The efficient interaction of light with quantum emitters is crucial to most applications in nano and quantum photonics, such as sensing or quantum information processing. Effective excitation and photon extraction are particularly important for the weak signals emitted by a single atom or molecule. Recent works have introduced novel collection strategies, which demonstrate that large efficiencies can be achieved by either planar dielectric antennas combined with high numerical aperture objectives or optical nanostructures that beam emission into a narrow angular distribution. However, the first approach requires the use of elaborate collection optics, while the latter is based on accurate positioning of the quantum emitter near complex nanoscale architectures; hence, sophisticated fabrication and experimental capabilities are needed. Here we present a theoretical and experimental demonstration of a planar optical antenna that beams light emitted by a single molecule, which results in increased collection efficiency at small angles without stringent requirements on the emitter position. The proposed device exhibits broadband performance and is spectrally scalable, and it is simple to fabricate and therefore applies to a wide range of quantum emitters. Our design finds immediate application in spectroscopy, quantum optics and sensing.

shaping, [12][13][14] sensing, [15,16] and nonlinear phenomena [17][18][19][20] are few examples demonstrating the strength of this approach for light management with sub-wavelength dielectric structures. However, with a few exceptions based on colloidal assembly, [21][22][23] hydrothermal growth, [20] solid state dewetting, [24][25][26][27][28][29][30] and aerosol spray, [31] most of these achievements were based on complex and expensive fabrication methods involving several steps (such as e-beam lithography and reactive ion etching). Top-down fabrication approaches limit the full exploitation of Mie resonators for unexpensive devices and broad areas production. In particular, given the rapidly rising interest in structural coloring and light filtering with dielectric metasurfaces [32][33][34][35][36][37][38][39][40][41] a versatile and scalable method is highly desirable to overcome the gap separating mere proof of principles and industrial applications. In this framework, a major step forward would be the development of fabrication techniques fully compatible with back-end processing of C-MOS circuitry (e.g., keeping the maximal processing temperature below ≈450 °C) or more generally, on electronic devices such as LEDs and photovoltaic panels.So far, most studies on Mie resonators are based on Si or Ge materials, due to both their very large index of refraction and the possibility to exploit the well-developed nanofabrication approaches of nanoelectronics and nanophotonics. Among other materials, TiO 2 (titania) is recently attracting growing interest [35,[42][43][44][45][46] for its transparency up to near-UV frequencies and its relatively high refractive index. Indeed, TiO 2 -based Mie resonators systems can potentially outperform conventional Si and Ge-based dielectric metasurfaces, which suffer from larger absorption at short wavelength [47,48] (e.g., at 450 nm: n TiO2 = 2.55, k TiO2 = 1.2 × 10 −5 ; n Si = 4.5; k Si = 0.13; n Ge = 4; and k Ge = 2.24). A quite unique peculiarity of titania is the tunable porosity (adjustable by modifying the sol-gel fabrication process) and therefore permeability to liquids and gas. In addition to this, titania is an abundant, cheap, nontoxic, photocatalytic, mechanically strong, and chemically stable material, featuring a relatively low mass density (≈3.8 g cm −3 in the anatase form against ≈5 g cm −3 for MoS 2 ). These features make titania an ideal metamaterial providing several functions (e.g., tunable structural color, sensing small changes in the environment), for a novel photonic platform in view of multifunctional devices. Dielectric Mie resonators are taking momentum in the last years thanks to their peculiar properties in light management at visible and near-infrared frequencies. However, their full exploitation demands for cheap materials and versatile fabrication methods, extendible over large surfaces and potentially C-MOS compatible. Here, a sol-gel deposition and nanoimprint lithography method is used to obtain titania-based Mie resonators over large areas (s...

The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10. 1002/adfm.201801958. tives to replace complex and bulky optical elements. This unique ability is due to strong modifications of the local density of optical states occurring in sub-micrometric objects made of materials featuring high dielectric constant and sufficiently small absorption losses.Most studies over the last years have mainly addressed silicon- [4][5][6][7][8][9][10] and germanium-based [11][12][13][14] Mie resonators, demonstrating that they could outperform their metallic counterpart supporting localized plasmonic resonances. However, the large absorption of group IV semiconductor compounds at short wavelengths induces strong optical losses, limiting their potential applicability as efficient devices especially at blue and near-UV frequencies [15,16] (e.g. at 450 nm: n Si = 4.5, k Si = 0.13; n Ge = 4.0, k Ge = 2.24). Furthermore, with a few exception based on colloids [4,17,18] and solid state dewetting, [13,[19][20][21][22][23] typical nanofabrication methods of Si(Ge)-based Mie resonators rely on top-down technologies that are not easy to scale-up at affordable prices.TiO 2 -based optical devices are an interesting alternative to Si, since Titania has a relatively high refractive index and is fully transparent up to UV frequencies [24,25] (e.g.: at 450 nm: n TiO2 = 2.55, k TiO2 = 1.2 × 10 −5 ; at 370 nm: n TiO2 = 2.83, k TiO2 = 1 × 10 −3 ) rendering it, for instance, a strategic material to manipulate the light emitted by conventional GaN-based blue LEDs (at about 450 nm). TiO 2 can be prepared by high-throughput chemical processes, which is a prerequisite for applications requiring large surface systems. It also has many other advantages over Si and metals that are its high chemical, mechanical, and thermal stability, nontoxicity, and relative natural abundance.To date, several groups have studied the properties of Titania particles as dielectric resonators prepared using conventional top-down microfabrication technologies [26][27][28][29][30] or soft-nanoimprint lithography. [31,32] They all confirmed that electromagnetic resonances could be generated within these metal oxide objects. However, the limited exploitation of this material is mainly due to the difficulty in applying conventional top-down fabrication methods to TiO 2 . Additionally, such approaches do not allow the preparation of spherical resonators, [33] which may be interesting for many applications with effective metamaterials, such as beam steering and back-scattering-free optics, [11,[34][35][36][37][38][39][40][41][42][43][44][45]

