Full Visible Region Research Articles

Broadband emission and flat optical gain glass containing Ag aggregates for tunable laser

AbstractSpectroscopic properties of Sm3+‐doped borate glass with silver aggregates were investigated, and it was found that the glass presented broad excitation and emission band covering violet‐infrared region. Furthermore, the optical gain coefficients at various wavelengths were measured via an amplified spontaneous emission technique, it was confirmed that the glass displayed flat net optical gain coefficient in almost full visible region. In addition, the fluorescent temperature quenching of the glass was examined, and it was seen that about 50% of room temperature emission intensity was kept when the sample was heated up to 325°C.

Photocatalytic properties of attached BiOCl-(0 0 1) nanosheets onto AgBr colloidal spheres toward MO and RhB degradation under an LED irradiation

BiOCl-(0 0 1) nanosheets were attached on the highly dispersed AgBr colloidal spheres to form AgBr/BiOCl-(0 0 1) composite by a simple one-pot method. The composite were characterized by SEM, TEM, DRS and PL spectroscopy. The results showed that AgBr/BiOCl-(0 0 1) exhibited an enhancement of photoabsorption in the full visible region, a lower recombination of photogenerated electrons and holes and a longer lifetime of charge carriers. AgBr/BiOCl-(0 0 1) afforded excellent photocatalytic performance toward methyl orange (MO) and Rhodamine B (RhB) degradation under an LED irradiation.

A Transparent, Highly Stretchable, Autonomous Self-Healing Poly(dimethyl siloxane) Elastomer.

An innovative self-healing polydimethylsiloxane (PDMS) elastomer, namely, PDMS-TFB, is reported by incorporating the reversibly dynamic imine bond as the self-healing points into the PDMS networks. The PDMS-TFB elastomer features good optical transmittance (80%) in full visible light region, high stretchability (≈700%), and excellent autonomous self-healing ability at room temperature. Surprisingly, the self-healing behavior can take place in water and even at a temperature as low as -20 °C in air, showing a promising outlook for broader applications. As a proof-of-concept, this study demonstrates the use of the PDMS-TFB elastomer for preparing anticorrosion coating and adhesive layer, and also the use of such an elastomer to be the platform for fabricating the flexible interconnector and chemical sensor. Remarkably, no significant difference is observed between the pristine and healed samples. Taking full advantage of these unique properties, it is anticipated that such a PDMS-TFB elastomer shows wide applications in the fields of materials science, electronics, biology, optics, etc.

Luminescent manganese-doped CsPbCl3 perovskite quantum dots

Nanocrystalline cesium lead halide perovskites (CsPbX3, X = Cl, Br, and I) form an exciting new class of semiconductor materials showing quantum confinement. The emission color can be tuned over the full visible spectral region making them promising for light‒emitting applications. Further control over the optical and magnetic properties of quantum dots (QDs) can be achieved through doping of transition metal (TM) ions such as Mn2+ or Co2+. Here we demonstrate how, following QD synthesis in the presence of a Mn‒precursor, dropwise addition of silicon tetrachloride (SiCl4) to the QDs in toluene results in the formation of Mn‒doped CsPbCl3 QDs showing bright orange Mn2+ emission around 600 nm. Evidence for successful doping is provided by excitation spectra of the Mn2+ emission, with all features of the CsPbCl3 QD absorption spectrum and a decrease of the 410 nm excitonic emission life time with increasing Mn‒concentration, giving evidence for enhanced exciton to Mn2+ energy transfer. As a doping mechanism we propose a combination of surface etching and reconstruction and diffusion doping. The presently reported approach provides a promising avenue for doping TM ions into perovskites QDs enabling a wider control over optical and magnetic properties for this new class of QDs.

