Dye-doped Polymer Film Research Articles

Facile Z-scan determination of nonlinear refractive index and absorption coefficient of dye-doped polymer film

Facile Z-scan determination of nonlinear refractive index and absorption coefficient of dye-doped polymer film

Aggregation/Crystallization-Induced Emission in Naphthyridine-Based Carbazolyl-Modified Donor-Acceptor Boron Dyes Tunable by Fluorine Atoms.

Four donor-acceptor boron difluoride complexes based on the carbazole electron donor and the [1,3,5,2]oxadiazaborinino[3,4-a][1,8]naphthyridine acceptor were designed, synthesized, and systematically spectroscopically investigated in solutions, in dye-doped polymer films, and in the solid states. The dyes exhibit an intense blue to red solid-state emission with photoluminescence quantum yields of up to 59 % in pure dye samples and 86 % in poly(methyl methacrylate) films. All boron complexes show aggregation-induced emission and reversible mechanofluorochromism. The optical properties of these dyes and their solid state luminescence can be tuned by substitution pattern, i. e., the substituents at the naphthyridine unit. Exchange of CH3 - for CF3 -groups does not only increase the intramolecular charge transfer character, but also provides a crystallization-induced emission enhancement.

2D tunable all-solid-state random laser in the visible

A two-dimensional (2D) solid-state random laser emitting in the visible is demonstrated, in which optical feedback is provided by a controlled disordered arrangement of air-holes in a dye-doped polymer film. We find an optimal scatterer density for which threshold is minimum and scattering is the strongest. We show that the laser emission can be red-shifted by either decreasing scatterer density or increasing pump area. We show that spatial coherence is easily controlled by varying pump area. Such a 2D random laser provides with a compact on-chip tunable laser source and a unique platform to explore non-Hermitian photonics in the visible.

Random laser emission from dye-doped polymer films enhanced by SiC nanowires

As the third-generation semiconductor electronic material, silicon carbide (SiC) has good chemical stability and mechanical properties, leading to wide use in optoelectronic components, fiber sensing and detectors. However, there are few important reports on its application in the research of random laser. Hereby, we built a polymer random laser system with SiC nanowires as a scattering medium doped with dye by the spin coating method. The effect of different SiC concentrations on random laser properties and the enhancement mechanism are studied. The lasing intensity increases and threshold decrease in large concentration SiC nanowires at the same lasing system, and the minimum threshold is 20 μJ/pulse. By increasing the SiC concentration, the mean free path of photon scattering decreases, which promotes the photon gain effect and improves the laser performance. However, when the concentration of SiC nanowires is too large, the mean free path of photon scattering decreases further, and the self-absorption of fluorescence radiation emerges. Thus, fluorescence quenching is produced, leading to a negative effect on laser performance. Furthermore, the lasing wavelength can be adjusted by tuning the SiC nanowires concentrations, reaching 14 nm. The random laser enhanced by SiC nanowires is stable and pumped repeatable, which could pave the way to promote the application of SiC and achieve low-cost and high-performance random laser.

Organic Synthetic Photonic Systems with Reconfigurable Parity-Time Symmetry Breaking for Tunable Single-Mode Microlasers.

Synthetic photonic materials exploiting the quantum concept of parity-time (PT) symmetry lead to an emerging photonic paradigm-non-Hermitian photonics, which is revolutionizing the photonic sciences. The non-Hermitian photonics dealing with the interplay between gain and loss in PT synthetic photonic material systems offers a versatile platform for advancing microlaser technology. However, current PT-symmetric microcavity laser systems only manipulate imaginary parts of the refractive indices, suffering from limited laser spectral bandwidth. Here, an organic composite material system is proposed to synthesize reconfigurable PT-symmetric microcavities with controllable complex refractive indices for realizing tunable single-mode laser outputs. A grayscale electron-beam direct-writing technique is elaborately designed to process laser dye-doped polymer films in one single step into microdisk cavities with periodic gain and loss distribution, which enables thresholdless PT-symmetry breaking and single-mode laser operation. Furthermore, organic photoisomerizable compounds are introduced to reconfigure the PT-symmetric systems in real-time by tailoring the real refractive index of the polymer microresonators, allowing for a dynamically and continuously tunable single-mode laser output. This work fundamentally enhances the PT-symmetric photonic systems for innovative design of synthetic photonic materials and architectures.

