Optical Materials Research Articles

Water-Vapor-Triggered Dual-Mode Optical Responses in Rare-Earth-Doped Hollow Nanospheres.

Multimode responsive optical materials are garnering ever-increasing attention due to their diverse applications. This work showcases a film assembled with rare-earth-doped CaF2 hollow nanospheres that exhibit water-vapor-triggered dual-mode optical responses. Upon exposure to flowing water vapor, the film rapidly (less than 1.5 s for a 7.7 μm thickness) transitions to a transparent state and simultaneously undergoes a sharp decrease in the photoluminescence intensity. Both of these changes fully reverse upon water evaporation, demonstrating an impressive reversibility over at least 200 cycles. The water-vapor-induced dual-mode responses are attributed to the altered incident light propagation path stemming from the similar refractive indices between CaF2 and water, coupled with the water-induced energy loss of the rare-earth ions. The fabrication of encryption patterns displaying separate signals in multiple channels, as well as the demonstration of noncontact sensing for water vapor distribution, underscore the promising application potential of this dual-mode responsive system.

Unleashing the nonlinear optical response of layered vanadium diselenide towards the deep mid-infrared regime

Broadband nonlinear optical materials towards the deep mid-infrared regime are highly required in medical diagnostics, environmental pollution monitoring, etc. Here, we report the ultra-broadband nonlinear optical absorption behavior of the layered vanadium diselenide (VSe2) towards deep mid-infrared regime experimentally. The layered VSe2 prepared by the liquid-phase exfoliation method exhibits broadband and wavelength-dependent nonlinear saturable absorption and a large modulation depth of over 8% in the 3-10 µm spectral range. By utilizing the layered VSe2 for optical modulation, stable nanosecond pulse with a low Q-switched threshold has been delivered successfully from an erbium-doped ZBLAN fiber laser. The experimental findings can deepen the understanding of the nonlinear optical response of the transition metal dichalcogenides towards the deep mid-infrared regime, and may make inroads for the advancement of mid-IR optoelectronic devices.

Titanium Dioxide: A Versatile Earth‐Abundant Optical Material for Photovoltaics

AbstractTitanium dioxide (TiO2) has long been receiving attention as a promising material for enhancing the performance of photovoltaic devices due to its tunable optoelectronic properties. This paper reviews the utilization of TiO2 in recent photovoltaic applications, focusing primarily on its role as an optical material. The fundamental properties of TiO2 are reviewed, such as its wide bandgap and unique property of tunable refractive index. Furthermore, various strategies are discussed to harness the fundamental properties of TiO2 to improve light absorption and charge carrier generation within various photovoltaic devices. Overall, the pivotal role of TiO2 as an Earth‐abundant and non‐critical optical material is highlighted for future advances in the power conversion efficiency and viability of photovoltaic technologies, paving the way for future research and developments aimed at achieving sustainable and cost‐effective solar energy conversion.

Revealing Dinitrogen Activation via Mesoionic Carbenes: A Computational Design with Frustrated Lewis Pairs

Activating dinitrogen under metal‐free conditions remains a significant challenge in chemistry. In this study, we computationally designed a frustrated Lewis pair (FLP) system incorporating a bis(trimethylsilyl)boryl substituent on a mesoionic carbene (MIC) framework. Our models show both kinetic and thermodynamic favorability for dinitrogen activation. Aromaticity enhancement along the potential energy surface (PES) plays a critical role in driving the reaction. This work provides insights into utilizing main‐group elements for dinitrogen activation and offers potential applications in inert molecule activation and optical materials.

Construction of Luminescent Terpyridine-Based Metallo-Bowties with Alkyl Chain-Bridged Dimerized Building Blocks.

