Laser Emission from Dye-Doped Organic-Inorganic Particles of Microcavity Structure

Interaction between laser light and a micrometer-size spherical particle causes an optical resonance in its interior since a spherical wall acts as a cavity. The present work seeks to investigate the preparation of organicinorganic particles containing laser dyes and demonstrate their lasing behavior. Rhodamine 6G was incorporated into organic-inorganic spherical particles of micrometer-size using sol-gel technique. Phenyl triethoxy silane was used as a starting material for particles. Particle size was 1–10 μm and dye content was 1–7 × 10⁻⁵ mol/g. A particle was set on a glass plate in air and pumped by a second harmonic pulse ofQ-switched Nd-YAG laser (532 nm wavelength). From a particle of 6 μm in diameter, a strong laser emission peak was observed at 598 nm wavelength which corresponded to the whispering-gallery mode resonance.     

Mesostructured Dye‐Doped Titanium Dioxide for Micro‐Optoelectronic Applications

Optically transparent, mesostructured titanium dioxide thin films were fabricated using an amphiphilic poly(alkylene oxide) block copolymer template in combination with retarded hydrolysis of a titanium isopropoxide precursor. Prior to calcination, the films displayed a stable hexagonal mesophase and high refractive indices (1.5 to 1.6) relative to mesostructured silica (1.43). After calcination, the hexagonal mesophase was retained with surface areas >300 m² g^?1. The dye Rhodamine 6G (commonly used as a laser dye) was incorporated into the copolymer micelle during the templating process. In this way, novel dye‐doped mesostructured titanium dioxide films were synthesised. The copolymer not only directs the film structure, but also provides a solubilizing environment suitable for sustaining a high monomer‐to‐aggregate ratio at elevated dye concentrations. The dye‐doped films displayed optical thresholdlike behaviour characteristic of amplified spontaneous emission. Soft lithography was successfully applied to micropattern the dye‐doped films. These results pave the way for the fabrication and demonstration of novel microlaser structures and other active optical structures. This new, high‐refractive index, mesostructured, dye‐doped material could also find applications in areas such as optical coatings, displays and integrated photonic devices.     

Dynamical behavior of magnetic polarizable microsphere using whispering gallery mode

In this article, analytical and experimental studies are carried out to investigate the dynamical behavior of polymer microspheres that are doped with magnetic polarizable microparticles. The effect of a static and harmonic inductive magnetic field on the elastic deformation of the microsphere is investigated. The elastic deformation that is induced by the magnetic forces (magnetostrictive effect) acting on the microsphere is measured using an optical technique that is based on the whispering gallery mode (WGM) of the microsphere. The WGMs experience a shift when the morphology of the resonator is perturbed by the elastic deformation. Therefore, the elastic deformation of the microsphere is measured by monitoring the shift of the optical resonances. For these studies, the microsphere has a radius of ∼600 µm and is fabricated by mixing polyvinyl chloride (PVC) with magnetic polarizable microparticles. The microsphere is further coated with a thin layer of pure PVC that serves as a wave‐guide for the optical modes. Experiments are carried out to validate the analysis. Measurements are taken up to a frequency of 200 Hz, showing that the microspheres can be used as magnetic field sensors or as element for the fabrication of smart structures. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 598–603     

A tunable 3D optofluidic waveguide dye laser via two centrifugal Dean flow streams

This paper presents a tunable optofluidic waveguide dye laser utilizing two centrifugal Dean flows. The centrifugal Dean flow increases the light confinement of the dye laser by shaping a three-dimensional (3D) liquid waveguide from curved microchannels. The active medium with the laser dye is dissolved in the liquid core and pumped with an external pump laser to produce stimulated emission. The laser's Fabry-Pérot microcavity is formed with a pair of aligned gold-coated fiber facets to amplify the fluorescent emission. The advantage of the 3D optofluidic waveguide dye laser is its higher efficiency, thus to obtain lasing at a reduced threshold (60%) with higher output energy. The demonstrated slope efficiency is at least 3-fold higher than its traditional two-dimensional equivalent. In addition, the laser output energy can be varied on demand by tuning the flow rates of the two flows. This technique provides a versatile platform for high potential applications microfluidic biosensor and bioanalysis.     

