Halide perovskite nanocrystals are excellent materials for light-emitting devices and hold promise for quantum information technologies as well. Isovalent transition metal doping has been shown to further enhance luminescence yields, yet the underlying mechanism had been previously unclear.

Using transient optical spectroscopy, I will first show that such luminescence efficiency gains result from reduced nonradiative losses but also, surprisingly, from enhanced radiative rates upon doping [1]. I will explain these observations in the context of local lattice periodicity breaking and subsequent localization effects, and generalize these mechanisms for Mn, Zn, and Ni doping [2].

Then, I will introduce a new ambient room temperature synthesis route, giving easy access to controlled doping of Mn, Ni, or Zn into CsPbX3nanocrystals (with X = Cl, Br, I) across various sizes, including for the first time the doping of small, truly confined nanocrystals, which had been inaccessible using hot-injection approaches so far – with profound consequences for the light-emitting properties of the resulting materials [3].

Time permitting, I will conclude with the (spin-)photophysics of new nanocrystal materials investigated in our lab [4].

[1] J. Am. Chem. Soc. 2021, 143, 23, 8647–8653

[2] J. Am. Chem. Soc. 2022, 144, 34, 15862–15870

[3] J. Am. Chem. Soc. 2025, 147, 19, 16536–16544

[4] Unpublished results 2026

CC

Colloidal quantum dots (QDs) must be transferred from their native hydrophobic environment into water for various applications, particularly those involving bio-interfaces, while preserving their optical properties and colloidal stability.¹ Several strategies have been developed over the years for such transfer, including polymeric coating, silica shell encapsulation, and thiol ligand exchanges.¹ Among these approaches, ligand exchange with short-chain thiols is preferred when charge transfer is required for the target application.¹ However, the transfer yield of these exchanges is generally suboptimal, and, more importantly, surface trap states are introduced that can negatively impact charge-transfer rates.² In addition, the release of photo-oxidised ligands might occur, which may cause precipitation of the QDs and can deactivate biological co-catalysts.³

Herein, we propose a colloidal atomic layer deposition (c-ALD) strategy to enable high-yield (~100%) transfer of colloidal QDs in water while preserving their optical properties and colloidal stability. The c-ALD enables surface modification of QDs with a few metal-oxide (MOx) monolayers.^4,5 The introduction of polar carboxylate ligands (PCL) during the c-ALD anchors them to the surface via a proton-exchange mechanism rather than hard-soft acid-base interactions, which generally occur on MOx surfaces. The c-ALD-enabled ligand binding generated QDs with photo- and colloidal stability for at least 10 days. As a proof of concept, we coupled TiOx-coated CdSe QDs with an [Fe-Fe] hydrogenase for photocatalytic H₂ production and observed a 50-fold enhanced activity compared to state-of-the-art thiol-capped QDs.

Altogether, the above results highlight the promise of c-ALD as a water-transfer method for photocatalytic applications of colloidal QDs in biohybrid systems and beyond.

The self-assembly of nanocrystals (NCs) into ordered mesocrystals enables collective phenomena driven by long-range inter-particle correlations. High order requires a delicate balance between sufficientlyhigh NC density to drive assembly and sufficient dynamic freedom allowing particles to find energetically favourable positions upon densification. Understanding how NC diffusivity evolves during densification is therefore essential for achieving reliable, high-yield outcomes. Accessing NC diffusivity at high particle densities remains challenging due to their fast motion, determined by a multitude of interconnected factors. Here, we map the spatio-temporal evolution of CsPbBr₃ NC diffusion during evaporation-driven self-assembly into mesocrystals by X-ray photon correlation spectroscopy (XPCS) using a nanofocused high-flux X-ray beam at a fourth-generation synchrotron. Our results reveal that spatial heterogeneity in collective diffusivity directly determines local mesocrystal yield. Near the evaporation front, collective NC diffusivity slows during densification but stabilizes at a slowed-down-but-mobile plateau. In contrast, regions far from the evaporation front undergo premature agglomeration and kinetic arrest before long-range order can develop. These findings demonstrate that local diffusive dynamics determine whether assembly proceeds towards ordered mesocrystals or kinetically
arrested aggregates. By correlating the measured diffusivity directly with the NC volume fraction, structural evolution and predictions from theoretical models, we propose solvent mediated hydrodynamic interactions between NCs to be the dominant factor controlling collective NC diffusivity and agglomeration during evaporation. Our results highlight that long range hydrodynamic ligand-ligand and ligand-solvent interactions largely determine whether NCs agglomerate randomly or form orderd mesocrystals. This points to solvent viscosity, evaporation rate, and solvent mixtures as direct design criteria for improving mesocrystal yield and spatial homogeneity through tailored solvent and ligand choice. 

