Visible Light Emission Research Articles

Investigation of Photoluminescence and Annealing Effect of PS Layers

N-type porous silicon (PS) layers and thermally oxidized PS layers have been characterized by various measuring techniques such as photoluminescence (PL), Raman spectroscopy, IR, HRSEM and transmittance measurements. The top surface of PS layer shows a stronger photoluminescence peak than its bottom part, and this is ascribed to the difference in number of fine silicon particles of 2~3 nm in diameter. Observed characteristics of PL spectra are explained in terms of microstructures in the n-type PS layers. Common features for both p-type and n-type PS layers are as follows: the parts which can emit visible photoluminescence are not amorphous, but crystalline, and such parts are composed of nanocrystallites of several nm’s whose orientations are slightly different from Si substrate, and such fine silicon particles absorb much hydrogen atoms near the surfaces. Light emission is strongly dependent on such fine silicon particles. Photoluminescence is due to charge carrier confinement in such three dimensional structure (sponge-like structure). Characteristics of visible light emission from ntype PS can be explained in terms of modification of band structure accompanied by bandgap widening and localized levels in bandstructure. It is also shown that hydrogen and oxygen atoms existing on residual silicon parts play an important role on emission stability.

Photoluminescence property adjustment of ZnO quantum dots synthesized via sol–gel method

Quantum dots (QDs) are zero dimensional nanomaterials and promising materials in the fluorescent label, LED display, metal ions sensor, catalysis and so on. ZnO QDs are one kind of ideal QDs, due to their non-poisonous, easy prepared, plentiful, economical properties. The visible light emission colour and quantum yields of ZnO QDs is determined by their band structures and defect structures. Main method to adjust the optical performance is controlling the particle sizes, band structures and defect structures by adjusting synthesis method and doping. Therefore, it is important to investigate the mechanisms of particle growth and defects variation. In this paper, a sol–gel method were employed to synthesize stable ZnO QDs used in fluorescence labeling and solar cells. Effects of reactants concentration, material ratio and reaction time on particle sizes and defects structures of ZnO QDs synthesized by sol–gel method were studied. Changing the synthesis process of ZnO QDs can adjust their photoluminescence defects structures and particle sizes. The ZnO QDs synthesized with c(Zn2+) = 0.1 mol L− 1, n(OH−):n(Zn2+) = 2:1, for 1.5 h reaction showed the highest photoluminescence quantum yields (40%) with green emission under 359 nm UV-light excitation. The visible light emission of the ZnO QDs synthesized with c(Zn2+) = 0.025 mol L− 1, n(OH−):n(Zn2+) = 3:1, for 1.5 h min is blue-green colour excited under 337 nm.

Evolution of Structural and Optical Properties of ZnO Nanorods Grown on Vacuum Annealed Seed Crystallites.

In this study, the ambient condition for the as-coated seed layer (SL) annealing at 350 °C is varied from air or nitrogen to vacuum to examine the evolution of structural and optical properties of ZnO nanorods (NRs). The NR crystals of high surface density (~240 rods/μm2) and aspect ratio (~20.3) show greatly enhanced (002) degree of orientation and crystalline quality, when grown on the SLs annealed in vacuum, compared to those annealed in air or nitrogen ambient. This is due to the vacuum-annealed SL crystals of a highly preferred orientation toward (002) and large grain sizes. X-ray photoelectron spectroscopy also reveals that the highest O/Zn atomic ratio of 0.89 is obtained in the case of vacuum-annealed SL crystals, which is due to the effective desorption of hydroxyl groups and other contaminants adsorbed on the surface formed during aqueous solution-based growth process. Near band edge emission (ultra violet range of 360–400 nm) of the vacuum-annealed SLs is also enhanced by 44% and 33% as compared to those annealed in air and nitrogen ambient, respectively, in photoluminescence with significant suppression of visible light emission associated with deep level transition. Due to this improvement of SL optical crystalline quality, the NR crystals grown on the vacuum-annealed SLs produce ~3 times higher ultra violet emission intensity than the other samples. In summary, it is shown that the ZnO NRs preferentially grow along the wurtzite c-axis direction, thereby producing the high crystalline quality of nanostructures when they grow on the vacuum-annealed SLs of high crystalline quality with minimized impurities and excellent preferred orientation. The ZnO nanostructures of high crystalline quality achieved in this study can be utilized for a wide range of potential device applications such as laser diodes, light-emitting diodes, piezoelectric transducers and generators, gas sensors, and ultraviolet detectors.