The enhancement and regulation of lasing in dye-doped multi-layer polymer film systems

As a new research hotspot in nano-materials and nano-structures, photoluminescence is widely used in medical imaging, biosensors, integrated devices and other fields because of its excellent optical performance and good stability. The design and fabrication of these nanostructures are expensive and complex, meanwhile, the influence of film structure change on lasing characteristics has not been systematically summarized. Thus, there are still challenges to realizing lasing regulation by using a multilayer film system. In this study, a dye-doped multilayer system was prepared by a convenient spin-coating method on polyethylene glycol terephthalate (PET) film. The effects of sandwich-like film and Au nanoparticles on the lasing characteristics were studied. The results show that the sandwich-like film can form a mirror symmetry plane and increase the photon scattering frequency. Furthermore, the band-gap edge effect can effectively improve the photon gain, enhancing the optical feedback and realizing band-edge lasing. The lasing intensity in the sandwich-like film is nearly 30% higher than that of the bilayer film system at the same pump energy. By adding Au nanoparticles as scatterers, the local electromagnetic field can be enhanced because of the surface plasmon resonance, improving the transition rate of dye molecules. Meanwhile, the photon scattering frequency among the scattering cross-section can also be increased, increasing the interaction between photons and dye. The lasing intensity can be enhanced by 160% at the same pump energy because of the interaction between the plasmon resonance effect and the scattering effect. The fabrication method in this study is convenient and easy to implement, which is conducive to improving the lasing intensity and provides an effective technical way for the realization of a modulated random laser.

Photoluminescence enhancement of dye-doped polymer films covered with electrospun nanofibers

The photoluminescence (PL) enhancement of a dye-doped polymer film covered with electrospun nanofibers has been demonstrated. The time variation of the PL intensity is measured while nanofibers are being formed on the surface of the sample by electrospinning. The PL intensity of the sample gradually increases during nanofiber electrospinning. The PL enhancement occurs along the front direction of the sample rather than along the horizontal direction. The total enhancement factor measured in an integrating sphere is approximately 1.2. These effects are brought about by improving the excitation efficiency and light extraction caused by the light scattering in the nanofibers.

Effect of nanoscale dielectric environments on concentration quenching

Abstract We have studied the dependence of concentration quenching of luminescence (donor–acceptor energy transfer) on the thickness d of dye-doped polymeric films (HITC:PMMA) and found its strong inhibition at small values of d. This phenomenon is tentatively explained by a limited number of acceptors, which donors’ excitation can reach in thin samples, if the film’s thickness is comparable to the diffusion length of the energy transfer. The latter mechanism, along with effective reduction of the dye concentration, is responsible for an inhibition of the concentration quenching of dye molecules impregnating porous alumina membranes. The elongation of emission kinetics in thick (≥3 μm) HITC:PMMA films is cautiously attributed to the samples’ crystallinity.

Lasing peculiarities in cholesteric multilayer structure with dye-doped polymer film depending on the concentration of laser dye and pumping energy

We have experimentally investigated lasing peculiarities in a cholesteric liquid crystal – dye-doped polymer layer – cholesteric liquid crystal three-layer wedge-cell system with different laser dye concentration changing pumping energy. It was theoretically and experimentally shown that there are photonic defect modes in cholesteric photonic bandgap of the wedge-cell system. The problem was solved by Ambartsumian’s layer addition modified method. It was shown that in the mentioned above system it is possible to obtain lasing generation and it should be noted that in our case the observed lasing peculiarities are not because of the isotropic defect (planar polymer layer) but the observed features are due to the cholesterics, namely by changing the thickness of the layer of cholesterics, we are able to ensure a change in the laser wavelength, due to the pitch jumps and therefore helix pitch gradient. The advantage of our experiment is the continuous change in the thickness of the cholesteric liquid crystal layer. To prevent degradation of the molecules, decrease of the fluorescence output as well as to except convective flows for higher pumping energies the dye concentration in the polymer was chosen 10−4mol/l. We have experimentally shown the dependences of the intensity and displacement of the lasing peaks’ on the pumping power.

