Phase transformation and photoluminescence properties of nanocrystalline ZrO2 powders prepared via the Pechini-type sol-gel process

Nanocrystalline ZrO2 fine powders were prepared via the Pechini-type sol-gel process followed by annealing from 500 to 1000 degrees C. The obtained ZrO2 samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), electron paramagnetic resonance (EPR), and photoluminescence spectra (PL), respectively. The phase transition process from tetragonal (T) to monoclinic (M) was observed for the nanocrystalline ZrO2 powders in the annealing process, accompanied by the change of their photoluminescence properties. The 500 degrees C annealed ZrO2, powder with tetragonal structure shows an intense whitish blue emission (lambda(max) = 425 nm) with a wide range of excitation (230-400 nm). This emission decreased in intensity after being annealed at 600 degrees C (T + M-ZrO2) and disappeared at 700 (T + M-ZrO2), 800 (T + M-ZrO2), and 900 degrees C (M-ZrO2). After further annealing at 1000 degrees C (M-ZrO2), a strong blue-green emission appeared again (lambda(max) = 470 nm).

Synthesis and luminescence properties of monodisperse spherical Y2O3 : Eu3+@SiO2 particles with core-shell structure

Y2O3: Eu3+ phosphor layers were deposited on monodisperse SiO2 particles with different sizes ( 300, 500, 900, and 1200 nm) via a sol-gel process, resulting in the formation of Y2O3: Eu3+@SiO2 core-shell particles. X-ray diffraction ( XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy ( TEM), time-resolved photoluminescence ( PL) spectra, and lifetimes were employed to characterize the Y2O3: Eu3+@SiO2 core-shell samples. The results of XRD indicated that the Y2O3: Eu3+ layers began to crystallize on the silica surfaces at 600 degrees C and the crystallinity increased with the elevation of annealing temperature until 900 degrees C. The obtained core-shell particles have perfect spherical shape with narrow size distribution and non-agglomeration. The thickness of the shells could be easily controlled by changing the number of deposition cycles ( 60 nm for three deposition cycles). Under the excitation of ultraviolet ( 250 nm), the Eu3+ ion mainly shows its characteristic red ( 611 nm, D-5(0)-F-7(2)) emissions in the core-shell particles from Y2O3: Eu3+ shells.

Luminescent properties of a new blue long-lasting phosphor Ca2P2O7:Eu2+, Y3+

A new pyrophosphate long-lasting phosphor with composition of Ca1.96P2O7:0.02Eu(2+), 0.02Y(3+) is synthesized via the high-temperature solid-state reaction method. Its properties are systematically investigated utilizing XRD, photoluminescence, phosphorescence and thermoluminescence (TL) spectra. The phosphor emits blue light that is related to the characteristic emission of Eu2+ due to 5d-4f transitions. For the optimized sample, bright blue long-lasting phosphorescence (LLP) could be observed by naked eyes even 6 h after the excitation source is removed. The TL spectra show that the doping of Y3+ ions greatly enhanced intensity of 335 K peak and created new TL peak at about 373 K that is also responsible for the blue LLP. Based on our study, Y3+ ions are suggested to act as electron traps to improve the performance of the blue phosphorescence of Eu2+ such as intensity and persistent time.

Facile Hydrothermal Synthesis and Luminescent Properties of Large-Scale GdVO4:Eu3+ Nanowires

Large-scale GdVO4:Eu3+ nanowires with diameters of about 15 nm and lengths of several micrometers were achieved by a facile hydrothermal method in the presence of disodium ethylenediamine tetraacetate (Na2H2L). The influences of several parameters, such as pH value, reaction temperature, and molar ratio of Na2H2L to Gd3+ on the final products were investigated. The formation mechanism of the as-obtained GdVO4:Eu3+ nanowires is proposed on the basis of time-dependent experiments. It is found that the organic additive Na2H2L, which acts as a shape modifier, has a dynamic effect by adjusting the growth rates of different facets, resulting in the formation of the GdVO4:Eu3+ nanowires. The luminescent spectrum of GdVO4:Eu3+ nanowires shows the strong characteristic dominant emission of the Eu3+ ions at 614 nm.

