Structure and luminescence properties of Mn-doped Zn2SiO4 prepared with extracted mesoporous silica

Zn₂SiO₄:Mn powders were prepared by solid-state reaction using extracted SBA-15 as silica source. The well crystalline willemite Zn₂SiO₄:Mn can be obtained at 800 °C, much lower than the conventional solid-state reaction temperature and lower than using the calcined SBA-15. This can be attributed to the high reactive activity of the extracted SBA-15 due to its high density silanol groups, large surface areas, and non-crystalline structure. Ultraviolet (UV) and vacuum ultraviolet (VUV) excitation spectra reveal the host lattice absorption band around 162 nm and the charge transfer transition band around 245 nm. The Zn₂SiO₄:Mn phosphor exhibits a strong green emission around 527 nm. The Zn₂SiO₄:Mn phosphor with an Mn doping concentration of 0.06, i.e., Zn_1.94Mn_0.06SiO₄, shows the highest relative emission intensity. Upon 147 nm excitation, the luminescence decay time of the green emission of Zn_1.94Mn_0.06SiO₄ around 527 nm is 8.87 ms.     

Synthesis and photoluminescence of nano-Y2O3:Eu phosphors

We report nano-Y₂O₃:Eu³⁺ phosphors with particle size of about 50 nm and relatively high photoluminescence (PL) intensity which is close to the standard for application. The influences of the dope amount, the surfactant and the precipitation pH on the PL intensity, the particle size and the dispersion have been studied. It has been found that 4% is the best Eu³⁺ molar concentration to get the highest PL intensity for both nano- and micro-Y₂O₃:Eu³⁺. The addition of butanol as a surfactant inhibits the grain growth and the agglomeration of particles efficiently by reducing the oxygen bridge bonds. As the pH rises, the PL intensity and the particle size increase due to the formation of oxygen bridge bonds.     

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.     

Hydrothermal synthesis and vacuum ultraviolet-excited luminescence properties of novel Dy-doped LaPO4 white light phosphors

Novel LaPO₄:Dy³⁺ white light phosphors with monoclinic system were successfully synthesized by hydrothermal method at 240 °C. The strong absorption at around 147 nm in excitation spectrum was assigned to the host absorption which suggested that the vacuum ultraviolet-excited energy was efficiently transferred from the host to the Dy³⁺ ion. The f-d transition of Dy³⁺ ion was observed locating at 182 nm. Under 147 nm excitation, La_1−xPO₄:xDy³⁺ phosphor exhibited two emission bands locating at 571 nm (yellow) and 478 nm (blue) which corresponded to the hypersensitive transitions ⁴F_9/2-⁶H_13/2 and ⁴F_9/2-⁶H_15/2. It was the two emission bands that lead to the white light.     

Direct synthesis of strontium titanate phosphor particles with high luminescence by flame spray pyrolysis

SrTiO₃:Pr, Al phosphor particles with high luminescence intensities were directly prepared by flame spray pyrolysis without post-treatment. They had better crystallinity than those prepared by general spray pyrolysis with post-treatment and solid-state reaction methods. In addition, they had complete spherical shape and narrow size distribution. On the other hand, the particles prepared by general spray pyrolysis had irregular shape, and poorer brightness than those prepared by solid-state reaction method, while the particles prepared by flame spray pyrolysis had comparable photoluminescence and cathodoluminescence intensities with those of particles prepared by solid-state reaction method. The photoluminescence intensity of SrTiO₃:Pr, Al particles prepared by flame spray pyrolysis was as much as 4.7 times higher than that of particles prepared by general spray pyrolysis.     

Photoluminescence properties Pr and Bi-codoped CaTiO3 phosphor prepared by a peroxide-based route

CaTiO₃:Pr³⁺ phosphors codoped with Bi³⁺ ions were synthesized by a peroxide-based route (PBR). The effect of codopants on the structural and luminescence properties was studied. Boric acid used as flux material was proved to be effective in improving the luminescence property. The phosphors prepared by the PBR method showed advantages of lower sintering temperature, shorter heating time, and small grain size. The CaTiO₃:Pr³⁺,Bi³⁺ demonstrated to be a potential red-emitting phosphor for white light-emitting diodes.     

