Nanostructured CaWO4, CaWO4:Eu3+ and CaWO4:Tb3+ particles: sonochemical synthesis and luminescent properties

Nanostructured CaWO4, CaWO4:Eu3+, and CaWO4:Tb3+ phosphor particles were synthesized via a facile sonochemical route. X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, photoluminescence, low voltage cathodoluminescence spectra, and photoluminescence lifetimes were used to characterize the as-obtained samples. The X-ray diffraction results indicate that the samples are well crystallized with the scheelite structure of CaWO4. The transmission electron microscopy and field emission scanning electron microscopy images illustrate that the powders consist of spherical particles with sizes from 120 to 160 nm, which are the aggregates of even smaller nanoparticles ranging from 10 to 20 nm. Under UV light or electron beam excitation, the CaWO4 powder exhibited a blue emission band with a maximum at 430 nm originating from the WO4/2- groups, while the CaWO4:Eu3+ powder showed red emission dominated by 613 nm ascribed to the 5D0 --> 7F2 of Eu3+, and the CaWO4:Tb3+ powders showed emission at 544 nm, ascribed to the 5D4 --> 7F5 transition of Tb3+. The PL excitation and emission spectra suggest that the energy is transferred from WO4/2- to Eu3+ CaWO4:Eu3+ and to Tb3+ in CaWO4:Tb3+. Moreover, the energy transfer from WO4/2- to Tb3+ in CaWO4:Tb3+ is more efficient than that from WO4/2- to EU3+ in CaWO4:Eu3+. This novel and efficient pathway could open new opportunities for further investigating the novel properties of tungstate materials.     

Nanostructured CaWO4, CaWO4 : Pb2+ and CaWO4 : Tb3+ particles: polyol-mediated synthesis and luminescent properties

Nano-submicrostructured CaWO4, CaWO4 : Pb2+ and CaWO4 : Tb3+ particles were prepared by polyol method and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier transform infrared spectra (FT-IR), thermogravimetry-differential thermal analysis (TG-DTA), photoluminescence (PL), cathodo-luminescence (CL) spectra and PL lifetimes. The results of XRD indicate that the as-prepared samples are well crystallized with the scheelite structure of CaWO4. The FE-SEM images illustrate that CaWO4 and CaWO4 : Pb2+ and CaWO4 : Tb3+ powders are composed of spherical particles with sizes around 260, 290, and 190 nm respectively, which are the aggregates of smaller nanoparticles around 10-20 nm. Under the UV light or electron beam excitation, the CaWO4 powders exhibits a blue emission band with a maximum at about 440 nm. When the CaWO4 particles are doped with Pb2+, the intensity of luminescence is enhanced to some extent and the luminescence band maximum is red shifted to 460 nm. Tb(3+)-doped CaWO4 particles show the characteristic emission of Tb3+ 5D4-7FJ (J = 6 - 3) transitions due to an energy transfer from WO4(2-) groups to Tb3+.     

Temperature characteristics of NaY(MoO4)2: Sm3+ and effect of Li+ doping on luminescent properties of phosphors

Journal of Materials Science: Materials in Electronics - Intense orange phosphors NaY(MoO4)2: Sm3+ were successfully synthesized by means of a conventional solvothermal process in the presence of...     

Patterning of red, green, and blue luminescent films based on CaWO4:Eu3+, CaWO4:Tb3+, and CaWO4 phosphors via microcontact printing route

The multicolor patterned luminescent films of CaWO(4):Eu(3+) (red), CaWO(4):Tb(3+) (green), and pure CaWO(4) (blue) on quartz substrates were fabricated by the facile and low-cost microcontact printing (μCP) method combining with the Pechini sol-gel route. On the basis of the μCP process, a hydrophobic self-assembled monolayer (SAM) was first created on the hydrophilic surface of quartz substrates by poly(dimethylsiloxane) (PDMS) mold printing, and then, the multicolor patterned luminescent films were selectively deposited on the hydrophilic regions via a spin coating process and heating treatment. The X-ray diffraction, optical microscopy, scanning electron microscopy, and photoluminescence (PL) spectra were used to characterize the structure and fluorescence properties of the corresponding samples. The results demonstrate that the μCP process can be used for patterning the inorganic phosphor materials and have potential for fabricating rare-earth luminescent pixels for the applications of display devices.     

