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.

Nanocrystalline LaGaO3 : Tm3+ as an efficient blue phosphor for field emission displays with high color purity

Nanocrystalline Tm3+-doped LaGaO3 phosphors were prepared through a Pechini-type sol-gel process [M. P. Pechini, U.S. Patent No. 3,330,697 (11 July 1967)]. X-ray diffraction, field emission scanning electron microscopy, photoluminescence, and cathodoluminescence (CL) spectra were utilized to characterize the synthesized phosphors. Under the excitation of ultraviolet light and low voltage electron beams (0.5-3 kV), the Tm3+-doped LaGaO3 phosphors show the characteristic emissions from the LaGaO3 host lattice and the Tm3+ (D-1(2), (1)G(4)-F-3(4), and H-3(6) transitions), respectively. The blue CL of the Tm3+-doped LaGaO3 phosphors, with a dominant wavelength of 458 nm, had better Commission International I'Eclairage chromaticity coordinates (0.1552, 0.0630) and higher emission intensity than the commercial product (Y2SiO5:Ce3+).

Sol-gel synthesis and characterization of SiO2@NaGd(WO4)(2): Eu3+ core-shell-structured spherical phosphor particles

Monodisperse, core-shell-structured SiO2@NaGd(WO4)(2):Eu3+ particles were prepared by the sol-gel method. The samples were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, photoluminescence (PL), and low-voltage cathodoluminescence (CL) as well as time-resolved PL spectra and lifetimes. PL and CL study revealed that the core-shell-structured SiO2@NaGd (WO4)(2):Eu3+ particles show strong red emission dominated by the D-5(0) - F-7(2) transition of Eu3+ at 614 nm with a lifetime of 0.74 ms. The PL and CL emission intensity can be tuned by the coating number of NaGd(WO4)(2):Eu3+ phosphor layers on SiO2 and by accelerating voltage and the filament current, respectively.

Synthesis and characterization of monodisperse spherical core-shell structured SiO2@Y3Al5O12 : Ce3+/Tb3+ phosphors for field emission displays

Nanocrystalline Y3Al5O12: Ce3+/Tb3+ ( average crystalline size 30 nm) phosphor layers were coated on non-aggregated, monodisperse and spherical SiO2 particles by the sol-gel method, resulting in the formation of core-shell structured SiO2@Y3Al5O12:Ce3+/Tb3+ particles. X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, photoluminescence, cathodoluminescence spectra, as well as lifetimes were utilized to characterize the core-shell structured SiO2@Y3Al5O12: Ce3+/Tb3+ phosphor particles. The obtained core-shell structured phosphors consist of well-dispersed submicron spherical particles with a narrow size distribution. The thickness of the Y3Al5O12:Ce3+/Tb3+ shells on the SiO2 cores ( average size about 500 nm, crystalline size about 30 nm) could be easily tailored by varying the number of deposition cycles (100 nm for four deposition cycles). Under the excitation of ultraviolet and low-voltage electron beams (1-3 kV), the core-shell SiO2@Y3Al5O12:Ce3+/ Tb3+ particles show strong yellow-green and green emission corresponding to the 5d-4f emission of Ce3+ and D-5(4)-F-7(J) ( J = 6, 5, 4, 3) emission of Tb3+, respectively.

Pechini sol-gel deposition and luminescent properties of SrLa1-xRExGa3O7 (RE = Eu, Tb) phosphor films

SrLa1-xRExGa3O7 (RE = EU3+, Tb3+) phosphor films were deposited on quartz glass substrates by a simple Pechim sol-gel method. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), atomic force microscopy, field-emission scanning electron microscopy, photoluminescence spectra, and lifetimes were used to characterize the resulting films. The results of XRD indicated that the films began to crystallize at 700 degrees C and crystallized fully at 900 degrees C. The results of FNR spectra were in agreement with those of XRD. Uniform and crack-free films annealed at 900 degrees C were obtained with average grain size of 80 nm, root mean square roughness of 46 nm and thickness of 130 nm The RE ions showed their characteristic emission in crystalline SrLa1-xRExGa3O7 films, i.e., Eu3+ D-0-F-7(J) (J = 0, 1, 2, 3, 4), Tb3+5D4 -(7) F-J (J = 6, 5, 4, 3) emissions, respectively. The optimum concentrations (x) of Eu3+ and Tb3+ were determined to be 50, and 80 mol% in SrLa(1-x)RE(x)GGa(3)O(7) films, respectively.

