Pyramid-Shaped Quantum Dot Superlattice Exhibiting Tunable Room-Temperature Superfluorescence via Oriented Attachment

doi:10.21203/rs.3.rs-4329418/v1

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Pyramid-Shaped Quantum Dot Superlattice Exhibiting Tunable Room-Temperature Superfluorescence via Oriented Attachment

https://doi.org/10.21203/rs.3.rs-4329418/v1

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Superfluorescence (SF), characterized by the collective emission of photons from a dense ensemble of excited emitters, has emerged as a promising phenomenon for quantum optics and nanophotonics applications. However, SF has historically been limited to extremely low temperatures due to thermal decoherence. Here we show room-temperature tunable SF from perovskite quantum dot (QD) superlattices. Our approach involves the mesocrystallization of CsPbBr₃-based QD superlattices driven by oriented attachment, which yields pyramidal-like solids with extended atomic coherency. This level of atomic-scale to nanoscale orientational structure control cannot be realized in previous QD superlattices, and it allows for quantum coherence to persist at ambient conditions. As a result, we observe multiple narrowband coherent emissions at room temperature, which we attribute to SF. Our results establish superlattices as an emerging materials platform capable of robust quantum coherence without cryogenic constraints, opening up new possibilities for quantum optics and nanophotonics applications.

Physical sciences/Chemistry/Physical chemistry/Chemical physics

Physical sciences/Nanoscience and technology/Nanoscale materials/Quantum dots

Physical sciences/Nanoscience and technology/Nanoscale materials/Structural properties

Physical sciences/Chemistry/Materials chemistry/Optical materials

Physical sciences/Nanoscience and technology/Nanoscale devices/Quantum information

With the surging interest in quantum information, the central to the progression is the capability to govern and safeguard macroscopic quantum states. However, this undertaking invariably mandates the execution of operations within cryogenic temperatures, a requisite measure to mitigate the deleterious impact of thermal fluctuations that could otherwise disrupt the coherence of these quantum states ¹. Superfluorescence (SF), one such macroscopic quantum states that generates collective emission of photons from materials composed of densely packed excited emitters ^{2, 3, 4, 5, 6}, has attracted significant attention in quantum optics due to its inherent many-body quantum phenomena ^{7, 8, 9, 10, 11}. The elusive prospect of extending SF observation beyond cryogenic conditions and/or high magnetic field (> 10 T) ⁹ persists due to the susceptibility of coherence to thermal noise. Nonetheless, recent investigations have revealed instances of room-temperature SF in 2D perovskite materials ^{12, 13}and upconversion nanocrystal assemblies ¹⁴, suggesting the potential of coherence manipulation through the design quantum dots (QDs) superlattices. The building units of these QD superlattices are described as naturally-occurring quantum “shock absorbers”-quasiparticles known as polarons that shield excited electrons from all lattice vibrations bar their own ¹⁰.

Inspired by the observations of nature's masterpiece, wherein the oriented attachment mechanism of biological mineral formation and geology ^{15, 16, 17}, we explore mesocrystalline QD superlattices as a platform for room-temperature SF. This oriented attachment process involves the transformation of crystallographical orientation and the alignment of atomic lattices within the growth and aggregation of nanocrystals ^{18, 19, 20, 21, 22, 23}. The physical-chemical process is particularly significant due to its ability to facilitate the minimization of surface energy and facet selectivity, resulting in crystalline structures with lower total free energy and enhanced atomic coherency ^{24, 25}. In this work, we present mesocrystalline perovskite QD superlattices featuring a pyramid structure, which are formed through the oriented attachment of perovskite QDs that exhibit SF at room temperature. The process of oriented attachment leads to the formation of an organized mesocrystalline structure fused along specific (100) crystallographic directions. The resulting structure exhibits strong dipole-dipole coupling, quantum confinement, and highly synchronized light emission, enabling SF even under ambient temperatures. Notably, we provide empirical evidence that the extent of oriented attachment, and consequently the proportion of coupled emission to uncoupled emission, influences the SF characteristics, offering a tunable approach to achieving tunable room-temperature SF.