Fluorescent and laser properties of pyrromethene 567 (PM567) doped into multi-precursors derived gel glasses

In this work, the laser dye PM567 was incorporated into various organically modified silicate gel glasses (ORMOSILs) derived by methyltriethoxysilane (MTES) and vinyltriethoxysilane (VTES) precursors mixed in various ratios. The laser performances of PM567 doped into MTES–VTES-derived ORMOSILs including the laser slope efficiency, threshold and lifetime together with the spectroscopic properties were investigated. Blue-shifts of fluorescent peaks, extended fluorescent lifetime, improved laser efficiency and lifetime of PM567 doped into ORMOSILs derived by mixed precursors of MTES and VTES have been observed, which might related to the microstructures and micro-chemical environment of the dye in ORMOSILs.     

Sol-gel-derived micron scale optical fibers for chemical sensing

We report for the first time on the preparation of organically-doped room temperature processed sol-gel-derived micron scale optical fibers as platforms for chemical- and bio-sensors. Micron scale optical fibers are drawn from fluorescent dye-doped tetraethoxysilane (TEOS)-derived sol-gel solution processed under ambient conditions. Such a simple methodology to entrap organic and even bioactive species within the optical fiber offers many advantages over more conventional ways of immobilizing organic probes for the development of optical sensors. Specifically, we report on the photophysical properties of fluorescein (a pH sensitive fluorescent dye) and rhodamine 6G (R6G; laser dye) entrapped within sol-gel-derived optical fibers. We present the preliminary results on the viability of such doped optical fibers for chemical sensing. Our results demonstrate that a fluorescein-doped sol-gel-derived optical fiber responds to ammonia and acid vapors with a response time of 1–2 seconds.     

A Photoisomerization-Activated Intramolecular Charge-Transfer Process for Broadband-Tunable Single-Mode Microlasers

Miniaturized lasers with high spectral purity and wide wavelength tunability are crucial for various photonic applications. Here we propose a strategy to realize broadband-tunable single-mode lasing based on a photoisomerization-activated intramolecular charge-transfer (ICT) process in coupled polymer microdisk cavities. The photoisomerizable molecules doped in the polymer microdisks can be quantitatively transformed into a kind of laser dye with strong ICT character by photoexcitation. The gain region was tailored over a wide range through the self-modulation of the optically activated ICT isomers. Meanwhile, the resonant modes shifted with the photoisomerization because of a change in the effective refractive index of the polymer microdisk cavity. Based on the synergetic modulation of the optical gain and microcavity, we realized the broadband tuning of the single-mode laser. These results offer a promising route to fabricate broadband-tunable microlasers towards practical photonic integrations.     

A Photoisomerization‐Activated Intramolecular Charge‐Transfer Process for Broadband‐Tunable Single‐Mode Microlasers

Miniaturized lasers with high spectral purity and wide wavelength tunability are crucial for various photonic applications. Here we propose a strategy to realize broadband‐tunable single‐mode lasing based on a photoisomerization‐activated intramolecular charge‐transfer (ICT) process in coupled polymer microdisk cavities. The photoisomerizable molecules doped in the polymer microdisks can be quantitatively transformed into a kind of laser dye with strong ICT character by photoexcitation. The gain region was tailored over a wide range through the self‐modulation of the optically activated ICT isomers. Meanwhile, the resonant modes shifted with the photoisomerization because of a change in the effective refractive index of the polymer microdisk cavity. Based on the synergetic modulation of the optical gain and microcavity, we realized the broadband tuning of the single‐mode laser. These results offer a promising route to fabricate broadband‐tunable microlasers towards practical photonic integrations.     