Effect of metallic substrates and cavities on emission kinetics of dye-doped polymeric films

We have studied emission kinetics in dye-doped polymeric films (HITC:PMMA), deposited on top of glass and silver and embedded in Fabry–Perot cavities (metal-insulator-metal waveguides). For highly doped films on glass, we observed strong concentration quenching, as evidenced by a dramatic shortening of the emission kinetics, consistent with our previous studies. However, for the same dye-doped films on top of silver, slower emission kinetics were observed despite the high decay rates of individual dye molecules near the metallic surface. The concentration quenching rates in Fabry–Perot cavities were nearly identical to those of HITC:PMMA films deposited on top of silver. These findings are explained within a theoretical model for the inhibition of Förster energy transfer near a metallic surface. Furthermore, the emission kinetics of the dye-doped films on top of silver were approximately single exponential—consistent with the strong coupling of excited molecules with propagating surface plasmons.

External feedback assisted reduction of the lasing threshold of a continuous wave random laser in a dye doped polymer film and demonstration of speckle free imaging

The applications of random laser (RL) are still restricted, due to its complexity, high lasing threshold, unstable nature, difficulty in tuning and modulating its light emission characteristics. However, here a low threshold, continuous wave (CW) RL system has been designed in a fluoresecent laser dye (namely DCM) -doped in a polymer film with ZnO micro-cabbages as scatterers. Interestingly, by putting the active medium inside an external feedback (ExFB) system, a narrowed and stable RL emission at ~598 nm is observed with the subsequent reduction of CW lasing threshold (CWITh) by ~2.4 times. The effective cavity length (Leff) has been varied by an ingenious approach to demonstrate the role of Leff over the RL emission characteristics and the experimental results are supported by a theoretical explanation. The statistical fluctuation in the position of generated modes over time and the role of pump volume amplification on the emission characteristics of the developed RL has been studied in detailed. Thus, it is found here that due to the presence of ExFB, reinjection of pump light into scattering-formed cavities has taken place which has led to the generation of stable RL modes with the reduction of CWITh. The temporal coherency of the ExFB based RL light is found to be ~3.2 times less than that of a conventional He–Ne laser light. As a result, we could demonstrate here speckle free imaging with much lowered value of speckle contrast (C) on two different model systems, such as commercially available carbon film-coated TEM grid and cell membrane of Allium cepa. It is expected that this report will open up new possibilities for the development of stable and tunable RLs with other laser dyes for various optoelectronic applications including in bio-imaging.

PHENANTHROIMIDAZOLE-AZO DERIVED POLYMER BASED FLUORESCENCE SENSOR DESIGN FOR MONITORING OF Fe (III) IONS

Dye doped polymer films which are sensitive to Fe (III) ions have been developed for using in the aqueous medium. PVC films were obtained by spreading the cocktail mixture onto a mylar film used as a supporting material. PMMA films were prepared with solvent casting method. Cation responses were examined for two different polymer films. Emission bands were obtained at different concentrations of Fe (III) ions. Because polymer films had the highest response to them. The calibration graphics were plotted for emission values at different Fe (III) concentrations. Besides, interference effects of Cr (III) and Fe (II) ions to Fe (III) ions were studied. Additionally, regeneration studies were carried out to examine application properties of the dye doped polymer films developed as a sensor for Fe (III) cations.

Fluorescent 2-phenyl-2H-benzotriazole dyes with intramolecular N–H···N hydrogen bonding: Synthesis and modulation of fluorescence properties by proton-donating substituents