Macroscale CsPbBr₃-based QD superlattices with lateral dimensions ranging from approximately 1 to 20 µm were fabricated via solvent evaporation approach ²⁶, manifesting as cuboidal clustered islands dispersed 10 ~ 20 µm apart (Supplementary Fig. 1). Previous theoretical frameworks predict that QD superlattices composed of tightly oriented-packed, diminished sized constituents exhibit enhanced interparticle coupling energies conducive to augmented SF decay kinetics and a higher potential for high-temperature SF realization ^{27, 28}. To maximize the potential SF, the micrometer-sized cube-shaped superlattices were delicately subjected to annealing treatment in the temperature range of 25 ~ 80 degrees Celsius to facilitate the oriented attachment. It has been observed that the initially cube-shaped QD superlattices undergo morphological changes and transform into pyramidal-like islands after undergoing thermal annealing treatment (Fig. 1a and Supplementary Fig. 2). To compare the effects of structure on photoluminescent (PL) properties, three different types of QD solids incorporating random packing structures, cube-shaped close packing superlattices, pyramidal-like mesocrystalline superlattices were prepared via spin-coating, interface self-assembly and annealing after self-assembly.

Strikingly, these mesocrystalline QD superlattices exhibit distinct SF emission at room temperature under optical excitation, which is remarkable considering the challenges associated with maintaining quantum coherence at elevated temperatures. As Fig. 2a, b demonstrates, two distinct emission profiles emerge from the material's glow, wherein a yellow radiative decay with a sharp peak appears at 2.18 eV originates centrally, while green luminescence (2.36 eV) is observed at the morphological boundaries. The green emission coincides with PL of the disordered CsPbBr₃ QD film deposited on glass (Fig. 2b, green line), which exhibits its peak at 2.40 eV. This we assign as the reference peak represents the emission characteristics of individual QDs without any interparticle interactions. Yet, within this context, there is also the presence of a SF that exhibits a red-shift of 220 meV, which aligns with previous observations made at ultra-low temperatures ¹⁰. The analysis of the 2.18 eV PL line shape indicates a Lorentzian function in FWHM (full width at half maximum) 27 meV, which is ~ 3 times narrower than the normal emission peak (FWHM: 98 meV), which suggests a high degree of coherence despite elevated temperature. Significantly, under ambient temperature conditions, SF was only observed above an excitation intensity threshold of approximately 500 µJ cm^− 2, transitioning from incoherent NC fluorescence to cooperative SF emission. The linear increase in the SF peak intensities with increasing excitation fluence above a threshold is one of expected behaviors for SF phenomena (Fig. 2c). Below this threshold, the emission exhibited characteristics of incoherent fluorescence from individual QDs, which is analogous to the PL of random packing QD ensembles (Supplementary Fig. 3). In contrast, when cooled to a cryogenic temperature of below 80 K (21K, 70K), superradiant emission from the mesocrystalline QD superlattices could be stimulated from a much lower excitation density of only 2 µJ cm^− 2 (Supplementary Fig. 4). Another notable characteristic of SF is the alteration of radiative lifetimes compared to incoherent fluorescence, which can be observed through time-resolved PL decay measurements. Time-resolved PL decay measurements were conducted on mesocrystalline QD superlattices at an excitation density of 3400 µJ cm^− 2 to investigate their decay profile. The results showed an accelerated PL decay profile compared to randomly aggregated assemblies and QD superlattices. The 1/e decay times were measured as τ_MSL = 122 ps (Fig. 2d) and τ_SL = 1100 ps (Supplementary Fig. 5) at 300 K for the QD superlattices with and without annealing treatment, respectively. The observation of an initially delayed increase (τ_D) followed by a distinct peaked pulse in Fig. 2d, as well as subsequent successive pulses, are hallmark signatures of SF emission, distinguishing it from Amplified spontaneous emission (ASE) ²⁹. This manifested as a decrease in the SF PL lifetime, furnishing direct evidence of superradiance arising from the phase-matched dipolar interactions between the QDs when organized into the mesocrystalline configuration. The radiative decay rate amplification is ascribed to a cooperative emission mechanism wherein the excitation is delocalized across numerous QDs via quantum coupling enabled by the long-range structural order. The extent of oriented attachment governs the ratio of coupled (coherent) to uncoupled (incoherent) emission, thereby modulating the SF characteristics, such as the emission intensity, linewidth, and decay dynamics ²⁷.