Compression and heating of a laser-produced plasma using single and double induction coils

The results of an experiment on magnetohydrodynamic compression and heating of a laser-produced plasma in vacuum are described. The plasma was produced by laser ablation of copper at 2 J cm−2. A pulsed magnetic field, with an amplitude of 0.3 T and a period of 2.2 µs, was produced by a three-turn spiral induction coil placed 10 mm above the ablation spot. Time-resolved imaging revealed that the magnetic field had a strong influence on both the plasma between the coil and the target, and on the plasma which flows through the aperture in the coil. The plasma flow through the coil aperture is strongly pinched due to the Lorentz interaction of the induced current and the coil magnetic field. Heating of the plasma is evidenced by strong enhancement of the overall visible light emission and the appearance of Cu+ line emission. Magnetic compression and plasma heating were also observed in a setup using two induction coils separated by 10 mm. This technique could be used to enhance the sensitivity of laser-induced breakdown spectroscopy, increase the ion yield in laser plasma ion sources, or control the ablation plume expansion in pulsed laser deposition.

Fabrication of UV photodetector using needle-shaped ZnO nanostructure arrays prepared on porous silicon substrate by a facile low-temperature method

Arrays of vertically well-aligned ZnO nanoneedles were successfully grown on seeded porous silicon substrate through electric field-assisted aqueous solution method. The surface morphologies of needle-like ZnO nanostructures were studied using field-emission scanning electron microscopy and transmission electron microscopy. Meanwhile, structural and morphological analyses displayed wurtzite nanostructures with strong c-axis oriented crystal structure and preferred (0 0 2) orientation. The photoluminescence spectra revealed intensive and sharp ultraviolet light emission at 382 nm with high intensity and low broad visible light emission in a 500–700 nm wavelength range confirming high optical quality of the formed ZnO nanoneedles. The fabrication and characterization of a metal–semiconductor–metal ultraviolet photodetector based on ZnO nanoneedles were studied. Upon exposure to 325 nm light (1.6 mW/cm2) at 3 V bias voltage, the device displayed 1.98 A/W responsivity and 10.48 photosensitivity. Furthermore, the response and the recovery times measured under these conditions were 86 and 83 ms, respectively.

Mathematical Model for Laboratory System of Bioluminescent Whole-Cell Biosensor with Optical Element

The fiber-optic biosensor with encapsuled bioreporters use a special optical element (OE) from pure silica with an active layer contents bioluminescent bioreporters was developed as a real in-situ detector for on-line measurement in remote localities. The active layer of biosensor contents bioluminescent bioreporters – genetic modified cells, which are sensitive to its surrounding environment-immobilized in silica matrix on the end of OE. Bioreporters are able to react by emission of visible light (≈500 nm) – bioluminiscence reaction (BL) – in presence of specific analyte. The genetic modified bacterial stain Pseudomonas putida TVA8 was chosen as biorecognition part of biosensor producing BL in the presence of benzene, toluene, ethylbenzene and xylens (BTEX). Very low level of BL signal was detected by high-sensitive photon-counter. The sensitivity of biosensor depends on a value of detected BL and it can be very low. The signal is also affected by number of cells (light sources) immobilized into the active layer and transmission through OE. Mathematical model of OE shape was developed based on geometric optics. The numerical model is built around the MATLAB scripting language. Simulation of ray transmission was calculated for OE with different shape.