Orientational control of liquid crystal molecules via carbon nanotubes and dichroic dye in polymer dispersed liquid crystal

Polymer dispersed liquid crystals (PDLCs) using nematic liquid crystal and photo-curable polymer (NOA 65) were prepared by polymerisation-induced phase separation technique, in equal ratio (1:1) of polymer and liquid crystal (LC). We demonstrate that doping of small amount (0.125%, wt./wt.) of multiwall carbon nanotubes (CNTs) and orange azo dichroic dye in PDLC generously controlled the molecular orientation, dynamics of LC in droplet and size of droplets. The effects of multiwall CNTs and dye on PDLCs were studied in terms of transition temperature, droplet morphology, transmittance characteristic, contrast ratio and response time. The results exhibited that the values of the threshold electric fields were reduced from 8 V/µm (pure PDLC) to 1.18 and 1.72 V/µm, doped with multiwall CNTs and dye, respectively. The CNTs-doped PDLC shows faster switching response as compared with pure PDLC and dye-doped PDLC. However, dye-doped PDLC shows much higher contrast among all PDLC samples. Further, the results also illustrate that the birefringence value of LC in PDLCs was changed with doping of CNTs and dye.     

Synthesis,Separation, and Characterization of Small and Highly Fluorescent Nitrogen‐Doped Carbon NanoDots

A facile bottom‐up approach to carbon nanodots (CNDs) is reported, using a microwave‐assisted procedure under controlled conditions. The as‐prepared nitrogen‐doped CNDs (NCNDs) show narrow size‐distribution, abundant surface traps and functional groups, resulting in tunable fluorescent emission and excellent solubility in water. Moreover, we present a general method for the separation of NCNDs by low‐pressure size‐exclusion chromatography, leading to an even narrower size distribution, different surface composition, and optical properties. They display among the smallest size and the highest FLQYs reported so far. ¹³C‐enriched starting materials produced N¹³CNDs suitable for thorough NMR studies, which gave useful information on their molecular structure. Moreover, they can be easily functionalized and can be used as water‐soluble carriers. This work provides an avenue to size‐ and surface‐controllable and structurally defined NCNDs for applications in areas such as optoelectronics, biomedicine, and bioimaging.     

Synthesis,Separation, and Characterization of Small and Highly Fluorescent Nitrogen‐Doped Carbon NanoDots

A facile bottom‐up approach to carbon nanodots (CNDs) is reported, using a microwave‐assisted procedure under controlled conditions. The as‐prepared nitrogen‐doped CNDs (NCNDs) show narrow size‐distribution, abundant surface traps and functional groups, resulting in tunable fluorescent emission and excellent solubility in water. Moreover, we present a general method for the separation of NCNDs by low‐pressure size‐exclusion chromatography, leading to an even narrower size distribution, different surface composition, and optical properties. They display among the smallest size and the highest FLQYs reported so far. ¹³C‐enriched starting materials produced N¹³CNDs suitable for thorough NMR studies, which gave useful information on their molecular structure. Moreover, they can be easily functionalized and can be used as water‐soluble carriers. This work provides an avenue to size‐ and surface‐controllable and structurally defined NCNDs for applications in areas such as optoelectronics, biomedicine, and bioimaging.     

Fast Raman spectroscopy of cytochrome c using intracavity resonance Raman amplification

The resonance Raman spectrum of cytochrome c (5 × 10^?4 M) was obtained using the method of resonance Raman amplification (RRA) in a dye laser resonator in 30 ns. The second harmonic of a Q-switched Nd glass laser was used as an excitation source and the spectra were recorded using a photographic plate.     

Fullerene Derivatives Embedded in Hybrid Sol-Gel Glasses: Nonlinear Optical Properties and Optical Limiting Performances

