Ultraviolet Emission Properties Research Articles

Testing AGN outflow and accretion models with SDSS quasar demographics

AbstractOne commonly-invoked launching mechanism for AGN outflows is radiation line driving. This mechanism depends closely on the SED of the ionizing continuum, and so is inherently linked to the structure of the accretion flow. Theories of radiation line-driven winds therefore provide testable predictions as a function of black hole (BH) mass and accretion rate. In this work we confront these predictions using the ultraviolet emission line properties of 190,000 quasars from SDSS DR17. We quantify how the shape of CIV 1549Å and the equivalent width (EW) of HeII 1640Å depend on the BH mass and Eddington ratio inferred from MgII 2800Å. The blueshift of the CIV emission line is commonly interpreted as a tracer of quasar outflows, while the HeII EW traces the strength of the 10-100 eV continuum which photo-ionizes the ultraviolet emission line regions. Above L/LEdd > 0.2, there is a strong mass dependence in both CIV blueshift and HeII EW. Large CIV blueshifts are observed only in regions with both high BH mass and high accretion rate, consistent with predictions for radiation line driven winds. The observed trends in HeII and 2 keV X-ray strength are broadly consistent with theoretical models of AGN SEDs, where the ionizing SED depends on the accretion disc temperature and the strength of the soft excess. At L/LEdd < 0.2, we find a dramatic switch in behaviour: the ultraviolet emission properties show much weaker trends, and no longer agree with SED models, hinting at changes in the structure of the broad line region. Overall the observed emission line properties are generally consistent with the radiation line driving scenario, where quasar winds are governed by the SED, which itself results from the accretion flow and hence depends on both the SMBH mass and accretion rate.

Testing AGN outflow and accretion models with C iv and He ii emission line demographics in z ≈ 2 quasars

ABSTRACT Using ≈190 000 spectra from the 17th data release of the Sloan Digital Sky Survey (SDSS), we investigate the ultraviolet emission line properties in z ≈ 2 quasars. Specifically, we quantify how the shape of C iv λ1549 and the equivalent width (EW) of He ii λ1640 depend on the black hole mass and Eddington ratio inferred from Mg ii λ2800. Above L/LEdd ≳ 0.2, there is a strong mass dependence in both C iv blueshift and He ii EW. Large C iv blueshifts are observed only in regions with both high mass and high accretion rate. Including X-ray measurements for a subsample of 5000 objects, we interpret our observations in the context of AGN accretion and outflow mechanisms. The observed trends in He ii and 2 keV strength are broadly consistent with theoretical qsosed models of AGN spectral energy distributions (SEDs) for low spin black holes, where the ionizing SED depends on the accretion disc temperature and the strength of the soft excess. High spin models are not consistent with observations, suggesting SDSS quasars at z ≈ 2 may in general have low spins. We find a dramatic switch in behaviour at L/LEdd ≲ 0.1: the ultraviolet emission properties show much weaker trends, and no longer agree with qsosed predictions, hinting at changes in the structure of the broad line region. Overall, the observed emission line trends are generally consistent with predictions for radiation line driving where quasar outflows are governed by the SED, which itself results from the accretion flow and hence depends on both the SMBH mass and accretion rate.

Vacuum Ultraviolet Emission Properties of Rocksalt‐Structured MgZnO Microcrystals Prepared on Quartz Glass Substrates

Rocksalt‐structured (RS) MgZnO crystals are grown on quartz glass substrates by the mist chemical vapor deposition (mist CVD) method. Cathodoluminescence (CL) emission properties are comparatively studied with those for the RS‐MgZnO epitaxial film prepared on MgO substrate to explore their potential for vacuum ultraviolet (VUV) emitter. In the experiment, the newly developed VUV spectroscopy system is employed, where the CL and optical transmittance spectra are simultaneously measured. Growths of RS‐MgZnO on quartz glass substrate indicate formation of microcrystals (MCs). The MCs dominantly exhibit a near‐band‐edge VUV emission at 6.20 eV (200 nm) at 6 K and 6.07 eV (204 nm) at 300 K. Moreover, the MCs show a noticeable higher energy shoulder at 6.6 eV (188 nm) at 6 K and 6.4 eV (194 nm) at 300 K. The results ensure potential of RS‐MgZnO crystals for active element in VUV emitter regardless of the substrate material.

