Enhanced luminescence properties of YBO3:Eu phosphors by Li-doping

Different concentrations of Li-doped YBO₃:Eu³⁺ phosphors have been prepared by the conventional solid state reaction method and were characterized by X-ray diffraction, field emission scanning electron microscopy, photoluminescence excitation and emission measurements. An intense reddish orange emission is observed under UV excitation and the emitted radiation was dominated by an orange peak at 594 nm resulted from the ⁵D₀ → ⁷F₁ transitions of Eu³⁺ ions. The brightness of the YBO₃:Eu³⁺ phosphor was found greatly improved with Li-doping accompanied by slight improvement in the purity of the color which might be attributed to improvement in crystallinity, grain sizes and creation of oxygen vacancies with Li-doping. The observed results have been discussed in comparison with similar reported works.     

Structural and luminescence characterization of Eu3+/ZnS nanoparticle-doped ZrO2/PEG composites

ZnS nanoparticles of varying concentrations were incorporated into Eu³⁺ doped ZrO₂/PEG composite system through non-hydrolytic sol–gel method. The presence of the nanoparticles was confirmed by XRD and TEM analyses. The elemental composition of the prepared sample was verified using EDX analysis. Different vibrational modes of the composite system were found out by FTIR spectra. Thermal stability of the as-prepared sample was measured using TGA and DTA analyses. The optical bandgap of the composite system was calculated from the absorption spectrum. The excitation spectrum shows the broad excitation bands of the sensitizer (ZnS) and Host (ZrO₂/PEG) as well as the characteristic excitation peaks of the activator (Eu³⁺). The emission spectra reveal that the characteristic emission of Eu³⁺ can be obtained using 392 nm as well as the excitation wavelength of the sensitizer (275 nm). The CIE chromaticity analysis shows a change in the emission colour of the co-doped samples from yellow to reddish orange corresponding to a change in the excitation wavelength from 392 to 275 nm. These results suggest the applicability of the as-synthesized composite system as a potential candidate in various optoelectronic devices.

     

Solar photocatalysts from Gd–La codoped TiO2 nanoparticles

Gd–La codoped TiO₂ nanoparticles with diameter of 10 nm were successfully synthesized via a sol–gel method. The photocatalytic activity of the Gd–La codoped TiO₂ nanoparticles evaluated by photodegrading methyl orange has been significantly enhanced compared to that of undoped or Gd or La monodoped TiO₂. Ti⁴⁺ may substitute for La³⁺ and Gd³⁺ in the lattices of rare earth oxides to create abundant oxygen vacancies and surface defects for electron trapping and dye adsorption, accelerating the separation of photogenerated electron–hole pairs and methyl orange photodegradation. The formation of an excitation energy level below the conduction band of TiO₂ from the binding of electrons and oxygen vacancies decreases the excitation energy of Gd–La codoped TiO₂, resulting in versatile solar photocatalysts. The results suggest that Gd–La codoped TiO₂ nanoparticles are promising for future solar photocatalysts.     

Application of orange peel xanthate for the adsorption of Pb from aqueous solutions

Pristine orange peel was chemically modified by introducing sulfur groups with the carbon disulfide treatment in alkaline medium. The presence of sulfur groups on orange peel xanthate were identified by FTIR spectroscopic study. Equilibrium isotherms and kinetics were obtained and the effect of various parameters including equilibrium pH, contact time, temperature and initial ion concentration on adsorption of Pb²⁺ were studied by batch experiments. The maximum adsorption capacity of orange peel xanthate was 204.50 mg g⁻¹, which was found to increase by about 150% compared to that of pristine orange peel. The adsorption process can attain equilibrium within 20 min, and kinetics was found to be best-fit pseudo-second-order equation. Temperature has little effect on the adsorption capacity of orange peel xanthate. In addition, the adsorption mechanism was suggested to be complexation.     