Hybrid organic-inorganic materials are investigated as suitable materials for inclusion of fullerene derivatives and for fabrication of laser protection devices. A specific synthesis has been developed in order to optimize non-linear optical performances of fullerene derivatives. 3-glicydoxypropyltrymethoxysilane has been used as an inorganic and organic network former to obtain the host material. The sol-gel synthesis consists of the hydrolysis and condensation in acidic conditions of the inorganic network. Epoxy polymerization has been achieved by using zirconium or BF₃ alkoxides precursors. Bulk and multilayer materials doped with a fullerene derivative have been fabricated. They show good optical requirements: high fullerenes concentration, high microstructural homogeneity, high laser damage threshold and high optical limiting efficiency. Optical limiting (OL) mechanisms have been investigated. The most effective in the sol-gel materials is the reverse saturable absorption (RSA) one. However, different mechanisms, like non-linear (NL) scattering and NL refraction contribute to a different extent. Open- and closed-aperture OL and z-scan measurements on sol-gel samples show the contribution of NL scattering and NL refraction at 690 nm. Laser damage threshold has been characterized as a function of the structure of the samples and of the optical configurations (f/66 and f/5).     

Production of highly aligned microfiber bundles from polymethyl methacrylate via stable jet electrospinning for organic solid-state lasers

The fabrication of micron-sized poly(methyl methacrylate) (PMMA) polymer optical fibers doped with rhodamine B as an organic dye is demonstrated. Highly aligned and defect-free fibers are fabricated by using the stable jet electrospinning (SJES) method and systematically varying critical parameters such as solvent type and polymer concentration. At optimal conditions, for example, a polymer concentration of 35 wt% of PMMA in butanone, ribbon-shaped fibers with a smooth surface and diameter of about 20 μm could be spun using SJES mode and deposited on a rotating drum as target in a highly aligned manner. Photoluminescence spectra of the doped fibers excited longitudinally and transversely with a laser show an excitation peak with full-width-at-half-maximum of only 5.05 nm and a low lasing threshold at a pump energy of 0.55 μJ, indicating that SJES could become a new source of amplified optics components or organic solid-state fiber lasers.     

Preparation of polymer optical fibers doped with nonlinear optical active organic chromophores

We synthesized two novel organic nonlinear optical chromophores—chiral S(+)‐N‐[p‐(4‐nitrostyryl) phenyl] prolinol and non‐chiral [p‐(4‐nitrostyryl) phenyl] piperdine—as potential laser‐active dyes for photonic applications. Both materials show good optical transmittance in the telecommunication frequency region, desirable solubility in acrylic polymer optical fiber matrices, and attractive fluorescence properties that are advantageous for laser‐gain materials and devices. Subsequently, these two chromophores were incorporated into poly(methyl methacrylate) and poly(ethyl methacrylate) and drawn into polymer optical fibers. The relevant properties of these organic dye‐doped fibers have been studied, revealing essential attributes of laser‐active characteristics. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1794–1801, 2001     

Fluorescent Supramolecular Polymersomes Based on Pillararene/Paraquat Molecular Recognition for pH-controlled Drug Release

Researchers have put significant efforts on developing versatile fluorescent polymeric systems due to their promising biological/biomedical labelling, tracking, monitoring, imaging, and diagnostic applications. However, complicated organic/polymeric synthesis or post-modification of these functionalized platforms is still a big obstacle for their further application and thereby provides clear motivation for exploring alternative strategies for the design and fabrication of easily available fluorescent systems. The marriage of supramolecular polymers and fluorescent imaging can provide a facile and dynamic manner instead of tedious and time-consuming synthesis due to the dynamic and reversible nature of noncovalent interactions. Herein, based on water-soluble pillararene/paraquat molecular recognition, we successfully prepare two amphiphilic polypseudorotaxanes which can self-assemble into supramolecular polymersomes in water. These polymersomes can be reversibly destroyed and reformed by tuning the solution p H. Attributed to the aggregation-induced emission of tetraphenylethylene groups,intense fluorescence can be introduced into the obtained supramolecular polymersomes. Furthermore, p H-triggered release of an encapsulated water-insoluble drug(doxorubicin) from the self-assembled fluorescent supramolecular polymersomes is also investigated.     