Intriguingly, further oriented attachment growth through annealing (60 degrees Celsius for 10 minutes) of the mesocrystalline QD superlattices, reveal a phenomenon of exciton splitting of the PL emission (Fig. 3a). At room temperature, the primary green emission resolves into three fine-structured peaks at 2.47 eV, 2.40 eV and 2.37 eV. This phenomenon, where the primary green emission resolves into multiple fine-structured peaks, is typically observed in strongly confined systems and is attributed to the lifting of the degeneracy of the bright excitonic state due to electron-hole exchange interactions ³⁰. This fragmentation of the radiative recombination peak indicates the presence influence of electron-hole exchange interactions, lifting the intrinsic degeneracy of the bright excitonic state. The measured splitting energy of tens of meV aligns with earlier findings of this phenomenon in CsPbBr₃ NCs at low temperatures ^{30, 31, 32}, which could be attributed to isotropic electron–hole exchange. Remarkably, the presence of excitonic coupling at ambient conditions provides compelling evidence that strongly-bound electron-hole pairs (excitons) govern the optical properties of these mesocrystalline materials. Spatially resolving the split emission across individual domains has the potential to provide novel insights into exciton delocalization and coherent coupling effects in QD superlattices or hybrid organic-inorganic perovskites.

To preliminary investigate the phenomenon of exciton splitting in the green PL emission, a spectral-temporal dissection resolved three distinctive recombination signatures within the emission envelope, which were attributed to primary excitons, secondary biexcitons, and charged exciton quasiparticles (trions) ³³. The splitting of the green PL peak into these sub-peaks becomes more pronounced and obvious as the excitation fluence is further increased (Fig. 3b). The peaks at 2.47 eV, 2.40 eV, and 2.37 eV were observed to have substantially reduced narrow linewidths (FWHM: 22–26 meV). Additionally, these peaks exhibited gradually decreasing decay times down to the timescale of 200 picoseconds (Fig. 3c), indicating a potential transition from superradiant to superfluorescent behavior. While exciton splitting has been observed in QD superlattices or disordered ensembles at cryogenic conditions ^{10, 34, 35}, the high degree of resolution and clarity with which we have observed excitonic substructure within the optical emission profile of these mesocrystalline assemblies at ambient temperature represents a significant advancement.

To investigate the structural factors in microscale influencing room temperature SF, we first examined the pyramidal morphology of the mesocrystalline QD superlattices using microscopy. At a magnification of 50x, distinct pyramid-shaped structures with well-defined facets were observed (Fig. 4). Darkfield and brightfield imaging of the mesocrystalline QD superlattices, influenced by Bragg reflection and their own PL (Fig. 4a, b and Supplementary Fig. 2), revealed color differentials between the centers and edges, suggestive of variations in thickness across the structures. Specifically, the mesocrystalline QD superlattices appeared darker in the centers compared to the edges under both imaging modes. This thickness gradient was observed across mesocrystalline QD superlattices of various overall sizes, indicating a relatively thin “hollow” region potentially present in the centers (inset of Fig. 4a, b).

Confocal laser scanning PL imaging further unveiled spatial heterogeneity in the emission characteristics of the mesocrystalline QD superlattices. The central regions predominantly displayed yellow SF PL and green PL (Fig. 4c, d and Supplementary Fig. 6, 7), which can be attributed to the densely packed, partially oriented-attached CsPbX₃ QDs - nanoscale ‘LEGO’ bricks constituting the superlattice (Fig. 1a). In contrast, the peripheral regions in proximity to the edges exhibited only green PL (Supplementary Fig. 7b). The fluorescence intensity distribution indicates that the stronger fluorescence of green emission in the edge regions (Fig. 4c, d).

