UV Luminescence Research Articles

Simplified approach for modeling ZnO luminescence dependence on excitation level with and without surface plasmon resonance

The research of excitation level dependence of ZnO UV and visible luminescence was carried out. To describe the behavior of radiation intensity there was proposed the model based on the set of rate equations. The simultaneous equations include the set of parameters which characterizes processes participating in luminescence. The values of parameters were estimated using experimental dependence of luminescence intensity on excitation level. Proposed model can give the way for optimization of samples structure to maximize the effect of surface plasmon resonance influence on luminescence intensity.

Enhanced UV Emission From Silver/ZnO And Gold/ZnO Core-Shell Nanoparticles: Photoluminescence, Radioluminescence, And Optically Stimulated Luminescence.

The optical properties of core-shell nanoparticles consisting of a ZnO shell grown on Ag and Au nanoparticle cores by a solution method have been investigated. Both the ZnO/Ag and ZnO/Au particles exhibit strongly enhanced near-band-edge UV emission from the ZnO when excited at 325 nm. Furthermore, the UV intensity increases with the metal nanoparticle concentration, with 60-fold and 17-fold enhancements for the ZnO/Ag and ZnO/Au, core-shell nanoparticles respectively. Accompanying the increase in UV emission, there is a corresponding decrease in the broad band defect emission with nanoparticle concentration. Nonetheless, the broad band luminescence increases with laser power. The results are consistent with enhanced exciton emission in the ZnO shells due to coupling with surface plasmon resonance of the metal nanoparticles. Luminescence measurements during and after exposure to X-rays also exhibit enhanced UV luminescence. These observations suggest that metal nanoparticles may be suitable for enhancing optical detection of ionizing radiation.

2-(Alkylamino)-3-aryl-6,7-dihydrobenzofuran-4(5H)-ones: Improved Synthesis and their Photophysical Properties.

Furans are an important class of compounds and exhibit a diverse range of activities and properties. As such, improved synthetic access to furans is an important research goal. In the present report, a solvent- and catalyst-free reaction between 5,5-dimethyl-1,3-cyclohexanedione (dimedone), an aryl aldehyde and an isocyanide under microwave irradiation is presented. This method is significantly improved from previously described protocols in terms of applicability of wide ranging aryl aldehydes, better yields, shorter reaction times, facile work up and essentially no need of column chromatography. The photophysical properties of this series of compounds were studied for their possible applicability in the field of metal ion sensors. In solution, two compounds, 2-(cyclohexylamino)-3-(1H-indol-3-yl)-6,6-dimethyl-6,7-dihydrobenzofuran-4(5H)-one (1 i) and 2-(tert-butylamino)-3-(1H-indol-3-yl)-6,6-dimethyl-6,7-dihydrobenzofuran-4(5H)-one (1 j), underwent an observable color change from yellow to colorless in the presence of aluminum(III) ions. Further studies to investigate the UV absorption and luminescence behavior of these compounds revealed their utility as “naked-eye sensors” for aluminum detection.

Ultraviolet luminescence of commercial cerium-doped yttrium aluminum garnet phosphors

The origin of the intense UV luminescence of commercial YAG: Ce phosphors has been established based on the data of X-ray diffraction, optical spectroscopy and scanning electron microscopy.

UV and yellow luminescence in phosphorus doped crystalline and glassy silicon dioxide