Thermoluminescence properties of Ce3+-doped LiSr4(BO3)(3) phosphor

Borates LiSr4(BO3)(3) were synthesized by high-temperature solid-state reaction. The thermoluminescence (TL) and some of the dosimetric characteristics of Ce3+-activated LiSr4(BO3)(3) were reported. The TL glow curve is composed of only one peak located at about 209 degrees C between room temperature and 500 degrees C. The Optimum Ce3+ concentration is 1 mol% to obtain the highest TL intensity. The TL kinetic parameters of LiSr4(BO3)(3):0.01Ce(3+) were studied by the peak shape method. The TL dose response is linear in the protection dose ranging from 1 mGy to 1 Gy. The three-dimensional thermoluminescence emission spectra were also studied, peaking at 441 and 474 nm due to the characteristic transition of Ce3+.

Improved optical photoluminescence by charge compensation in the phosphor system CaMoO4: Eu3+

It has been found that charge compensated CaMoO4:Eu3+ phosphors show greatly enhanced red emission under 393 and 467 nm-excitation, compared with CaMoO4:Eu3+ without charge compensation. Two approaches to charge compensation, (a) 2Ca(2+) -> EU3+ + M+, where M+ is a monovalent cation like Li+, Na+ and K+ acting as a charge compensator; (b) 3Ca(2+) -> 2EU(3+) + vacancy, are investigated. The influence of sintering temperature and Eu3+ concentration on the luminescent property of phosphor samples is also discussed.

Reduction from Eu3+ to Eu2+ in BaAl2O4 : Eu phosphor prepared in an oxidizing atmosphere and luminescent properties of BaAl2O4 : Eu

A reduction phenomenon of Eu3+ -> Eu2+ was observed for the first time when Eu3+ ions were doped into an AlO4-tetrahedron-containing compound BaAl2O4 in an oxidizing atmosphere of air by high-temperature solid-state reaction. X-ray powder diffraction patterns and photoluminescent spectra are used to confirm the compound structure and detect the simultaneous existence of both divalent and trivalent europium ions, respectively. The abnormal Eu3+ -> Eu2+ reduction is explained by a charge compensation model. Spectroscopic properties of BaAl2O4:Eu are discussed and Eu2+ emission spectrum shows consistence with the results reported by Katsumata et a]. [J. Cryst. Growth 198/199 (1999) 869.] and Lin et al. [Mater. Chem. Phys. 70 (2001) 156.].

Phase conversion and spectral properties of long lasting phosphor Zn-3 (PO4)(2): Mn2+, Ga3+

A red long lasting phosphor Zn-3(PO4)(2): Mn2+ Ga3+ (ZPMG) was prepared by ceramic method, and phase conversion and spectral properties were investigated. Results indicated that the phase conversion from alpha-Zn-3(PO4), beta-Zn-3(PO4)(2) to gamma-Zn-3(PO4)(2) occurs with different manganese concentration incorporated and sinter process. The structural change induced by the phase transformation results in a remarkable difference in the spectral properties. The possible luminescence mechanism for this red LLP with different forms has been illustrated.

Synthesis and photoluminescence of the Y2O3 : Eu3+ phosphor nanowires in AAO template

The monodisperse array and nanowires Of Y2O3:Eu3+ phosphor were synthesized using anodic aluminum oxide (AAO) template by sol-gel method. Scanning electron microscope (SEM) images indicated that Y2O3:Eu3+ nanowires are parallelly arranged, all of which are in uniform diameter of about 50 nm. The high-magnification SEM image showed that each nanowire is composed of a lot of agglutinating particles. The patterns of selected-area electron diffraction confirmed that Y2O3:EU3+ nanowires mainly consist of polycrystalline materials. Excitation and emission spectra Of Y2O3:E U3+/AAO composite films were measured. The characteristic red emission peak of EU3+ ion attributed to D-5(0)-->F-7(2) transition in Y2O3:EU3+/AAO nanowires broadened its halfwidth.

