Optical bound states in the continuum (BICs) provide a way to engineer resonant response in photonic crystals with giant quality factors. The extended interaction time in such systems is particularly promising for enhancement of nonlinear optical processes and development of a new generation of active optical devices. However, the achievable interaction strength is limited by the purely photonic character of optical BICs. Here, 1 arXiv:1905.13505v1 [cond-mat.mes-hall] 31 May 2019 we mix optical BIC in a photonic crystal slab with excitons in atomically thin transition metal dichalcogenide MoSe 2 via strong coupling to form exciton-polaritons with Rabi splitting exceeding 27 meV. We experimentally show BIC-like behavior of both upper and lower polariton branches, with complete suppression of radiation into far-field at the BIC wavevector and strongly varying Q-factor in its vicinity. Owing to an effective disorder averaging through motional narrowing, we achieve small polariton linewidth of 2 meV and demonstrate linewidth control via angle and temperature tuning. Our results pave the way towards developing tunable BIC-based polaritonic devices for sensing, lasing, and nonlinear optics. Optical bound states in the continuum (BICs), supported by photonic crystal structures of certain geometries, have received much attention recently as a novel approach to generating extremely spectrally narrow resonant responses. 1,2 Since BICs are uncoupled from the radiation continuum through symmetry protection 3 or resonance trapping, 4 their high quality factors, while reaching 10 5 − 10 6 , can be robust to perturbations of photonic crystal geometric parameters. This enables a broad range of practical applications, including recently demonstrated spectral filtering, 5 chemical and biological sensing, 6,7 and lasing. 4Providing an efficient light-trapping mechanism, optical BICs are particularly attractive for enhancing nonlinear optical effects, with recent theoretical proposals discussing enhanced bistability 8 and Kerr-type focusing nonlinearity. 9 However, for practical realization of these proposals, a significantly stronger material nonlinear susceptibility is needed than generally available in dielectric-based photonic crystals.An attractive approach to the enhancement of effective nonlinearity is through the use of exciton-polaritons -hybrid quasi-particles that inherit both the coherent properties of photonic modes and interaction strength of excitons. 10,11 Hybrid nanophotonic systems incorporating atomically thin transition metal dichalcogenides (TMDs) have proven to be a particularly promising platform owing to their ease of fabrication and possibility of room temperature operation. [12][13][14] In addition to conventional microcavity-based designs, TMD

Halide perovskites are promising materials for optoelectronics with an attractive radiation resistance property. In this article, we study the effect of 30 keV Ga+ ion irradiation on the photoluminescence (PL) of CsPbBr3 halide perovskite single crystals. The high crystal quality and liquid helium temperature studies make it possible to distinguish the radiation-defect-related PL band. A model to explain the band shifts with radiation dose and pulsed pump intensity has been developed. Bright defect PL allows the visualization of the irradiated areas using PL mapping. Manipulation of optical properties using focused ion beams opens wide opportunities for halide perovskite nanofabrication for optoelectronics.

Nanocolloidal gels are emerging as a promising class of materials with applications as inks in 2D and 3D printing. Polymer nanoparticles (NPs) offer many advantages as potential building blocks of nanocolloidal gels, due to the ability to control NP dimensions, charge, surface chemistry, and functionality; however, their applications as inks in printing are yet to be explored. Here, functional nanocolloidal hydrogels formed by percolating oppositely charged latex NPs with different dimensions and charge densities are reported. The shear-thinning and self-healing properties of the nanocolloidal gels and the mechanical properties of the resulting printed films are examined. NP functionality is achieved by covalently labeling them with different fluorescent dyes that emit at two distinct wavelengths. Using these NPs, a facile route for 3D printing of multicolored fluorescence patterns is shown, with each color being visualized under a specific, well-defined excitation wavelength.

Allabogdanite, (Fe,Ni)2P, is the only known natural high-pressure phase reported in the Fe–Ni–P system. The mineral, which was previously described from a single meteorite, the Onello iron, is now discovered in the Santa Catharina and Barbianello nickel-rich ataxites. The occurrence of allabogdanite in Santa Catharina, one of the largest and well-studied meteorites, suggests that this mineral is more common than was believed. The formation of allabogdanite-bearing phosphide assemblages in a given meteorite provides evidence that it experienced peak pressure of at least 8 GPa at a temperature above 800 °C. Since the pressure-temperature stability parameters of allabogdanite fall within the margins of the stishovite (rutile-type SiO2) stability area, the former can be employed as a convenient stishovite-grade indicator of significant impact events experienced by iron and stony-iron meteorites and their parent bodies.

Cyclophosphates are a class of energy-rich compounds whose hydrolytic decomposition (ring opening) liberates energy that is sufficient for initiation of biomimetic phosphorylation reactions. Because of that, cyclophosphates might be considered as a likely source of reactive prebiotic phosphorus on early Earth. A major obstacle toward adoption of this hypothesis is that cyclophosphates have so far not been encountered in nature. We herein report on the discovery of these minerals in the terrestrial environment, at the Dead Sea basin in Israel. Cyclophosphates represent the most condensed phosphate species known in nature. A pathway for cyclophosphate geosynthesis is herein proposed, involving simple pyrolytic oxidation of terrestrial phosphides. Discovery of natural cyclophosphates opens new opportunities for modeling prebiotic phosphorylation reactions that resulted in the emergence of primordial life on our planet.