Synthesis and luminescent properties of Eu3+ and Dy3+ doped BiPO4 phosphors for near UV-based white LEDs

The phosphors BiPO₄:Eu³⁺ co-doped with Dy³⁺ were synthesized by the conventional solid-state reaction method. XRD and scanning electron microscopy results showed that the crystalline phase of the samples BiPO₄:Eu³⁺ transforms from high-temperature monoclinic phase to low-temperature monoclinic phase with the increase of Dy³⁺ concentration. The photoluminescence properties of the samples showed that the colors shifting from red–orange area to blue–green area are close to those of ideal white light by readjusting the doping concentration ratio of Eu³⁺ and Dy³⁺. The Eu³⁺and Dy³⁺ doped BiPO₄ phosphors may be potential applications in white light near-UV light-emitting diodes.     

Effects of co-doped Li+ ions on luminescence of CaWO4:Sm3+ nanoparticles

CaWO₄, CaWO₄:Sm³⁺ and CaWO₄:(Sm³⁺, Li⁺) nanoparticles were synthesized by the precipitation method with addition of PEG 200. The X-ray diffraction patterns show that the obtained samples have a pure tetragonal phase. The CaWO₄ sample shows an emission peak at 418 nm originating from the charge-transfer transitions within the WO₄ ^2? complex. CaWO₄:Sm³⁺ and CaWO₄:(Sm³⁺, Li⁺) samples show emission peaks originating from the f–f forbidden transitions of the 4f electrons of Sm³⁺ ions. The charge compensator of Li⁺ can enhance the emission intensity effectively. It is found that the emission intensity of CaWO₄:(3 mol% Sm³⁺, 4 mol% Li⁺) phosphor is about double that of CaWO₄:3 mol% Sm³⁺ phosphor.     

Synthesis and luminescent properties of Tb3+ activated AWO4 based (A = Ca and Sr) efficient green emitting phosphors

Optically efficient terbium activated alkaline earth metal tungstate nano phosphors (AWO₄ [A = Ca, Sr]) with different doping concentrations have been prepared by mechanochemically assisted solid state metathesis reaction at room temperature for the first time. The prepared phosphors were characterized by the X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscope (SEM), Fourier transform Raman (FT-Raman) spectroscopy, photoluminescence and diffuse reflectance spectroscopy measurements. The XRD and Raman spectra results showed that the prepared powders present a scheelite-type tetragonal structure. FTIR spectra exhibited a high absorption band situated at around 850 cm^?1, which was ascribed to the W–O antisymmetric stretching vibrations into the [WO₄]^2? tetrahedron groups and the SEM images reveal that the particle sizes were in the range of 20–60 nm. The excitation and the emission spectra were measured to characterize the luminescent properties of the phosphors. The excitation spectrum exhibits a charge transfer broad band along with some sharp peaks from the typical 4f–4f transitions of Tb³⁺. Under excitation of UV light, these AWO₄:xTb³⁺ (A = Ca, Sr) phosphors showed a strong emission band centered at 545 nm (green) which corresponds to ⁵ D ₄ → ⁷ F ₅ transition of Tb³⁺. Analysis of the emission spectra with different Tb³⁺ concentrations revealed that the optimum dopant concentration for CaWO₄:xTb³⁺ and SrWO₄:xTb³⁺ phosphors are about 8 and 6 mol% of Tb³⁺. The green emission intensity of the solid state meta-thesis prepared CaWO₄:0.08Tb³⁺ and SrWO₄:0.06Tb³⁺ phosphors are 1.5 and 1.2 times greater than that of the commercial LaPO₄:Ce, Tb green phosphor. All properties show that AWO₄:Tb³⁺ (A = Ca, Sr) is a very appropriate green-emitting phosphor for fluorescent lamp applications.     

Pressure effects on the luminescence properties of CaWO4:Pr3+

Steady state and time resolved emission measurements of CaWO₄ doped with Pr³⁺ have been carried out as a function of hydrostatic pressure in the 1–315 kbar range. The increase of pressure induces several effects: a progressive red shift of the spectral features and a decrement of the decay times of both ³P₀ and ¹D₂ emitting levels, the decrease of the intensity of the ³P₀ emission, that is completely quenched at around 100 kbar, and the increase of the ¹D₂ emission intensity in the 1–120 kbar range followed by a fast decrease at higher pressures. In addition, a variation in the structure of the emission manifolds has been observed in the 80–100 kbar range as a consequence of the tetragonal to monoclinic phase transition of the host lattice induced by pressure. These effects have been accounted for by means of a model that takes into account the role played by a praseodymium trapped exciton in the excited state dynamics of the investigated material.     