Sol-ogel deposition and luminescence properties of lanthanide ion-doped Y2(1-x)Gd2xSiWO8 (0 <= x <= 1) phosphor films

Y2(1-x) Gd2xSiWO8 : A ( 0 <= x <= 1; A= Eu3+, Dy3+, Sm3+, Er3+) phosphor films have been prepared on silica glass substrates through the sol - gel dip-coating process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), atomic force microscope (AFM), scanning electron microscopy (SEM) and photoluminescence spectra as well as lifetimes were used to characterize the resulting films. The results of the XRD indicated that the films began to crystallize at 800 degrees C and crystallized completely at 1000 degrees C. The AFM and SEM study revealed that the phosphor films, which mainly consisted of closely packed grains with an average size of 90 - 120 nm with a thickness of 660 nm, were uniform and crack free. Owing to an efficient energy transfer from the WO42- groups to the activators, the doped lanthanide ion ( A) showed its characteristic f - f transition emissions in crystalline Y2(1-x) Gd2xSiWO8 (0 <= x <= 1) films. The optimum concentrations for Eu3+, Dy3+, Sm3+, Er3+ were determined to be 21, 5, 3 and 7 mol% of Y3+ in Y2SiWO8 films, respectively.

Effects R3+ on the photoluminescent properties of Ca2R8(SiO4)(6)O-2 : A (R = Y, La, Gd; A= Eu3+, Tb3+) phosphor films prepared by the sol-gel process

Using CaCO3, metal oxides (all dissolved by nitric acid) and tetraethoxysilane Si(OC2H5)(4) (TEOS) as the main starting materials, Ca2R8(SiO4)(6)O-2:A (R = Y, La, Gd; A = EU3+, Tb3+) phosphor films have been dip-coated on quartz glass substrates through the sol-gel process. X-ray diffraction (XRD), atomic force microscope (AFM), scanning electron microscope (SEM) and photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting films. The results of XRD indicated that the 1000 degreesC annealed films are isomorphous and crystallize with the silicate oxyapatite structure. AFM and SEM studies revealed that the phosphor films consisted of homogeneous particles ranging from 30 to 90 nm, with an average thickness of 1.30 mum. The Eu3+ and Tb3+ show similar spectral properties independent of R 3, in the films due to their isomorphous crystal structures. However, both the emission intensity and lifetimes of Eu3+ and Tb3+ in Ca2R8(SiO4)(6)O-2 (R = Y, La, Gd) films decrease in the sequence of R = Gd > R = Y > R = La, which have been explained in accordance with the crystal structures.

Fabrication, patterning and luminescence properties of X-2-Y2SiO5 : A (A = Eu3+, Tb3+, Ce3+) phosphor films via sol-gel soft lithography

X-2-y(2)SiO(5):A (A = Eu3+, Tb3+, Ce3+) phosphor films and their patterning were fabricated by a sol-gel process combined with a soft lithography. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), atomic force microscopy (AFM), scanning electron microscopy (SEM) optical microscopy and photoluminescence (PL) were used to characterize the resulting films. The results of XRD indicated that the films began to crystallize at 900 degreesC with X-1-Y2SiO5, which transformed completely to X-2-Y2SiO5 at 1250 degreesC. Patterned thin films with different band widths (5 pin spaced by 5 pm and 16 pm spaced by 24 pm) were obtained by a soft lithography technique (micromoulding in capillaries, MIMIC). The SEM and AFM study revealed that the nonpattemed phosphor films were uniform and crack free, and the films mainly consisted of closely packed grains with an average size of 350 run. The doped rare earth ions (A) showed their characteristic emissions in X-2-Y2SiO5 phosphor films, i.e., D-5(0)-F-7(J) (J = 0, 1, 2,3,4) for Eu3+, D-5(3), (4)-F-7(J) (J = 6, 5, 4, 3) for Tb3+ and 5d (D-2)-4f (F-2(2/5),(2/7)) for Ce3+, respectively. The optimum doping concentrations for EU3+, Tb3+ were determined to be 13 and 8 mol% of Y3+ in X-2-Y2SiO5 films, respectively.