Hydrothermal synthesis and photoluminescence properties of nano-crystalline GdBO3:Eu phosphor

Nano-crystalline GdBO₃:Eu³⁺ was prepared by a hydrothermal method and the effects of some processing variables such as pH, temperature were investigated. The as-synthesized powders were spherical shaped agglomerates of nanoparticles. The luminescent properties were compared with samples synthesized by conventional solid-state reaction method. Both the photoluminescence intensity and chromaticity were improved and a red-shift in the CT band was observed for the hydrothermally synthesized samples. Possible mechanisms of phase formation were investigated and explanations for the changes in optical properties are proposed.     

Luminescence characterization of (Ca1−xZnx)Ga2S4:Eu phosphors for a white light-emitting diode

We investigated the luminescence properties of (Ca_1−xZn_x)Ga₂S₄:Eu²⁺ phosphor as a function of Zn²⁺ and Eu²⁺ concentrations. The luminescence intensity was markedly enhanced by increasing the mole fraction of Zn²⁺ at Ca²⁺ sites. Lacking any Zn²⁺ ions, CaGa₂S₄:0.01Eu²⁺ converted only 18.1% of the absorbed blue light into luminescence. As the Zn²⁺ concentration increased, the quantum yield increased and reached a maximum of 24.4% at x = 0.1. Furthermore, to fabricate the device, the optimized green-yellow (Ca_0.9Zn_0.1)Ga₂S₄:Eu²⁺ phosphor was coated with MgO. White light was generated by combining the MgO-coated phosphor and the blue emission from a GaN chip.     

Synthesis of ultrafine YAG:Tb phosphor by nitrate-citrate sol-gel combustion process

Ultrafine terbium-doped yttrium aluminum garnet (YAG:Tb) phosphor powders are prepared by a nitrate-citrate sol-gel combustion process using 1:1 ratio of citrate/nitrate. Phase evolution of the synthesized powder is determined by X-ray diffraction (XRD) techniques. Single-phase cubic YAG:Tb crystalline powder is obtained by calcinating the amorphous materials at 900 °C and no intermediate phase is observed. Transmission electronic microscope (TEM) morphology shows that the resultant YAG:Tb powders have uniform size and good homogeneity. The particle size of the product is investigated as a function of the calcination temperature. The photoluminescence (PL) spectrum of Tb³⁺ substituted for Y³⁺ in YAG with 5.0% content has been measured on samples calcined at different temperatures.     

Indium sulfide microflowers: Fabrication and optical properties

With the assistance of urea, uniform 2D nanoflakes assembled 3D In₂S₃ microflowers were synthesized via a facile hydrothermal method at relative low temperature. The properties of the as-obtained In₂S₃ flowers were characterized by various techniques. In this work, the utilization of urea and l-cysteine, as well as the amount of them played important roles in the formation of In₂S₃ with different nanostructures. Inferred from their morphology evolution, a urea induced precursor-decomposition associated with the Ostwald-ripening mechanism was proposed to interpret these hierarchical structure formation. Furthermore, the optical properties of these In₂S₃ microflowers were investigated via UV–vis absorption and photoluminescence (PL) spectroscopies in detail.     

Cathodoluminescence of CaWO4 and SrWO4 thin films prepared by spray pyrolysis

Thin films of CaWO₄ and SrWO₄ were prepared on glass substrates by spray pyrolysis. The effects of preparation conditions and monovalent, bivalent and trivalent cation doping on cathodoluminescence (CL) properties of the films were studied. Polycrystalline CaWO₄ and SrWO₄ films formed a scheelite structure after being annealed above 300°C. They exhibited analogous cathodoluminescence consisting of a blue emission band at 447 nm and a blue-green emission band at 487 nm. The blue and blue-green emission intensities increased with substrate and annealing temperature. Annealing atmosphere and doping with Ag⁺, Pb²⁺ and La³⁺ did not influence the characteristics of the blue and blue-green emissions, whereas Eu³⁺ did. The results indicated both the blue and blue-green emissions originated from the WO₄²⁻ molecular complex. The luminance and efficiency for CaWO₄ film were 150 cd/m² and 0.7 lm/W at 5 kV and 57 μA/cm².     