D-π-D type fluorescent compounds based on dehydroabietic acid triarylamine: Synthesis, photophysical properties and application as hole-transporting materials in perovskite solar cells

D-π-D hole-transporting materials have the potential to be excellent dopant-free hole-transporting materials (HTMs) for perovskite solar cells (PSCs) because of their tunable energy levels, high charge mobility, good solubility, and excellent film-forming properties. In this paper, two series of D-π-D type compounds, Series 1 (2TPA-CZ1~2TPA-CZ3) and Series 2 (2DTPA-CZ1~2DTPA-CZ3), were synthesized by linking a carbazole derivative (as a π-bridge) to triaryamine or dehydroabietic acid triarylamine groups (the donor groups) via C–C coupling reactions. The optical, electrochemical, thermal, and photovoltaic properties in PSCs of these compounds were fully investigated. The two series of compounds exhibit good ultraviolet absorption, fluorescence emission, and electrochemical and thermal properties. In addition, their highest occupied molecular orbital levels and energy gaps make them suitable for use as hole-transporting materials in PSCs. Among the PSCs developed, Device 1, based on 2TPA-CZ1, showed the best performance, with a power conversion efficiency (PCE) of 12.27%, a open circuit voltage (VOC) of 1.13 V, a short-circuit photocurrent density (JSC) of 15.10 mA cm−2, and a fill factor (FF) of 71.61%, which is comparable to that of a device based on the conventional hole-transporting material Spiro-OMeTAD. While the PCE of Devices 4–6 was lower than the PCE of Devices 1–3, Devices 4–6 exhibit better stability. This may be due to the higher Tg and better film-forming properties of compounds formed using the dehydroabietic acid skeleton. In additional, the introduction of alkyl groups on the carbazole moiety decreased the efficiency of the PSC devices. These results demonstrate that the 2TPA-CZ1 compounds are promising HTMs for PSC applications.

Three series π-extended fluorescent compounds based on dehydroabietic acid triarylamine moiety: Syhthesis, photophysical properties and hole transporting properties

Fluorescent compounds based on a dehydroabietic acid skeleton with favorable photophysical properties show promise for use as the hole-transporting layer in organic light-emitting diodes (OLEDs). In this work, we report the synthesis of three series of compounds (15 in total), series 1 (1a–1e), series 2 (2a–2e), and series 3 (3a–3e), by linking polycyclic aromatic hydrocarbons (PAHs) to dehydroabietic acid-based triaryamine moiety through C-C coupling reactions. The three series of compounds exhibited ultraviolet absorption, fluorescence emission, electrochemical, and thermal properties, as well as highest occupied molecular orbital levels and energy gaps that made them suitable for use as hole-transporting materials. OLEDs with 1a, 2a, or 3d as a hole-transporting layer showed better performance in terms of maximum brightness, turn-on voltage, maximum of external quantum efficiency, maximum luminous efficiency and power efficiency than that of a comparable device based on a conventional hole-transporting material. In particular, the device with 1a exhibited the most promising performance, with a high maximum brightness of 21445 cd/m2, low turn-on voltage of 2.8 V, maximum of external quantum efficiency of 1.62%, maximum luminance efficiency of 4.9 cd/A, and maximum power efficiency 3.7lm/W. The present work highlights the potential of π-extended compounds based on dehydroabietic acid for use in luminescent material applications.

IRIS Observations of Magnetic Interactions in the Solar Atmosphere between Preexisting and Emerging Magnetic Fields. II. UV Emission Properties

Abstract Multiwavelength ultraviolet (UV) observations by the Interface Region Imaging Spectrograph satellite in active region NOAA 12529 have recently pointed out the presence of long-lasting brightenings, akin to UV bursts, and simultaneous plasma ejections occurring in the upper chromosphere and transition region during secondary flux emergence. These signatures have been interpreted as evidence of small-scale, recurrent magnetic reconnection episodes between the emerging flux region (EFR) and the preexisting plage field. Here we characterize the UV emission of these strong, intermittent brightenings and study the surge activity above the chromospheric arch filament system (AFS) overlying the EFR. We analyze the surges and the cospatial brightenings observed at different wavelengths. We find an asymmetry in the emission between the blue and red wings of the Si iv λ1402 Å and Mg ii k λ2796.3 lines, which clearly outlines the dynamics of the structures above the AFS that form during the small-scale eruptive phenomena. We also detect a correlation between the Doppler velocity and skewness of the Si iv λλ1394 and 1402 line profiles in the UV burst pixels. Finally, we show that genuine emission in the Fe xii λ1349.4 line is cospatial to the Si iv brightenings. This definitely reveals a pure coronal counterpart to the reconnection event.