Invisibility cloak with image projection capability

Investigations of invisibility cloaks have been led by rigorous theories and such cloak structures, in general, require extreme material parameters. Consequently, it is challenging to realize them, particularly in the full visible region. Due to the insensitivity of human eyes to the polarization and phase of light, cloaking a large object in the full visible region has been recently realized by a simplified theory. Here, we experimentally demonstrate a device concept where a large object can be concealed in a cloak structure and at the same time any images can be projected through it by utilizing a distinctively different approach; the cloaking via one polarization and the image projection via the other orthogonal polarization. Our device structure consists of commercially available optical components such as polarizers and mirrors, and therefore, provides a significant further step towards practical application scenarios such as transparent devices and see-through displays.

Highly Emissive Whole Rainbow Fluorophores Consisting of 1,4-Bis(2-phenylethynyl)benzene Core Skeleton: Design, Synthesis, and Light-Emitting Characteristics.

To create the whole-rainbow-fluorophores (WRF) having the small Δλem (the difference of λem between a given fluorophore and nearest neighboring fluorophore having the same core skeleton) values (<20 nm) in full visible region (λem: 400-650 nm), the high log ε (>4.5), and the high Φf (>0.6), we investigated molecular design, synthesis, and light-emitting characteristics of the π-conjugated molecules (D/A-BPBs) consisting of 1,4-bis(phenylethynyl)benzene (BPB) modified by donor groups (OMe, SMe, NMe2, and NPh2) and an acceptor group (CN). As a result, synthesized 20 D/A-BPBs (1a-5d) were found to be the desired WRF. To get the intense red fluorophore (Φf > 0.7, λem > 610 nm), we synthesized new compounds (5e-5i) and elucidated their photophysical properties in CHCl3 solution. As a result, 5h, in which a 4-cyanophenyl group is introduced to the para-position of two benzene rings in the terminal NPh2 group of 5d, was found to be the desired intense red fluorophore (log ε = 4.56, Φf = 0.76, λem = 611 nm). The intramolecular charge-transfer nature of the S1 state of WRF (1a-5d) was elucidated by the positive linear relationship between optical transition energy (νem) from the S1 state to the S0 state and HOMO(D)-LUMO(A) difference, and the molecular orbitals calculated with the DFT method. It is demonstrated that our concept (Φf = 1/(exp(-Aπ) + 1)) connected with the relationship between Φf and magnitude (Aπ) of π conjugation length in the S1 state can be applied to WRF (1a-5d). It is suggested that the prediction of Φf from a structural model can be achieved by the equation Φf = 1/(exp(-((ν̃a - ν̃f)(1/2) × a(3/2)) + 1), where ν̃a and ν̃f are the wavenumber (cm(-1)) of absorption and fluorescence peaks, respectively, and a is the calculated molecular radius. From the viewpoint of application of WRF to various functional materials, the light-emitting characteristics of 1a-5i in doped polymer films were examined. It was demonstrated that 1a-5i dispersed in two kinds of polymer film (PST and PMMA) emit light at the whole visible region and have the small Δλem values (<20 nm) and the high Φf values (>0.6). Therefore, the present D/A-BPBs can be said to be the desired WRF even in the doped polymer film.

A Novel Method To Prepare B/N Codoped Anatase TiO2

B/N codoping is an effective way to narrow the band gap of TiO2 to enhance the photocatalytic activity. However, the traditional doping method using ammonia as N source is still unsatisfactory because of its safety risks and high cost. In this work, a benign and cost-effective method has been developed to prepare the B/N codoped TiO2. First, we use TiB2 as the raw material to prepare B-doped TiO2 via a hydrothermal method followed by heat treatment. Then the B/N codoped TiO2 can be simply produced by annealing the mixture of the as-prepared B-doped TiO2 and urea. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results show that the samples present anatase structure and spherical morphology. X-ray photoelectron spectroscopy (XPS) analysis indicates that B and N atoms exist not only on the surface but also in the bulk. Moreover, the content of N atoms decreases with the depth in the sample while Ti3+ content gradually increases with the depth. The UV–vis absorption spectrum shows an extension of light absorption into the full visible region. More importantly, the B/N codoped TiO2 exhibits promoted photocatalytic activity under both UV and visible light than the B-doped TiO2.

