Materials for optics

The realization of large-scale exciton–polariton platforms operating at room temperature and exhibiting long-lived, strongly interacting excitons has been elusive. Here, the authors demonstrate a room-temperature perovskite-based polaritonic platform with a polariton lattice size of up to 10 × 10.

A multiscale modelling platform combining nanoscale resonant scattering, mesoscale multiple scattering and macroscale light transport effectively predicts the macroscopic visual effects created by optical metamaterials with disordered nanostructures.

Gauge fields are essential for detecting and controlling quantum dynamical systems, but their potential has yet to be fully exploited. Here, the authors insert a single-unit-cell synthetic gauge flux into a sonic crystal with the gauge phase ranging from 0 to 2π, leading to topological Wannier cycles.

Organic blends based on cationic photoredox catalyst dopants in neutral donor hosts show p-type charge transport behaviour. This favours reduced reactivity to oxygen in organic long-persistent luminescence materials responsive to visible light.

Triplet exciton harvesting through thermally activated delayed fluorescence is shown to be effective also under X-ray excitation, increasing the efficiency and imaging quality of X-ray detectors based on organic scintillation.

The authors demonstrate ultrafast symmetry breaking by optically driven photocurrents.

A strategy to confine phosphorescent organic chromophores within ionic crystals proves effective in suppressing non-radiative recombination channels and increasing the phosphorescence efficiency of blue-emitting heavy-atom-free emitters.

An outlook on the potential of lead-halide perovskites as a playground for exciton-polariton studies and for the development of polaritonic devices operating at room temperature is provided.

A coherent condensate of exciton–polaritons, extending spatially up to 4 µm and spin-polarizable with an external magnetic field, is observed at cryogenic temperatures in a MoSe₂ monolayer embedded in a vertical microcavity.

Stacked elastomeric arrays containing plasmonic nanoparticles show efficient chiral responses that can be fully controlled by mechanical compression and stack rotation. These simple layered materials may be useful modulators for photonic applications.

Symmetry is utilized to realize a phononic higher-order Weyl semimetal.

The optical emission of graphene under pumping with femtosecond laser pulses contains a strong component linked to plasmon emission from the hot electrons in the system.

Femtosecond optical pulses are used to generate coherent phonons that break inversion symmetry and drive anisotropic terahertz photocurrents in the topological material ZrTe₅.

Periodic patterns with varying cross-linking densities are realized in conjugated polydiacetylene films, creating multiple holographic images—all dynamically responsive to exposure to various solvents—simultaneously in the same polymeric structures.

Comparison of hexagonal boron nitride samples grown with different techniques and with varying carbon-doping content provides evidence that the defects emitting single photons in the visible range are carbon related.

A carbazole isomer, typically present as an impurity in commercially produced carbazole batches, is shown to be responsible for the ultralong phosphorescence observed in these compounds and their derivatives.

Infrared nanoimaging of phonon polaritons in twisted α-phase molybdenum trioxide bilayers reveals tunable wavefront geometries and topological transitions over a broad range of twist angles, offering a configurable platform for nanophotonic applications.

The integration of barium titanate thin films with silicon-based waveguides enables the operation of efficient electro-optic switches and modulators at temperatures as low as 4 K, with potential applications in quantum computing and cryogenic computing technologies.

An investigation on the electronic transitions of organic radicals allows us to identify design rules to increase the oscillator strength of these emitters and obtain efficient radical-based light-emitting diodes operating in the visible range.

Repulsive dipole–dipole interactions between localized interlayer excitons are shown to modify the optical response of van der Waals heterobilayers, forming the basis to obtain strong optical nonlinearity and excitonic many-body states in two-dimensional materials.

Defects in hexagonal boron nitride exhibit room-temperature quantum emission, but their unknown structural origin challenges their technological utility. A combination of optical and electron microscopy helps to distinguish at least four classes of defects and correlate them with local strain.

Triplet excited states related to partial molecular structures are shown to mediate spin-flip between lowest singlet and triplet excited states in multiple donor–acceptor charge-transfer-type organic molecules.

Local tuning of quantum dots embedded in a photonic waveguide can be achieved through the strain produced by laser heating of a thin layer of HfO₂ deposited around the waveguide. The method is exploited to tune three quantum dots in resonance.

A large photoresponse is observed in the type-II Weyl semimetal TaIrTe₄, and attributed to the diverging Berry curvature of the Weyl nodes.