Luminescent properties of Cu+/Sn2+-activated aluminophosphate glass

A robust aluminophosphate glass matrix containing substantial amounts of Cu₂O and SnO has been prepared by the melt-quenching technique, and the luminescent properties have been assessed. The as-prepared material exhibits tunable luminescence by variation of excitation wavelength, in connection with the distinct excitation/emission properties of Cu⁺ ions and twofold-coordinated Sn centers in the host. Under excitation of both Cu⁺ and Sn species at 300 nm, the co-doped material exhibits a bright whitish luminescence, whereas excitation at 360 nm produces an intense orange emission arising merely from Cu⁺ ions. Thus, white light generation is deemed realizable by combination of cool-bluish emission intrinsic to Sn centers with the warm-orange emission from Cu⁺ ions. The optical properties of the material after heat treatment have been also investigated. Results indicate the chemical reduction of ionic copper via Sn²⁺ ultimately producing Cu nanoparticles as evidenced by the surface plasmon resonance. Consequently, the excitation-wavelength dependent photoluminescence bands appear suppressed in relation to Cu⁺ basically and show a dip attributed to light reabsorption by the plasmonic Cu particles.     

基于CS-SVM的山梨酸钾的荧光光谱检测法研究

通过分析山梨酸钾的橙汁溶液的荧光光谱特征,发现山梨酸钾在激发波长为375nm、发射波长为450～510nm范围的光谱图有毛刺,说明橙汁被激发的荧光会干扰山梨酸钾的荧光光谱。构建布谷鸟搜索算法（CS）优化支持向量机（SVM）模型对15个样本进行训练,并预测7个样本的山梨酸钾的浓度。CS-SVM的平均回收率为99.07%,均方误差为1.21×10^-5g/L,结果表明CS-SVM能够精确测定橙汁溶液中山梨酸钾的浓度,CS-SVM训练过程和对预测结果的平均回收率、误差都优于PSO-SVM和GA-SVM。     

Blue–white–orange tunable luminescence from Ca6La2Na2(PO4)6F2:Eu,Mn phosphors excited by UV light

New Eu²⁺ and/or Mn²⁺ activated Ca₆La₂Na₂(PO₄)₆F₂ phosphors were prepared and their photoluminescence properties upon ultraviolet excitation were investigated. Phosphor Ca₆La₂Na₂(PO₄)₆F₂:Eu²⁺,Mn²⁺ shows a broad blue emission band and an orange emission band, which originates from Eu²⁺ and Mn²⁺, respectively. The resonant type energy transfer from Eu²⁺ to Mn²⁺ was demonstrated, and the energy transfer efficiency was also calculated according to their PL decay curves. Tuning of the content of Mn²⁺ can generate the varied hues from blue to white and eventually to orange. Our results demonstrate that the phosphor is promising for producing UV-LED-based white LEDs.     

Electroluminescent properties of chemically synthesized zinc sulfide nanocrystals doped with manganese

High-field electroluminescence (EL) of chemically synthesized ZnS:Mn nanocrystals with a crystallite size of 4 nm was investigated using a device consisting of glass substrate/indium–tin oxide/ZnS:Mn NC emission layer/Al. For electric fields over ca. 1 MV/cm, the current was turned on, and orange EL was observed. The maximum luminance was 0.45 cd/m² at a DC voltage of 42 V. The EL spectrum comprises a single peak with a peak wavelength of 593 nm, which is ascribed to the ⁴T₁–⁶A₁ transitions of Mn²⁺ ions. The excitation mechanism of the Mn²⁺ ions is discussed according to a scheme of impact excitation by hot-electrons.     

Excitation mechanism of europium ions embedded into TiO2 nanocrystalline matrix

In this work, the excitation mechanism of Eu³⁺ ions embedded into nanocrystalline TiO₂ film obtained by Low Pressure Hot Target Reactive Sputtering has been investigated by means of photoluminescence, photoluminescence excitation, transmission and surface photovoltage spectroscopy.The strong emission related to europium ions in the visible range has been observed at a non resonant excitation wavelength suggesting an efficient excitation transfer from the matrix to the ions. Based on obtained results, indirect excitation mechanism of europium ions has been confirmed and discussed. Moreover, surface activity strongly depending on environment conditions, has been also observed.     

