Perfluorination of ligands is commonly employed to enhance the luminescence efficiency of Ln3+ coordination compounds by reducing C-H vibrational quenching. In this study, we challenge this chemical design strategy by synthesizing and investigating a series of Eu3+, Tb3+ and Gd3+ complexes with 1,3-bis(perfluorophenyl)propane-1,3-dione. Comprehensive spectroscopic analysis including steady-state, time-resolved and ultrafast transient absorption spectroscopy has revealed that fluorination induces charge-transfer state quenching that competes with ion-centered emission. In the Eu3+ complex, this results in the reduced energy transfer efficiency and lower luminescence quantum yields compared to its non-fluorinated analogue - the sensitization efficiency drops from 0.47 to 0.01. Surprisingly, the perfluorinated Gd3+ complex exhibits bright room-temperature phosphorescence, which is an exceptionally rare and valuable effect in lanthanide coordination compounds. By uncovering the nuanced interplay between ligand structure and excited-state dynamics, this work provides new insights for the rational design of advanced luminescent materials.

Twocolor laser filamentation is considered a promising strategy for deep transformations of the spectrum and generating ultrashort light pulses, which is critically important for developing effective methods to control broadband coherent radiation in attosecond physics and ultrafast spectroscopy. We present the results of our experiments on the study of the spectral dynamics of supercontinuum generated during collinear twocolor filamentation of femtosecond pulses at the fundamental (800 nm) and second harmonic (400 nm) frequencies in Ar, N2, and CO2 gases at pressures up to 11 atm. We demonstrate that the transition to multiple filamentation in high pressure gases qualitatively changes the interaction dynamics between the color components. We demonstrate that instead of a simple merging of spectra broadened during filamentation, a complex, nonmonotonic dependence of the shape of the twocolor supercontinuum on the time delay between pulses is observed, including selective suppression of radiation in the 400 nm region. For the first time, significant differences are identified between the dynamics of twocolor filamentation in atomic and molecular gases. Particularly, in CO2, spectral transformation is preserved at picosecond interpulse delays, which is explained by the strong contribution of molecular rotational wave packets to the effective nonlinear polarizability. Our results demonstrate the possibility of controlled redistribution of spectral energy and dynamic switching off of individual regions of supercontinuum in atomic and molecular gases as their pressure changes, which fills the gap in understanding the spatiotemporal evolution of multiple two color filaments and paves the way for the controlled formation of ultrashort laser pulses.

Quantized vortices are ubiquitous in physics, spanning superconductivity, astrophysics, superfluid condensed matter systems, and nonlinear optics. Yet embedding vorticity into topologically protected nonlinear states has remained a major challenge, with all previously observed corner solitons in higher-order topological insulators (HOTIs) exhibiting only trivial phase distributions. Here, we report on the first realization of stable topological corner vortex solitons in a photonic fractal HOTI. Using an array of laser-written waveguides in the shape of Sierpiński gasket with a controllable distortion, we design linear topological vortex modes, from which nonlinear corner vortex solitons bifurcate. Moreover, we demonstrate that these solitons exhibit exceptional robustness across a broad power range and, unlike vortex solitons in topologically trivial lattices, form without a power threshold. Our results introduce the angular momentum degree of freedom into the physics of topological corner modes, opening prospects for topologically protected vortex-based photonics.

Higher-order topological insulators (HOTIs) are unique topological materials supporting edge states with the dimensionality at least by two lower than the dimensionality of the underlying structure. HOTIs are observed on lattices with different symmetries, but only in geometries, where truncation of HOTI produces a finite structure with the same order of discrete rotational symmetry as that of the unit cell, thereby setting the geometry of insulator edge. Here, a new type of 2D HOTI based on the Kekulé-patterned lattice is experimentally demonstrated, whose order of discrete rotational symmetry differs from that of the unit cells of the constituent honeycomb lattice, with hybrid boundaries that help to produce all three possible corners that support effectively 0D corner states of topological origin, especially the one associated with spectral charge 5/6. It is also shown that linear corner states give rise to rich families of stable hybrid nonlinear corner states bifurcating from them in the presence of focusing nonlinearity of the material. Such new types of nonlinear corner states are observed in hybrid HOTI inscribed in transparent nonlinear dielectric using fs-laser writing technique. The results complete the class of HOTIs and open the way to observation of topological states with new internal structure and symmetry.