Meanwhile, the mapping of 3D construction of PL contrast across the pyramidal facets corroborated these observations (Supplementary Fig. 9), implying variations in the dynamics of exciton recombination and interactions among QDs between the less concentrated central regions containing CsPbX₃ crystallites versus the highly dense outer boundary regions. These variations in exciton dynamics and interactions are likely influenced by the differences in QD packing density, coupling, and oriented attachment across different regions of the mesocrystalline superlattice. In general, microscopy and fluorescence microscopy revealed that spatially distinct optical signatures within the pyramidal mesocrystalline QD superlattices, differentiating the central and peripheral regions of the packing arrangement of the nanoscale ‘LEGO’ bricks. Such spatial heterogeneity suggests the presence of variations in the coupling strength, packing density, and oriented attachment of QDs within different regions of the mesocrystalline superlattice architecture.

Electron microscopy elucidates the structural evolution from QD superlattices to atomically coherent mesocrystalline QD superlattices upon annealing treatment. SEM (Supplementary Fig. 10) and Scanning transmission electron microscopy (STEM) images (Fig. 5a, b) revealed the initial self-assembly of QDs into simple cubic packing clusters with a ~ 9 nm unit cell in the as-prepared superlattices. The edge boundary and [100]_QD lattice fusion of QDs can be clearly observed along QD superlattices [100]_superlattice plane of the simple cubic package under HR-TEM (Fig. 5b). While the corresponding selected area electron diffraction (SAED) further indicated partial crystallographic alignment of QDs within the superlattice (selected area 190 nm*190 nm, Fig. 5c). The angular width of the (200)_QD and (300)_QD reflections in QD superlattice is approximately 15–22°. Within the QD superlattice, which is initially ordered in mesoscale yet disordered in the nanoscale, the presence of planar defects at the grain boundaries separate crystalline domains with limited crystal orientation.

Thermal annealing initiated oriented attachment, a process in which interfacial boundaries between QD domains underwent dynamic reorganization driven by the reduction of overall surface energy and the minimization of interfacial strain between the QDs. This process led to the annihilation of planar defects and mosaic-type boundaries, yielding atomically coherent mesocrystalline QD superlattices with enhanced long-range orientational order and diminished crystal defects ²⁰. The SAED of the annealed, pyramid-shaped mesocrystalline QD superlattices (Fig. 6c) revealed highly crystalline, single-domain orientations across the nanoparticle facets, in contrast to the limited long-range order observed in the as-prepared cube-shaped superlattices (Fig. 5c). The angular width of the (200)_QD and (300)_QD reflections in mesocrystalline QD superlattice is approximately 3–8°. Notably, SAED patterns acquired from the central region of the mesocrystalline QD superlattices exhibited more pronounced orientational alignment and crystallization compared to the edge areas (Supplementary Fig. 8). This observation implies that thermal annealing drives further heteroepitaxial fusion between QD surfaces, leading to optimized oriented attachment across the mesocrystalline superlattice, particularly in the central region. SAED analysis confirmed spatial heterogeneity in the crystalline order and orientational alignment within the mesocrystalline QD superlattices, with the central region exhibiting a higher degree of crystalline perfection and orientational coherence compared to the edge areas.

Furthermore, HR-TEM micrographs (Figs. 1c and 6a) unveiled a markedly thinner central mesocrystalline superlattice domain, averaging 20 nm * 20 nm, with a depression relative to the elevated peripheral lattice planes. Such ‘hollow’ pyramidal morphology of the mesocrystalline QD superlattices is notable, as it introduces a microcavity structure that is conducive to enhancing SF ³⁶. Further enlarging the ‘hollow’ area, the HR-TEM in Fig. 6b and Supplementary Fig. 11 provide clear evidence of a centrally situated mesocrystalline superlattice domain composed of fused atomic lattices exhibiting exceptional crystalline quality and a predominate crystallographic alignment. Such micrographs signify redistribution of initially adjacent QD constituents throughout oriented-attachment in a manner annihilating any discernable boundaries between composite nanobuilding blocks to yield an epitaxially coherent mesoscopic crystalline phase.