Solvothermal synthesis of La-based metal-organic frameworks and their color-tunable photoluminescence properties

A series of La-based metal?organic frameworks (La-MOFs) phosphors have been successfully synthesized by a facile solvothermal method without assistance of any surfactant or template. The results show that the ethanol volume ratio is important to obtain adjustable shape and size of La-MOFs in the synthesis process. The obtained samples possess flake-like architectures with about 3–5 μm in length. Under UV excitation, all the La-MOFs:Tb³⁺, Eu³⁺ phosphors exhibit the characteristic emissions of Tb³⁺ and Eu³⁺. Moreover, the emitting color of the as-obtained products can be acquired from green, green-yellow, yellow, yellow-orange, orange, to red owing to the efficient energy transfer (ET) between Tb³⁺ and Eu³⁺ions. The ET efficiency of the samples was calculated, and the maximum was found about 96.84%. Furthermore, the dipole–quadrupole interaction has been reasonable proved by the energy transfer between Tb³⁺ and Eu³⁺. These results indicated that La-MOFs:Tb³⁺, Eu³⁺ might be as a novel potential candidate as phosphors for displays and lightings.

     

Excitation of 3S, 3P, and 3P° Levels of Cadmium Atom in Collisions with Slow Electrons

The excitation cross sections and optical excitation functions are experimentally determined for transitions arising as a result of population of the ³ S, ³ P, and ³ P° levels in collisions of slow electrons with cadmium atoms. The dependence of cross sections on the principal quantum number of the upper level is obtained for four spectral series of CdI, which is indicative of the absence of significant perturbation of these series. The obtained results are compared with the data of previous studies.     

Efficiency and stability of polymer light-emitting diodes

The operation characteristics of polymer light-emitting diodes (PLEDs) are strongly dependent on materials, processing and the structure of the device. The device structure developed at Philips Research is presented together with some typical results for brightness, efficiency, response times and stability. The PLEDs typically operate at a voltage of 3–4 V for a brightness of 100 cd m^-2 and have an efficiency ranging from 2 cd A^-1 for orange emitting polymers (610 nm) up to 16 cd A^-1 for green emitting polymers (550 nm). The response time under conditions for display operation is determined by the charge carrier transport properties and amounts to 43 ns. Lifetimes of several thousand hours have been obtained for large orange emitting devices of 8 cm² for daylight visibility at room temperature.     

Synthesis of PANI/TiO<Subscript>2</Subscript>–Fe<Superscript>3+</Superscript> nanocomposite and its photocatalytic property

A convenient method for synthesizing highly photocatalytic activity PANI/TiO₂–Fe³⁺ nanocomposite was developed. The effect of calcination temperature on the phase composition of TiO₂ nanopowder was investigated. It was found that higher temperature could promote the formation of rutile phase. The nanocomposite was characterized by atomic force microscopy (AFM), transmission electron microscopy (TEM), infrared spectroscopy (IR) and X-ray diffraction (XRD). The results indicated that the nanohybrid was composed of TiO₂, Fe³⁺ and PANI. The photocatalytic property of the nanocomposite was evaluated by the degradation of methyl orange. In the presence of this catalyst, the degradation rate of methyl orange of 95.2% and 70.3% could be obtained under the UV and sunlight irradiation within 30 min, respectively. The apparent rate constant was 5.64 × 10⁻² which is better than that of the Degussa P25.     