Crystal structure, spectral, thermal, optical, laser damage, NLO study and quantum chemical calculations of a noncentrosymmetric crystal N, N′-diphenylguanidinium p-toluenesulphonate

A novel NLO active crystal diphenylguanidinium p-toluenesulphonate (DPGPTS) single crystals were grown successfully by slow-evaporation solution growth technique and the structure was confirmed by single crystal X-ray diffraction technique. The crystal was subjected to FT-IR and NMR spectroscopic techniques in order to elucidate functional group and the arrangement of carbons and hydrogens. High transparency (70%) and low energy band gap of 4.25 eV in DPGPTS was confirmed through UV-NIR study. The Laser damage threshold of DPGPTS was measured using Nd:YAG (λ = 1064 nm) laser. Thermal stability of the crystal was studied through TG/DTA thermogram. Green, violet and ultra violet emission properties were analysed by photoluminescence. Low HOMO-LUMO energy gap of 4.75 eV measured in theoretical calculations proves the eventual charge transfer taking place within the system. Frontier Molecular Orbital analysis clearly depicts the occurrence of intermolecular NH⋯O hydrogen bond influencing the charge transfer in the system. Optimized geometry also proves that the hydrogen bonding interaction's role in the electronic charge transfer between cationic and anionic moiety. The presence of various hyperconjugative interactions were evaluated through Natural Bond Orbital analysis. Molecular Electrostatic Potential study predicts the possible sites for hydrogen bonding nucleophilic and electrophilic interactions. Mulliken charge analysis demonstrates the accumulation of positive and negative charge on atoms and their participation in hydrogen bonding interactions. The calculated first order hyperpolarizability is found to be 6.25 times than that of urea.

The Sloan Digital Sky Survey Quasar Catalog: Fourteenth data release

We present the data release 14 Quasar catalog (DR14Q) from the extended Baryon Oscillation Spectroscopic Survey (eBOSS) of the Sloan Digital Sky Survey IV (SDSS-IV). This catalog includes all SDSS-IV/eBOSS objects that were spectroscopically targeted as quasar candidates and that are confirmed as quasars via a new automated procedure combined with a partial visual inspection of spectra, have luminosities Mi [z = 2] < −20.5 (in a Λ CDM cosmology with H0 = 70 km s−1 Mpc−1, Ω M =0.3, and Ω Λ = 0.7), and either display at least one emission line with a full width at half maximum larger than 500 km s−1 or, if not, have interesting/complex absorption features. The catalog also includes previously spectroscopically-confirmed quasars from SDSS-I, II, and III. The catalog contains 526 356 quasars (144 046 are new discoveries since the beginning of SDSS-IV) detected over 9376 deg2 (2044 deg2 having new spectroscopic data available) with robust identification and redshift measured by a combination of principal component eigenspectra. The catalog is estimated to have about 0.5% contamination. Redshifts are provided for the Mg II emission line. The catalog identifies 21 877 broad absorption line quasars and lists their characteristics. For each object, the catalog presents five-band (u, g, r, i, z) CCD-based photometry with typical accuracy of 0.03 mag. The catalog also contains X-ray, ultraviolet, near-infrared, and radio emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra, covering the wavelength region 3610–10 140 Å at a spectral resolution in the range 1300 < R < 2500, can be retrieved from the SDSS Science Archiver Server.

Microstructure and optical properties of ZnO nanorods prepared by anodic arc plasma method.

A one-dimensional ZnO nanostructure is a versatile and multifunctional n-type semiconductor. In this paper, ZnO nanorods were successfully prepared by the anodic arc plasma method in an oxidizing atmosphere. The composition, morphology, crystal microstructure, and optical properties of ZnO nanorods were characterized by using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and the corresponding selected-area electron diffraction (SAED), X-ray energy dispersive spectrometry (XEDS), ultraviolet-visible (UV-VIS) spectroscopy, Raman scattering spectrum (Raman), and photoluminescence spectrum (PL). The experiment results show that ZnO nanorods synthesized by this method possess hexagonal wurtzite crystal structure with good crystallization, no other impurity phases are observed, the crystalline size is about 18 nm, and the lattice constant distortion occurs compared to that of bulk ZnO. The morphology of the sample is a rod-like shape, the length ranges from 100 nm to 300 nm, the average diameter is approximately 20 nm, and the aspect ratio is relatively high. The UV-VIS absorption spectrum occurs red shift, The Raman spectrum further demonstrates that the major peaks are assigned to ZnO optical vibrational modes, and the PL spectrum exhibits coexistence properties of ultraviolet (UV) and green emission. The results prove that ZnO nanorods with hexagonal wurtzite crystal structure were successfully prepared by the anodic arc plasma method in an oxidizing atmosphere.