The packing structures of the nanoscale ‘LEGO’ bricks determines the fluorescent properties of the QD superlattice. The enhanced long-range crystallinity and diminished crystal defects visualized through SAED and HR-TEM directly correlate with the emergence of narrowband, room-temperature SF that not present in the initially QD superlattice. Therefore, SAED and HR-TEM provides critical evidence that the cooperative emission behaviors result from the collectively coupled excited states enabled by the mesocrystalline superlattice's highly oriented, single-crystalline-like architecture. Previous quantitative structural characterization and coupling electronic or photonic properties, validated the manifestation of a singularly favored crystallographic progression and growth vector within these mesocrystalline QD superlattices ^{25, 37, 38, 39}, notable for its divergence from the prevalence of arbitrarily assorted QD dispersions prepared by spin coating techniques or close-packed yet orientationally nondescript supraparticle congregations precipitated solely through liquid/air interface self-organization lacking hierarchical crystallization controls.

Meanwhile, the evacuation of trapped ligands at interstitial QD junctions during the thermal annealing process was also revealed via in-situ Fourier-transform infrared (FTIR) spectroscopy (Supplementary Fig. 12). Surface-capping ligands employed during QD synthesis are prone to entrapment at interstices separating proximal nanocrystal facets following organization ^{19, 40}. Residual ligand occupation physically isolates constituent QDs, disrupting the potential for hybridized wavefunction topographies ²⁵. The results suggest that within the first two minutes of thermal treatment, approximately 10% of the original ligand content was lost. Significantly, further annealing over the following 8 minutes led to at least an additional 20% reduction of the remaining ligand fraction. Controlled thermal annealing activates surface-diffusion dynamics, providing the mobility necessary for ligands to egress from interfacial crevices between sintered QD bricks (Supplementary Fig. 13) ^{41, 42}. Excision of such steric barriers permits nanocrystals to assemble in contiguity, nearly fusing inorganic surfaces at nanometer-scale proximity. Without spacer molecules obstructing boundary regions, chalcogenide anionic and metallic cationic orbitals comprising successive nanocrystal facets achieve unimpeded orbital fusion, coalescing into continuous delocalized networks pervading multiple nanocrystal constituents ⁴¹. Specifically, interfaces exhibit robust hybridization of iodide p-orbitals spanning nanocrystal limits ⁴³. Strengthened electronic delocalization emerging from proximal facet-contact is evidenced through augmented inter-QD coupling integrals extracted from spectroscopic measurements. Concomitantly, excitonic wavefunction profiles diffuse further spatially through the mesocrystalline matrix. Hence, annealing meticulously evacuates residuals that confine electronic wavefunction topographies, unlocking the potential for orbitally fused networks to achieve long-range wavefunction continuity and exciton delocalization across this organized mesoscopic assembly of QDs.

It is posited that the optimized mesocrystalline structure, which has transitioned from cube-shaped superlattice to Pyramid-Shaped mesocrystalline superlattice, enables room temperature SF emitted by the embedded QDs matrix through a quantum acoustic vibration isolation (QAVI) mechanism proposed by Gundogdu et al ²⁹. Conventionally, thermally driven phononic interactions would cause significant decoherence into an excitonic system at ambient conditions. However, in the case of this precisely periodic mesocrystalline solid, intrinsic lattice distortions obtained via inter-particulate oriented attachment, especially within the central area of these mesocrystalline QD superlattices, suggest a mechanistic pathway by which such organization promotes polaron formation akin to ‘giant dipole’ (Fig. 1a), constituting a quantum acoustic analog of thermal vibration insulation for the electronic excited state.

In CsPbBr₃, the polaron binding energy is reported to be within 34–47 meV ^{44, 45, 46}. At room temperature (~ 300 K), the average thermal energy kT (where k is the Boltzmann constant and T is temperature) is about 26 meV which is slightly lower than the energy required for the thermal dissociation of polarons. The interaction between polaronic entities and phononic thermal oscillations occurs preferentially through the lattice strain component versus the electronic dipole itself ⁴⁷. As such, the photonic coherence of the electronic excitation achieves effective isolation from electron-phonon scattering vectors that would otherwise induce dephasing under ambient conditions. Crucially, the polarization of electronic-lattice coupling dynamics within the polaron quasiparticle suppresses thermal relaxation channels including phonon scattering and Auger recombination (Fig. 1a). Thus, the QAVI mediated by the mesocrystalline matrix realizes a form of large polarons in QDs that provide a quantum analog of vibration isolation to electronic excitation (Supplementary Fig. 13), circumventing ordinary decoherence even at ambient conditions to realize room-temperature SF.

