Strongest Emission Intensity Research Articles

Effects of SO2−4 or SiO2−3 Doping on the Photoluminescence of NaEu(MoO4)2 Nanophosphors for Light-Emitting Diodes

A series of red nanophosphors including NaEu(MoO4)2-x(SO4)x as well as NaEu(MoO4)2-x(SiO3)x (x = 0, 0.10, 0.20, 0.30, 0.40) were synthesized by hydrothermal and subsequent heat-treatment processes. The as-prepared pure and anion (SO4(2-) or SiO3(2-))-doped NaEu(MoO4)2 phosphors were indexed as a scheelite structure, which was revealed by X-ray diffraction data. The morphologies of SO4(2-)-doped NaEu(MoO4)2 powders were almost regularly spherical, and their grain sizes ranged from 300 to 400 nm. However, the grains of SiO3(2-)-doped phosphors appeared to be seriously inordinate and unconsolidated, as indicated by their scanning electron microscopy studies. All of the samples were excited with near-UV 395 nm light and showed the characteristic red emission of the Eu3+ 5D0 --> 7F2 transition. With the incorporation of SO4(2-) into the host, the red emission intensities of Eu3+ increased obviously and reached a maximum at x = 0.30. Nevertheless, the intensities of Eu3+ emission reduced dramatically after the SiO3(2-) doping. The optimized NaEu(MoO4)1.70(SO4)0.30 nanophosphor powders, with well-distributed fine grains and strong emission intensity, may be applied in the fabrication of phosphor-converted light-emitting diodes (LEDs).

ZnO films deposited by optimized PLD technique with bias voltages

AbstractThe pulsed laser deposition (PLD) technique with bias voltage application for formation of high quality ZnO films was investigated. Oxygen ambient in the PLD chamber significantly decreased the photoluminescence (PL) intensity of near band edge (NBE) emission. Then, instead of using oxygen ambient, the PLD technique with bias voltage application was optimized to attain the stoichiometric composition of the ZnO films. As the deposition temperature was increased, the X‐ray spectrum width diffracted from the (0002) planes was decreased and it showed a minimum value at 700 °C. The PL intensity of the NBE emission also had its maximum value for the film deposited at 700 °C. For the ZnO films deposited at 700 °C, the X‐ray spectrum width showed the minimum value under a bias voltage of –50 V. The PL intensity of the NBE emission also had a maximum value under the same bias voltage. Thus, ZnO films deposited under a bias voltage of –50 V at 700 °C had strong NBE emission intensities. These results could be explained not only by attaining the stoichiometric composition of the ZnO film but also by decreasing the number of high energy O2– ions which caused non‐radiative recombination centers in the film. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Development of photostable near-infrared cyanine dyes

With the emerging interest in optical in vivo imaging, there is an increasing demand of photostable near-infrared (NIR) dyes. Herein we report the rational design of an amine tricarbocyanine structure with improved photostability (CyNA) and its combinatorial derivatization to render CyNA-414 as a NIR-fluorescent dye with stronger emission intensity and higher photostability than the NIR standard IndoCyanine Green (ICG).

Oxygen-proof fluorescence temperature sensing with pristine C70encapsulated in polymernanoparticles

We report the first successful encapsulation of pristine fullerene C70 in polymer nanoparticles with very low size polydispersity. We obtained water-dispersed polystyrene (PS) nanoparticles with diameters from 60 nm to 190 nm using a miniemulsion polymerization technique. Contrarily to pristine fullerenes, which are insoluble in most solvents and materials, the nanoparticles containing fullerene C70 (PS-C70) are stable in water and can be easily incorporated in different materials. When blended with polyacrylonitrile (PAN), a virtually oxygen-impermeable polymer, the PS-C70 nanoparticles show a strong temperature dependence of the thermally activated delayed fluorescence (TADF) intensity and lifetimes, even when exposed to air. This is the first fluorescence temperature sensor based on TADF that can operate in the presence of oxygen. Unlike other fluorescence temperature sensors, our sensor material is insensitive to oxygen, has emission lifetimes in the millisecond range, and shows a strong emission intensity increase when the temperature increases. This sensor exhibits a very broad sensitivity in a working range from −75 °C to at least 105 °C (based on fluorescence intensity), surpassing the performance of other temperature fluorescence sensors at high temperatures.

