New near-IR electroluminescent complexes of Pr³⁺, Nd³⁺, Ho³⁺, Er³⁺, Tm³⁺, Yb³⁺ with N,O-chelated ligands, Ln₂(OON)₆ (OON = 2-(2-benzoxyazol-2-yl)phenolate) and Ln₂(SON)₆ (SON = 2-(2-benzothiazol-2-yl)phenolate), were synthesized by the reaction of Ln[N(SiMe₃)₂]₃ and the corresponding N,O-chelating ligand. X-Ray analysis for the Pr and Nd compounds reveals centrosymmetric dimeric structures of the complexes. The solid-state electronic absorption spectra and the electroluminescent spectra show long-wavelength 4f–4f transitions which provide potential use of the compounds as NIR emitting materials in organic light-emitting devices (OLEDs). When constructing OLEDs based on Ln₂(OON)₆ and Ln₂(SON)₆, the best results were achieved with the Nd³⁺ and Yb³⁺ complexes, where the NIR wall plug efficiency of the ITO/TPD/Ln-complex/BATH/Yb system is 0.82 and 1.22 mW W⁻¹, respectively.

All-inorganic lead halide perovskites of various compositions have emerged as a prospective family of materials for light-emitting devices and photonic applications. However, a comprehensive study of their structural and electronic properties is still missing. Moreover, thin film fabrication of these perovskites comprising heterohalide anions by wet chemistry approaches also remains challenging. Here we fabricate high-quality CsPbBr_3−xCl_x perovskite thin films using a wet chemical method accompanied by a chemical vapor anion exchange procedure, which allows rigorously studying their optical and structural properties at different compositions. Namely, we present both the numerical and experimental studies of the electronic properties of all-inorganic mixed-halide perovskites, showing their optical absorption, excitonic photoluminescence and exciton binding energy, phase, chemical composition, and band structure and the band gap evolution with a gradual change in x in CsPbBr_3−xCl_x. The results reveal that as Cl ions substitute for Br ones in the perovskite crystal lattice the room-temperature phase does not change its orthorhombic symmetry, whereas the energy of the direct electronic transition from the valence to conduction band at the Γ-point increases nonlinearly. By using the experimentally derived nonlinear dependence it is easy to accurately predict the band gap for any CsPbBr_3−xCl_x perovskite thin film consisting of grains with sizes beyond the quantum confinement regime.

Efficient second harmonic generation (SHG) in nanophotonic designs based on all-dielectric nanostructures demands materials with large values of the quadratic nonlinear susceptibility, low dissipative losses, and high refractive index. One of the best materials meeting all these parameters is gallium phosphide (GaP). However, second-order nonlinearity requires high crystallinity and morphology quality of the GaP layer grown for further lithographic processing. Here we develop a method to fabricate high-quality crystalline GaP metasurfaces, which demonstrate pronounced linear and nonlinear optical properties. Direct growth of a GaP layer on a sapphire substrate tackles the previous problem of wafer bonding, because of high optical contrast between fabricated resonant nanoparticles and the substrate. As a result, the fabricated GaP metasurface supports bound state in continuum mode with an experimental quality factor around 100 yielding a strong enhancement of SHG in narrow spectral range. We believe that the developed approach will become a versatile platform for nonlinear all-dielectric nanophotonics.