Visible light emission from surface of nickel bombarded by slow Xeq+ (4 q 20) ion

Bombarded by slow highly charged ion (SHCI), particles including ions and atoms of metal are excited and ejected from the sample. Optical emission can be observed for the radiative de-excitation of some excited atomic particles. The important information about particle ejection and incident ion neutralization, as well as the nature, the kinetic energy, and the number of the sputtered excited particles can be obtained by studying the optical emission process. The optical emission from the the collisions between slow (V~0.38 VBohr) highly charged Xeq+ (4 q 20) ions and high purity Ni (99.995%) surface is studied. The experiment is carried out at the 320 kV for multi-discipline research with HCIs in the Institute of Modern Physics, Chinese Academy of Sciences. The spectral lines are analyzed by using an Sp-2558 spectrometer equipped with a pattern of 1200 groves/mm blazed at 500 nm and an R955 photomultiplier tube at the exit slit. The target beam current corresponding to the dwell time is recorded, which can be translated into the incident ion current. Based on the formula of Y=N/(t/Ceq), the spectral line intensity is normalized. The normalized spectrum can be obtained from the interaction of 0.38VBohr Xe20+ ions with Ni surface in a wavelength range of 400-510 nm. The species at excited state can be identified by comparing the wavelengths of spectral lines with those in the standard spectroscopic table. Most of the observed spectral lines are identified as being from the electron transitions of Ni I 3d9(2D)4p-3d9(2D5/2)4d, Ni I 3d8(3F)4s4p(3P)-3d84s(4F)5s and Ni Ⅱ 3p63d9-3p63d8(3P)4s, as well as Xe I 5p5(2P3/2)6s-5p5(2P3/2)8p, Xe Ⅱ 5p4(3P2)6p-5p4(3P2)6d and Xe Ⅲ 5s25p3(2D)6s-5s25p3(2D)6p. Compared with the single charged ion, some neutralized incident ions yield Xe I, Xe Ⅱ, Xe Ⅲ spectral lines. The photon yields of spectral lines, such as Xe Ⅱ 410.419, Xe Ⅲ 430.444, Xe Ⅱ 434.200, Xe Ⅱ 486.254, Ni I 498.245, Ni I 501.697, Ni I 503.502, Ni I 505.061 and Ni I 508.293 nm, are presented each as a function of charge state of incident ion. The results show that the photon yield increases with the increase of the charge state, which is consistent with the potential energy of the incident ion. The potential energy is the driving force for photon emission of excited Ni atom. The neutralization of Xeq+ is in good agreement with that indicated by the classical over-the-barrier model.

Brazilian Bioluminescent Beetles: Reflections on Catching Glimpses of Light in the Atlantic Forest and Cerrado.

Bioluminescence - visible and cold light emission by living organisms - is a worldwide phenomenon, reported in terrestrial and marine environments since ancient times. Light emission from microorganisms, fungi, plants and animals may have arisen as an evolutionary response against oxygen toxicity and was appropriated for sexual attraction, predation, aposematism, and camouflage. Light emission results from the oxidation of a substrate, luciferin, by molecular oxygen, catalyzed by a luciferase, producing oxyluciferin in the excited singlet state, which decays to the ground state by fluorescence emission. Brazilian Atlantic forests and Cerrados are rich in luminescent beetles, which produce the same luciferin but slightly mutated luciferases, which result in distinct color emissions from green to red depending on the species. This review focuses on chemical and biological aspects of Brazilian luminescent beetles (Coleoptera) belonging to the Lampyridae (fireflies), Elateridae (click-beetles), and Phengodidae (railroad-worms) families. The ATP-dependent mechanism of bioluminescence, the role of luciferase tuning the color of light emission, the "luminous termite mounds" in Central Brazil, the cooperative roles of luciferase and superoxide dismutase against oxygen toxicity, and the hypothesis on the evolutionary origin of luciferases are highlighted. Finally, we point out analytical uses of beetle bioluminescence for biological, clinical, environmental, and industrial samples.

Bioluminescent In Vivo Imaging of Orthotopic Glioblastoma Xenografts in Mice.

Orthotopic rodent xenografts are an essential tool for studying glioblastoma in vivo. Xenograft growth as a function of time can only be monitored by noninvasive imaging. This chapter describes in detail how to assess xenograft size and growth using bioluminescent imaging with IVIS (in vivo imaging system). This form of imaging (a) can be performed without the help of a trained technician, (b) is a very quick procedure, allowing simultaneous imaging of up to five animals at a total experimental duration of 15 min, and (c) is cheaper than the alternatives (small animal MRI or CT). This technique relies on the stable expression of luciferase by the xenografted GBM cells. Luciferin, the substrate of luciferase, which is injected into host mice intraperitoneally, distributes throughout the mouse body and crosses the blood brain barrier. Luciferase expressed by the xenografted cells uses this substrate in a catalytic reaction, leading to the emission of visible light, which is detected by the CCD camera of the IVIS imaging system. The intensity of this emitted light correlates to the size of a given xenograft and allows comparisons of xenograft size across different animals, as well as within the same animal across different time points.