Numerous metallo-supramolecules with well-defined sizes and shapes have been successfully constructed via the strong coordination interaction between terpyridine (TPY) moieties and ruthenium cations. However, the pseudo-octahedral geometry of <TPY-Ru-TPY> unit hampers the luminescent properties of such metallo-architectures, thus limiting their applications as optical materials. To address this issue, we herein use a flexible alkyl chain to bridge TPY building blocks, replacing conventional <TPY-Ru-TPY> linkage. The introduction of alkyl chain guides the self-assembly into desired architecture while simultaneously eliminating the quenching effects typically associated with the <TPY-Ru-TPY> linkage. More importantly, this design strategy enables the precise construction of bowtie-shaped metallo-supramolecules with significantly enhanced emission. The incorporation of alkyl chain linkage not only maintains structural integrity but also enhances optical performance, making these metallo-supramolecular assemblies highly promising for applications in advanced photonic and luminescent materials. This study offers a versatile approach to construct complex metallo-supramolecular architectures with desired optical properties.

Unveiling Noncentrosymmetric Pyridine Carboxylates from Centrosymmetric Templates through Motif Configuration Modulation in Zero-Dimensional System.

Developing approaches to induce noncentrosymmetric (NCS) frameworks through atomic-scale structural optimizations is crucial due to the growing need for new ultraviolet (UV) nonlinear optical (NLO) materials. Herein, the first two new NCS pyridine carboxylates, ZnBr(C6H3.5FNO2)2 (1) and Cd(C6H3FNO2)2(H2O)2 (2), were successfully synthesized using centrosymmetric (CS) templates and rational structural reconstructions induced by different ionic radius. Both compounds crystallize in the orthorhombic system and feature metal-centered zero-dimensional (0D) isolated clusters. Substituting the [ZnO2N2O] pyramid in the CS pyridine carboxylate with the [ZnO2N2Br] pyramid in compound 1 breaks the centrality, leading to an NCS framework with a second harmonic generation (SHG) response of 1.7 × KH2PO4 (KDP). Introducing a larger Cd2+ cation results in a trans-to-cis transition of the [MO4N2] (M = Zn, Co, and Ni in CS templates, Cd in 2) octahedra, forming a wing-shaped asymmetric 0D cluster with an SHG response of 2.1 × KDP. These findings indicate an approach that can effectively induce NCS structures of 0D organic-inorganic hybrid materials.

Optically accessible, 3D-printed flow chamber with integrated sensors for the monitoring of oral multispecies biofilm growth in vitro

The formation of pathogenic multispecies biofilms in the human oral cavity can lead to implant-associated infections, which may ultimately result in implant failure. These infections are neither easily detected nor readily treated. Due to high complexity of oral biofilms, detailed mechanisms of the bacterial dysbiotic shift are not yet even fully understood. In order to study oral biofilms in more detail and develop prevention strategies to fight implant-associated infections, in vitro biofilm models are sorely needed. In this study, we adapted an in vitro biofilm flow chamber model to include miniaturized transparent 3D-printed flow chambers with integrated optical pH sensors – thereby enabling the microscopic evaluation of biofilm growth as well as the monitoring of acidification in close proximity. Two different 3D printing materials were initially characterized with respect to their biocompatibility and surface topography. The functionality of the optically accessible miniaturized flow chambers was then tested using five-species biofilms (featuring the species Streptococcus oralis, Veillonella dispar, Actinomyces naeslundii, Fusobacterium nucleatum, and Porphyromonas gingivalis) and compared to biofilm growth on titanium specimens in the established flow chamber model. As confirmed by live/dead staining and fluorescence in situ hybridization via confocal laser scanning microscopy, the flow chamber setup proved to be suitable for growing reproducible oral biofilms under flow conditions while continuously monitoring biofilm pH. Therefore, the system is suitable for future research use with respect to biofilm dysbiosis and also has great potential for further parallelization and adaptation to achieve higher throughput as well as include additional optical sensors or sample materials.