Luminescence of phosphorus doped crystalline α-quartz and phosphosilicate glass with content 3P2O5·7SiO2 was studied. Water and OH groups are found by IR spectra in these materials. The spectrum of luminescence contains many bands in the range 1.5–5.5eV. The luminescence bands in UV range at 4.5–5eV are similar in those materials. Decay duration in exponential approximation manifests a time constant about 37ns. Also a component in µs range was detected. PL band of µs component is shifted to low energy with respect to that of ~37ns component. This shift is about 0.6eV. It is explained as singlet–triplet splitting of excited state. Below 14K increase of luminescence kinetics duration in µs range was observed and it was ascribed to zero magnetic field splitting of triplet excited state of the center.Yellow–red luminescence was induced by irradiation in phosphorus doped crystalline α-quartz, phosphosilicate glasses. The yellow luminescence contains two bands at 600 and 740nm. Their decay is similar under 193nm laser and may be fitted with the first order fractal kinetics or stretched exponent. Thermally stimulated luminescence contains only band at 600nm. The 248nm laser excites luminescence at 740nm according to intra center process with decay time constant about 4ms at 9K.Both type of luminescence UV and yellow were ascribed to different defects containing phosphorus.P-doped α-quartz sample heated at 550°C become opalescent. IR spectra related to water and OH groups are changed. Photoluminescence intensity of all three bands, UV (250nm), yellow (600nm) and red (740nm) strongly diminished and disappeared after heating to 660°C. Radiation induced red luminescence of non-bridging oxygen luminescence center (NBO) appeared in crystal after heat treatment. We had observed a crystalline version of this center (Skuja et al., Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms. 2012; 286: pp. 159–168). Effect of heat treatment explained as sedimentation of phosphorus in some state. Keeping of treated sample at 450–500°C leads to partial revival of ability to create yellow luminescence center under irradiation.

Continuous sensing of hydrogen peroxide and glucose via quenching of the UV and visible luminescence of ZnO nanoparticles

We report on an indirect optical method for the determination of glucose via the detection of hydrogen peroxide (H2O2) that is generated during the glucose oxidase (GOx) catalyzed oxidation of glucose. It is based on the finding that the ultraviolet (~374 nm) and visible (~525 nm) photoluminescence of pristine zinc oxide (ZnO) nanoparticles strongly depends on the concentration of H2O2 in water solution. Photoluminescence is quenched by up to 90 % at a 100 mM level of H2O2. The sensor constructed by immobilizing GOx on ZnO nanoparticles enabled glucose to be continuously monitored in the 10 mM to 130 mM concentration range, and the limit of detection is 10 mM. This enzymatic sensing scheme is supposed to be applicable to monitoring glucose in the food, beverage and fermentation industries. It has a wide scope in that it may be extended to numerous other substrate or enzyme activity assays based on the formation of H2O2, and of assays based on the consumption of H2O2 by peroxidases.

New Layered Metal Phosphonates Based on Functionalized Phosphonic Acids

Hydrothermal reactions of ZnII or MnII ion with 1-C10H7-CH2N(CH2COOH)(CH2PO3H2)(H3L1), 3-HOOC-C6H4-CH2N(CH2COOH)(CH2PO3H2)(H4L2), and 4-HOOC-C6H4-CH2N(CH2COOH)(CH2PO3H2)(H4L3) afforded six new layered metal phosphonates, namely, [Zn3(HL1)3]·3H2O (1), [Zn(HL1)]·CH3COOH (2), [Zn(H2L2)] (3), [Mn(H3L2)2] (4), [Mn(H3L3)2] (5), and [Zn(H2L3)]·H2O (6). Compounds 1–6 are characterized by single-crystal X-ray diffraction (XRD), powder XRD, IR spectroscopy, elemental analysis, and thermogravimetric analysis (TGA). In compounds 1–3 and 6, each [ZnO4] tetrahedron shares three corners with three neighboring [PCO3] tetrahedra to generate a Zn–O–P layer, which consists of eight and four member rings (MRs). While in compounds 4 and 5, each [MnO6] octahedron shares four corners with neighboring four [PCO3] tetrahedra into a Mn–O–P layer containing eight MRs. The organic groups hang on two sides of a Zn–O–P or Mn–O–P layer to form two-dimensional (2D) sandwich-like frameworks of compounds 1–6. TGA and powder XRD reveal that 2D frameworks of compounds 2, 3, 4, and 6 are thermally stable up to 180, 250, 230, and 250 °C under an air atmosphere, respectively. It is interesting that compounds 1–2 display bright UV luminescence, which can be irreversibly quenched by UV irradiation. In addition, the blue luminescence of solid 6 can be transformed into blue-green emission by simply a heating treatment.