Preparation, characterization and luminescence of La2TeO6 phosphor doped with Eu

Phosphors of La₂TeO₆ doped with Eu³⁺ ions have been synthesized by the oxidation of the corresponding rare-earths oxytellurides of formula La_2−xEu_xO₂Te (x = 0.02, 0.06, and 0.1) at 1050 K. Powder X-ray diffraction confirms that the as prepared materials consist of the orthorhombic La₂TeO₆ as main phase. The photoluminescence (PL) of red-emitting La_2−xEu_xTeO₆ powder phosphors is reported. The emission spectrum, exhibits an intense emission peak due to ⁵D₀ → ⁷F₂ transition at 616 nm, which indicates that the Eu³⁺ ion occupies a non-centrosymmetric site in the host lattice. These materials could find application for use as lamp phosphors in the red region.     

Hydrothermal synthesis and luminescent properties of LaPO4:Eu 3D microstructures with controllable phase and morphology

Three types of Eu³⁺-doped LaPO₄ three-dimensional (3D) microstructures have been hydrothermally prepared by adjusting pH value and the molar ratio of La³⁺ and Eu³⁺ to phosphorus of Na₅P₃O₁₀ (Ln/P) at 180 °C. As the pH value was 0.15 and the molar ratio of Ln/P was in the range of 1/1 to 1/4, 5 μm urchinlike spheres composed of long nanorods of hexagonal LaPO₄:Eu were obtained. As the pH value was 1.00 and the molar ratio of Ln/P was 1/1, 3 μm hollow spheres consisting of short nanorods of monoclinic LaPO₄:Eu were prepared. Keeping the pH value at 1.0 and the molar ratio of Ln/P at 1/4, 6 μm core-shell spheres of monoclinic LaPO₄:Eu formed. Luminescent measurements were performed. Hollow spheres of monoclinic LaPO₄:Eu had the strongest emission intensity. However, the emission intensity of monoclinic core/shell structure was even lower than that of hexagonal LaPO₄:Eu urchinlike spheres.     

Synthesis and characterization of spherical ZrO2:Eu phosphors by spray pyrolysis process

Europium doped zirconia (ZrO₂:Eu³⁺) powder phosphors consisting of spherical, dense and submicrometer size particles were successfully synthesized by a spray drying process followed by a post annealing treatment process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), scanning electron microscope (SEM), photoluminescence (PL) spectra as well as lifetimes were utilized to characterize the prepared samples. The results of XRD indicated that the samples began to crystallize at 500 °C, and the crystallinity increased with increasing the annealing temperature. The powders with metastable tetragonal symmetry were obtained at relatively low temperature. The effects of annealing temperature, the Eu³⁺ concentration as well as the morphology on the PL intensity were investigated in this work.     

Synthesis and upconversion properties of GdOBr:Er phosphors

GdOBr:Er³⁺ phosphors were synthesized by a simple solid-state reaction method. Under 980 nm and (or) 785 nm laser excitation, GdOBr:Er³⁺ (1%) samples present strong green and red upconverted emissions. The upconversion mechanisms were studied in detail through laser power dependence and excited state absorption process is discussed as the possible upconversion mechanisms. More interesting, the bright green upconverted emission is visible to the naked eye for GdOBr:Er³⁺ (1%) samples even excited by 1 mW 980 nm laser. Such phenomenon indicates that GdOBr:Er³⁺ may be used as upconversion phosphors.     

Luminescent properties of Na3YSi3O9 doped with Eu under UV-VUV excitation

The luminescent properties of Na₃Y_1−xSi₃O₉:xEu³⁺ (0.05 ≦ x ≦ 0.80) powder crystals were investigated in UV-VUV region. The Eu³⁺-O²⁻ charge transfer band (CTB) was observed to be located at around 233 nm and the environmental parameter (h_e) was estimated to be about 0.730. The excitation spectrum monitoring the 613 nm red emission from Eu³⁺ ions reveals the host absorption band (HAB) to be around 145 nm. The calculated Commission Internationale de l’Eclairage (CIE) chromaticity coordinates indicate the emission by 233 nm rather than by 147 nm excitation has the better color purity and the possible mechanisms have been proposed. The Eu³⁺-emission showed high quenching concentration due to the isolated YO₆ octahedra in the host and the small h_e for the Eu³⁺ ions and the optimum concentration was determined to be as high as x = 0.65 and 0.30 with 233 and 147 nm excitation, respectively.     