The photoluminescence of Ce-doped Lu 4Si 2O 7N 2 green phosphors

Cerium-doped Lu 4Si 2O 7N 2 green phosphors were synthesized by a high-temperature solid-state reaction method under nitrogen atmosphere. Compared with Ce-doped Y 4Si 2O 7N 2 phosphors, Ce-doped Lu 4Si 2O 7N 2 phosphors showed longer wavelengths of both excitation and emission, lower Stokes shift, and much stronger emission intensity. Based on the first-principles calculations of the two phosphors, the strong emission intensity originates from the large density of states. At last, the effects of Ce 3+ concentration on photoluminescence were also examined.

Nanostructures of ZnO Prepared by Direct-Current Magnetron Sputtering Technique

We present a technique for growing wurtzite zinc oxide (ZnO) nanostructures on glass substrates using a direct-current magnetron sputtering method without catalysts. The ZnO nanostructures grown on directly glass substrates exhibit remarkably strong visible emission intensity, which is nearly 100 times stronger than that of the ZnO thin films, and narrow peak distribution. This technique opens the simplicity of creating ZnO and doped ZnO nanostructures which can cover large-area glass substrates.

Synthesis and characterization of Ce-doped Lu 2SiO 5 powders by the solid-state reaction with Li 2SO 4 flux

Ce-coped Lu 2SiO 5 powders were prepared by the solid-state reaction method. The effects of flux and atmosphere on the powders structure and properties were investigated by X-ray diffraction (XRD) and spectral measurement. The XRD results show that the samples calcined at 1300 °C without using flux were mainly Lu 2O 3, SiO 2 and a small amount of Lu 2SiO 5, while the samples with Li 2SO 4 flux are mainly Lu 2SiO 5. Furthermore, atmosphere is little effective on powder structure. Absorption band of Lu 2SiO 5 powders shows five peaks at 215 nm, 241 nm, 275 nm, 318 nm and 382 nm, the absorption intensity of samples prepared in air is higher than that of samples prepared in reduced atmosphere. Broad emission band and stronger emission intensities have been found in Lu 2SiO 5 powders prepared in reduced atmosphere. The excitation spectra of Lu 2SiO 5 powders prepared in reduced atmosphere are composed of four bands at 240 nm, 271 nm, 302 nm and 360.6 nm. It can be concluded that flux and atmosphere during preparation is favorable for LSO powders emission and is an effective method to decrease calcining temperature.

Luminescent properties of Eu 3+ activated MLa 2(MoO 4) 4 based (M = Ba, Sr and Ca) novel red-emitting phosphors

Eu 3+-activated novel red phosphors, MLa 2(MoO 4) 4 (M = Ba, Sr and Ca) were synthesized by the conventional solid state method. The excitation and emission spectra indicate that these phosphors can be effectively excited by UV (395 nm) and blue (466 nm) light, and exhibit a satisfactory red performance at 614 nm. Upon excitation with a 466 nm light, our synthesized phosphors have stronger emission intensity than the sulfide red phosphors used in white LEDs. Due to high emission intensity and a good excitation profile, the Eu 3+-doped CaLa 2(MoO 4) 4 phosphor may be a promising candidate in solid-state lighting applications.

Controlled Synthesis and Optical Properties of Pure Gold Nanoparticles

Gold nanoparticles were synthesized by laser ablation of a gold metallic disc at wavelengths of 532 nm and 355 nm with 7 ns pulse duration in the pure water. The colloidal gold nanoparticles were characterized by ultraviolet-visible absorption spectroscopy, transmission electron microscopy, and fluorescence spectrometry. The presence of a surface plasmon resonance peak around ∼ 524 nm indicates the formation of gold nanoparticles. The formation efficiencies of gold nanoparticles in colloids were found to increase when ablating the gold metallic disc with a laser having a longer wavelength. The size distributions of the gold nanoparticles thus produced were measured by transmission electron microscopy. A reduction in mean diameter of the particles was observed with a decrease in the laser wavelength under the irradiation at a high fluence of 25 mJ/pulse. The fluorescence spectroscopy demonstrated that these gold nanoparticles are fluorescent, showing a strong blue emission intensity at 458 nm.