Synthesis of semiconductor oxide nanosheets, nanotetrapods and nanoplane-suite like grown on metal foil using different method

ZnO production nanostructure using different method: first method, electrochemical deposition on Zn foil using 0.3 M zinc sulfate heptahydrate (ZnSO4·7H2O) and sulfuric acid aqueous solution at a current density of 30 and 35 mA/cm2 for deposition time 40 min at room temperature and second method, Zn foils were thermally oxidized in a conventional tube furnace at a temperature equal range of 700–900 °C in air for 5 h or less in static air to prepared semiconductor nanomaterials ZnO nanorods, nanotetrapods and nanoplane. The XRD diffraction of higher intensity peaks at (101) and (002) miller indices for two methods can be recognized to a hexagonal wurtzite structure unit cell. Surface morphology images with different magnifications which clearly shows that the whole Zn foil and rod substrate obtained ZnO nanosheets, nanotetrapods, nanorods and growth nanoplanes were also found. The length of these nanotetrapods and nanorods lies in the equal range of 1–1.5 µm with an average diameter of 80 nm. It was well known that ZnO nano crystal exhibited two emission peaks. One was located at about 365 nm wavelength (UV luminescence band), and the other peak position at 475 nm wavelength (green luminescence band).

Habit-modifying additives and their morphological consequences on photoluminescence and glucose sensing properties of ZnO nanostructures, grown via aqueous chemical synthesis

Generally, the anisotropic shape of inorganic nano-crystal can be influenced by one or more of different parameters i.e. kinetic energy barrier, temperature, time, and the nature of the capping molecules. Here, different surfactants acting as capping molecules were used to assist the aqueous chemical growth of zinc oxide (ZnO) nanostructures on Au coated glass substrates. The morphology, crystal quality and the photoluminescence (PL) properties of the ZnO nanostructures were investigated. The PL properties of the prepared ZnO nanostructures at room temperature showed a dominant UV luminescence peak, while the “green–yellow” emissions were essentially suppressed. Moreover, the ZnO nanostructures were investigated for the development of a glucose biosensor. An adsorbed molecule has direct contribution on the glucose oxidase/ZnO/Au sensing properties. We show that the performance of a ZnO-based biosensor can be improved by tailoring the properties of the ZnO–biomolecule interface through engineering of the morphology, effective surface area, and adsorption capability.

Structural and optical studies of nickel-cobalt-ferric oxides nanocomposite

In this study single salts of nickel oxide, cobalt oxide, ferric oxide and the nanocomposite of nickel-cobalt-ferric oxide was prepared by the well-known co-precipitation method. The samples were annealed at different temperatures and were characterized using SEM, EDAX, TGA, FTIR, XRD, UV and Photo luminescence (PL). UV analysis showed that the nanocomposite can be suitably tuned to a wide band gap material. The Photo Luminescence analysis showed that the nanocomposite can be used as light emitters in visible region.

Plasma luminescence from femtosecond filaments in air: evidence for impact excitation with circularly polarized light pulses.

Filaments produced in air by intense femtosecond laser pulses emit UV luminescence from excited N(2) and N(2)(+) molecules. We report on a strong dependence at high intensities (I≥1.4×10(14) W/cm(2)) of this luminescence with the polarization state of the incident laser pulses. We attribute this effect to the onset of new impact excitation channels from energetic electrons produced with circularly polarized laser pulses above a threshold laser intensity.

Slanted n-ZnO nanorod arrays/p-GaN light-emitting diodes with strong ultraviolet emissions

Both of oblique angle deposition and conventional deposition techniques were used by a RF sputtering system to grow the slanted (β = 32°) and planar (β = 0°) n-ZnO films on p-GaN, respectively. These two kinds of n-ZnO/p-GaN heterojunctions were then fabricated the light-emitting diodes (LEDs). The electrical and optical properties of these two kinds of LEDs were investigated systematically. The results show that the slanted n-ZnO/p-GaN LEDs have a lower turn-on voltage and less leakage current than that of planar n-ZnO/p-GaN LEDs. Moreover, different from the planar n-ZnO/p-GaN LEDs which emitting colors changes with injection current, the slanted n-ZnO/p-GaN LEDs retains UV emissions (385-400 nm) under the entire range of injection currents we applied. The dominant UV luminescence of slanted n-ZnO/p-GaN LEDs is attributed to the ZnO near band edge transitions, indicating the high quality of slanted ZnO films and exhibiting the essential property dedicated to nano-sized heterojunctions. Hence, we have demonstrated that the slanted n-ZnO/p-GaN LEDs fabricated by oblique angle deposition have better performance than the planar n-ZnO/p-GaN LEDs fabricated by convention deposition means.