Study on the optical properties of Sm3+ doped bismuth silicate crystals based on first principles

Abstract This study systematically investigated the effect of Sm3+ doping on the optical properties of bismuth silicate (Bi4Si3O12, abbreviated as BSO) crystals using first principles calculations based on density functional theory (DFT). By calculating the dielectric function, reflectivity, absorption coefficient, refractive index, conductivity, and energy loss function of BSO crystals under different Sm3+ doping ratios, we found that moderate Sm3+ doping can increase the dielectric function of BSO crystals, and the real part of the dielectric function represents the material's ability to respond to the electric field, that is, the macroscopic polarization degree. Therefore, moderate Sm3+ doping enhances the polarization ability of BSO crystals. Simultaneously doping an appropriate amount can effectively enhance the conductivity and light (visible and infrared) absorption ability of BSO crystals, and reduce the energy loss between electrons in BSO crystals, thereby improving their luminescence performance. Specifically, when the Sm3+ doping ratio is 1/6, the optical properties of BSO crystals are significantly improved. These findings not only enhance the understanding of the mechanism of optical performance changes in rare earth ion doped BSO crystals, but also provide a theoretical basis for the development of new rare earth doped optical materials.

Quantum chemical tailoring of intrinsic donor–acceptor configurations as efficient nonlinear optical materials

Quantum chemical tailoring of intrinsic donor–acceptor configurations as efficient nonlinear optical materials

Advances in Lanthanide-Based NIR-IIb Probes for In Vivo Biomedical Imaging.

The past decades have witnessed the significant development and practical interest of in vivo biomedical imaging technologies and optical materials in the second-near infrared (NIR-II, 1000-1700 nm) window. Imaging with the extended emission wavelength toward the long-wavelength end (NIR-IIb, 1500-1700 nm) further offers micrometer imaging resolution and centimeter tissue penetration depth by taking advantage of the much-reduced photon scattering and near-zero tissue autofluorescence background, which have become a very hot research area. This review focuses on the recent advances in the development of lanthanide-based NIR-IIb probes for in vivo biomedical applications. The progress including ratiometric imaging, multiplexed imaging for wide-field and microscopy, lifetime multiplexing and sensing, persistent luminescence, and multimodal imaging is summarized. Challenges and future directions concerning the investigation of the photophysical and photochemical properties of NIR-IIb probes, the selection of near-infrared cameras as well as the potential extension of the NIR-IIb imaging sub-window are pointed out. This review will inspire readers who have a strong interest in developing optical imaging technology and long-wavelength fluorescence probes for high-contrast in vivo biomedical applications.

Lead‐Sulfide‐Based Hybrid Inorganic‐Organic Superlattice Particles for Prominent Nonlinear Optical Absorption

AbstractSimultaneously optimizing nonlinear absorption coefficient and modulation depth is a considerable challenge for nonlinear optical materials. Here we present an effective solution through constructing PbS2‐based inorganic‐organic superlattice. PbS2/Cn superlattice particles are synthesized, where n (4, 6, and 8) denotes the number of carbon atoms in the organic component. First‐principles simulations indicate the formation of covalent bonds and van der Waals interaction between PbS2 unit and interlayer organic molecules. All samples exhibit strong nonlinear absorption under femtosecond laser excitation with a wavelength range between 515 nm and 900 nm, and the nonlinear absorption coefficient increases with interlayer distance. The optimized sample, PbS2/C8, demonstrates outstanding nonlinear absorption and substantial modulation depth under 800 nm (the third‐order nonlinear absorption coefficient βeff, 10449 ± 609 cm GW−1; modulation depth, 39.1%) and 900 nm (the fifth‐order nonlinear absorption coefficient γeff, 6465 ± 68 cm3 GW−2; modulation depth, 88.1%), which exhibits saturable absorption under 515 nm (βeff, ‐4932 ± 818 cm GW−1; modulation depth, 48.1%). It exhibits a small optical limiting threshold of 1.23 mJ cm−2. These performances surpass those of typical single‐/few‐layer metal chalcogenides. Structural and spectral analyses elucidate that the remarkable optical nonlinearity can be attributed to quantum confinement in the inorganic layer and the dielectric enhancement of the superlattice.