In higher-order topological insulators (HOTIs), topologically nontrivial phases are usually associated with the shift of Wannier centers to topologically nontrivial positions on the edges of the unit cells, and the emergence of fractional spectral charges in the corners of the lattice upon its truncation that keeps the number of its unit cells integer. Here we propose theoretically and illustrate experimentally a different approach to the construction of HOTIs. This approach utilizes lattices with incomplete unit cells and achieves localized modes of topological origin across a broader parameter space. When truncation disrupts translational symmetry by cutting through the interior of multiple unit cells, boundary modes in our system emerge for both trivial and topologically nontrivial positions of the Wannier centers. We link these modes to the appearance of fractional Wannier centers. We also demonstrate that linear boundary states give rise to rich families of stable solitons bifurcating from them in the presence of focusing nonlinearity. Multiple types of thresholdless topological solitons with different internal symmetries are observed in waveguide arrays with triangular configurations featuring incomplete unit cells for any dimerization of waveguide spacings. Our results expand the family of HOTIs and pave the way for the observation of boundary states with different symmetries.

Achieving high quantum yields for Yb3+ ion emission in complexes with organic ligands is a challenging task, as most Yb3+ complexes with such ligands typically exhibit efficiencies below 3.5%. Our research demonstrates that the introduction of heavy atom-containing ancillary ligands, such as TPPO or TPAO, along with the careful engineering of the main β-diketone ligand, can increase the luminescence efficiency up to 20-fold by the alteration of the energy migration pathway. It is demonstrated that the combination of two distinct organic ligands leads to the blockage of singlet–triplet intersystem crossing (ISC), alongside electronic energy transfer from β-diketone to Yb3+ ions through charge transfer states. The synthesized complexes exhibit quantum yields of 6.5% and 7.0% in the solid state, which places them at the top globally among this class of materials with simple non-deuterated and non-fluorinated ligands.

The generation of coherent optical radiation with an anomalously broadened spectral content (supercontinuum) during the nonlinear propagation of high-power femtosecond laser pulses in transparent media, including highpressure gases, holds considerable practical interest for the obtaining of extremally ultrashort (attosecond) optical pulses. This capability is crucial for advancing modern attosecond spectroscopy and the study of matter under extreme conditions. In this work, we report the results of systematic experiments on the generation of broadband supercontinuum in an optical cell filled with various atomic and molecular gases (He, Ar, N2, CO2) at pressures ranging from 1 to 50 bar achieved through the focused filamentation of 40 fs pulses from a titaniumsapphire laser. Our measurements demonstrate that, with the exception of helium, all supercontinuum spectra exhibit similar pressure-dependent behavior: an initial strong spectral broadening is followed by saturation of the spectral bandwidth and, in the case of CO2, even a noticeable reduction relative to its maximum achievable width. To elucidate these findings, we carry out theoretical simulations based on the unidirectional propagation equation for an ultrashort wave packet (UPPE). This analysis reveals that the most likely explanation for the observed effects is the enhanced role of kinetic processes, such as absorption and refraction of the laser pulse within the self-generated plasma as the gas pressure increases. These findings provide valuable insights into the mechanisms governing supercontinuum generation in high-pressure gaseous media.

A novel method for identifying counterfeit goods based on the difference between photobleaching rates of spectroscopic marker components is proposed. Controlled photobleaching of the dye is achieved via introduction of halogens (I, Cl, Br, and F) into the aromatic moiety of the dibenzoylmethane (DBM) ligand in coordination compounds of Eu3+. A spectroscopic marker model that consists of two coordination compounds with different halogens is developed. These compounds exhibit indistinguishable luminescence spectra and emission intensities at low irradiation power. However, exceeding the threshold irradiation power results in rapid photobleaching of the marker fragment derived from the complex with the highest charge number of halogen atoms. This approach introduces new possibilities for quality control of goods that require storage in light-protected environments. The results obtained during the research have both practical and fundamental significance. For the first time, it is established that the halogenation of the DBM ligand leads to the intersystem crossing process termination. Energy of electronic excitation transfers from the singlet excited state to the ion through a charge transfer state instead of the triplet excited state. Such energy transfer pathways sensitize luminescence of Eu3+ more effectively, resulting in an increase in quantum yield up to 64% upon the introduction of chlorine atoms.

High-power optical pulses experience self-focusing when propagating in a gaseous medium due to the manifestation of the cubic (Kerr-like) nonlinearity. The magnitude of this effect depends on the Kerr nonlinearity coefficient n2, which in turn may depend on the parameters of laser radiation and the propagation medium. We present experimental data on the coefficient n2 for atomic Ar, molecular N2 and CO2 with a pressure change from 1 to 11 bar and optical pulse duration from 50 to 500 fs of propagating femtosecond near-IR laser radiation (800 nm). Importantly, all three gases under study possess close n2-values in the short pulse limit (50 fs) over the entire pressure range. According to our data, for the first time, as far as we know, the Kerr nonlinearity in CO2 is obtained at atmospheric pressure equal to n2(CO2) = 10.0 +/- 1.1 & sdot;10- 24 m2/W. Meanwhile, with increasing gas pressure, effective n2 also increases due to the manifestation of aberrations in optical pulse during self-focusing caused by the development of modulation instability. In addition, according to our approximate estimate, the magnitude of the inertial component in the cubic nonlinearity of molecular gases (N2, CO2) is substantial and increases with both pulse duration and gas pressure.