Characterization and optoelectronics investigations of mixed donor ligand directed semiconductor ZnO nanoparticles

The optical properties of mixed donor ligand directed semiconductor ZnO nanoparticles are evaluated and imine linked receptor is used as capping agents. The ZnO nanoparticles are prepared using precipitation method. The ligand is synthesized using condensation reaction between 2-aminothiophenol and 2-thiophenecarboxaldehyde. The formation of ligand is confirmed with spectroscopic methods including NMR and mass spectroscopy. However, UV–Vis absorption, photoluminescence, X-ray diffraction, energy dispersive X-ray and FTIR spectroscopy techniques are used for characterization of the ligand coated ZnO nanoparticles. The capping with ligand resulted in the successful amendment of the surface of ZnO nanoparticles, as it particularly reduced the defects related visible emission known as green luminescence and hence resulted in improvement in the UV luminescence. The UV–Vis absorption spectra also showed blue shift in the UV region for the ligand based ZnO nanoparticles due to the effect of quantum confinement. The composite (ZnO-ligands) stability is confirmed theoretically with Density Functional Theory.

Role of micro-strain and defects on band-gap, fluorescence in near white light emitting Sr doped ZnO nanorods

We report tunable band gap (red shift in band gap) of ZnO driven by the Sr doping. It is observed that enhanced white light like luminescence from Sr doped ZnO nanorods. Raman studies have carried out to get insight of phonon related vibrational properties. Dopant induced local vibrational mode appeared after Sr incorporation has been identified from Raman studies. Photoluminescence studies show that doped ZnO nanorods fluorescence covers the entire visible region apart from the characteristic exciton related UV luminescence. Crystallite size variation, defects formation, and relaxation of micro strain after doping shows a strong dependence on the luminescence of the prepared samples. The increase in luminescence with increasing dopant concentration is attributed to doping induced changes in crystallinity, micro strain, and defects formation in the samples.

Enhanced UV luminescence from InAlN quantum well structures using two temperature growth

InAlN/AlGaN multiple quantum wells (MQWs) emitting between 300 and 350nm have been prepared by metalorganic chemical vapor deposition on planar AlN templates. To obtain strong room temperature luminescence from InAlN QWs a two temperature approach was required. The intensity decayed weakly as the temperature was increased to 300K, with ratios IPL(300K)/IPL(T)max up to 70%. This high apparent internal quantum efficiency is attributed to the exceptionally strong carrier localization in this material, which is also manifested by a high Stokes shift (0.52eV) of the luminescence. Based on these results InAlN is proposed as a robust alternative to AlGaN for ultraviolet emitting devices.

Deep-level emission in ZnO nanowires and bulk crystals: Excitation-intensity dependence versus crystalline quality

The excitation-intensity dependence of the excitonic near-band-edge emission (NBE) and deep-level related emission (DLE) bands in ZnO nanowires and bulk crystals is studied, which show distinctly different power laws. The behavior can be well explained with a rate-equation model taking into account deep donor and acceptor levels with certain capture cross sections for electrons from the conduction band and different radiative lifetimes. In addition, a further crucial ingredient of this model is the background n-type doping concentration inherent in almost all ZnO single crystals. The interplay of the deep defects and the background free-electron concentration in the conduction band at room temperature reproduces the experimental results well over a wide range of excitation intensities (almost five orders of magnitude). The results demonstrate that for many ZnO bulk samples and nanostructures, the relative intensity R = INBE/IDLE can be adjusted over a wide range by varying the excitation intensity, thus, showing that R should not be taken as an indicator for the crystalline quality of ZnO samples unless absolute photoluminescence intensities under calibrated excitation conditions are compared. On the other hand, the results establish an all-optical technique to determine the relative doping levels in different ZnO samples by measuring the excitation-intensity dependence of the UV and visible luminescence bands.