The effect of Eu2+ doping concentration on luminescence properties of BaAl2Si2O8：Eu2+ blue phosphor

The BaAl2Si2O8：Eu2+ blue phosphor was synthesized by one-step calcination of the precursor prepared by chemical coprecipitation. X-ray diffraction and fluorescence spectrophotometry were used to investigate the structural and luminescent properties of the BaAl2Si2O8：Eu2+ blue phosphor. The result showed the BaAl2Si2O8：Eu2+ synthesized by the process was pure. The excitation spectrum of the BaAl2Si2O8：Eu2+ blue phosphor extended from 240 to 410 nm， and the peak appeared around 320 nm，thus the phosphor can be excited effectively by InGaN chip in the range of 350—410 nm. The emission spectrum excited by 365 nm showed a characteristic wide band with the peak at about 465 nm. The emission spectrum intensity firstly increased with Eu2+ doping concentration increasing，then decreased. The strongest emission intensity was obtained when Eu2+ doping concentration reached 3.5mol%. The concentration quenching mechanism was caused by the exchange interaction of Eu2+ ions according to the Dexter theory.

On the desired properties of a conjugated polymer-electrolyte blend in a light-emitting electrochemical cell

We present results from a systematic study on the influence of the conjugated polymer (CP) on the performance of planar light-emitting electrochemical cells (LECs) with a device structure of Au/{CP + poly(ethylene oxide) (PEO) + KCF 3SO 3}/Au. We have employed six different CPs, and we demonstrate that in order to attain a fast turn-on time and a strong light emission intensity, it is critical that the p-type doping (oxidation) potential of the CP is situated within the electrochemical stability window of the {PEO + KCF 3SO 3} electrolyte. We also find that a high ionic conductivity of the active material correlates with a small phase separation between the CP and the {PEO + KCF 3SO 3} electrolyte, and that a doping concentration of ∼0.1 dopants/CP repeat unit is a generic feature of the progressing doping fronts in all investigated devices. Finally we report the first observation of a light emission zone positioned in close proximity to the positive anode in a CP-based LEC.

Photoluminescence of Perovskite Nanosheets Prepared by Exfoliation of Layered Oxides, K2Ln2Ti3O10, KLnNb2O7, and RbLnTa2O7 (Ln: Lanthanide Ion)

Luminescent perovskite nanosheets were prepared by exfoliation of single- or double-layered perovskite oxides, K2Ln2Ti3O10, KLnNb2O7, and RbLnTa2O7 (Ln: lanthanide ion). The thickness of the individual nanosheets corresponded to those of the perovskite block in the parent layered compounds. Intense red and green emissions were observed in aqueous solutions with Gd1.4Eu0.6Ti3O10- and La0.7Tb0.3Ta2O7-nanosheets, respectively, under UV illumination with energies greater than the corresponding host oxide band gap. The coincidence of the excitation spectrum and the band gap absorbance indicates that the visible emission results from energy transfer within the nanosheet. The red emission intensity of the Gd1.4Eu0.6Ti3O10-nanosheets was much stronger than that of the La0.90Eu0.05Nb2O7-nanosheets reported previously. The strong emission intensity is a result of a two-step energy transfer cascade within the nanosheet from the Ti-O network to Gd(3+) and then to Eu(3+). The emission intensities of the Gd1.4Eu0.6Ti3O10- and La0.7Tb0.3Ta2O7-nanosheets can be modulated by applying a magnetic field (1.3-1.4 T), which brings about a change in orientation of the nanosheets in solution. The emission intensities increased when the excitation light and the magnetic field directions were perpendicular to each other, and they decreased when the excitation and magnetic field were collinear and mutually perpendicular to the direction of detection of the emitted light.