An optimized design for a broad-area surface-emitting photonic-crystal laser leads to high brightness of over 300 MW cm^–2 sr^–1 and an output power of 10 W under pulsed excitation.

Reversible structural surface relaxation under laser exposure is observed for monolayers of 2D metal halide perovskites. These structural changes also induce reversible shifts in the photoluminescence peaks of these materials.

Long coherence times in a subset of states that allows for transitions in both microwave and optical range have been reported using an isotopically purified ¹⁷¹Yb³⁺:Y₂SiO₅ crystal, rendering the system suitable for quantum information applications.

Degenerately doped semiconductor nanocrystals exhibit localized surface plasmon resonance in the infrared. Semiconducting properties such as band structure modification due to doping and surface states are now shown to strongly affect plasmonic modulation.

Films of exfoliated crystals of two-dimensional hybrid metal halide perovskites with phenyl groups as organic cations show increased molecular rigidity, reduced electron–phonon interactions and blue emission with photoluminescence quantum yield approaching 80%.

Quantitative analysis of polymer LED degradation under current stress provides insight on the role of hole traps and their formation. Blending of the emitting material with large-bandgap semiconductors leads to trap dilution and improved stability.

Isotopic enrichment in hexagonal boron nitride is shown to enhance the propagation properties of phonon polaritons, achieving a threefold enhancement in their lifetime.

The activation of cleavable organometallic dimers upon exposure to ultraviolet radiation allows air-stable n-type doping of organic materials with electron affinity lower than the expected thermodynamic reducing strength of the dimers.

Stimulated emission under continuous-wave excitation from mercury telluride quantum dots at very low thresholds (compatible with electrical injection) is achieved by exploiting surface traps that render the quantum dots into four-level systems.

Designing fully tunable metamaterials for applications ranging from sensors to superlenses remains a challenge. A reversible electrotuneable liquid mirror based on voltage-controlled self-assembly/disassembly plasmonic nanoparticles is now reported.

Charge-transfer dynamics in organic semiconductors are shown to be altered by multi-layered hyperbolic metamaterial substrates, an effect linked to the number of metal–dielectric pairs used.

A blue-emitting phosphor without thermal quenching is reported. The emission losses at high temperatures are compensated by a counter mechanism, originating in energy transfer between electron–hole pairs and thermally activated defect levels.

Heteroepitaxial growth using aligned crystalline substrates allows extended metal–organic framework crystal growth oriented relative to the substrate

A theoretically proposed photonic crystal design with valley-dependent spin-split bulk bands allows for the independent control of valley and topology in a single system.

This Review discusses the properties of polariton modes (plasmon, phonon and exciton) in graphene, hexagonal boron nitride and transition metal dichalcogenides for applications across the terahertz to visible spectrum.

The spin-switching of optically induced polariton condensates can be externally controlled with an electric field, with switching energies below 0.5 fJ.

This review discusses exciton–polaritons in microcavities and their emerging technological applications, with emphasis on the materials challenges for operation at room temperature.

Zeolites encapsulating clusters of silver offer interesting optical properties. Here it is shown how the interactions between these clusters and the framework can be tuned to achieve photoluminescence quantum yields approaching unity.

Optically rewritable surface phonon–polariton resonators are demonstrated in a system combining phase-change materials that can reversibly switch between amorphous and crystalline phases, with polar crystals that support surface phonon–polaritons.

A highly sensitive plasmonic biosensor, based on hyperbolic metamaterials, can detect biomolecules of ultralow molecular weight at picomolar concentrations.

Topologically protected states at the interface of magnetic domain walls in a parallel plate waveguide with adjustable rods, are shown to be directed along different paths, as the waveguide geometry changes.

Femtosecond optical spectroscopy and single-shot electron diffraction measurements during the photoinduced amorphization of the phase-change material Ge₂Sb₂Te₅ demonstrate that optical properties can be separated from the structural state.

Phase matching in the backward direction—the so-called nonlinear mirror effect—is demonstrated experimentally between the fundamental and second harmonic, using two distinct modes in a metal–dielectric–metal waveguide.

A surface-initiated solution growth method is used to synthesize single-crystal nanowires of organic–inorganic perovskite that show very low lasing threshold. Coating the nanowires with metallic films marginally affects the lasing performance.

A design rule to synthesize organic molecules with a phosphorescence lifetime longer than 1 second is presented. The molecules form H aggregates that promote the stabilization of triplet excitons and persistent luminescence under ambient conditions.