Metal halide perovskite nanocrystals exhibit outstanding optoelectronic properties, but their stability and performance is fundamentally governed by surface chemistry. A defining feature of these materials is the highly dynamic nature of their surfaces, where weakly bound ligands and mobile ions lead to continuous reorganization. In my prior work, I focused on identifying the most strongly binding, better-matched ligand chemistries that suppress surface dynamics, reduce nonradiative recombination, and maximize photoluminescence quantum yields. These studies established clear connections between ligand structure, surface stabilization, and light-emission efficiency in perovskite nanocrystals.

In this contribution, I will describe how these insights motivate a new research direction aimed at understanding and controlling charge extraction and injection at perovskite nanocrystal interfaces. Moving beyond light emission, we seek to determine how residual surface dynamics and trap states influence interfacial charge transfer processes, and whether slowing or selectively tuning these dynamics can enable more efficient and directional charge flow for applications like photocatalysis and photovoltaics. My group approaches this problem through the design and synthesis of custom ligands that modulate binding strength, surface reorganization, and interfacial energetics. I will conclude by discussing how time-resolved spectroscopic measurements can directly link ligand-controlled surface dynamics to charge transfer kinetics, providing molecular-level design rules for perovskite nanocrystal interfaces across a range of applications.

Lead halide perovskite nanocrystals have emerged as promising materials for light-emitting devices owing to their high photoluminescence quantum yield, narrow emission linewidth, and facile spectral tunability. Their optoelectronic properties, however, are governed not only by the inorganic nanocrystal core but also by the dynamic organic ligand sphere, which controls colloidal stability, self-assembly, charge injection, and interparticle coupling. Despite this central role, directly visualizing and quantitatively understanding the ligand shell remains a major challenge.

This presentation will discuss how complementary spectroscopic and scattering techniques can be combined to reveal the structure, dynamics, and function of ligand shells on lead halide perovskite nanocrystals and their assemblies. Quantitative nuclear magnetic resonance spectroscopy, neutron scattering, spectroelectrochemistry, and spatially resolved fluorescence microscopy provide direct insight into ligand density, binding dynamics, and electrochemical charge injection. These studies reveal how ligand exchange, ligand stripping, and dynamic surface equilibria modify the nanocrystal surface and govern collective properties in assembled supercrystals.

Building on this microscopic understanding, the ligand sphere can be engineered to tailor optoelectronic functionality. Tailored ligand design enables tuning of charge-injection barriers through molecular inductive effects, improves the robustness of nanocrystal supercrystals by controlled ligand-density reduction, and facilitates the integration of mechanically stable assemblies into photonic architectures. Together, these examples illustrate how visualizing the ligand sphere provides the foundation for designing surface chemistries that translate directly into improved performance of nanocrystal-based lighting and optoelectronic devices.

Ligands are small organic molecules that bind to nanocrystal surfaces and make them soluble, stable, and processable. In perovskite nanocrystal superlattices, ligands play many additional roles: they define surfaces, influence structure, reactivity, and optical properties. In this talk, I will discuss CsPbBr₃ perovskite nanocrystals and their superlattices as systems in which ligands act as structural, chemical, and photophysical components.

I will discuss how the ligands influence superlattice structure, giving rise to structural coherence, periodic displacements, and structural transitions. Beyond structure, ligands also regulate optical properties. By controlling the spacing between nanocrystals, shorter and longer ligands tune the strength of electronic coupling between the nanocrystals. When weakly bound, ligands can promote nanocrystal coalescence and hydrolysis, leading to loss of quantum confinement and the formation of localized lower-bandgap domains that act as energy funnels. When chiral ligands are used, weak ligand-induced chirality can be converted into measurable circularly polarized luminescence in superlattices.

Together, these examples show that ligands determine what perovskite nanocrystal superlattices may become: single-crystalline materials with dynamic structures, evolving stability, and emergent optical properties.