Pentacene-Based Photodetector in Visible Region With Vertical Field-Effect Transistor Configuration

Electrical and detection performances of pentacene-based photodetector with vertical field-effect transistor (VFET) configuration were investigated in full visible region. By comparing with planar FET-based photodetector ITO/ PMMA(520 nm)/Pentacene(35 nm)/Au, the VFET-based photodetector ITO/Pentacene(80 nm)/Al(15 nm)/Pentacene(80 nm)/ Au exhibits better performance. At an output current of ca. -8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-7</sup> A, the threshold voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> ) was -0.61 V for the VFET-based device at V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</sub> = -2 V, but V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> = -7.1 V for the planar one at V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</sub> = -12 V. The performance of photodetectors depends on incident monochromatic light, and the VFET-based photodetector showed a maximum responsivity of 188 mA/W and a photosensitivity peak of 588 under 350-nm light, which were ~11.75 and 2.83 times as that of the planar one, respectively. Therefore, it provides an easy way to get the VFET-based organic photodetectors in full visible region with excellent photosensitivity, responsivity, and light selectivity, showing its promising application in all-organic image sensors working at low voltages.

Spectroscopic Study on Eu3+ Doped Borate Glasses Containing Ag Nanoparticles and Ag Aggregates.

Transparent Eu(3+)-doped borate glasses containing Ag nanoparticles and Ag aggregates with composition (40 - x) CaO-59.5B2O3-0.5Eu2O3-xAgNO3 were prepared by a simple one-step melt-quenching technique. The X-ray diffraction (XRD) patterns of the glasses reveal amorphous structural properties and no diffraction peaks belonging to metal Ag particles. Ag particles and Ag aggregates were observed from the absorption spectra. Effective energy transfers from the Ag aggregates to the Eu3+ ions were observed in the excitation spectra from monitoring the intrinsic emission of Eu3+x .5D0 --> 7F2. The glasses with higher Ag content can be effectively excited by light in a wide wavelength region, indicating that these glasses have potential application in the solid state lighting driven by semiconductor light emitting diodes (LEDs). The emission spectra of the samples with higher Ag contents exhibit plenteous spectral components covering the full visible region from violet to red, thus indicating that these glass materials possess an excellent and tunable color rendering index. The color coordinates for all the glass samples were calculated by using the intensity-corrected emission spectra and the standard data issued by the CIE (Commission International de l' Eclairage) in 1931. It was found that the color coordinates for most samples with higher Ag contents fall into the white region in the color space.

Atmospheric Self-induction Synthesis and Enhanced Visible Light Photocatalytic Performance of Fe3+ Doped Ag-ZnO Mesocrystals

Ag-loaded ZnO mesocrystals with Fe3+ doped (FAZ) can be quantity-produced through an atmospheric self-induction synthesis method. This synthesis method avoids the use of a high-pressure instrument for the synthesis of mesocrystal catalysts. Compared with traditional Ag-ZnO catalysts, the threshold wavelength of 1FAZ mesocrystals was shifted to the full visible light region and the absorbance of catalyst in the visible region increased to more than 300%. The content of iron ion was found to be significant to the photocatalytic efficiency of FAZ mesocrystals. The experimental results demonstrated that the most optimal molar ratio of Fe3+ to Zn atoms was 1%, and the photocatalytic activity of 1FAZ mesocrystals was increased by 145% compared with Ag-ZnO obtained under visible light. A feasible water purification system with a continuous photodegradation reactor using FAZ mesocrystals was manufactured to utilize solar light as the energy to drive the running of the water purification system.

Influence of the Dielectric PMMA Layer on the Detectivity of Pentacene-Based Photodetector With Field-Effect Transistor Configuration in Visible Region

In this paper, the influence of dielectric polymethylmethacrylate (PMMA) layer on the detectivity of pentacene-based photodetectors with field-effect transistor (FET) configuration were investigated in a visible region. By changing the thickness of the PMMA layer, from 230 nm to 520 nm and 800 nm, electrical parameters, such as the capacitance, “on/off” current ratio, and carrier mobility, of the pentacene-based photodetector decrease with increasing the thickness of the PMMA layer, which influences its detectivity directly. The photosensitivity and responsivity of the FET-based pentacene photodetector with 520-nm PMMA varied with incident monochromatic light from 350 nm to 750 nm, and it showed a maximum responsivity of 149 mA/W with a photosensitivity peak of 1.7 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> at 450 nm, which is of the same order as that of the standard Si-based photodetector. Therefore, it is an applicable way to get such kind of FET-based full-organic photodetectors in a full visible region with excellent photosensitivity, responsivity, and selectivity.