Progress in observation of solitons in photonic topological insulators is discussed. Results are presented of experiments with nonlinear topological states in Su-SchriefferHeeger arrays fabricated using the femtosecond writing technique that are static, i.e., invariable in the direction of light propagation, and dynamically modulated (primarily periodically) in the direction of light propagation. Such objects are one of the simplest models of a topologically nontrivial structure. Solitons in topological insulators bifurcate with increasing laser beam power from linear edge states in the topological bandgap, inheriting their topological protection. The spatial localization of the soliton and the position of its propagation constant in the topological bandgap depend in a nonlinear medium on peak power and can be effectively controlled. Experimental observation of the switching of the edge topological modes in the bandgap between two closely spaced dimerized Su-Schrieffer-Heeger arrays is presented. The switching, whose rate depends on radiation intensity, can be completely arrested in a strongly nonlinear regime. In trimer waveguide arrays, whose spectrum in the topological phase features two simultaneously emerging topological bandgaps with edge states of different symmetries, two coexisting types of topological solitons exhibiting different degrees of stability were observed. We also discuss experimental observations of TE-solitons nonlinear topological Floquet states periodically reproducing their profiles in 1D- and 2D-dimensional Su-Schrieffer-Heeger arrays modulated in the direction of propagation of radiation.

Filamentation of high-power femtosecond optical pulses in high-pressure gases has gained increasing academic and practical interest from the viewpoint of studying large-scale spectral and temporal transformations occurring with pulsed laser radiation and obtaining super-broadened spectra and extremely short (attosecond) wave packets. Experimentally and theoretically, for the first time to the best of our knowledge, we show that as a result of femtosecond titanium-sapphire laser pulse filamentation in an optical cell filled with pressurized up to 50 bar nitrogen or argon, the pulse spectrum can reach maximally about eightfold broadening. This limiting pulse spectral width is reached at a gas pressure of about 20 bar and with further pressure increase exhibits saturation and even a slight decrease relative to the limiting value. As a possible reason for this evidence, we propose the enhancement of pulse energy depletion in the self-created plasma at high gas pressure.

Higher-order topological insulators (HOTIs) are unique materials hosting topologically protected states, whose dimensionality is at least by 2 lower than that of the bulk. Topological states in such insulators may be strongly confined in their corners which leads to considerable enhancement of nonlinear processes involving such states. However, all nonlinear HOTIs demonstrated so far were built on periodic bulk lattice materials. Here, we demonstrate the first nonlinear photonic HOTI with the fractal origin. Despite their fractional effective dimensionality, the HOTIs constructed here on two different types of the Sierpiński gasket waveguide arrays, may support topological corner states for unexpectedly wide range of coupling strengths, even in parameter regions where conventional HOTIs become trivial. We demonstrate thresholdless spatial solitons bifurcating from corner states in nonlinear fractal HOTIs and show that their localization can be efficiently controlled by the input beam power. We observe sharp differences in nonlinear light localization on outer and multiple inner corners and edges representative for these fractal materials. Our findings not only represent a new paradigm for nonlinear topological insulators, but also open new avenues for potential applications of fractal materials to control the light flow.

The formation of a set of filaments and plasma channels in a femtosecond optical vortex has been studied experimentally and numerically. A longitudinal distribution of color center tracks with a length of 1 cm written in a LiF crystal by an axially asymmetric beam in the single-pulse regime has been detected experimentally for the first time. It has been shown that, at a sufficient excess of the peak power over the critical value, two hot points on the annular profile of vortex beam separated by the phase dislocation region form sequences of color center tracks; each sequence in the cross section of the beam is localized near the initial hot point. Secondary filaments and the corresponding tracks appear with an increase in the pulse energy. The parameters of femtosecond filaments in LiF have been numerically estimated.

Floquet systems with periodically varying in time parameters enable realization of unconventional topological phases that do not exist in static systems with constant parameters and that are frequently accompanied by appearance of novel types of the topological states. Among such Floquet systems are the Su-Schrieffer-Heeger lattices with periodically-modulated couplings that can support at their edges anomalous π modes of topological origin despite the fact that the lattice spends only half of the evolution period in topologically nontrivial phase, while during other half-period it is topologically trivial. Here, using Su-Schrieffer-Heeger arrays composed from periodically oscillating waveguides inscribed in transparent nonlinear optical medium, we report experimental observation of photonic anomalous π modes residing at the edge or in the corner of the one- or two-dimensional arrays, respectively, and demonstrate a new class of topological π solitons bifurcating from such modes in the topological gap of the Floquet spectrum at high powers. π solitons reported here are strongly oscillating nonlinear Floquet states exactly reproducing their profiles after each longitudinal period of the structure. They can be dynamically stable in both one- and two-dimensional oscillating waveguide arrays, the latter ones representing the first realization of the Floquet photonic higher-order topological insulator, while localization properties of such π solitons are determined by their power.