Facile chemical conversion synthesis and luminescence properties of uniform Ln3+ (Ln = Eu, Tb)-doped NaLuF4 nanowires and LuBO3 microdisks

Uniform NaLuF(4) nanowires and LuBO(3) microdisks have been successfully prepared by a designed chemical conversion method. The lutetium precursor nanowires were first prepared through a simple hydrothermal process. Subsequently, uniform NaLuF(4) nanowires and LuBO(3) microdisks were synthesized at the expense of the precursor by a hydrothermal conversion process. The whole process was carried out in aqueous condition without any organic solvents, surfactant, or catalyst. The conversion processes from precursor to the final products have been investigated in detail. The as-obtained Eu(3+) and Tb(3+)-doped LuBO(3) microdisks and NaLuF(4) nanowires show strong characteristic red and green emissions under ultraviolet excitation or low-voltage electron beam excitation. Moreover, the luminescence colors of the Eu(3+) and Tb(3+) codoped LuBO(3) samples can be tuned from red, orange, yellow, and green-yellow to green by simply adjusting the relative doping concentrations of the activator ions under a single wavelength excitation, which might find potential applications in the fields such as light display systems and optoelectronic devices.

Uniform Lanthanide Orthoborates LnBO(3) (Ln = Gd, Nd, Sm, Eu, Tb, and Dy) Microplates: General Synthesis and Luminescence Properties

A variety of uniform lanthanide orthoborates LnBO(3) (Ln = Gd, Nd, Sm, Eu, Tb, and Dy) microplates have been successfully prepared by a general and facile conversion method. One-dimensional (ID) lanthanide hydroxides were first prepared through a simple hydrothermal process. Subsequently, uniform LnBO(3) microplates were synthesized at the expense of the ID precursors during a hydrothermal conversion process. The whole process in this method was carried out in aqueous condition without the use of any organic solvents, surfactant, or catalyst. The as-obtained rare earth ions doped GdBO3 and TbBO3 microplates show strong light emissions with different colors coming from different activator ions under ultraviolet excitation or low-voltage electron beam excitation, which might find potential applications in fields such as light phosphor powders and advanced flat panel display devices.

Facile Synthesis and Luminescence Properties of Highly Uniform MF/YVO4:Ln(3+) (Ln = Eu, Dy, and Sm) Composite Microspheres

Uniform MF/YVO4:Ln(3+) (Ln = Eu, Dy, and Sm) composite microspheres have been prepared via a simple and economical wet-chemical route at ambient pressure and low temperature. Monodisperse micrometer-sized melamine formaldehyde (MF) colloidal particles were first fabricated by a condensation process of melamine with formaldehyde. Subsequently, well-dispersed YVO4 nanoparticles were successfully grown onto the MF microspheres to form core-shell structured composite particles in aqueous Solution. The as-obtained composite microspheres with perfect spherical shape are uniform in size and distribution, and the thickness and roughness of the YVO4 shells on MF cores could be tuned by varying the reaction temperature. The MF/YVO4:Ln(3+) composite phosphors show strong light emissions with different colors coming from different activator ions under ultraviolet excitation, which might find potential applications in fields such as light phosphor powders and advanced flat panel displays.