Growth, Structure and Optical Properties of Silicon Nanowires Formed by Metal-Assisted Chemical Etching

Silicon nanowires (SiNWs) formed by metal(silver)-assisted chemical etching of lowly boron-doped (100)-oriented single crystalline silicon substrates in hydrofluoric acid solutions are investigated by means of the electron microscopy and optical spectroscopy (absorption and reflection measurements, photoluminescence spectroscopy and imaging). The growth rate of SiNWs is found to depend nonlinearly on the time of etching. The formed SiNW arrays demonstrate a strong decrease of the total reflectance below 1% in the full visible and near infrared region between 300 and 1000 nm and the samples show the similar optical properties as “Black Silicon,” which can be used as antireflection coating in photovoltaic applications. The prepared SiNWs exhibit efficient photoluminescence in the spectral region of 600–1000 nm and it is explained by the radiative recombination of excitons confined within nanostructured sidewall of SiNWs. The excitons luminescence is also observed in aqueous suspensions of SiNWs, whose application in bio-imaging is demonstrated in vitro.

Thickness, Surface Morphology, and Optical Properties of Porphyrin Multilayer Thin Films Assembled on Si(100) Using Copper(I)-Catalyzed Azide−Alkyne Cycloaddition

We report the structure, optical properties and surface morphology of Si(100) supported molecular multilayers resulting from a layer-by-layer (LbL) fabrication method utilizing copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC), also known as "click" chemistry. Molecular based multilayer films comprised of 5,10,15,20-tetra(4-ethynylphenyl)porphyrinzinc(II) (1) and either 1,3,5-tris(azidomethyl)benzene (2) or 4,4'-diazido-2,2'-stilbenedisulfonic acid disodium salt (3) as a linker layer, displayed linear growth properties up to 19 bilayers. With a high degree of linearity, specular X-ray reflectivity (XRR) measurements yield an average thickness of 1.87 nm/bilayer for multilayers of 1 and 2 and 2.41 nm/bilayer for multilayers of 1 and 3. Surface roughnesses as determined by XRR data fitting were found to increase with the number of layers and generally were around 12% of the film thickness. Tapping mode AFM measurements confirm the continuous nature of the thin films with roughness values slightly larger than those determined from XRR. Spectroscopic ellipsometry measurements utilizing a Cauchy model mirror the XRR data for multilayer growth but with a slightly higher thickness per bilayer. Modeling of the ellipsometric data over the full visible region using an oscillator model produces an absorption profile closely resembling that of a multilayer grown on silica glass. Comparing intramolecular distances from DFT modeling with experimental film thicknesses, the average molecular growth angles were estimated between 40° and 70° with respect to the substrate surface depending on the bonding configuration.

White polymeric light-emitting diodes with high color rendering index

The efficient white polymeric light-emitting diodes based on a white emissive polymer doped with a red phosphorescent dopant were fabricated by spin-coating method. The emission spectrum of the device is broadened to cover the full visible region by doping the red phosphorescent dye and thereby realizes white emission with high color-rendering index (CRI). By controlling the contents of the doped electron-transporting 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole and the red phosphorescent dopant, a luminous efficiency as high as 5.3cd∕A and a power efficiency of 3lm∕W were obtained with a CRI of 92.