Energy transfer based photoluminescence spectra of co-doped (Dy3+ + Sm3+): Li2O-LiF-B2O3-ZnO glasses for orange emission

The present paper brings out the results concerning the preparation and optical properties of Sm³⁺ and Dy³⁺ each ion separately in different concentrations (0.3, 0.5, 1.0 and 1.5 mol.%) and also together doped (x mol.% Dy³⁺ + 1.5 mol.% Sm³⁺): Li₂O-LiF-B₂O₃-ZnO (where x = 0.5, 1.0 and 1.5 mol.%) glasses by a melt quenching method. Structural and thermal properties have been extensively studied for those glasses by XRD and TG/DTA. The compositional analysis has been carried out from FTIR spectral profile. Optical absorption spectral studies were also carried out. Sm³⁺: LBZ glasses have displayed an intense orange emission at 603 nm (⁴G_5/2 → ⁶H_7/2) with an excitation wavelength at 403 nm and Dy³⁺: LBZ glasses have shown two emissions located at 485 nm (⁴F_9/2 → ⁶H_15/2; blue) and 574 nm (⁴F_9/2 → ⁶H_13/2; yellow) with an excitation wavelength at 385 nm. Remarkably, it has been identified that the significant increase in the reddish orange emission of Sm³⁺ ions and diminished yellow emission pertaining to Dy³⁺ ions in the co-doped LBZ glass system under the excitation of 385 nm which relates to Dy³⁺ ions. This could be due energy transfer from Dy³⁺ to Sm³⁺. The non-radiative energy transfer from Dy³⁺ to Sm³⁺ is explained in terms of their emission spectra, donor lifetime, energy level diagram and energy transfer characteristic factors. These significantly enhanced orange emission exhibited glasses could be suggested as potential optical glasses for orange luminescence photonic devices.     

Enhanced novel orange red emission in LiSr4−x (BO3)3:xSm3+ by K+

LiSr_4?x (BO₃)₃:xSm³⁺ and LiSr_3.985?x (BO₃)₃:0.015Sm³⁺, xK⁺ phosphors were prepared by solid-state reactions. The phases and luminescent properties of the obtained phosphors were characterized. The results demonstrate that the phosphors particles emit an intensive reddish orange light emission under excitation at 403 nm. LiSr_4?x (BO₃)₃:xSm³⁺ phosphor can be efficiently excited by ultraviolet and blue light, and the emission spectrum consists of three emission peaks at 564, 601 and 647 nm. The introduction of the charge compensator K⁺ into the LiSr_4?x (BO₃)₃:xSm³⁺ phosphor matrix promotes the increase of the emission intensity, as well as the decrease of the E _g value. Results suggest that LiSr_3.97(BO₃)₃:0.015Sm³⁺, 0.015 K⁺ is a promising orange–red emitting phosphor for UV LED applications.     

Optical properties of aluminophosphate glasses containing silver, tin, and dysprosium

The spectroscopic properties of a Dy³⁺-doped aluminophosphate glass containing silver and tin were reported. Different oxidation and aggregation states of silver were obtained by varying silver concentration and glass thermal history. The addition of silver and tin at the lowest concentration studied results in Dy³⁺ ions emission under nonresonant UV excitation in connection with the appearance of an excitation band around 270 nm, which is associated to isolated Ag⁺ ions and twofold-coordinated Sn centers. The increase in silver and tin concentration leads to a broadening of aforementioned band and to the presence of charged silver dimers as evidenced by the appearance of an excitation band around 330 nm. The data indicated that light absorption might take place at ionic silver species and twofold-coordinated Sn centers, followed by energy transfer to Dy³⁺ ions. After heat treatment, ionic silver species were reduced to atomic Ag by tin with the subsequent formation of Ag nanoparticles (NPs) inside the dielectric host. A quenching effect in Dy³⁺ ions luminescence was shown with the presence of the Ag NPs, most notably for excitation of ⁶H_15/2 → ⁴F_9/2, ⁴I_15/2, ⁴G_11/2 transitions, which were in resonance with the dipole absorption mode of the particles. The silver NPs were believed to provide radiationless pathways for excitation energy loss in Dy³⁺ ions.     