A series of 2-(2-phenyl)benzotriazole derivatives having amino, N-methyl amino, and acetamido groups on the ortho position of the phenyl group were synthesized to elucidate the effects of amino/amido substitutions on the molecular structures and photophysical properties. 1H NMR spectra and DFT calculations of the present dyes revealed the formation of N–H∙∙∙N intramolecular hydrogen bonds between benzotriazole and amino/amide groups in the ground state. Amino-functionalized dyes showed absorption bands that were assigned to HOMO-LUMO transition with a partial charge-transfer feature. The dye with an acetoamido group in which the acidity of NH proton was increased by the effect of electron-withdrawing acetyl groups exhibited absorption bands attributable to intramolecular hydrogen-bonded “closed” conformers in CHCl3 and non-hydrogen-bonded “open” conformers in DMSO. In comparison to 2-phenylbenzotriazole, which had no acidic proton involved in intramolecular hydrogen bonding, the present derivatives exhibited weak fluorescence emissions with quite low quantum yields, suggesting that non-radiative deactivation of ESIPT states also operated in the N–H∙∙∙N hydrogen bonded 2-phenylbenzotriazoles just as in O–H∙∙∙N intramolecular hydrogen-bonded 2-hydroxyphenylbenzotriazoles, which are known as UV absorbers. Taking a closer look at the fluorescence spectra, dyes with amino and N-methylamino groups showed faint but dual emissions from charge-transfer excited states in CHCl3 and blue-shifted single emission in DMSO. Fluorescence emissions of the acetamido-functionalized dye were unimodal in each solvent and stronger than those of amino-functionalized dyes. Thus, the fluorescence properties of these dyes depended on substitutions at amino groups. The luminescence of these derivatives was enhanced in the polymer matrix in which conformation changes and molecular motions were suppressed. Dye-doped polymer films have absorption bands in the UV range (360–400 nm) and emitted at the visible region (450–510 nm), and thus could be used as organic materials for light conversion films that convert UV light into visible light.

Synthesis, optical limiting behavior, thermal blooming and nonlinear studies of dye-doped polymer films

Homogenous (poly (6,6′-(2-hydroxy-5-(phenyldiazenyl)-1,3-phenylene) bis (methylene) bis (2-ethylphenol)) (PHPP) film has been properly deposited using the spin coating method. In this paper, the polymer film was characterized by Atomic Force Microscopy (AFM), histogram characterization, intensity distribution of the film, and scan of the microscopic surface. The bandgap $$E_{\text{g}}$$ value was investigated by different ways. The Nonlinear Refractive Index (NLR) and Nonlinear Absorption (NLA) of the Flu-doped polymer, PbPc-doped polymer, and CuPc-doped polymer are determined using the Z-scan technique. Experimentation was conducted via a 532 nm diode laser and 3.554 KW/cm2 incident laser intensity. The effects of concentration of dye-doped PHPP films on the behavior optical limiting have been discussed. Additionally, multiple induced self-diffraction patterns generated in dye-doped PHPP polymer films using the same diode laser were observed through the study. The thermooptic coefficient (dn/dT) of the Flu-doped polymer, PbPc-doped polymer, and CuPc-doped polymer has been formed equivalent to − 0.409 × 10−5 K−1, − 0.88 × 10−5 K−1, and − 1.133 × 10−5 K−1, respectively.

Gold nano-urchins for plasmonic enhancement of random lasing in a dye-doped polymer

We report our results on a plasmonic random laser with three-dimensional (3D) gold nano-urchins as scatterers distributed in rhodamine 6G dye-doped polymer film. The performance of anisotropic urchin scatterers is first studied using electromagnetic simulations for absorption/scattering cross-section and local field enhancement. This is compared to gold nanospheres of similar size. The simulation results indicate a two-fold local field enhancement, a higher scattering cross-section, and a low absorption cross-section in the 400 nm–570 nm spectral region of interest for nano-urchins. The effective scattering mean free path for urchins is calculated to be 90 µm less than nanoparticles. This suggests nano-urchins are efficient scatterers over conventional nanospheres for random lasing. A random laser is then experimentally demonstrated using gold nano-urchin scatterers, and incoherent lasing emission is observed for very low urchin number density of order ∼108 cm−3. A three-fold increase in scatterer concentration is shown to reduce the threshold energy from 0.8 mJ to 0.28 mJ per pulse. This is accompanied by a linewidth decrease from the rhodamine 6G emission bandwidth of 58 nm to up to 3 nm. Along with particle scattering, the waveguiding mechanism is identified to provide additional feedback for the lasing. This has been validated by the angular measurement of emission and by using spot pumping scheme. With low gold nano-urchin concentration, being incoherent and in film form, this plasmonic random laser could be an economical solution for speckle-free imaging applications.