Highly Uniform Gd(OH)(3) and Gd2O3:Eu3+ Nanotubes: Facile Synthesis and Luminescence Properties

Uniform Gd(OH)(3) nanotubes have been prepared via a simple wet-chemical route at ambient pressure and low temperature, without any catalysts, templates, or substrates, in which Gd(NO3)(3) was used as the gallium source and ammonia as the alkali. SEM and TEM images indicate that the as-obtained Gd(OH)3 entirely consists of uniform nanotubes in high yield with diameters of about 40 nm and lengths of 200-300 nm. The temperature-dependent morphological evolution and the formation mechanism of the Gd(OH)(3) nanotubes were investigated in detail. Furthermore, the Gd2O3 and Eu3+-doped Gd2O3 nanotubes, which inherit their parents' morphology, were obtained during a direct annealing process in air. The corresponding Gd2O3:Eu3+ nanotubes exhibit the strong red emission corresponding to the D-5(0)-F-7(2), transition of the Eu3+ ions under UV light or low-voltage electron beam excitation, which might find potential applications in the fields such as light-emitting phosphors, advanced flat panel displays, or biological labeling.

Facile Surfactant- and Template-Free Synthesis and Luminescent Properties of One-Dimensional Lu2O3:Eu3+ Phosphors

Uniform Lu2O3:Eu3+ nanorods and nanowires have been successfully prepared through a simple solution-based hydrothermal process followed by a subsequent calcination process without using any surfactant, catalyst, or template. On the basis of X-ray diffraction, thermogravimetric analysis and differential scanning calorimetry, and Fourier transform infrared spectroscopy results, it can be assumed that the as-obtained precursors have the structure formula of Lu4O(OH)(9)(NO3), which is a new phase and has not been reported. The morphology of the precursors could be modulated from nanorods to nanowires with the increase of pH value using ammonia solution. The as-formed precursors could transform to cubic Lu2O3:Eu3+ with the same morphology and a slight shrinkage in size after an annealing process, Both the Lu2O3:Eu3+ nanorods and nanowires exhibit the strong red emission corresponding to the D-5(0)-F-7(2) transition of the Eu3+ ions under UV light excitation or low-voltage electron beam excitation.

Y2O3 : Eu3+ microspheres: Solvothermal synthesis and luminescence properties

Y2O3 : Eu3+ microspheres, with an average diameter of 3 mu m, were successfully prepared through a large-scale and facile solvothermal method followed by a subsequent heat treatment. X-ray diffraction, Fourier transform infrared spectroscopy, energy-dispersive X-ray spectra, thermogravimetric and differential thermal analysis, inductive coupled plasma atomic absorption spectrometric analysis, scanning electron microscopy, transmission electron microscopy, photoluminescence spectra, as well kinetic decays, and cathodoluminescence spectra were used to characterize the samples. These microspheres were actually composed of randomly aggregated nanoparticles. The formation mechanisms for the Y2O3 : Eu3+ microspheres have been proposed on an isotropic growth mechanism. The Y2O3 : Eu3+ microspheres show a strong red emission corresponding to D-5(0) -> F-7(2) transition (610 nm) of Eu3+ under ultraviolet excitation (259 nm) and low-voltage electron beams excitation (1-5 kV), which have potential applications in fluorescent lamps and field emission displays.

Growth of highly crystalline CaMoO4 : Tb3+ phosphor layers on spherical SiO2 particles via sol-gel process: Structural characterization and luminescent properties

Highly crystalline CaMoO4:Tb3+ phosphor layers were grown on monodisperse SiO2 particles through a simple sol-gel method, resulting in formation of core-shell structured SiO2@CaMoO4:Tb3+ submicrospheres. The resulting SiO2@CaMoO4: Tb3+ core-shell particles were fully characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectra (EDS), transmission electron microscopy (TEM), photoluminescence (PL), low-voltage cathodoluminescence (CL), and kinetic decays. The XRD results demonstrate that the CaMoO4:Tb3+ layers begin to crystallize on the SiO2 spheres after annealing at 400 degrees C and the crystallinity increases with raising the annealing temperature. SEM and TEM analysis indicates that the obtained submicrospheres have a uniform size distribution and obvious core-shell structure. SiO2@CaMoO4:Tb3+ submicrospheres show strong green emission under short ultraviolet (260 nm) and low-voltage electron beam (1-3 kV) excitation, and the emission spectra are dominated by a D-5(4) -F-7(5) transition of Tb3+(544 nm, green) from the CaMoO4:Tb3+ shells.