Photoluminescence properties of a novel red-emitting phosphor Ba<Subscript>2</Subscript>LaV<Subscript>3</Subscript>O<Subscript>11</Subscript>:Eu<Superscript>3+</Superscript>

Ba₂LaV₃O₁₁:Eu³⁺ phosphors were firstly synthesized by the traditional solid-state reaction method at 1100 °C. Their luminescence properties were investigated by photoluminescence excitation and emission spectra. The excitation spectrum shows a broad band centered at about 275 nm in the region from 200 to 370 nm, which is attributed to an overlap of the charge transfer transitions of O^2??→?V⁵⁺ and O^2??→?Eu³⁺. The phosphors exhibit the red emissions of Eu³⁺ and the emission intensity ratio of ⁵D₀?→?⁷F₂ to ⁵D₀?→?⁷F₁ is dependent on the Eu³⁺ concentration due to an environment change about Eu³⁺ ions. Concentration quenching occurs at 30 mol% in the phosphors and exchange interaction is its main mechanism. Ba₂LaV₃O₁₁:Eu³⁺ displays tunable CIE color coordinates from yellow orange to red depended on Eu³⁺ content, which may have a potential application for illuminating and display devices.     

A two-dimensional model of glow discharge in view of vibrational excitation of molecular nitrogen

A two-dimensional model is suggested of dc glow discharge with parallel electrodes. The model includes equations for electron and ion concentrations, which are related to the Poisson equation for electric potential. The collision ionization and electron-ion recombination are described using empirical relations. Processes of vibrational excitation of N₂ molecules are considered. The vibrational kinetics of nitrogen are described in view of excitation by electron impact, vibrational exchange, and vibrational-translational relaxation. The finite-difference model used for solving kinetic equations is described. Results are obtained for a two-dimensional model of glow discharge in nitrogen at a pressure of 5 torr and an emf of 2000 V. The obtained fields of distribution of electron temperature and populations of vibrational levels of nitrogen are analyzed. The results enable one to estimate the fraction of electric field energy utilized for the excitation of vibrational states.     

Nd-doped fluoride film grown on LiYF4 substrate by pulsed laser deposition

The realization of a monocrystalline nanofilm of Nd³⁺-doped fluoride on LiYF₄ substrates by pulsed laser deposition is reported. The film was obtained by laser ablation with 355 nm photons of a bulk LiYF₄ crystal doped with Nd³⁺ ions at 1.5% atomic concentration. The measurements of the sample thickness obtained by an in situ interferometric technique, and the film optical characteristics analyzed via laser induced fluorescence spectroscopy upon UV and IR excitation, are presented. Lifetime measurements of the fundamental Nd³⁺ ion transition in the film were also performed. All the results were compared with those obtained in a Nd³⁺:LiYF₄ bulk crystal. The emission spectra of the deposited film following IR excitation seem to indicate the obtained deposit is Nd³⁺:YF₃.     

Optical properties of Mn-doped ZnS semiconductor nanoclusters synthesized by a hydrothermal process

Undoped and Mn-doped ZnS nanoclusters have been synthesized by a hydrothermal approach. Various samples of the ZnS:Mn with 0.5, 1, 3, 10 and 20 at.% Mn dopant have been prepared and characterized using X-ray diffraction, energy-dispersive analysis of X-ray, high resolution electron microscopy, UV-vis diffusion reflection, photoluminescence (PL) and photoluminescence excitation (PLE) measurements. All the prepared ZnS nanoclusters possess cubic sphalerite crystal structure with lattice constant a = 5.408 ± 0.011 ?. The PL spectra of Mn-doped ZnS nanoclusters at room temperature exhibit both the 495 nm blue defect-related emission and the 587 nm orange Mn²⁺ emission. Furthermore, the blue emission is dominant at low temperatures; meanwhile the orange emission is dominant at room temperature. The Mn²⁺ ion-related PL can be excited both at energies near the band-edge of ZnS host (the UV region) and at energies corresponding to the Mn²⁺ ion own excited states (the visible region). An energy schema for the Mn-doped ZnS nanoclusters is proposed to interpret the photoluminescence behaviour.