We present a detailed experimental investigation of the carrier recombination dynamics in CsPbBr 3 films by means of picosecond time-resolved photoluminescence. Temperaturedependent measurements show that carrier capture and release from the nanocrystals (NCs) surfaces determine the observed increase of the recombination lifetime with the increase of temperature. This result opens the way to probe the surface of the NCs, which is of the utmost relevance for optoelectronic applications, and to eventually give feedback for surface treatments of NCs.

We demonstrate a simple self-assembly method based on solid state dewetting of ultra-thin silicon films and germanium deposition for the fabrication of efficient anti reflection coatings on silicon for light trapping. Via solid state dewetting of ultra-thin silicon on insulator and epitaxial deposition of Ge we fabricate SiGe islands with a high surface density, randomly positioned and broadly varied in size. This allows to reduce the reflectance to low values in a broad spectral range (from 500 nm to 2500 nm) and a broad angle (up to 55 degrees) and to trap within the wafer a large portion of the impinging light (∼40%) also below the band-gap, where the Si substrate is non-absorbing. Theoretical simulations agree with the experimental results showing that the efficient light coupling into the substrate mediated by Mie resonances formed within the SiGe islands. This lithography-free method can be implemented on arbitrarily thick or thin SiO2 layers and its duration only depends on the sample thickness and on the annealing temperature.

Random dielectrics defines a class of non‐absorbing materials where the index of refraction is randomly arranged in space. Whenever the transport mean free path is sufficiently small, light can be confined in modes with very small volume. Random photonic modes have been investigated for their basic physical insights, such as Anderson localization, and recently several applications have been envisioned in the field of renewable energies, telecommunications, and quantum electrodynamics. An advantage for optoelectronics and quantum source integration offered by random systems is their high density of photonic modes, which span a large range of spectral resonances and spatial distributions, thus increasing the probability to match randomly distributed emitters. Conversely, the main disadvantage is the lack of deterministic engineering of one or more of the many random photonic modes achieved. This issue is solved by demonstrating the capability to electrically and mechanically control the random modes at telecom wavelengths in a 2D double membrane system. Very large and reversible mode tuning (up to 50 nm), both toward shorter or longer wavelength, is obtained for random modes with modal volumes of the order of few tens of (λ/n)3.

Flexible and stretchable photonics are emerging fields aiming to develop novel applications where the devices need to conform to uneven surfaces or whenever lightness and reduced thickness are major requirements. However, owing to the relatively small refractive index of transparent soft matter including most polymers, these materials are not well adapted for light management at visible and near-infrared frequencies.Here we demonstrate simple, low cost and efficient protocols for fabricating Si 1−x Ge x -based, sub-micrometric dielectric antennas over record scales (50 mm wafers) with ensuing hybrid integration into different plastic supports. The transfer process has a near-unity yield: up to 99.94% for disordered structures and 99.5% for the ordered counterpart. Finally, we benchmark the optical quality of the dielectric antennas with light scattering measurements, demonstrating the control of the islands structural color and the onset of sharp Mie modes after encapsulation in plastic. Thanks to the ease of implementation of our fabrication methods, these results are relevant for the integration of SiGe-based dielectric Mie resonators in flexible substrates over large surfaces.

We demonstrate an efficient, simple, and low-cost approach for enhanced nanoscopy in individual green emitting perovskite (CsPbBr3) nanocrystals via TiO2 dielectric nanoantenna. The observed three- to five-fold emission enhancement is attributed to near-field effects and emission steering promoted by the coupling between the perovskite nanocrystals and the dielectric sub-micrometric antennas. The dark-field scattering configuration is then exploited for surface-enhanced absorption measurements, showing a large increase in detection sensitivity, leading to the detection of individual nanocrystals. Due to the broadband spectral response of the Mie sub-micrometric antennas, the method can be easily extended to electronic transitions in other spectral regions, paving the way for absorption nanoscopy of many different quantum emitters from organic molecules to quantum dots.