLR is tuned either to the near band-edge (NBE) emission of ZnO or to the excitation wavelength. We experimentally demonstrate that NBE emission can be increased up to a factor of 3 compared to bare ZnO. The underlying PL enhancement mechanisms are experimentally investigated and compared with numerical simulations. We also demonstrate that SLRs are more efficient for the ZnO luminescence enhancement compared to localized surface plasmon resonances.

Purcell Enhancement of a Cavity-Coupled Emitter in Hexagonal Boron Nitride.

Integration of solid-state quantum emitters into nanophotonic circuits is a critical step towards fully on-chip quantum photonic-based technologies. Among potential materials platforms, quantum emitters in hexagonal boron nitride (hBN) have emerged as a viable candidate over the last years. While the fundamental physical properties have been intensively studied, only a few works have focused on the emitter integration into photonic resonators. Yet, for a potential quantum photonic material platform, the integration with nanophotonic cavities is an important cornerstone, as it enables the deliberate tuning of the spontaneous emission and the improved readout of distinct transitions for a quantum emitter. In this work, the resonant tuning of a monolithic cavity integrated hBN quantum emitter is demonstrated through gas condensation at cryogenic temperature. In resonance, an emission enhancement and lifetime reduction are observed, with an estimate for the Purcell factor of ≈15.

Consecutive multicomponent syntheses of N-substituted 3-arylallylidene indolones – Solid-state emitters and photoisomerization

A series of variably substituted 3-arylallylidene indolones were synthesized as diastereomeric mixtures applying a novel consecutive three-component Heck-condensation sequence in the sense of a one-pot synthesis. The N-substitution pattern was found to be crucial for the fluorescence in the solid state. Accordingly, the synthetic route was extended to a consecutive four-component reaction to generate a diverse compound library of Boc-substituted 3-arylallylidene indolones. Studying the structure-property relationship by Hammett correlation revealed a discontinuous behavior of the longest wavelength absorption bands of these compounds. 3-Arylallylidene indolones exclusively fluoresce in the solid state. Exceptions are strongly donor-substituted derivatives, which also luminesce in solution and reveal positive emission solvatochromism. With the N-tosyl derivative, an AIE (aggregation induced emission) chromophore was discovered and for the (p-anisyl)2N-substituted derivative aggregation induced emission enhancement (AIEE) was found. The absorption spectra of the 3-arylallylidene indolones can be plausibly rationalized by TD(DFT) calculations. Interestingly, the diastereomers, which can be photoisomerized, are very similar in their photophysical properties.