Plasmon-induced chemistry, which harnesses the energy of the collective oscillations of conduction electrons in metallic nanoparticles (NPs) upon light irradiation, has become a powerful tool for driving chemical reactions under mild conditions. This field shows great potential for applications ranging from catalysis and energy conversion to sensing and biomedicine. Plasmonic catalysts can be viewed as complete reactors, since all light-initiated processes can influence the reaction pathway. For example, the plasmonic electric field can attract and orient molecules, while energetic charge carriers (electrons and holes) and localized heating from plasmon excitation can trigger redox reactions or lower the activation energy of other processes, facilitating chemical transformations that would otherwise be unfavorable.[1] While several aspects of plasmon-enhanced reactions are well understood, a critical gap remains in our understanding of the initial steps, specifically the role of molecular adsorption on the metallic nanoparticle surface and its influence on subsequent photoreactivity. Existing literature often treats the adsorption process in a simplistic manner, neglecting the intricacies of surface coverage, molecular orientation, and surface complex formation.[1] Most studies use thiols to perform such experiments; however, thiols are strong directing agents and do not reproduce the complexities of a free molecule interacting with a metal surface. This study investigates the complex interaction between the adsorption of halogenated adenines, specifically 2- and 8-halogen adenine, as well as 8-halogen adenosine, on gold and silver nanoparticles, and their subsequent reactivity. We show that the adsorption configuration and the molecule-surface orientation differ significantly between gold and silver nanoparticles. The results show that the molecule's orientation strongly affects the reaction rate in gold nanoparticles, whereas in silver, the overall reaction proceeds very efficiently, independent of the molecule. These results are supported by Raman spectra simulated using density functional theory of the molecules adsorbed on metal clusters. Our results show that molecules with multiple interaction points can be activated by plasmonic nanoparticles, but the reaction outcome is still dependent on the leaving group orientation; if it is closer to the metal surface, the reaction is suppressed. By establishing this link between the orientation of halogenated adenines and reaction outcome, we can go beyond purely experimental methods and develop design principles for highly effective plasmonic catalysts tailored to specific bio-related applications.

Halide perovskite nanocrystals combine bright, spectrally narrow, and compositionally tunable emission with low-temperature solution processing, making them attractive building blocks for next-generation optoelectronic and photonic materials. However, their practical use remains limited by environmental instability, ion migration, and the difficulty of controlling nanocrystal formation and organization across length scales. In this talk, I will discuss how polymer-based strategies can address these challenges by turning the polymer environment from a passive host into an active design element for synthesis, stabilization, and functionality.

I will first present our work on block-copolymer micelles as nanoscale reactors for the synthesis of lead halide perovskite nanocrystals [1]. In these systems, the polymer shell confines nanocrystal growth while simultaneously protecting the perovskite core from moisture-induced degradation and suppressing halide ion migration. Building on this concept, I will discuss how stability-optimized perovskite nanocrystals can be used to study and exploit energy transfer in hybrid nanocrystal assemblies [2], highlighting the role of nanoscale spacing, encapsulation, and optical coupling.

The second part of the talk will focus on translating these concepts into thin-film emitters. By combining block-copolymer-templated nanocrystal synthesis with post-synthetic treatment and UV-induced cross-linking, we recently demonstrated stable red, green, and blue perovskite nanocrystal films [3]. Cross-linking the polymer matrix renders the films insoluble and strongly suppresses halide interdiffusion while preserving the optical properties of the embedded nanocrystals, enabling multicolor and white-light-emitting all-perovskite nanocrystal films.

Finally, I will discuss our recent efforts to understand the formation of block-copolymer-encapsulated MAPbBr₃ nanocrystals using in situ optical spectroscopy and structural characterization [4]. These studies provide insight into how precursor chemistry, polymer confinement, and growth dynamics determine the final optical properties of the hybrid material.

Together, these results establish polymer-controlled perovskite nanocrystals as a versatile platform in which synthesis, stability, energy transfer, and film processing can be engineered through the nanocrystal–polymer interface. This approach offers general design principles for robust, solution-processable nanomaterials for light emission, photonics, and integrated optoelectronic devices.