Polymer-Coated Hollow Fiber Optofluidic Laser for Refractive Index Sensing

Optofluidic laser is an emerging method for biochemical sensing. The topic on, which kind of structure is the best to integrate the laser resonator and microfluidic channel, is worth to be explored. Here, we report a hollow optical fiber optofluidic laser based on a dye-doped polymer film. This fiber microstructure is a promising candidate that serves both as a laser microresonator and a compact microfluidic channel. The refractive index of the polymer film is higher than silica so that the whispering gallery mode can be supported. The coating process is explored in detail. The laser spectra and threshold properties of the HOF microlaser are investigated. The dye-doped polymer film can be controlled to be as thin as 1.6 μm and a threshold of below 1 μJ/mm2 can be reached. Thanks to the strong light-liquid interaction enabled by the polymer coating on the inner interface of HOF, sensitive refractive index detection is demonstrated by monitoring the laser wavelength shift, which has the potential for wavelength division multiplexing. This laser sensor is promising for label-free biochemical detection.

Investigation of spectroscopic and thermo-mechanical behaviors of different phenanthroimidazole-azo dyes in solvent and polymer medium

The aim of this study is the investigation of the interaction between dyes and polymers which have different polarities. Dye doped polymer films have larger application areas because of the fact that dye is more stable when doped in polymer compared to solvent medium. However, dye dispersion in the polymer medium affects both the spectroscopic and mechanical properties of the polymer. The polymer-dye interaction must be high for a good dispersion,. In this study, polypropylene with apolar character and polymethylmethacrylate with polar groups were chosen as a solid phase to examine polymer-dye interactions. The photophysical properties of phenanthroimidazole-azo compounds synthesized previously were examined with UV–visible and fluorescence spectroscopy techniques in tetrahydrofuran and two polymer media. Also, photostability tests of azo dyes in THF and polymer films were performed. Surface roughness characterizations of polymer films were carried out with AFM. Additionally, the viscoelastic behaviors of the polymethylmethacrylate and polypropylene films under sinusoidal vibrations at different temperatures were studied by dynamic mechanical analysis technique.

Synthesis and Characterization of Dye-Doped Polymer Films for Non-linear Optical Applications

Synthesis and Characterization of Dye-Doped Polymer Films for Non-linear Optical Applications

Tunable plasmonic random laser based on a wedge shaped resonator

Abstract A wedge-shaped random laser consisting of disordered silver nanowires embedded in a dye-doped polymer film was fabricated by using a press-coating method. The optical feedback was supported by the scattering effect and the localized plasmonic enhancement of silver nanowires in the wedge-shaped resonator, facilitating a coherent random lasing action. The lasing wavelength can be tuned continuously from 561 nm to 578 nm by simply changing the excitation position along the thickness gradient of the wedge shaped resonator, which was attributed to the reabsorption of R6G. Besides, as the thickness increased, more lasing modes were observed. These properties can be used in wavelength tuning and mode selecting. The design of wedge shaped resonator provides simple approach of a multi-wavelength random lasing emission, promoting the improvement of lighting source.

A study on optical limiting properties of Eosin-Y and Eriochrome Black-T dye-doped poly (vinyl alcohol) composite film

A poly (vinyl alcohol) PVA/Eriochrome Black-T (EBT) dye, and PVA/Eosin-Y (EY) dye composite film was prepared using a solution casting process. The dye-doped composite polymer films were characterized by UV–vis spectroscopy. An optical band gap (Eg) of pure PVA reduced from 4.22 eV to 2.80 eV for PVA/EBT film and 2.14 eV for PVA/EY film respectively. This result indicates the occurrence of inter-molecular hydrogen bonding between the –OH functional group in PVA chains and sulfonate (EBT) and carboxyl group (EY) in dye molecules, respectively. Moreover, the experimental result of PVA/EBT and PVA/EY composite film showed the excellent properties of a large scale cut-off filter in the ultraviolet and visible range region.