Fabrication of ZnO Thin Films by Sol–Gel Spin Coating and Their UV and White-Light Emission Properties

ZnO thin films have been fabricated by the sol–gel spin-coating technique and annealed under different conditions, and their ultraviolet (UV) and white-light emission properties investigated. Different ambient conditions including oxygen, nitrogen, zinc-rich nitrogen, and vacuum were used to tune the main properties of the ZnO thin films. The resistivity varied from the conductive to semi-insulating regime, and the luminescence emission from fairly intense UV to polychromatic. The emission intensity was also found to be a function of the annealing conditions. Possible routes to compensate the loss of emission characteristics are discussed. X-ray photoelectron spectroscopy (XPS) analysis was carried out to detect the chemical states of the zinc/oxygen species. The changes in the electrical and emission properties are explained based on annihilation/formation of inherent donor/acceptor-type defects. Such ZnO thin films could have potential applications in solid-state lighting.

The Sloan Digital Sky Survey Quasar Catalog: Twelfth data release

We present the Data Release 12 Quasar catalog (DR12Q) from the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey III. This catalog includes all SDSS-III/BOSS objects that were spectroscopically targeted as quasar candidates during the full survey and that are confirmed as quasars via visual inspection of the spectra, have luminosities Mi [z = 2] < −20.5 (in a ΛCDM cosmology with H0 = 70 km s-1 Mpc-1, ΩM = 0.3, and ΩΛ = 0.7), and either display at least one emission line with a full width at half maximum (FWHM) larger than 500 km s-1 or, if not, have interesting/complex absorption features. The catalog also includes previously known quasars (mostly from SDSS-I and II) that were reobserved by BOSS. The catalog contains 297 301 quasars (272 026 are new discoveries since the beginning of SDSS-III) detected over 9376 deg2 with robust identification and redshift measured by a combination of principal component eigenspectra. The number of quasars with z > 2.15 (184 101, of which 167 742 are new discoveries) is about an order of magnitude greater than the number of z > 2.15 quasars known prior to BOSS. Redshifts and FWHMs are provided for the strongest emission lines (C iv, C iii], Mg ii). The catalog identifies 29 580 broad absorption line quasars and lists their characteristics. For each object, the catalog presents five-band (u, g, r, i, z) CCD-based photometry with typical accuracy of 0.03 mag together with some information on the optical morphology and the selection criteria. When available, the catalog also provides information on the optical variability of quasars using SDSS and Palomar Transient Factory multi-epoch photometry. The catalog also contains X-ray, ultraviolet, near-infrared, and radio emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra, covering the wavelength region 3600–10 500 Å at a spectral resolution in the range 1300 < R < 2500, can be retrieved from the SDSS Catalog Archive Server. We also provide a supplemental list of an additional 4841 quasars that have been identified serendipitously outside of the superset defined to derive the main quasar catalog.

Vacuum ultraviolet spectral emission properties of Ga, In and Sn droplet-based laser produced plasmas

The Emission Spectra of gallium, indium and tin droplet-based laser produced plasmas are presented in the Vacuum Ultraviolet (VUV) emission range from 30nm to 160nm. The Ga ion transitions are investigated in detail as a function of background pressure level and laser irradiance. Different wavelength emission regions were detected according to the level of background gas. At short wavelengths (i.e. 30–50nm) the line emission from the higher charge states is reduced with increasing pressure, while at longer wavelengths (i.e. 100–160nm) the trend is inverted, as the plasma emission intensity of the lower charge states increases with higher background gas pressure level. The emitted lines are fitted with Voigt profiles to determine the electron density. The electron temperature is obtained from a fit based on the Planck distribution. These estimations are then used to identify the relevant processes that lead to the different charge state emissions as a function of background gas. Langmuir Probe measurements are also reported for evaluating the ion kinetic energy as a function of background gas. The gallium spectra are calibrated in units of spectral radiance, together with spectra from indium and tin. This calibration allows absolute power estimations from the light source in the VUV region. The presented experimental results are relevant as fundamental plasma emission spectroscopic measurements in an almost unexplored wavelength region as well as for applications such as Extreme Ultraviolet Lithography to determine the so-called Out-of-Band (OoB) radiation emission and for metrology applications for future inspection tools.