ＩＩ族元素を添加したデラフォサイト型ＣｕＬａＯ２の作製と発光特性

Single-phase delafossite-type CuMxLa1-xO2 (M=Mg, Ba, Ca, Sr, Mg, Zn, Cd) was synthesized by means of the solid-state reaction of a stoichiometrically mixed powder of binary oxides at 1273 K, for 10 h in an argon flow, and their luminescent properties were investigated. Undoped CuLaO2 exhibited a weak yellow-green photoluminescence-emission band due to the Cu+ interconfiguration transition at room temperature. The effect of II-group element doping on the photoluminescent properties was classified into two types. CuSrxLa1-xO2, CuBaxLa1-xO2 and CuZnxLa1-xO2 (x≤0.01) exhibited the emission slightly shifted to the shorter-wavelength side than that of undoped CuLaO2 and a strong emission intensity, with increasing doping concentration. These emission behaviors in CuSrxLa1-xO2, CuBaxLa1-xO2 and CuCaxLa1-xO2 was considered to be due to the formation of new emission centers upon doping Sr, Ba and Ca, respectively. CuZnxLa1-xO2, CuCdxLa1-xO2 and CuMgxLa1-xO2 (x≤0.01) exhibited the emission similar to one due to the Cu+ interconfiguration transition in undoped CuLaO2 and a weaker emission intensity, with increasing doping.

Study on successively preparation of nano-TiO 2 ethanol colloids by pulsed laser ablation and fluorescence property

Nano-TiO 2 colloids have been successively prepared by focused, pulsed laser ablation (PLA) at the interface of solid titanium dioxide and flowing liquid. Three factors influenced the luminescence of the nano-TiO 2 colloids. The first factor was the flowing rates of the flowing liquid. The second factor was the pulsed laser output power. The third factor was the age of the colloids. The nano-TiO 2 colloids products were characterized by transmission electron microscopy (TEM), ultraviolet visible spectroscopy (UV–vis) and fluorescence spectroscopy. The results revealed that anhydrous ethanol was the best flowing liquid, and cyclohexane or water was found to be not suitable for this system; under the conditions of the lowest flowing rates of the flowing liquids in the range of 0.017–0.15 mL/s, the highest pulsed laser output power in the range of 100–250 mJ/pulse and with the proper aging time of the colloids, nano-TiO 2 ethanol colloids with strong fluorescence emission intensity at about 414 nm can be obtained.

Efficient and bright non-doped blue light-emitting diodes based on glassy styrylcarbazoles

A series of styrylcarbzole fluorophores 9-Ethyl-3-{(E)-2-[4-(1,1,1-triphenylsilyl) phenyl]-1-ethenyl}-9H-carbazole (Cz–SiPh), {4-[2-(9-Ethyl-9H-carbazol-3-yl)-vinyl]-phenyl}-naphthalen-2-yl-phenyl-amine; Cz–NPh and 3-(2-Anthracen-9-yl-vinyl)-9-ethyl- 9H-carbazole (Cz–Ph3) were synthesized via Horner–Emmons–Wadsworth condensation. Fluorophores Cz–SiPh and Cz–NPh emit a blue hue, whereas Cz–Ph3 emits a green hue. Strong emission intensity, stable glassy morphology and blue emission from the solid film make fluorophores Cz–NPh and Cz–SiPh as promising blue emitters. Non-doped organic light emitting devices were fabricated using these fluorophores as an emitting layer directly; 1,3,5-tris( N-phenylbenzimidazol-2-yl)benzene and 4,4′-bis( N-naphth-1-yl- N-phenylamino)-biphenyl were used as the electron-transporting layer and the hole-injection layer, respectively. Among these devices, the Cz–NPh-based device exhibits excellent performance, including high brightness (8207 cd/m 2), large power efficiency (1.9 cd/A or 1.2 lm/W), high external quantum efficiency (2.3%), high color purity CIE (0.14, 0.09) and good operation stability.

Li-DOPING EFFECT ON THE CATHODOLUMINESCENT PROPERTIES OF Y2O3:Eu3+ PHOSPHORS

Influence of lithium doping on the crystallization, the surface morphology, the chemical states and the luminescent properties of Y 2 O 3: Eu 3+ phosphors was investigated. The structural, surface morphology characteristics and chemical states of the phosphors were analyzed by using X-ray diffraction (XRD), scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS), respectively. The crystallinity, the surface morphology, and the cathodoluminescence (CL) of phosphors highly depended on the Li doping. The relationship between the crystalline and morphological structures and the luminescent properties was studied, and Li + doping affected not only the crystallinity but also the luminescent brightness of Y 2 O 3: Eu 3+ phosphors. In particular, the incorporation of the Li + ion into the Y 2 O 3 lattice could induce remarkable increase in the CL intensity. The enhanced photoluminescence brightness with Li doping may result both from the improved crystallinity leading to higher oscillating strengths for the optical transitions, and the increased surface area due to the larger particle sizes. The strongest emission intensity was observed with Li doped Y 2 O 3: Eu 3+ ceramics whose brightness was increased by a factor of 1.8 in comparison with that of Y 2 O 3: Eu 3+ ceramics.