Remarkable changes in the optical properties of CeO2 nanocrystals induced by lanthanide ions doping

Highly uniform and well-dispersed CeO2 and CeO2:Eu3+ (Sm3+, Tb3+) nanocrystals were prepared by a nonhydrolytic solution route and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), UV/vis absorption, and photoluminescence (PL) spectra, respectively. The result of XRD indicates that the CeO2 nanocrystals are well crystallized with a cubic structure. The TEM images illustrate that the average size of CeO2 nanocrystals is about 3.5 nm in diameter. The absorption spectrum of CeO2:Eu3+ nanocrystals exhibits red-shifting with respect to that of the undoped CeO2 nanocrystals. Under the excitation of 440 nm (or 426 nm) light, the colloidal solution of the undoped CeO2 nanocrystals shows a very weak emission band with a maximum at 501 nm, which is remarkably enhanced by doping additional lanthanide ions (Eu3+, Tb3+, Sm3+) in the CeO2 nanocrystals. The emission band is not due to the characteristic emission of the lanthanide ions but might arise from the oxygen vacancy which is introduced in the fluorite lattice of the CeO2 nanocrystals to compensate the effective negative charge associated with the trivalent ions.

Highly uniform and monodisperse beta-NaYF4 : Ln(3+) (Ln = Eu, Tb, Yb/Er, and Yb/Tm) hexagonal microprism crystals: Hydrothermal synthesis and luminescent properties

beta-NaYF4:Ln(3+) (Ln = Eu, Tb, Yb/Er, and Yb/Tm) hexagonal microprisms with remarkably uniform morphology and size have been synthesized via a facile hydrothermal route. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL) spectra as well as kinetic decays were used to characterize the samples. It is found that sodium citrate as a shape modifier introduced into the reaction system plays a critical role in the shape evolution of the final products. Furthermore, the shape and size of the products can be further manipulated by adjusting the molar ratio of citrate/RE3+ (RE represents the total amount of Y3+ and the doped rare earth elements such as Eu3+, Tb3+, Yb3+/Er3+, or Yb3+/Tm3+). Under the excitation of 397 nm ultraviolet light, NaYF4:xEu(3+) (x = 1.5, 5%) shows the emission lines of Eu3+ corresponding to D-5(0-3) -> F-7(J) (J = 0-4) transitions from 400 to 700 nm (whole visible spectral region) with different intensity, resulting in yellow and red down-conversion (DC) light emissions, respectively.

Tunable luminescence properties of Tb3+-doped LaGaO3 nanocrystalline phosphors

Nanocyrstalline Tb3+-doped LaGaO3 phosphors were prepared through a Pechini-type sol-gel process. X-ray diffraction, field-emission scanning electron microscopy (FESEM), photoluminescence, cathodoluminescence spectra, and lifetimes were utilized to characterize the synthesized phosphors. XRD results reveal that the sample begins to crystallize at 900 degrees C and pure LaGaO3 phase can be obtained at 1000 degrees C. FESEM images indicate that the Tb3+-doped LaGaO3 phosphors are composed of aggregated spherical particles with sizes ranging from 40 to 80 nm. Under the excitation of ultraviolet light and low-voltage electron beams (0.5-3 kV), the Tb3+-doped LaGaO3 phosphors show the characteristic emissions from the LaGaO3 host lattice and the Tb3+ (D-5(3,4)-F-7(6,5,4,3) transitions). The emission colors of Tb3+-doped LaGaO3 phosphors can be tuned from blue to green by changing the excitation wavelength of ultraviolet light and the doping concentration of Tb3+ to some extent. Relevant luminescence mechanisms are discussed.

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. Tb3+-doped CaWO4 particles show the characteristic emission of Tb3+ D-5(4)-F-7(J) (J=6-3) transitions due to an energy transfer from WO42- groups to Tb3+.