arXiv subjects

Christoph Lambert

Publications and source records attributed to Christoph Lambert.

4 recordsLinked to original sources

arXiv2026

Background-free measurement of exciton-exciton annihilation by two-quantum fluorescence-detected pump-probe spectroscopy

We introduce two-quantum (2Q) fluorescence-detected pump-probe (F-PP) spectroscopy as a tool to probe ultrafast multiparticle interactions in many-body systems. We describe a pulse-shaper-based fully collinear setup utilizing phase cycling to capture the 2Q F-PP signal simultaneously with the one-quantum (1Q) F-PP signal. Thus, we investigate the dynamics of energy transfer and diffusion-limited annihilation. We apply a data post-processing strategy to isolate excited-state dynamics from spurious background. The technique is applied to a squaraine heterodimer and a squaraine copolymer to demonstrate the removal of so-called incoherent mixing that generally plagues action-detected nonlinear spectroscopy on multichromophoric systems. Specifically, we show that this approach is not only applicable to 1Q but also to 2Q F-PP signals, eliminating incoherent mixing contributions as well as other "parasitic" signals that result from pulse-overlap ambiguities. As a result, we retrieve background-free spectral and dynamical information of doubly excited electronic states.

physics.chem-ph↗

arXiv2026

Liquid-phase encapsulation of $\pi$-conjugated dyes in boron nitride nanotubes: Ensemble and single-nanotube optical characterization

Boron nitride nanotubes (BNNTs) provide wide-bandgap, optically transparent one-dimensional hosts for molecular dyes, limiting direct electronic participation of the host. Whether dye@BNNT systems produce bright, well-defined J- or H-aggregates or instead heterogeneous emissive ensembles whose character depends on chain length and local packing remains only partly resolved. We address this question using ensemble extinction, photoluminescence, quantum-yield measurements, and TCSPC-derived radiative and non-radiative rates, together with polarization-resolved single-nanotube microscopy on encapsulated quaterthiophene, sexithiophene, octithiophene, and Nile Red, selected from a ten-dye screening. In the oligothiophene series, confinement modifies spectra and excited-state dynamics in a length-dependent manner, with all three oligothiophenes forming weakly emissive ensembles with suppressed effective radiative rates and 6T showing the strongest redistribution between effective radiative and non-radiative decay. The absence of radiative-rate enhancement or fluorescence-lifetime shortening across the series disfavors bright J-aggregate assignments. Polarization-resolved single-nanotube microscopy reveals strongly polarized emission, but with tube-to-tube and intratube variations, identifying oligothiophene@BNNTs as ordered yet structurally heterogeneous confined ensembles. Nile Red provides a complementary case in which the dominant response is dielectric tuning of a solvatochromic charge-transfer state rather than oligothiophene-like aggregate formation. These findings establish dye-filled BNNTs as optically quiet nanoconfined systems in which molecular ordering, dielectric confinement, and guest-guest coupling can be distinguished through combined ensemble and single-nanotube spectroscopy.

cond-mat.mtrl-sci↗

arXiv2026

Optical Modulation Due to Energy Exchange Between Photonic and Exciton Modes in the Intermediate Coupling Regime

Actively tunable photonic devices are vital for next-generation optoelectronics requiring rapid switching and high bandwidth. Although organic optoelectronic devices have found wide application, their use as optical modulators has been limited by low absorption in the critical near-infrared (NIR) region, slow response time, and weak nonlinearities. To address these limitations, we developed a scheme based on intermediate exciton-photon coupling in a NIR absorbing squaraine-dye based photonic structure. Using energy-momentum resolved pump-probe spectroscopy, we show that the sign and magnitude of the optical response of our system depends strongly on the energy detuning between the excitonic and photonic modes. These data are analyzed using temporal coupled-mode theory to show that near resonance, a distinct energy exchange process emerges in the cross-over regime between strong and weak light-matter coupling. This effect enables dynamical control over the photoinduced response, providing a pathway for broadband optical signal modulation extending into the NIR spectral region.

physics.optics↗

arXiv2010

Polymeric Squaraine Dyes as Electron Donors in Bulk Heterojunction Solar Cells

A polysquaraine low band gap polymer was synthesized by Yamamoto coupling of a monomeric dibromo indolenine squaraine dye. The resulting polymer has a weight average molar mass in the order of Mw ~30.000-50.000 and a polydispersity of ca. 1.7 as determined by gel-permeation chromatography (GPC). The electronic properties of monomer and polymer were investigated by cyclic voltammetry, absorption and emission spectroscopy. Owing to exciton coupling the absorption bands of the polymer are red-shifted and strongly broadened compared to the monomer squaraine dye. Bulk heterojunction solar cells were prepared from blends of the polysquaraine with the fullerene derivative [6,6]-phenyl C61-butyric acid methyl ester (PCBM) in different weight ratios (1:3 to 1:1). The power conversion efficiencies under simulated AM 1.5 conditions yielded 0.45 % for these non-optimized systems. The external quantum efficiency (EQE) shows that the photoresponse spans the range from 300 to 850 nm, which illustrates the promising properties of this novel organic semiconductor as a low band gap donor material in organic photovoltaics.

cond-mat.mtrl-sci↗