Perylene polyphenylmethylsiloxanes for optoelectronic applications

The incorporation of fluorescent organic dyes in an encapsulating matrix represents a route to generate stable and processable materials for optoelectronic devices. Here, we present a method to embed perylene dyes into a high refractive index (HRI) polysiloxane matrix applying an allyl functionalized perylene dye and hydrosilylation chemistry. In a first approach, the dye molecules were covalently integrated into the backbone of linear polyphenylmethylsiloxane chains. The fluorescent and liquid polymers were synthesized with molecular weights from 5660 up to 8400 g mol^?1. In a second approach, the dye itself was used as a cross‐linking agent between linear polyphenylmethylsiloxane chains. These preformed fluorescent batch polymers are liquids with dye concentrations between 0.025 and 8 wt %. The applied synthetic methods incorporated the dye covalently into the polymer structure and avoided the crystallization of the dye molecules and thus the formation of excimers, which would reduce the optical emission. The resulting products can be easily incorporated into curable commercially available HRI polyphenylmethylsiloxane resins. The formed materials are ideal LED encapsulants with a solid and flexible consistency, a uniform dispersion of the dyes, and adjustable mechanical properties, realized by changing the amount of perylene polymers. Further properties of the obtained materials are thermal stabilities up to 478 °C, quantum yields larger than 0.97, and high photostabilities. Thus, the covalent integration of dyes into polyphenylsiloxane structures represents a possible route for the stabilization of the organic dyes against the extreme irradiance and thermal conditions in LED applications. © 2019 The Authors. Journal of Polymer Science Part B: Polymer Physics published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1062–1073     

Facile and sustainable synthesis of sodium lignosulfonate derived carbon quantum dots for the detection of total Mn and ascorbic acid

A fluorescent nanoprobe based on sodium lignosulfonate derived carbon quantum dots (SLS-CQDs) was fabricated through a facile and sustainable one-step hydrothermal treatment. The obtained SLS-CQDs had excellent fluorescence properties and were applied to detect total Mn and ascorbic acid (AA). The fluorescence of SLS-CQDs could be effectively quenched by Mn based on a static quenching process and recovered by the addition of AA. An “on–off-on” fluorescent nanoprobe was established to determine total Mn and AA with the detection limits of 6.9 µg/L and 0.65 µM with the corresponding linear ranges of 0.25–2.25, 5–25 mg/L, and 5–110 µM, respectively. This nanoprobe could accurately detect total Mn in surface water and AA in Vitamin C effervescent tablet samples. The proposed method is simple and can be performed easily, indicating that SLS-CQDs might be used in environmental monitoring, food and drug testing.     

Multifunctional particles: Magnetic nanocrystals and gold nanorods coated with fluorescent dye-doped silica shells

Multifunctional colloidal core-shell nanoparticles of magnetic nanocrystals (of iron oxide or FePt) or gold nanorods encapsulated in silica shells doped with the fluorescent dye, Tris(2,2′-bipyridyl)dichlororuthenium(II) hexahydrate (Rubpy) were synthesized. The as-prepared magnetic nanocrystals are initially hydrophobic and were coated with silica using a microemulsion approach, while the as-prepared gold nanorods are hydrophilic and were coated with silica using a Stöber type of process. Each approach yielded monodisperse nanoparticles with uniform fluorescent dye-doped silica shells. These colloidal heterostructures have the potential to be used as dual-purpose tags—exhibiting a fluorescent signal that could be combined with either dark-field optical contrast (in the case of the gold nanorods), or enhanced contrast in magnetic resonance images (in the case of magnetic nanocrystal cores). The optical and magnetic properties of the fluorescent silica-coated gold nanorods and magnetic nanocrystals are reported.     

Vibrational spectroscopy of size-selected sodium-doped water clusters

The vibrational OH stretch spectra have been measured for Na(H2O)n clusters in the size range from n = 8 to 60. The complete size selection is achieved by coupling the UV radiation of a dye laser below the ionization threshold with the tunable IR radiation of an optical parametric oscillator. The spectra are dominated by intensity peaks around 3400 cm(-1) which we attribute to an increased transition dipole moment of delocalized electrons in this type of doped cluster. Aside from the positions of free (3715 cm(-1)) and double donor (3560 cm(-1)) bonds which are known from pure water clusters, specific transitions are observed at 3640 cm(-1) and in the range of the single donor bonds between 3000 and 3200 cm(-1).