Deep‐UV exciton emission from Mg1 − xCaxO—A first‐principle investigation

AbstractIn order to investigate the ultraviolet and electron emission properties of rock‐salt Mg1 − xCaxO, first‐principle calculations are carried out with x ranging from 0 to 0.5. The electron–hole interaction is taken into account by solving the Bethe–Salpeter equation. In pure MgO, the calculated exciton binding‐energy value of 83 ± 3 meV is quite close to the published experimental values. The electronic properties of doped MgO are investigated based on the super‐cell model. Both the optical bandgap and the exciton binding energy of the super cell of Mg1 − xCaxO are calculated for five discrete compositions, with an increasing amount x of CaO. The results show that there are strong excitonic effects in all of these materials. A rapid reduction in bandgap value is observed for Mg1 − xCaxO, when increasing the x value. The exciton binding energy of Mg1 − xCaxO shows a minimum value of about 40 meV around x = 0.2. In all of these cases, the exciton is stable at room temperature. The lowest excitation levels in Mg1 − xCaxO are determined by dark excitons. The occurrence of these dark excitons might explain why Mg1 − xCaxO is a strong source of delayed electron emission, after being bombarded by ions in a plasma.

Fabrication of Co-doped ZnO nanowires and their temperature-dependent ultraviolet emission properties

Co-doped ZnO nanowires have been fabricated through a high temperature vapor–solid deposition process. The temperature-dependent ultraviolet emission properties of Co-doped ZnO nanowires under 10–300 K were reported. The results show that there are multipeak emissions situated at the ultraviolet region. The investigation of the excitonic transition in Co-doped ZnO nanowires shows that there is an intensive ultraviolet periodic emission of Co-doped ZnO nanowires under low temperature. The oscillatory structure has an energy periodicity about 70 meV. The oscillatory structure is mainly attributed to the longitudinal optical phonon replicas of the free exciton. The ultraviolet emission shows an obvious redshift with the increasing temperature.

Structural, Optical And Magnetic Properties Of (Fe, Ag) Co-doped ZnO Nanostructures

The (Fe, Ag) co-doped ZnO nanostructures are developed through chemical precipitation method at various percentages of Fe. The X-ray diffraction studies suggest that all the as-synthesized (Fe, Ag) doped ZnO nanopowders have single phase wurtzite structure with no secondary phases. However, the positions of diffracted peaks slightly shifted towards lower (2θ) angles. Photoluminescence studies reveal that 1 mol% of Fe doped ZnO sample has the best ultra violet (UV) emission properties than the other samples. On the other hand, 5 mol% of Fe doped ZnO nanopowders consists of strong green emission band, which belongs to oxygen interstitial defect states. Magnetization analysis shows that 5 mol% of Fe doped ZnO nanopowders have highest room temperature ferromagnetism (RTFM) than the RTFM of other samples. The observed RTFM in co-doped ZnO nanopowders is discussed with the help of structural and emission studies. The results strongly suggest the future development of efficient luminescence and magnetic materials at normal laboratory temperatures with (Fe, Ag) co-doped ZnO nanostructures.

Mechanical stress in silicon nanosized architectures: Defects of SOD processed silica filler

The mechanical stress in nanosized silicon architectures is studied in shallow trench isolation systems with different liners and spin on dielectrics processed silica filler by means of Raman spectroscopy. The nanopatterning of silicon wafers causes a tensile stress of the system whereas the presence of the filler induces a compressive stress which depends on the interaction between silica filler and liner: by changing the liner from silicon dioxide to silicon nitride one can induce a larger compressive stress. The analysis of the ultraviolet excited emission properties in the visible range (nanosecond lasting bands at 2.5, 3.0 and 3.3eV) allowed us to individuate and locate silica related defects and to correlate their presence to the induced compressive stress.