Influence of Deposition Conditions on the Characteristics of Luminescent Silicon Carbonitride Thin Films

The influence of the substrate temperature and argon gas flow on the compositional, structural, optical, and light emission properties of amorphous hydrogenated silicon carbonitride (a-SiCxNy:H) thin films were studied. Thin films were fabricated using electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR PECVD) at a range of substrate temperatures from 120 to 170°C (corresponding to deposition temperatures of 300 to 450°C) in a mixture of SiH4, N2, and CH4 precursors. Variable angle spectroscopic ellipsometer (VASE), elastic recoil detection (ERD), and Rutherford backscattering spectrometry (RBS) verified optical bandgap widening, layer densification, and an increase of the refractive index at higher substrate temperatures. The microstructure of a-SiCxNy:Hz thin films was determined by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy. The substrate temperature strongly affected the binding state of all atoms, and in particular, carbon atoms attached to silicon and nitrogen, as well as hydrogen-terminated bonds. We correlated the films' microstructural changes to a higher species' mobility arriving on the growin layer at higher temperatures. Photoluminescence (PL) measurements showed that the total intensity of visible light emission increased. A systematic blueshift of the centroid of the wide PL peak was observed following the increase of optical gap.

Formation of Long-Lived Color Centers for Broadband Visible Light Emission in Low-Dimensional Layered Perovskites.

We investigate the origin of the broadband visible emission in layered hybrid lead-halide perovskites and its connection with structural and photophysical properties. We study ⟨001⟩ oriented thin films of hexylammonium (HA) lead iodide, (C6H16N)2PbI4, and dodecylammonium (DA) lead iodide, (C12H28N)2PbI4, by combining first-principles simulations with time-resolved photoluminescence, steady-state absorption and X-ray diffraction measurements on cooling from 300 to 4 K. Ultrafast transient absorption and photoluminescence measurements are used to track the formation and recombination of emissive states. In addition to the excitonic photoluminescence near the absorption edge, we find a red-shifted, broadband (full-width at half-maximum of about 0.4 eV), emission band below 200 K, similar to emission from ⟨110⟩ oriented bromide 2D perovskites at room temperature. The lifetime of this sub-band-gap emission exceeds that of the excitonic transition by orders of magnitude. We use X-ray diffraction measurements to study the changes in crystal lattice with temperature. We report changes in the octahedral tilt and lattice spacing in both materials, together with a phase change around 200 K in DA2PbI4. DFT simulations of the HA2PbI4 crystal structure indicate that the low-energy emission is due to interstitial iodide and related Frenkel defects. Our results demonstrate that white-light emission is not limited to ⟨110⟩ oriented bromide 2D perovskites but a general property of this class of system, and highlight the importance of defect control for the formation of low-energy emissive sites, which can provide a pathway to design tailored white-light emitters.

Study on electrical structure and magneto-optical properties of W-doped ZnO

For W-doping amounts ranging from 0.0417 to 0.0833, experimental UV–visible absorption spectra blue shift and red shift results have been reported in the literatures. However, there is few literature reported research on magnetic mechanism. To solve this problem, this study investigates the disagreement about blue shift and red shift results and research on magnetic mechanism. The band structures, density of states, absorption spectra and magnetism have been investigated using first-principles planewave ultrasoft pseudopotential method based on the density functional theory. The calculated results showed that increased W-doping amounts first increase the volumes, and then reduce the volumes, decrease the formation energies, and stabilize the doped system. The band gaps become narrower and the absorption spectrum exhibits a significant red shift in UV and visible light emission. Moreover, the covalent bond vertical to c-axis strengthens, and the ionic bond parallel to c-axis weakens. Increased W-doping amounts decrease the magnetism of doped system. The magnetism of doped system originates from the electron exchange among W-5d, O-2p and Zn-3d orbitals of the W-doped ZnO. In W double-doped system, the ferromagnetic Curie temperature can be above room temperature when the doped system has a longer W-W distance.