FUNCTIONAL OPTICAL MATERIALS BASED ON AEROGELS

Sol-chemistry is an efficient physico-chemical method for the preparation of porous glassy or nanocrystalline materials with tailored electrical, thermal or optical properties. This paper focuses on the dependence preparation–structure-properties of hydrophobic silica aerogel granules, powders and composites with a potential application as optical materials. Using the technique of subcritical preparation of silica aerogel powders, multicolour emitting composites containing Eu(phen)2(NO3 )3 or Tb(phen)2(NO3 )3 nanocrystals are obtained and characterized with luminescence spectroscopy, quantum yield determination and texture measurements. A dependence of the luminescence quantum yield on the degree of hydrophobicity α of the silica aerogel powders is described.

Luminescent Anthracene-based Elastic Mixed Molecular Crystals for Flexible and FRET-Assisted Optical Waveguides

Abstract Optical waveguides based on elastic molecular crystals are of interest as flexible and compact optical communication materials. Low emission efficiency is often a problem in terms of communication signal strength, and an increase in the loss factor α due to fluorescence reabsorption in the crystal reduces the photon transport efficiency. Here, we report the development and improvement of Förster resonance energy transfer (FRET)-assisted optical waveguides using anthracene-based elastic mixed molecular crystals. 9,10-Dicyanoanthracene was selected as the dopant for solution-grown crystallization of 9,10-dibromoanthracene. 1H NMR measurements of the obtained crystals showed that the acceptor doping to be 1%-5%. Elastic behavior was observed even when doped with a few percent of the acceptor. The quantum efficiency was 0.016, a dramatic improvement over the previous luminescent EMMC (0.004). The α value (92 dB/cm) of this crystal containing 1%-doped 9,10-dicyanoanthracene is much lower than that of the crystal consisting of only 9,10-dibromoanthracene (1258 dB/cm) due to the reduced reabsorption in the FRET system. We have demonstrated a practical approach towards developing improved fluorescent, highly efficient, and flexible optical waveguides by constructing the mixed crystal structure by selecting appropriate acceptor molecules and their low doping ratios.

Photoinduced On and Off Polymeric Room Temperature Phosphorescence Based On Polycyclic Aromatic Hydrocarbon Isomers.

As family members of polycyclic aromatic hydrocarbons, compound anthracene (Ant) and phenanthrene (Phe) as isomers are widely used in organic optical materials and electronic materials. But their photochemical and physical properties are very different. In this work, the room temperature phosphorescence (RTP) properties of PVA-B-Ant and PVA-B-Phe are discussed carefully which are prepared by B-O click reaction through polyvinyl alcohol (PVA) with 9-anthraceneboronic acid (B-Ant) and 9-phenanthrenylboronic acid (B-Phe), respectively. PVA-B-Phe 1 % film exhibits excellent fluorescence (FL) emission at 374 nm and RTP emission at 523 nm with green afterglow and around 1.9 s phosphorescence lifetime. However, PVA-B-Ant 1 % film only shows strong blue FL emission at 414 nm, and the emission intensity decreases seriously with the extension of irradiation time. Experimental and theoretical calculations results suggest that the photodimer of Ant which is formed in PVA matrix under the UV light irradiation would be competitive with the process of RTP emission. This work demonstrates that the RTP properties of organic molecules might be probably affected by the photostability of the organic phosphor under UV irradiation.

Enhancing the photovoltaic performance of dithienobenzodithiophene based polymer donors through backbone fluorination and radical polymer additives