To evaluate the hypothesized QAVI mechanism enabling macroscopically coherent SF at ambient temperature, rigorous interrogation of thermal processing protocols was conducted. Mesocrystalline QD superlattices were subjected to controlled crystallization regiments across a temperature series from 45–100°C, with structural evolution temporally monitored via periodic transmission electron diffraction.

The transformation of superradiative emission was quantitatively tracked t through PL spectroscopy, assessing peak intensity and temporal coherence over annealing durations ranging from 1–20 min. Through these interdigitated experiments, we observed an optimal temperature window between 60–75°C wherein extending treatment improved both long-range crystalline orders, as discerned through Rietveld refinement of electron diffractions. This demonstrates that higher quality structural order derived from stronger oriented attachment amplifies the cooperative interactions responsible for room-temperature SF over individual particle recombination, as evidenced by the dominance of the coherent superradiant mode. Correspondingly, a progressive sharpening and enhancement of the SF peak at 2.18 eV emission dynamics emerged over annealing intervals from 1–10 min confined to this delimited thermal regime (Fig. 7). However, exceeding either 75°C or 10 min degraded structural quality concomitant with diminished superradiance (Supplementary Fig. 14). This non-monotonic dependence upon annealing closely parallels theoretical models reliant upon maximizing QAVI effects.

Most interesting, the signature splitting of the green emission peaks underwent striking changes as annealing, and the bifurcated feature grew increasingly sharpened and refined (Fig. 7a, b). Time-resolved PL revealed multi-exponential 1/e decay profiles for the dominant green emission peaks at 2.47 eV, 2.40 eV and 2.37 eV (Fig. 7c) displayed progressively shorter decay times to around 120 ps with increasing excitation fluence (Supplementary Fig. 15). This intriguing finding of multi-exponential decay profiles for the green emission peaks indicates the possible occurrence of three additional SF processes, besides the observed SF behavior for the yellow emission peak, suggesting the presence of multiple cooperative emission mechanisms within the mesocrystalline QD superlattice. Figure 7d displays a streak camera image, obtained at an excitation fluence of 170 µJ cm^− 2, which is indicative of the characteristic property of SF, known as Burnham–Chiao ringing, wherein the presence of both a finite rise time and subsequent oscillation of the emission, alongside a significantly shortened radiative decay. This phenomenon suggests the nature of the optical transitions underlying these green emission peaks transformed from superradiant to superfluorescent behavior with further oriented attachment in mesocrystalline superlattice. The evolution towards faster collective emission kinetics is characteristic of the transition to a Dicke superradiant state, where long-range coherence established between QDs via annealing enhances the radiative coupling necessary for SF. This observation aligns with the proposed QAVI mechanism, wherein the optimized mesocrystalline structure facilitates the formation of polaron-like states that enable effective isolation of electronic excitations from thermal decoherence processes, allowing for the emergence of SF emission phenomena at room temperature.

The highly organized mesocrystalline QD superlattice allows for SF, while previously studied superlattices did not display this phenomenon at ambient conditions. In conventional QD superlattices, the emitters (QDs) are coupled only to nearest neighbors with short-range interaction. This is insufficient to achieve the critical long-range coupling and interaction timescales required by Dicke superradiance theory to overcome individual decoherence mechanisms at ambient conditions (Supplementary Fig. 13b, c) ^{48, 49}. Thermal fluctuations disrupt quantum coherence between insufficiently coupled emitters (Supplementary Fig. 13a). Nevertheless, in the mesocrystalline superlattice reported in this work, the oriented attachment growth mechanism leads to the formation of polaron quasiparticles that provide quantum acoustic vibration isolation. The QD matrix within mesocrystalline superlattice, with long-range coherence enabled by the oriented attachment, acts analogously to an array of coupled emitters required for Dicke superradiance, fulfilling the needed next-nearest neighbor coupling criteria. This suppresses local phonon-induced decoherence effects and prolongs the excitonic interaction range and timescale. The resulting next-nearest and even further neighbor coupling facilitated by the uniquely ordered mesocrystalline superlattice architecture satisfies the minimal criteria for collective Dicke superradiance ²⁸. The excitons become coherently delocalized over a large number of lattice sites. The cooperative enhancement of the emission rate outweighs individual thermal decoherence processes, inducing a superradiant phase transition observable as SF even at room temperature.