Luminescent investigations of Li6Lu(BO3)3:Tb3+, Dy3+ phosphors

In our novel work we report the luminescence properties of Terbium (Tb3+) and Dysprosium (Dy3+) ions in Li6Lu(BO3)3 (lithium lutetium borate) phosphors with its specific and productive use in various luminescent display systems. We have synthesized Tb3+ and Dy3+ doped Li6Lu(BO3)3 phosphors by the solid state reaction method. Concentration based optimization of activators is attained i.e. 2mol% for Tb3+ and 5mol% for Dy3+. XRD (X-ray diffraction) and FE-SEM (Field emission-scanning electron microscopy) were used to analyze the overall morphologies, crystalline structures and the grain sizes of the prepared phosphors. Moreover, the grain size of 20μm is confirmed via Scherrer’s formula. In order to characterize the luminescence properties of the synthesized phosphors, we measured its X-ray induced luminescence, proton induced luminescence and UV induced photoluminescence. Under UV luminescence Dy3+ doped phosphor, it displayed seven obvious peaks corresponding to transitions from 6H15/2 (f9) ground state to higher energy state of 4f9 whereas, UV-emission spectrum of Li6Lu(BO3)3:Tb3+ phosphor has shown five major transitions with each peak consists of several smaller lines, confirming the complicated transition (5Dj→7Fj) behavior of Tb3+. The light yield calculated for Li6Lu(BO3)3:Tb3+ is 75% that of (Y,Gd)2O3:Eu3+ phosphor which is a well known commercially available material for PDP (Plasma Display Panel). It is observed that due to the presence of Lutetium, the synthesized phosphor has high effective atomic number (Zeff=52) as well as high molecular weight (M.Wt=393g/mol) which makes lithium lutetium borate one of the promising candidates for X-ray imaging in medical field. Furthermore, the presence of 6Li and 10B could make Li6Lu(BO3)3 phosphor as a potential neutron detector.

UV luminescence of commercial YAG:Ce phosphors

It is established that the emission spectrum of synthesized YAG:Ce phosphors excited at a wave-length of 290 nm contains, in addition to a yellow-green band, two intense UV bands with maxima at ∼320 and ∼360 nm. The observed separation of these emission bands is related to the partial absorption of radiation by Ce3+ ions. Nonreabsorbed UV luminescence spectra have been measured and characterized.

Growth and Optical Properties of ZnO/MgO Core/Shell Nanoparticles

Octylamine capped ZnO/MgO core/shell nanoparticles with different shell thickness were grown by thermolysis of metal organic precursors. The as-grown nanoparticles and subsequently annealed ones were characterized by X-ray diffractometer, transmission electron microscope, high resolution transmission electron microscope, and Micro Raman spectroscope. ZnMgO alloys and amorphous MgO formed on the surface of the ZnO cores in the as-grown core/shell nanoparticles. MgO crystalline formed after annealing at 430 degrees C for 2 h. ZnO cores have strong UV emission and weak visible emission. Growth of the shells could enhance the intensity of ZnO UV emission by 4.2 times. The thinner shells promote the core luminescence more efficiently than thicker ones. After being annealed in air at high temperatures, UV luminescence intensities of both pure core and core/shell nanoparticles degraded, while the luminescence of the core/shell nanoparticles with thinner shells degraded more obviously.

Zinc oxide composites prepared by in situ process: UV barrier and luminescence properties

This work describes the preparation of composite films of zinc oxide (ZnO) embedded in a covalent copolymer substrate of triethylene glycol dimethacrylate and poly(ethyleneglycol) diacrylate. The ZnO-embedded copolymer was produced in situ from the reaction of a doped precursor zinc bis(2-thenoyltrifluoroacetonate) [Zn(TTA)2] in a hydrazine hydrate reflux system.The in situ production of ZnO nanoparticles with excellent optical qualities embedded in the copolymer substrate was demonstrated to be an effective approach to fabricating new advanced materials for use as a protective barrier that blocks UV rays.