Influence of Zn2+ and Si4+ codoping on luminescence properties of CaWO4:Eu3+ phosphor

The red afterglow phosphors of CaWO₄ doped with Eu³⁺, Zn²⁺ or (and) Si⁴⁺ were prepared by solid state reaction. All crystalline phases were identified by the X-ray powder diffraction (XRD). The photoluminescence spectra and decay curves as well as thermoluminecence (TL) curves of all samples were also investigated. In comparison to CaWO₄:Eu³⁺ phosphor, the luminescence and afterglow properties could be improved greatly after being doped with Zn²⁺ or (and) Si⁴⁺ ions.     

Preparation and luminescent properties of orange reddish emitting phosphor LaMgAl11O19:Sm3+

An orange reddish emitting phosphor, LaMgAl₁₁O₁₉:Sm³⁺, was synthesized by a high temperature solid-state reaction, and the phase formation, crystal structure and luminescence properties were investigated respectively. The LaMgAl₁₁O₁₉:Sm³⁺ phosphor presents a highly intense orange reddish emission peak under the near ultraviolet excitation at 403 nm, which is corresponds to the ⁴G_5/2 → ⁶H_J (J = 5/2, 7/2, 9/2 and 11/2) transitions of Sm³⁺ ions. It was found that the dipole–dipole interactions mainly results in the concentration quenching in the LaMgAl₁₁O₁₉:Sm³⁺ phosphor with a critical quenching concentration at about 5 mol%. The temperature dependence of luminescence properties was studied from 25 to 200 °C and indicated that LaMgAl₁₁O₁₉:0.05Sm³⁺ phosphors had a relatively higher quenching temperature. The chromatic properties of LaMgAl₁₁O₁₉:0.05Sm³⁺ phosphor have been found to have chromaticity coordinate of (0.578, 0.420). All these properties indicate that the orange reddish emitting LaMgAl₁₁O₁₉:Sm³⁺ phosphor has a potential application in w-LEDs.     

Synthesis and luminescent properties: Mn4+-doped Sr3NaNbO6 phosphor with far-red emission

Journal of Materials Science: Materials in Electronics - The unique luminescence properties of far-red emitting materials make them important components in the phosphor-converted LEDs (pc-LEDs) for...     

Luminescent properties of YAl3(BO3)4:Eu3+ phosphors

YAL₃(BO₃)₄:Eu³⁺ phosphors were fabricated by the sol-gel method. The structure properties were measured by x-ray diffraction (XRD) and infrared spectra (IR). Doping concentration of Eu³⁺ ions in YAL₃(BO₃)₄:Eu³⁺ phosphors of 0, 1, 3, 4, and 5 mol% were studied. The excitation spectra and emission spectra of YAL₃(BO₃)₄:Eu³⁺ phosphors were examined by fluorescent divide spectroscopy (FDS). The luminescent properties of YAL₃(BO₃)₄:Eu³⁺ phosphors are discussion. The optimal doping concentration of Eu³⁺ ions in YAL₃(BO₃)₄:Eu³⁺ phosphors was found to be approximately 3 mol%.     

燃烧法合成CaMoO4∶Eu3+及其发光性能的研究

采用柠檬酸作为燃料,通过燃烧法制备了CaMoO4蓝色以及CaMoO4:Eu3+红色荧光粉.研究了Eu3+的掺入、反应温度以及反应时间对所制得的CaMoO4:Eu3+的晶体结构以及发光性能的影响.XRD谱图分析显示合成样品CaMoO4和CaMoO4:Eu3+均为白钨矿型晶体结构,晶体的结晶度随着合成温度的升高以及保温时间...     

Hydrothermal synthesis and luminescent properties of GdVO4 : Eu3+ nanophosphors

Eu³⁺-doped GdVO₄ has been synthesised via hydrothermal method by altering the hydrothermal temperature, reaction time and surfactant. The microstructure and morphology information of the phosphors were investigated via the techniques of X-ray powder diffraction and scanning electronic microscopy, which show that the phosphors wear tetragonal phase and the products present various regular morphologies under different reaction conditions such as bulk and nanoparticle. Moreover, the morphologies of the products have been controlled by altering reaction temperature. In addition, the surfactant was also included to control the morphologies of the products and the phosphors present different morphologies. All the phosphors exhibit the characteristic fluorescence of Eu ion (⁵D₀ → ⁷F₂ and ⁵D₀ → ⁷F₂). The electric dipole transition ⁵D₀ → ⁷F₂ of Eu³⁺ is dominant indicating that most sites of Eu³⁺ ions in GdVO₄ have no inversion centre. Furthermore, we found that the reaction time and the morphologies have great influence on optical properties.