Wavelength Conversion Enhancement Achieved by Using Resonance in an Array of Nanocylinders

Upconversion (UC) materials are promising for harvesting visual light. However, the efficiency of UC processes is very low when applied to practical devices. Therefore, we propose an array of UC nanocylinders on a gold substrate and induce electric dipole (ED) and magnetic dipole (MD) resonances to increase the UC process efficiency by increasing light-matter interactions via the nanostructures. The nanocylinders not only increase the absorption of infrared light with a wavelength of 980 nm but also enhance the emission of visible light with a wavelength of 660 nm through surface plasmons and electric dipole resonances. The absorbance of the UC material can be enhanced by coupling with the surface plasmons and coupling with the MDs of each nanocylinder. On the other hand, the emission of visible light can be largely enhanced by increasing the spontaneous emission rate of the Purcell effect in electric dipole resonances and tailoring the output efficiency of the emitted light. In summary, we obtained an absorption enhancement of ×7.3, an average effective upward emission enhancement of ×21, and an improved total UC process of the proposed nanocylinder of ×155.

A Nanobionic Light-Emitting Plant.

The engineering of living plants for visible light emission and sustainable illumination is compelling because plants possess independent energy generation and storage mechanisms and autonomous self-repair. Herein, we demonstrate a plant nanobionic approach that enables exceptional luminosity and lifetime utilizing four chemically interacting nanoparticles, including firefly luciferase conjugated silica (SNP-Luc), d-luciferin releasing poly(lactic-co-glycolic acid) (PLGA-LH2), coenzyme A functionalized chitosan (CS-CoA) and semiconductor nanocrystal phosphors for longer wavelength modulation. An in vitro kinetic model incorporating the release rates of the nanoparticles is developed to maximize the chemiluminescent lifetimes to exceed 21.5 h. In watercress (Nasturtium officinale) and other species, the nanoparticles circumvent limitations such as luciferin toxicity above 400 μM and colocalization of enzymatic reactions near high adenosine triphosphate (ATP) production. Pressurized bath infusion of nanoparticles (PBIN) is introduced to deliver a mixture of nanoparticles to the entire living plant, well described using a nanofluidic mathematical model. We rationally design nanoparticle size and charge to control localization within distinct tissues compartments with 10 nm nanoparticles localizing within the leaf mesophyll and stomata guard cells, and those larger than 100 nm segregated in the leaf mesophyll. The results are mature watercress plants that emit greater than 1.44 × 1012 photons/sec or 50% of 1 μW commercial luminescent diodes and modulate "off" and "on" states by chemical addition of dehydroluciferin and coenzyme A, respectively. We show that CdSe nanocrystals can shift the chemiluminescent emission to 760 nm enabling near-infrared (nIR) signaling. These results advance the viability of nanobionic plants as self-powered photonics, direct and indirect light sources.

Rattling of Oxygen Ions in a Sub-Nanometer-Sized Cage Converts Terahertz Radiation to Visible Light.

A simple and robust approach to visualization of continuous wave terahertz (CW-THz) light would open up opportunities to couple physical phenomena that occur at fundamentally different energy scales. Here we demonstrate how nanoscale cages of Ca12Al14O33 crystal enable conversion of CW-THz radiation to visible light. These crystallographic cages are partially occupied with weakly bonded oxygen ions and give rise to a narrow conduction band that can be populated with localized, yet mobile electrons. CW-THz light excites a nearly stand-alone rattling motion of the encaged oxygen species, which promotes electron transfer from them to the neighboring vacant cages. When the power of CW-THz light reaches tens of watts, the coupling between forced rattling in the confined space, electronic excitation and ionization of oxygen species, and corresponding recombination processes result in emission of bright visible light.