Cathodoluminescent and nonlinear optical properties of undoped and erbium doped nanostructured ZnO films deposited by spray pyrolysis

We have deposited zinc oxide (ZnO) and erbium doped zinc oxide (ZnO:Er) thin films on heated glass substrates using spray pyrolysis technique. The effect of erbium dopant on structural, morphological, luminescent and nonlinear optical properties was studied. The deposited films have been analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), ex situ compositional analysis (ESCA), profilometry, cathodoluminescence (CL) and third harmonic generation (THG) measurements. All films were polycrystalline, having a preferential growth orientation along the ZnO (002) plane, with a corresponding average crystallite size of less than 41nm. Addition of erbium can effectively control the film surface morphology and its cathodoluminescent properties. The films containing low erbium concentration show a uniform surface covered with hexagonal shaped grains and a strong UV light emission intensity as well as TH response. In contrast, when the erbium doping ratio exceeds 3%, a porous surface with columnar textural growth becomes more pronounced, and a substantial reduction of the cathodoluminescent and TH response. A strong TH signal was obtained for the film with good crystalline quality at the concentration of 2%. Third order nonlinear optical susceptibility (χ〈3〉) values of the studied materials were in the remarkable range of 10−12esu.

Comparative study on the decomposition process of N-isopropylacrylamide in He, N2 and air plasmas

Emission spectroscopy was employed to observe decomposed species of N-isopropylacrylamide (NIPAAm) exposed to He, N2 and air plasmas, which were generated by an AC discharge at 3.0 Torr pressure. For the He plasma, several strong emissions were observed and assigned to the Hα and Hβ atomic lines, CH3O, CN(B 2Σ–X 2Π), CH(A 2Δ–X 2Π), , N2(C 3Πu–B 3Πg) and C3H5, CN, CHO, CH2O and transitions. These results suggest that plasma etching decomposed the NIPAAm monomer sample, and the resulting species emitted light near the surface.For the NIPAAm exposed to N2 plasma, the emission spectrum shows the presence of the following species: , N2, NH, NH+, CO and OH, while when the NIPAAm was exposed to the air plasma, the species observed were , N2, NH, NH+, CO, OH and O. Most of the bands and lines observed in helium plasma were not present in air and nitrogen plasmas. This implies that these species undergo significant chemical conversion in the plasma. The time dependence of the strong emission intensities of the observed species was also investigated. As N2 and air plasmas were exposed to the NIPAAm monomer, the surface was etched more rapidly than the He plasma.

Columnar Structures and Stress Relaxation in Thick GaN FilmsGrown on Sapphire by HVPE

Thick GaN films with high quality are directly grown on sapphire in ahome-built vertical hydride vapour phase epitaxy (HVPE) reactor. Theoptical and structural properties of large scale columnar domains nearthe interface are studied using cathodoluminescence and micro-Ramanscattering. These columnar domains show a strong emission intensity dueto extremely high free carrier concentration up to 2×1019 cm−3, which are related with impurities trapped instructural defects. The compressive stress in GaN film clearlydecreases with increasing distance from interface. The quasi-continuouscolumnar domains play an important role in the stress relaxation forthe upper high quality layer.

Polarized quantum dot emission from photonic crystal nanocavities studied under moderesonant enhanced excitation

We study the linear polarization of the emission from single quantum dots embedded in an "L3" defect nanocavity in a two-dimensional photonic crystal. By using narrow linewidth optical excitation in resonance with higher-order modes, we are able to achieve strong quantum dot emission intensity whilst reducing the background from quantum dots in the surrounding lattice. We find that all the dots observed emit very strongly linearly polarized light of the same orientation as the closest mode, despite the fact that these quantum dots may be spectrally detuned by several times the mode linewidth. We discuss the coupling mechanisms which may explain this behavior.