Spectroscopy

Abstract

Photochemical upconversion has several potential applications in optoelectronics. However, there is yet to be demonstrated a rational approach to high efficiencies in nanoscale solid-state devices. Here we demonstrate that the liquid triplet fusion medium, 9,10-bis(n-octyl-diisopropylsilylethynyl)anthracene (NODIPS-An), which behaves as a solid on excitonic timescales, can achieve high-efficiency upconversion on the nanoscale. Owing to its amorphous structure, there are highly-coupled sites that trap upconverted states and prevent the back transfer that plagues nanoscale upconversion systems. With NODIPS-An filling the pores of a sensitized alumina nano-scaffold, we achieve an absolute photon upconversion efficiency of 8.2(4)%. The majority of efficiency losses are attributed to fluorescence and triplet energy transfer yields, and thus the self-trapping of excitons within the triplet fusion medium is demonstrated to effectively prevent the back transfer of excitons to the sensitizer. Strategies are proposed to improve the fluorescence yield and triplet energy transfer to pursue higher efficiencies in nanoscale solid-state photochemical upconversion devices.

Abstract

Coumarin-based derivatives are recognized as tunable photonic building blocks due to their strong light–matter interaction and relevance for both linear and nonlinear optical applications. This work presents an investigation of the linear optical properties and multiphoton excitation response of four derivatives coupled with benzothiazole and benzimidazole moieties. The compounds 7-diethylamino-coumarin-benzothiazole, 6-bromo-coumarin-benzothiazole, and 7-diethylamino-coumarin-benzimidazole exhibit nearly identical absorption maxima (∼423–428 nm) and emission peaks (∼485 nm), while displaying pronounced differences in molar absorptivity and ground to first excited-state transition dipole moment (μ01). The 7-diethylamino-substituted derivatives show enhanced molar absorptivity (∼5.3 × 104 L mol–1 cm–1) and larger transition dipole moment (μ01 ∼ 8.1 D) compared to the bromo-substituted (μ01 ∼ 5.5 D). In contrast, 7-hydroxyl-coumarin-methyl-benzimidazole exhibits a distinct spectral signature characterized by a larger Stokes shift and lower molar absorptivity, with an intermediate μ01 ∼ 7.0 D reflecting a different electronic balance within the conjugated framework. Multiphoton excitation experiments using femtosecond laser pulses demonstrate efficient two-photon (800 nm) and three-photon (1200 nm) excited fluorescence for all derivatives. Remarkably, the hydroxylated derivative combines an exceptionally high fluorescence quantum yield (∼48%) with a measurable excited-state lifetime (∼3 ns), identifying it as the most promising candidate for bright photoluminescent probing under one-, two-, and three-photon excitation.

This article is from earlier in the year but I missed until now!

Abstract

The emergence of Batrachochytrium salamandrivorans (Bsal) poses an imminent threat to caudate biodiversity worldwide, particularly through anthropogenic-mediated means such as the pet trade. Bsal is a fungal panzootic that has yet to reach the Americas, Africa, and Australia, presenting a significant biosecurity risk to naïve amphibian populations lacking the innate immune defenses necessary for combating invasive pathogens. We explored the capability of near-infrared spectroscopy (NIRS) coupled with predictive modeling as a rapid, non-invasive Bsal screening tool in live caudates. Using eastern newts (Notopthalmus viridescens) as a model species, NIR spectra were collected in tandem with dermal swabs used for confirmatory qPCR analysis. We identified that spectral profiles differed significantly by physical location (chin, cloaca, tail, and foot) as well as by Bsal pathogen status (control vs. exposed individuals; p < 0.05). The support vector machine algorithm achieved a mean classification accuracy of 80% and a sensitivity of 92% for discriminating Bsal-control (-) from Bsal-exposed (+) individuals. This approach offers a promising method for identifying Bsal-compromised populations, potentially aiding in early detection and mitigation efforts alongside existing techniques.

Abstract: Miniaturization of mid-infrared (MIR) spectroscopy sources has progressed signifi- cantly during the past two decades, but a solution able to provide full integration, high optical power and wide tuneability in the so-called atmospheric window (2.5 - 5 μm) is still missing. In this context, we investigated a broadband frequency-tuneable source relying on difference frequency generation (DFG) in a periodically poled lithium niobate (PPLN) ridge waveguide. By employing tuneable lasers for the pump and signal wavelengths emitting at around 1 μm and 1.55 μm, respectively, we were able to fully cover the ≈ 3 - 3.5 μm spectrum, thus translating the technological maturity of data communication photonic sources to the MIR wavelength band.

Moreover, the use of a relatively large cross-section for the here proposed PPLN ridge waveguide compared to commonly employed thin-film lithium niobate (TFLN) waveguides has allowed us to achieve low propagation and coupling losses together with high damage threshold, thereby allowing us to reach mW-level power in the MIR wavelength band.

cross-posted from: https://sh.itjust.works/post/21614029

One of the OG YouTube chemists dabbles in some radiochemistry and spectroscopy.

PDF Link: https://arxiv.org/pdf/2312.12548.pdf