Optical materials and structures

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.

The morphology of donor–acceptor blends in organic photovoltaics dictates the efficiency of the exciton dissociation and charge diffusion, and thus the final device performance. Here, the authors show that filament assembly helps to maximize the output, further enabling a power conversion efficiency greater than 19%.

Cu₂O is a promising platform to host Rydberg exciton–polaritons, where excitons strongly couple to cavity photons, however their realization has been elusive. Here, the authors report Rydberg exciton–polaritons with principal quantum numbers up to n = 6.

Controlled synthesis of heterostructured III-V–II-VI nanocrystals shows that dipole moments formed at the core–shell interface can tune the optoelectronic properties of these nanomaterials and their performance in light-emitting devices.

Tamm plasmon thermal emitters can provide low-cost, efficient mid to long infrared emission, but have been limited by a challenging design. Here the authors apply an inverse design protocol to demonstrate tailorable multi-band emission on CdO films.

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.

This Review discusses the photophysical properties and nonlinear behaviour of single molecules, and their use as single-photon sources and in single-molecule sensing and quantum-sensing applications.

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.

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.

A second-order topological Weyl semimetal based on a 3D-printed acoustic crystal, exhibiting Weyl points, Fermi arc surface states, and hinge states, has been experimentally demonstrated.

The moiré pattern that is formed between well-aligned graphene and hexagonal boron nitride can modify the properties of WSe₂ (placed close by without intentional angle alignment), leading to the formation of a mini Brillouin zone and the folding of the bands in WSe₂.

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.

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.

Type-II van der Waals interfaces formed by different two-dimensional materials enable robust interlayer optical transitions, regardless of common issues such as lattice constant mismatch, layer misalignment or whether the constituent compounds are direct or indirect band semiconductors.

Multiple layers of diamond-like carbon films are shown to act as moisture barriers when conformally deposited on carbon fibre reinforced polymers used in space applications.

Repetitive electrical pulse stimulation of blue-phase liquid crystals promotes their reconfiguration into stable non-cubic structures with promising electro-optical responses for display technologies.

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.

This Review covers the basic physics of thermal emission, ways to engineer the thermal field radiated by hot objects in the far field and applications, such as thermophotovoltaics, radiative cooling, camouflage and privacy.

The droplet epitaxy technique has emerged as an alternative to the most commonly used Stranski–Krastanov for fabricating semiconductor nanostructures. This Review discusses the important aspects of droplet epitaxy quantum dots, from the growth mechanism to device application.

Plasmonic catalysis is believed to be mediated by energy transfer from nanoparticles to adsorbed molecules. Localized surface plasmon resonance on gold nanoparticles excited by electron beam is shown to drive site-selective CO disproportionation at room temperature.

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.

In this type of thermal cloak, when a fluid circulates around the object of interest, the temperature perturbation is minimized as the effective thermal conductivity of the fluid becomes very high due to convective effects.

Electro-optic modulators based on epitaxial barium titanate (BTO) integrated on silicon exhibit speeds up to 50 Gbit s^–1 while the Pockels coefficient of the BTO film is found to be approaching the bulk value.

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.

This Perspective describes the recent advances in understanding and controlling the properties of single-wall carbon nanotubes as well as the progress towards the fabrication of new electrically driven single-photon sources.

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 solution process for the diffusion of dopants in organic semiconducting films over a limited depth has been developed. The method is applied to single polymers and donor–acceptor mixtures, and for the realization of single-layer solar cells.

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.

Electrochromic films based on tin-doped indium oxide nanocrystals dispersed in a niobium oxide glass are now realized from solution at room temperature. The chain-like topology of niobium oxide improves the electrochemical properties of these films.

The photocurrent generated in organic photodetectors and solar cells can be enhanced by increasing light absorption in the active layer. It is now shown that an extended persistence length can increase the oscillator strength of conjugated polymers.

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

A review on toroidal excitations, from static toroidal moments in condensed matter, to dynamic toroidal multipoles demonstrated experimentally with metamaterials.

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.

Soft biomimetic microswimmers and microrobots made of photoactive liquid-crystal elastomers and whose body shape is controlled by structured light are able to self-propel and perform complex motion patterns on demand.

A renally cleared, water-soluble dye emitting in the near-infrared-imaging (NIR)-II window outperforms a clinically approved NIR-I dye in the in vivo imaging of tumours and their nearby blood and lymphatic vasculatures.

This Review discusses stimuli-responsive liquid crystalline polymer networks and elastomers as materials with programmable mechanics for use in functional devices.

An ultraslow-fluid-like unit cell composed of acoustic channels, arranged in a zigzag shape, exhibits various tunable Mie resonances. It is used for the construction of a highly reflective metasurface that can efficiently block low-frequency sound.

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.

Electron filling causes a reduction of the chemical potential in (Sr_1−x La_x)₃Ir₂O₇, which suggests negative electronic compressibility. Studying the concomitant change of the bandgap provides insight into the physical mechanism behind this effect.

A concept for the phase control of the nonlinear susceptibility using the left- and right-circular polarization basis for fundamental and harmonic generated light is introduced and tested using metasurfaces containing plasmonic antennas.

Fast fluorescence resonance energy transfer between CdSe nanoplatelets on a picosecond timescale is measured. This process is faster than Auger recombination and leads to the observation of multiexcitonic energy transfer in these materials.

An approach that exploits two bioorthogonal photochemistries to achieve reversible immobilization of full-length proteins in synthetic hydrogels allows for the reversible differentiation of human mesenchymal stem cells to osteoblasts.

Harnessing the optical properties of noble metals down to the nanoscale is crucial for fast information processing. Lateral confinement and delocalization of surface plasmons is now observed in self-assembled network chains of fused gold nanoparticles.

Inspired by Boolean binary algebra, an approach to design electromagnetic metamaterials with desired permittivity by using just two elemental building blocks is demonstrated analytically and numerically.

The dynamic control of thermal emission via the control of emissivity through intersubband absorption in n-type quantum wells, at a speed four orders of magnitude faster than is currently possible, is now demonstrated.

Until now, it has not been possible to switch chirality in plasmonic nanostructures at will and repeatedly. Now, thanks to DNA-regulated conformational changes, reconfigurable 3D plasmonic metamolecules with switchable chirality have been created.

Liquid-crystalline elastomers combine rubber-like elasticity with the optical properties of liquid crystals, yet some of their properties depend on the particular liquid-crystal phase. Now, stretchable gels of the liquid-crystalline blue-phase I are reported. The blue-phase gels are electro-optically switchable under a moderate applied voltage, and their optical properties can be manipulated by an applied strain.

Disordered photonic materials have the ability to control the flow of light through random multiple scattering. This has the drawback of randomizing both the direction and phase of the propagating light. Now, confined and interacting light modes are demonstrated for a two-dimensional disordered photonic structure.

Metamaterials are artificially fabricated materials that allow for the control of light and acoustic waves in a manner that is not possible in nature. This Review covers the recent developments in the study of so-called metasurfaces, which offer the possibility of controlling light with ultrathin, planar optical components.