Triboluminescence flashes from high-speed ruptures in carbon nanotube Macro-Yarns

During tensile tests of carbon nanotube (CNT) macrostructures (ribbons, ropes and tows) under dynamic strain rates (1000 s–1), we recorded temporally sporadic, spatially localized visible light emissions (“flashes”) of less than 1.5 µs duration. The flashes occurred at the fracture sites and were, depending on the sample morphology, either distributed randomly over time (for tows) or occurred all at once over larger areas of several pixels (for ribbons). In situ thermal camera measurements, as well as ex situ analysis by electron microscopy reveal a hierarchical mechanism of overall heating over the whole sample length during straining, and localized heating around the fracture surfaces. Temperatures around the fracture tip were calculated to be of 1800 K in average. We propose that the flashes are caused by charge separation due to CNT bond fracture and gas discharge of the surrounding gases. Triboluminescence, known for larger sugar crystals, has not been observed for carbon nanotubes previously. It results from the yarn-like morphology, the ultra-high strength and thermal conductivity of our CNT fibers, which at high strain rates concentrate the strain at CNT level and lead to CNT fracture, rather than bundle sliding.

Highly Enhanced Emission of Visible Light from Core–Dual‐Shell‐Type Hybridized Nanoparticles

AbstractCore–dual‐shell‐type hybridized nanoparticles (NPs) having Au‐core/dye‐doped silica inner shell/Au outer shell are successfully fabricated by developing a biphasic process that is a kind of so‐called “one‐pot” method. The resulting hybridized NPs exhibit evidently about 20‐fold enhancement of fluorescence intensity, increase in fluorescence quantum yield, and decrease in fluorescence lifetime. These effects depend on the metal nanostructure being optimized, compared with the reference hybridized NPs with neither a Au‐core nor a Au outer shell, due to the gap‐mode effect induced by localized surface plasmon resonance in the core–dual‐shell‐type MIM‐like nanostructure. More detailed elucidation concerning the enhancement mechanism will provide the possibility of photonic device application, for example as a high‐performance point light source, nanolaser, or sensor for bioimaging in the visible region in the near future.

Largely enhanced near band edge emission of ultrathin zinc oxide nanowire/gold nanoparticles composites by surface plasmon resonance

Ultrathin zinc oxide nanowires with diameter less than 50nm were synthesized by polyethyleneimine assisted solution method. Zinc oxide nanowire near band edge emission was enhanced obviously by gold nanoparticles coating, and a max 26 times enhancement was realized. The defects caused visible light emission was also quenched to noise level when gold was deposited more than 10s. The large near band edge emission enhancement was caused by surface plasmon resonance mediated luminescent energy transfer, which absorbed the visible light energy and transferred to the near band edge emission. The large surface to volume ratio enhanced the coupling strength between gold nanoparticles and ultrathin zinc oxide nanowires. This research provide a method to improve the luminescent efficiency of zinc oxide nanowires.

Studies on the functional properties of free-standing polyvinyl alcohol/(CoFe2O4/CoFe2) composite films

In this report, the functional properties of polyvinyl alcohol/(CoFe2O4/CoFe2) composite films fabricated through solution casting method were reported. Highly-magnetic CoFe2O4/CoFe2 composite was obtained through thermal reduction process and the effect of CoFe2O4/CoFe2 loading on the magnetic, optical, thermal and mechanical properties of PVA composite films was evaluated. At room temperature, the optical transparency was decreased from 68 to 38% but the magnetization was enhanced to 42.37emu/g by an increase of CoFe2O4/CoFe2 to 15wt%. Also, the visible-light emission intensity near 400–521nm was influenced. We demonstrated that the wt% of CoFe2O4/CoFe2 and -OH intramolecular interactions between the polymer-chains played an important role in controlling the functional properties of composites. The performance analysis and comparison of the results revealed that PVA-composite film fabricated with 5wt% of CoFe2O4/CoFe2 displayed significant magnetization, luminescence intensity, and high tensile-strength compared to others and was found to be a promising candidate for smart devices.

Review—Light Emission from Thin Film Solar Cell Materials: An Emerging Infrared and Visible Light Emitter

In the last decade, there have been extensive studies on fabrication and physics of thin-film solar cell materials and devices. Many high-efficiency solar cell devices have been developed, and the knowledge gained in these studies can be used advantageously to produce bright light-emitting devices. In this review, we summarize recent luminescence spectroscopic studies on new solar-cell materials and discuss their photocarrier dynamics with respect to efficient light emission.