This work unveils thermally-activated oriented attachment of QDs into a uniquely pyramidal mesocrystalline architecture, which allows for the realization of a periodic solid-state material capable of exhibiting SF emission on a macroscopic scale under ambient conditions. The as-prepared cube-shaped QD superlattice exhibits limited long-range order and orientation due to imperfect oriented attachment between particles during self-assembly. However, under the influence of annealing, the superlattice undergoes morphological transformation into a pyramid-shaped QD superlattice with highly ordered mesocrystalline domains. The annealing treatment provides the necessary energy for further optimized attachment between nearest neighbor QDs via heteroepitaxial growth. This results in extended twinning and fusion of facets between particles, culminating in a single crystalline-like mesocrystalline superlattice architecture with long-range atomic coherency and minimal grain boundaries. Through oriented attachment, long-range crystallographic orientation within superlattices is achieved composed of QD building units. Crucially, this oriented attachment maintains the quantum characteristics of each individual QD even as they interconnect into quasi-single-crystal solids. Rather than disrupting the nanoscale properties through fusion or intermixing, our approach gently guides the precise positioning of QDs during crystallization. Integrating structural, vibrational and quantum optical data conclusively corroborates that controlled thermally-driven mesocrystallization fosters sufficient phononic decoupling to preserve long-range coherence even at room temperature, directly underpinning the emergence of robust macroscopic SF from this periodic solid-state architecture. Concomitant structural, vibrational and quantum optical studies elucidate the critical role of optimizing this mesocrystalline superlattice's phononic properties through oriented attachmen, which suppressing thermal decoherence - attributes indispensable for realizing quantum synchronization and coherent interactions across a vast excitonic ensemble. Continued interrogation of this superlattice's crystallography, bandgap dynamics and superradiant output over varied fabrication parameters provides a roadmap towards finely tuning SF emission and many-body quantum phenomena at room temperature.

Acknowledgments

The authors acknowledge financial support from the National Natural Science Foundation of China (no. 22102058 and 62074060), Science and Technology Program of Guangzhou (no. 202103030001), Key-Area Research and Development Program of Guangdong Province (no. 2021B0101310003), and South China Normal University. We acknowledge Dr. Qilin Lian from Leica Microsystems (Shanghai) Trading Co., Ltd for his expertise in the manipulation and analysis of confocal fluorescent imaging.

Author contributions

The work idea originated from Z.L., who gained experience and inspiration in the Helmut Coelfen group. Z.L. prepared the samples with the assistance of X.Y.C and H.T. L., interpreted the data with input from X.L. and B.R.H., and wrote the manuscript with input from X.L. and B.R.H. Additionally, G.C.L. and R.Z.Y. performed photoluminescence experiments, and H.L.L. performed TRPL tests. The work was supervised by X.L. and G.C.L.

Competing interests

The authors declare no competing interests.

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Pyramid-Shaped Quantum Dot Superlattice Exhibiting Tunable Room-Temperature Superfluorescence via Oriented Attachment

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Abstract

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Introduction

Room-temperature superfluorescence from pyramidal-like mesocrystalline QD superlattice

Oriented attachment induced emission splitting

Mapping Emission Variations in Mesocrystalline QD superlattices

Packing Heterogeneity in Mesocrystalline QD superlattice and structural evolution

Room-temperature superfluorescence model

Tunable superfluorescence signatures via oriented attachment

Conclusions

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Acknowledgments

Author contributions

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