Colloidal quantum dots (QDs) have revealed promises as triplet sensitizers for organic reactions in place of conventional homogeneous catalysts.^[1,2] QDs triplet sensitizers are commonly functionalized with a molecular dye to form QD/dye hybrids.^[3,4] The dye is believed to serve as both energy shuttle and non-covalent binding site for the freely diffusing substrate, overcoming the physical barrier imposed by the native ligands shell.^[5] Yet, fundamental understanding of the impact that QDs surface ligands have in a triplet sensitized system is lacking, hampering the full exploitation of their potential. In this contribution, we look at the surface chemistry of low-toxicity ZnSe QDs and we investigate the role of native ligands in mediating the interaction and sensitization of organic substrates without relying on molecular dyes. We show that the dynamicity of ligands allows for the direct QD-substrate interaction. Furthermore, we observe that the presence of a dipole moment in the substrate favors the dynamic exchange with native ligands on the surface, resulting in a stronger QDs quenching. Finally, we test dye-free ZnSe QDs as sensitizers in the [2+2] cycloaddition of carbonyls. This work highlights the importance that QDs surface chemistry holds in triplet sensitization, as the dynamicity of ligands is found to not hamper the interaction with substrates. We envision that the surface can be exploited as an intrinsic binding site and ligands can be engineered instead of relying on the use of molecular dyes.

Surface ligands play a central role in defining the structural, electronic, and optical properties of colloidal semiconductor nanocrystals. Beyond providing colloidal stability, appropriately designed ligands offer a route to introduce new functionality through controlled modification of nanocrystal surfaces. In particular, chiral ligands have emerged as a promising strategy to impart chiroptical activity to otherwise achiral semiconductor nanocrystals, enabling phenomena such as circular dichroism (CD) and circularly polarized luminescence (CPL), with potential applications in spin-optoelectronics, quantum photonics, and next-generation display technologies.

This presentation will discuss ongoing efforts to investigate ligand-mediated chirality in metal halide perovskite nanocrystals through the incorporation of chiral zwitterionic surface ligands. We examine how ligand binding, surface structure, and nanocrystal composition influence the emergence of chiroptical responses and discuss experimental approaches for probing these ligand-induced effects. Preliminary results illustrate both the opportunities and remaining challenges associated with engineering robust chiral interfaces while preserving the exceptional optical properties of halide perovskite nanocrystals. These studies highlight the importance of understanding surface chemistry as a pathway toward designing nanocrystal systems with tailored chiroptical functionality.

Lead halide perovskite quantum dots (LHP QDs) stand out due to their compositionally tunable bandgaps, bright and narrow emission, and exceptional tolerance to defects. Their long optical coherence times combined with short radiative lifetimes at cryogenic temperatures make them particularly attractive as quantum light sources. However, to date, atomically resolved structures of LHP QDs remain elusive, particularly at complex heterointerfaces, such as those between the inorganic core and organic ligands. Surfaces strongly influence the stability, optical performance, and reactivity of QDs, making atomically precise insights essential for their rational improvement. To tackle this pressing need, we utilize colloidal ¹³³Cs nuclear magnetic resonance (NMR) spectroscopy, a powerful and non-invasive analytical tool that provides rich, element and site-specific information. To understand the factors governing the ¹³³Cs chemical shift, we combined solid-state NMR measurements of bulk CsPb(Br_xCl_1-x)₃ samples with DFT calculations on representative model systems. We show that the ¹³³Cs chemical shift is the result of the complex interplay between material structure and composition. Leveraging this understanding, we explore surface-ligand interactions unveiling local chemical environments and structural distortions. We present ¹³³Cs NMR spectra of CsPbBr₃ QDs capped with various cationic and zwitterionic ligands. Using the ¹³³Cs chemical shift as a structural descriptor, we assessed the impact of each ligand on the QD surface and identified structural motifs that induce the least surface strain at room temperature. Variable temperature (VT) ¹³³Cs solid-state NMR measurements down to 110 K revealed contraction of the QD core while the surface-associated chemical shift remained unchanged, demonstrating that even the most favourable ligand imposes strain across the QD at low temperature. Considering the operational conditions and associated temperatures needed for coherent quantum light sources these findings provide a basis for rational and application specific ligand design. Moreover, such understanding is crucial for developing reliable computational models that capture structure-property relationships, enabling the forward engineering of QDs with tailored functionalities.