Unveiling the corresponding relationship between the molecular architecture of organic semiconductor materials and the morphology within the active layer of the organic solar cells (OSCs) is essential for the innovation of novel optical materials and the refinement of device optimization strategies to overcome the bottlenecks in efficiency. In this work, three dithieno[3,2-b]benzo[1,2-b;4,5-b’]dithiophene(DTBDT)-alt-benzothiadiazole (BT) based polymer donors (PDTBDT-F-BT, PDTBDT-F-FBT, and PDTBDT-F-2FBT) with varying fluorine atom content within their acceptor segments were designed and synthesized, and the photovoltaic performances of these polymers when blended with Y6 were meticulously investigated. Incorporating fluorine atoms into the BT segment was observed to not only incrementally increase the optical bandgap, lower the HOMO energy level, and bolster the self-aggregation of the polymer, but also effectively reduce the surface energy of the resulting polymer, thereby altering the donor-acceptor (D-A) interfacial spacing and the phase separation in the blend films as illustrated by molecular dynamic simulations and morphology characterization. As a result, the OSCs fabricated using PDTBDT-F-FBT, which incorporates a single fluorine substitution in the BT unit, demonstrated the highest power conversion efficiency (PCE) of 9.92 %. More importantly, this blend film's morphology is likely to be more conducive to the incorporation of the radical polymer additive, GDTA. This has resulted in a notable reduction in voltage loss, ultimately achieving a higher PCE of 11.55 % for the PDTBDT-F-FBT:Y6 based OSCs. This research uncovered a synergistic impact of backbone fluorination and the incorporation of radical polymer additives, which contributed to reducing the energy loss and enhancing the efficiency of OSCs from DTBDT-based polymer donors.

Supramolecular Control of Helicene Circularly Polarized Luminescence Emitters in Molecular Solids and Bright Nanoparticles

AbstractCircularly polarized luminescence (CPL) from chiral molecules is attracting much attention due to its potential use in optical materials. However, formulation of CPL emitters as molecular solids typically deteriorates photophysical properties in the aggregated state leading to quenching and unpredictable changes in CPL behavior impeding materials development. To circumvent these shortcomings, a supramolecular approach can be used to isolate cationic dyes in a lattice of cyanostar‐anion complexes that suppress aggregation‐caused quenching and which we hypothesize can preserve the synthetically‐crafted chiroptical properties. Herein, we verify that supramolecular assembly of small‐molecule ionic isolation lattices (SMILES) allows translation of molecular ECD and CPL properties to solids. A series of cationic helicenes that display increasing chiroptical response is investigated. Crystal structures of three different packing motifs all show spatial isolation of dyes by the anion complexes. We observe the photophysical and chiroptical properties of all helicenes are seamlessly translated to water soluble nanoparticles by the SMILES method. Also, a DMQA helicene is used as FRET acceptor in SMILES nanoparticles of intensely absorbing rhodamine antennae to generate an 18‐fold boost in CPL brightness. These features offer promise for reliably accessing bright materials with programmable CPL properties.

Ultrasonic-assisted ultra-precision turning of zinc-selenide with straight-nosed diamond tools

This study proposes a novel ultra-precision machining technology that uses ultrasonic vibration and a straight-nosed diamond tool to improve the processing of the brittle optical material zinc selenide (ZnSe). This research addresses the challenges posed by Poisson's effect in ultrasonic vibration-assisted single-point diamond turning, which causes bending vibration along the depth of cut, resulting in lower machining efficiency and surface quality. This study analyses the relationship between one-dimensional ultrasonic vibrations at the diamond tool edge and induced bending vibrations using both theoretical and experimental methods. By investigating ultrasonic vibration dynamics in the feed direction and at the straight cutting edge, the results showed that ultrasonic vibration helps to improve the ductile-brittle transition ratio of the cutting area and surface quality. These improvements are accomplished by regulating the cutting position at the tool cutting edge, adjusting cutting parameters, and optimizing ultrasonic parameters. The machined surface roughness of ZnSe is reduced by approximately 30-46% at higher feed rates under ultrasonic vibration with straight-nosed diamond tools. The findings demonstrate the potential of this novel technology to reduce tool wear and brittle fractures, resolving the challenge of ultra-precision machining for optical materials.

Fluorescence Enhancement of Nonemissive Monodeprotonated Luteolin in a Poly(vinyl alcohol) Film.

