Xiping Jing

Synthesis, Structure, and Thermally Stable Luminescence of Eu2+-Doped Ba2Ln(BO3)2Cl (Ln = Y, Gd and Lu) Host Compounds

A new family of chloroborate compounds, which was investigated from the viewpoint of rare earth ion activated phosphor materials, have been synthesized by a conventional high temperature solid-state reaction. The crystal structure and thermally stable luminescence of chloroborate phosphors Ba(2)Ln(BO(3))(2)Cl:Eu(2+) (Ln = Y, Gd, and Lu) have been reported in this paper. X-ray diffraction studies verify the successful isomorphic substitution for Ln(3+) sites in Ba(2)Ln(BO(3))(2)Cl by other smaller trivalent rare earth ions, such as Sm, Eu, Tb, Dy, Ho, Er, Tm, and Yb. The detailed structure information for Ba(2)Ln(BO(3))(2)Cl (Ln = Y, Gd, and Lu) by Rietveld analysis reveals that they all crystallize in a monoclinic P2(1)/m space group. These compounds display interesting and tunable photoluminescence (PL) properties after Eu(2+)-doping. Ba(2)Ln(BO(3))(2)Cl:Eu(2+) phosphors exhibit bluish-green/greenish-yellow light with peak wavelengths at 526, 548, and 511 nm under 365 UV light excitation for Ba(2)Y(BO(3))(2)Cl:Eu(2+), Ba(2)Gd(BO(3))(2)Cl:Eu(2+), and Ba(2)Lu(BO(3))(2)Cl:Eu(2+), respectively. Furthermore, they possess a high thermal quenching temperature. With the increase of temperature, the emission bands show blue shifts with broadening bandwidths and slightly decreasing emission intensities. It is expected that this series of chloroborate phosphors can be used in white-light UV-LEDs as a good wavelength-conversion phosphor.

Ca1 − 2x Eu x Li x MoO4 : A Novel Red Phosphor for Solid-State Lighting Based on a GaN LED

A novel red phosphor Ca 1 - 2 x Eu x Li x MoO 4 with high performance is reported. Under the excitation of 254 nm UV light, its luminescent intensity is comparable to that of the commercial red phosphor Y 2 O 3 :Eu 3 + . With high Eu 3 + concentration, the phosphor has strong excitation due to f-f transitions of Eu 3 + appearing around 395 nm. Thus, it is a promising material for solid-state lighting based on GaN light-emitting diode (LED).

Photoluminescence and Raman Spectra of Double-Perovskite Sr2Ca ( Mo / W ) O6 with A- and B-Site Substitutions of Eu3 +

3+ have been synthesized using solid-state reactions and characterized by X-ray diffraction, Raman spectroscopy, and photoluminescence measurement. Raman spectra are used to identify the Aand B-site substitutions, because specific Raman peaks corresponding to different ions motion are sensitive to each situation. Raman data reveal that both the A- and B-site substituted solid solutions are formed. The photoluminescence intensity of the B-site substituted Sr2CaMoO6 is evidently higher than that of the A-site substituted phosphor. The WO6 group introduced into Sr2CaMoO6:Eu 3+ ,Li + acts as an energy obstacle to prevent energy transfer among MoO6 groups, leading to more energy being trapped by Eu 3+ , and a higher photoluminescence intensity is obtained. The phosphor with optimized composition Sr2Ca0.80Li0.10Eu0.10Mo0.10W0.90O6 shows a better luminescence intensity than the commercial phosphor Y2O2S:Eu under 395 nm excitations.

Novel phosphors of Eu3+, Tb3+ or Bi3+ activated Gd2GeO5

Abstract Novel phosphors of Eu 3+ , Tb 3+ or Bi3+ doped Gd2GeO5 were synthesized and their photoluminescent and cathodoluminescent properties were investigated. (Gd1−xEux)2GeO5 and (Gd1−xTbx)2GeO5 formed continuous solid solution in the range of x=0.0–1.0. Gd2GeO5:Eu3+ and Gd2GeO5:Bi3+ presented bright red and blue luminescence for both UV and cathode ray excitation, respectively. While Gd2GeO5:Tb3+ gave bright green cathodoluminescence. In all three phosphors, the energy transfer from Gd3+ to activators (e.g. Eu 3+ , Tb 3+ or Bi3+) occurred.