Low temperature synthesis and photoluminescent properties of CaMoO4:Eu red phosphor with uniform micro-assemblies

Scheelite-type Eu³⁺-doped CaMoO₄ red phosphor with uniform micro-assemblies has been successfully synthesized via a facile hydrothermal method at 120 °C for 10 h. The Eu³⁺-doped CaMoO₄ microstructures were assembled by small nanostructures and the morphology of materials was found to be manipulated by dropping different alkalis into the stock solution for the first time. The structure, morphology, and luminescent property were characterized and investigated by techniques of X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL). The luminescent investigations confirmed that the Eu³⁺ ions have been effectively doped into CaMoO₄ nanostructures. The successfully achieved Eu³⁺-doped CaMoO₄ nanostructures will be potential in technological applications on near UV chip-based white light emitting diode (WLED).     

Solvothermal synthesis of SrMoO4:Ln (Ln = Eu, Tb, Dy) nanoparticles and its photoluminescence properties at room temperature

Rare-earth ions (Eu³⁺, Tb³⁺, Dy³⁺) doped SrMoO₄ nanoparticles were prepared by solvothermal route using oleic acid as surfactant to control the particle shape and size. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), photoluminescence spectra (PL) and the kinetic decay times were applied to characterize the obtained samples. The XRD patterns reveal that all the doped samples are assigned to the scheelite-type tetragonal structure of SrMoO₄ phase. In addition, the as-synthesized SrMoO₄:Ln (Ln = Eu³⁺, Tb³⁺, Dy³⁺) particles are high purity well crystallized and with the average size of 30-50 nm. The possible formation process of SrMoO₄:Ln (Ln = Eu³⁺, Tb³⁺, Dy³⁺) nanoparticles have been discussed as well. Upon excitation by ultraviolet radiation, the as-synthesized SrMoO₄:Ln (Ln = Eu³⁺, Tb³⁺, Dy³⁺) nanoparticles exhibit the characteristic emission lines of corresponding Eu³⁺, Tb³⁺, Dy³⁺, respectively.     

Fine-sized LiCoO2 particles prepared by spray pyrolysis from polymeric precursor solution

Fine-sized LiCoO₂ particles with high discharge capacities and good cycle properties were prepared by spray pyrolysis from a spray solution with citric acid and ethylene glycol. The precursor particles obtained from the spray solution with citric acid and ethylene glycol transformed into fine-sized LiCoO₂ particles with regular morphology after post-treatment at temperatures between 700 and 900 °C. The mean size and aggregation degree of the primary particles were affected by the concentrations of polymeric precursors added into spray solutions. The LiCoO₂ particles obtained from the spray solution without polymeric precursors had irregular and aggregated morphology. The discharge capacities of the LiCoO₂ particles changed from 132 to 151 mAh/g when the concentrations of the citric acid and ethylene glycol changed from 0 to 1 M. The particles prepared from the spray solution containing 0.3 M each of citric acid and ethylene glycol had the maximum discharge intensity.     

Upconversion in Er-doped Gd2O3 nanocrystals prepared by propellant synthesis and flame spray pyrolysis

In this study, monoclinic luminescent Gd₂O₃ nanocrystals doped with different concentrations of Er³⁺ (0.1, 1, and 10 mol%) were produced by propellant synthesis and flame spray pyrolysis (FSP). A comparison of their optical and morphological properties is reported. Following 980 nm excitation, an increase of the emission intensity from the ²H_11/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions was observed with increasing Er³⁺ concentration in the Gd₂O₃ nanocrystalline samples prepared via both techniques. However, the overall upconversion emission intensity was greater for the samples obtained by FSP. Furthermore, as the Er³⁺ concentration was increased, the intensity of the red (⁴F_9/2 → ⁴I_15/2) emission was observed to increase more rapidly in comparison to the green (²H_11/2, ⁴S_3/2 → ⁴I_15/2) emission resulting in an overall enhancement of the red component in the upconversion emission. Although both synthetic routes yield average crystallite sizes in the nanoscale, the TEM and SEM images confirm a more homogeneous morphology and lower particle aggregation for the nanocrystals produced by FSP.