Solid polymer matrixes can modulate the electronic states of embedded chromophores and have been widely used in flexible optoelectronic and optical materials. Luteolin is one of the most common natural flavonoids, and its neutral and monodeprotonated forms are nonemissive in aqueous solution induced by ultrafast excited-state proton transfer (ESPT) followed by nonradiative relaxation. In this study, we have incorporated luteolin into poly(vinyl alcohol) (PVA) films and studied their fluorescence behaviors. Neutral and one monodeprotonated luteolin coexist in the PVA film. Weak steady-state fluorescence of neutral luteolin peaking at about 440 nm is observed for the first time. In addition, the monodeprotonated luteolin in PVA film exhibits obvious fluorescence peaking at 500 nm, with a fluorescence quantum yield of as high as 0.4 and a fluorescence lifetime of as long as 2.4 ns. Time-dependent density functional theory calculations have determined that the ESPT of neutral luteolin is barrierless but that of monodeprotonated luteolin needs to surmount a barrier, explaining their distinct emission properties. These results indicate the modulation ability of the PVA film in both ground-state deprotonation and ESPT, broadening the application areas of the solid polymer matrix.

Multicolor luminescence and high efficient optical thermometric performance of Eu3+ and Sm3+ in self-activated Na2LuMg2V3O12 garnet

To develop efficient luminescence and optical thermometry materials for color display and non-contact temperature measurement, novel RE3+ (RE = Eu, Sm) doped self-activated Na2LuMg2V3O12 phosphors were prepared by a typical solid-state reaction method. Their crystal structure, morphology, multi-color luminescence and temperature sensing properties were elaborately investigated. Under UV light excitation, an intense and broad green-yellow emission band from VO43– group is observed in the Na2LuMg2V3O12 matrix, indicating its potential application in solid state lighting. After the incorporation of Eu3+ and Sm3+ ions, efficient energy transfer (ET) from VO43– group to Eu3+/Sm3+ ions occurs and the emission color of the samples can be readily tuned among different color ranges. Besides, based on the change of luminescence intensity and lifetimes of VO43– group in Na2LuMg2V3O12:Eu3+ and Na2LuMg2V3O12:Sm3+, the ET efficiency was analyzed and the mechanism is illustrated. Finally, large discrepancy between the thermal stability of VO43– group and Eu3+/Sm3+ ions are observed in the temperature-dependent emission spectra of Na2LuMg2V3O12:Eu3+ and Na2LuMg2V3O12:Sm3+. By taking advantage of the luminescence intensity ratio (LIR) between VO43– group and Eu3+/Sm3+ ions in Na2LuMg2V3O12:0.01Eu3+ and Na2LuMg2V3O12:0.07Sm3+, two new types of optical thermometry mediums were designed and their basic temperature sensing parameters were calculated.

Liquid crystal phase behavior of oxalated cellulose nanocrystal and optical films with controllable structural color induced by centripetal force

Cellulose nanocrystal (CNC) is a sustainable bio-nanomaterial. The distinctive left-handed polarization properties render cellulose nanocrystal a promising candidate for optical film. Due to eco-friendliness, reliability, mildness and simplicity, the oxalate hydrolysis method stands out among various preparation methods for CNC. This study delved into the liquid crystal phase behavior of oxalated cellulose nanocrystal derived from pulp, and discovered the influences of CNC concentration and pH on suspension stability and phase transition, and evaluated its optical properties. The results demonstrated that oxalated CNC presented two different liquid crystal phases, the nematic phase and the cholesteric phase. The stability mechanism of CNC suspension and the regulatory principle of the liquid crystal phase transition were revealed. A novel CNC film-forming technology, the multilayer spin-coating technique, was developed for cellulose nanocrystal optical films. Driven by centrifugal force, cellulose nanocrystals were induced to self-assembly and formed the optical film with circular dichroism and structural color. This simple and efficient film-forming technology promised rapid processing (1 h) and controllable film structure and optical properties compared to traditional technologies. This work provided a theoretical understanding and practical prospects for integrating oxalated cellulose nanocrystal into sustainable advanced optical film materials.