The features of nonlinear propagation of high-intensity pulses in the short-wavelength infrared range in extended one-dimensional waveguide arrays with different spatial periods, formed in fused silica by laser writing, are studied. More than tenfold self-compression of femtosecond pulses up to a duration of several periods of the light field is experimentally observed.

Introduction of controllable deformations into periodic materials that lead to disclinations in their structure opens novel routes for construction of higher-order topological insulators hosting topological states at disclinations. Appearance of these topological states is consistent with the bulk-disclination correspondence principle, and is due to the filling anomaly that results in fractional charges to the boundary unit cells. So far, topological disclination states were observed only in the linear regime, while the interplay between nonlinearity and topology in the systems with disclinations has been never studied experimentally. We report here on the experimental observation of the nonlinear photonic disclination states in waveguide arrays with pentagonal or heptagonal disclination cores inscribed in transparent optical medium using the fs-laser writing technique. The transition between nontopological and topological phases in such structures is controlled by the Kekulé distortion coefficient r with topological phase hosting simultaneously disclination states at the inner disclination core and spatially separated from them corner-I, corner-II, and extended edge states at the outer edge of the structure. We show that the robust nonlinear disclination states bifurcate from their linear counterparts and that location of their propagation constants in the gap and, hence, their spatial localization can be controlled by their power. Nonlinear disclination states can be efficiently excited by Gaussian input beams, but only if they are focused into the waveguides belonging to the disclination core, where such topological states reside. Our results open new prospects for investigation of nonlinear effects in topological systems with disclinations and are relevant for different areas of science, including Bose-Einstein and polariton condensates, where potentials with the disclinations can be created.

We observe linear and nonlinear light localization at the edges and in the corners of truncated moiré arrays created by the superposition of periodic mutually twisted at Pythagorean angles square sublattices. Experimentally exciting corner linear modes in the femtosecond-laser written moiré arrays we find drastic differences in their localization properties in comparison with the bulk excitations. We also address the impact of nonlinearity on the corner and bulk modes and experimentally observe the crossover from linear quasilocalized states to the surface solitons emerging at the higher input powers. Our results constitute the first experimental demonstration of localization phenomena induced by truncation of periodic moiré structures in photonic systems.

The generation dynamics of plasma and color centers in a LiF crystal under conditions of multipulse filamentation by mid-IR femtosecond laser radiation has been experimentally and numerically investigated. A model describing the dynamic competition between the excitonic and electron–hole channels during saturation of the concentration of color centers (CCs) in LiF under exposure to multipulse femtosecond radiation is developed. The competition between the excitonic and electron–hole channels of CC generation is physically interpreted.

A series of novel /3-diketonate Eu3+ complexes with minor variations in the chemical structure of the diketone ligand were systematically studied. Six Eu3+ coordination compounds based on /3-diketones, bearing linear perfluorinated substituents of various length (C1, C2, C3 and C6) and fixed pyrazole moiety were obtained. In addition, two water molecules, 1,10-phenanthroline or 4,7-diphenyl-1,10-phenanthroline as an ancillary ligand in compounds with fixed /3-diketone ligand were used. Their photophysical properties were investigated by UV-Vis absorption and time-resolved femtosecond transient (fs-TA) absorption spectroscopy techniques. In this study, we investigate the impact of ancillary ligands and the fluorinated chain length of & beta;-diketone ligands on the ultrafast relaxation processes that occur in the ligand environment. Relying on the ultrafast transient absorption measurements, it was demonstrated that the extension of fluorinated chains of /3-diketone ligand leads to decrease of first excited singlet and triplet states relaxation rates. The compound with excessively long chain C6F13 exhibits the slowest relaxation of the triplet state T1. Besides, variation in the ancillary ligand alters the electronic energy transfer pathways in the whole complex. It was established, that introducing 4,7-diphenyl-1,10-phenanthroline (bath) instead of 1,10-phenanthroline (phen) dramatically changing the electronic energy transfer dynamics in the whole coordination compound. On the basis of the fs-TA measurements we conclude the bath ligand act as acceptor of electronic energy of diketone ligand in the excited state.

Analytically, numerically and experimentally the effect of the material dispersion of the dielectric on the oscillation period of the electric field in a single cycle wave packet (a light bullet) is investigated. Wave packet oscillates due to periodic phase shift between the envelope of the pulse and its carrier wave. The influence of nonlinear shift of phase and group velocities on the analytical estimation of the oscillation period of a light bullet with a different carrier wavelength is considered. Keywords: group velocity, phase velocity, material dispersion, absolute phase shift, single-cycle wave packet, filamentation, light bullet.