Luminescent Quantum Dot-Bioconjugates in Immunoassays, FRET, Biosensing, and Imaging Applications

Colloidal semiconductor nanocrystals (quantum dots, QDs), such as CdSe-ZnS core-shell, are highly luminescent and stable inorganic fluorophores that represent a promising alternative to organic dyes for a variety of biotechnological applications. They show size-tunable narrow photoluminescence spectra spanning nearly the full visible region of the optical spectrum for QDs with CdSe cores. We have developed several approaches to conjugate either one type or a combination of biologically distinct proteins to CdSe-ZnS core-shell QDs rendered water-soluble by surface ligation with dihydrolipoic acid (DHLA) groups. QD-protein conjugates prepared using these approaches were found to exhibit high specificity and stability in immunoassays and in Förster resonance energy transfer (FRET) assays as well as in prototype QD bioconjugate sensors. Tunable QD emission over a wide range of wavelengths permitted effective tuning of the degree of energy overlap between the QD donor and an acceptor dye, allowing control over the rate of FRET. Additionally, we have used these QD-bioconjugates in live cell labeling. These hybrid bioinorganic conjugates represent a promising tool for use in many biotechnological applications.

Broadband achromatic phase retarder by subwavelength grating

A broadband achromatic phase retarder in the full visible region (wavelength λ∈[400,800 nm] ) using subwavelength grating (SWG) is designed, fabricated and tested. For the first time, it is experimentally proved that the achromatic phase retarder in the full visible region can be realized by SWG. An improved method combining enumeration with optimization for designing the achromatic phase retarder with rectangular and sinusoidal SWG is presented. Rigorous coupled wave theory (RCWT) is applied to calculate the diffraction performances. Examples show that the designed phase retarders perform broadband achromatic phase retardation successfully. Compared with the previous methods, the improved method shows the advantages of good versatility and flexibility.

Enhancement and stability of luminescence in thin-film light-emitting devices based on heterostructure of ladder-type poly ( p-phenylene)

The microcavity thin-film light-emitting devices were fabricated, which use two organic material layers, ladder-type poly( p-phenylene) (LPPP) and (8-hydroxyquimalin) aluminum (Alq 3), sandwiched between two injecting electrodes. With the ribbon-type macromolecule structure, the LPPP exhibits higher thermal and chemical stability than its linear analog. The broad photoluminescence (PL) and electroluminescence (EL) emission means LPPP can be tuned over the full visible region. LPPP was the emitting layer and the cavity transporter. Alq 3 was the electron transporter. The investigation on EL and PL properties of the devices indicated that the microcavity effect has been achieved by adjusting the thickness of organic light-emitting layers. The experimental results showed that directional emission and net emission were efficiently enhanced. The heavily born-doped diamond electrode in place of the metal electrode aluminum can also greatly improve the stability of the devices.

Temperature Dependence of Charge-Transfer Fluorescence from Extended and U-shaped Donor−Bridge−Acceptor Systems in Glass-Forming Solvents

The behavior is reported of three fluorescent D−bridge−A systems that display a fascinating temperature dependence in glass forming solvents over the temperature range between 77 and 293 K. In two of these systems, a rigid, saturated alkane bridge maintains an extended conformation, and as a result, the charge-transfer (CT) state is of giant dipolar nature. This causes the position of the CT fluorescence to be an extremely sensitive probe for the reorientation polarization of the surrounding medium. As a result, the thermochromism of the continuous CT fluorescence maximum in 2-methyltetrahydrofuran (MTHF) covers the full visible region. In the higher temperature domain (above ca. 145 K), this thermochromism can be quantitatively described via the Lippert−Mataga relation. At lower temperatures, solvent relaxation slows down sufficiently to detect exceptionally large dynamic Stokes shifts of the fluorescence maximum on time scales up to ≥40 ns. The third D−bridge−A system studied features a U-shaped ground state conformation. Remarkably, this system displays a significant thermochromic shift over a narrow temperature region around 175 K in the nonpolar methylcyclohexane (MCH) in which the other systems display only very minor thermochromism. In this U-shaped system therefore, one monitors the temperature dependence of an internal reorganization instead of a medium relaxation. Extensive ab initio calculations indicate that this internal reorganization must be related to an electrostatically driven conformational collapse of the U-shaped system in the CT state.