The Sloan Digital Sky Survey quasar catalog: tenth data release

We present the Data Release 10 Quasar (DR10Q) catalog from the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey III. The catalog includes all BOSS objects that were targeted as quasar candidates during the first 2.5 years of the survey and that are confirmed as quasars via visual inspection of the spectra. The catalog also includes known quasars (mostly from SDSS-I and II) that were reobserved by BOSS. The catalog contains 166,583 quasars (74,454 are new discoveries since SDSS-DR9) detected over 6,373 deg$^{2}$ with robust identification and redshift measured by a combination of principal component eigenspectra. The number of quasars with $z>2.15$ (117,668) is $\sim$5 times greater than the number of $z>2.15$ quasars known prior to BOSS. Redshifts and FWHMs are provided for the strongest emission lines (CIV, CIII, MgII). The catalog identifies 16,461 broad absorption line quasars and gives their characteristics. For each object, the catalog presents five-band (u, g, r, i, z) CCD-based photometry with typical accuracy of 0.03 mag and information on the optical morphology and selection method. The catalog also contains X-ray, ultraviolet, near-infrared, and radio emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra cover the wavelength region 3,600-10,500\AA\ at a spectral resolution in the range 1,300$<$R$<$2,500; the spectra can be retrieved from the SDSS Catalog Archive Server. We also provide a supplemental list of an additional 2,376 quasars that have been identified among the galaxy targets of the SDSS-III/BOSS.

Study of excitonic UV emission stability, green luminescence and bandgap tune-ability in wurtzite (ZnO)1−x (Cr2O3)x composite

In this research article deep level green luminescence quenching, stability of ultraviolet excitonic emission and structural properties of composite (ZnO)1−x (Cr2O3)x (x = 0, 5, 10 and 15 mol%) are investigated. X-ray diffraction has demonstrated polycrystalline wurtzite structured ZnO and established proper incorporation of Cr3+ at most likely on the Zn lattice sites. More likely, the crystallite size and lattice constants (c, a) decrease while consequently the dislocation density is increased. A pronounced excitonic UV emission due to band–band transition and a weak deep level green emission caused by the oxygen vacancies are observed at peak-wavelengths (358–370) nm and (536–538) nm respectively. The UV luminescence shows a blue-shift and well-built stability up-to 10 mol% Cr2O3; however for 15 mol% Cr2O3, both the UV and green emissions are completely suppressed while an orange emission appears at 640 nm. This emission is attributed to radiative recombination of a delocalized electron closed to the conduction band with deeply trapped hole in the oxygen interstitials (Oi- centers). Energy bandgap (Eg) is finely tuned from 3.35 eV to 3.46 eV. The exhibited blue shift in the energy bandgap is attributed to Burstein–Moss shift explained by the photon energy dependent measurements. The favorable assorted luminescence mechanisms are explained explicitly.

Seven-photon ultraviolet upconversion emission of Er3+ induced by 1,540-nm laser excitation

The multi-photon ultraviolet upconversion emission properties and synergistic effect are investigated in BaSr2Y6O12:Er3+ phosphor. The deep-ultraviolet emissions centered at 274, 297 and 324-nm are observed under the 1,540-nm excitation, which results from a seven-, six- and six-photon upconversion process, respectively. A synergistic effect is found, which shows that the red emission intensity under 351- and 1,540-nm dual excitation is 4.7 % time stronger than the sum of red emission intensities under the 351 and 1,540-nm single excitation. This phenomenon is attributed to the 4I13/2 and 4I11/2 levels of Er3+ from non-radiative transition process under the 351-nm excitation are excited again to 4F9/2 level by absorbing 1,540-nm photon in the 351- and 1,540-nm dual-excitation process.

Investigation on the enhancement of ultraviolet emission in Ag-ZnO microrods

ZnO microrods with various Ag doping levels were synthesized by a hydrothermal method. The effects of Ag on the ultraviolet (UV) emission properties of ZnO were investigated. The results demonstrate that the UV emission peak of ZnO centered at 391nm has no shift after Ag doping, but the intensity of the UV emission is enhanced. It is very interesting that two peak values of the enhancement can be observed in the UV emission of ZnO with Ag doping levels of 0.05% and 0.20%, and the highest enhancement ratio of UV emission is 1.33, obtained from 0.20% Ag-ZnO. In this work, the enhancement of the UV emission of Ag-ZnO is regarded as a synergistic effect from the competition between the increase of the exciton concentration and the local field enhancement of metallic nanoparticles. In addition, the band gap values of ZnO slightly decreased with the increase of Ag doping level.