Preparation and X-ray characterization of low-temperature phases of R2SiO5 (R = rare earth elements)

Low-temperature phases of R2SiO5 (R 5 Y, Tb, Dy, Ho, Er, Tm, and Yb) were synthesized by the sol-gel method. The X-ray powder diffraction patterns for these new phases were indexed with the monoclinic unit cell, and the unit cell parameters were refined. The structure of Y2SiO5 with the space group P21/c was determined by powder diffraction data.

Promising Oxonitridosilicate Phosphor Host Sr3Si2O4N2: Synthesis, Structure, and Luminescence Properties Activated by Eu2+ and Ce3+/Li+ for pc-LEDs

A novel oxonitridosilicate phosphor host Sr(3)Si(2)O(4)N(2) was synthesized in N(2)/H(2) (6%) atmosphere by solid state reaction at high temperature using SrCO(3), SiO(2), and Si(3)N(4) as starting materials. The crystal structure was determined by a Rietveld analysis on powder X-ray and neutron diffraction data. Sr(3)Si(2)O(4)N(2) crystallizes in cubic symmetry with space group Pa ̅3, Z = 24, and cell parameter a = 15.6593(1) Å. The structure of Sr(3)Si(2)O(4)N(2) is constructed by isolated and highly corrugated 12 rings which are composed of 12 vertex-sharing [SiO(2)N(2)] tetrahedra with bridging N and terminal O to form three-dimensional tunnels to accommodate the Sr(2+) ions. The calculated band structure shows that Sr(3)Si(2)O(4)N(2) is an indirect semiconductor with a band gap ≈ 2.84 eV, which is close to the experimental value ≈ 2.71 eV from linear extrapolation of the diffuse reflection spectrum. Sr(3-x)Si(2)O(4)N(2):xEu(2+) shows a typical emission band peaking at ~600 nm under 460 nm excitation, which perfectly matches the emission of blue InGaN light-emitting diodes. For Ce(3+)/Li(+)-codoped Sr(3)Si(2)O(4)N(2), one excitation band is in the UV range (280-350 nm) and the other in the UV blue range (380-420 nm), which matches emission of near-UV light-emitting diodes. Emission of Sr(3-2x)Si(2)O(4)N(2):xCe(3+),xLi(+) shows a asymmetric broad band peaking at ~520 nm. The long-wavelength excitation and emission of Eu(2+) and Ce(3+)/Li(+)-doped Sr(3)Si(2)O(4)N(2) make them attractive for applications in phosphor-converted white light-emitting diodes.

Energy Transfer among Ce3 + , Eu2 + , and Mn2 + in CaSiO3

Energy-transfer processes from Ce 3+ to Eu 2+ /Mn 2 + and from Eu 2+ to Mn 2+ in host CaSiO 3 are studied. Co doping Ce 3+ /Mn 2+ or Eu 2+ /Mn 2+ is an effective approach to enhance the orange-reddish emission of Mn 2+ . The ion-size compensation effect between Eu 2+ and Mn 2+ causes more Eu 2+ to be doped into the CaSiO 3 lattice, which benefits the increase of the energy transfer efficiency from Eu 2+ to Mn 2+ . Additionally, the suitable spectrum overlapping of the Eu 2+ emission to the first excited state 4 T 1 of Mn 2+ as well as the formation of Eu 2+ /Mn 2+ clusters may be other causes of the enhanced Mn 2+ luminescence. Eu 2+ /Mn 2+ codoped samples can be very excited by near-UV. The excitation spectrum of Ce 3+ covers a different wavelength range from that of Eu 2+ (normally blue shift occurs); thus, replacement of Ce 3+ for Eu 2+ may make phosphors excited by shorter wavelengths. The results in this work may provide some clues for designing novel red phosphors for white-light UV light-emitting diode applications.

Assignment of Raman-active vibrational modes of MgTiO3

MgTiO3 ceramic sample was synthesized and its Raman spectra were recorded. The Raman-active vibrational modes of MgTiO3 were calculated using first-principle calculations (density functional theory). Based on experimental data and calculation results, the Raman peaks were assigned as 225 cm−1 (Ag), 306 cm−1 (Ag), 398 cm−1 (Ag), 500 cm−1 (Ag), 715 cm−1 (Ag) and 281 cm−1 (Eg), 328 cm−1 (Eg), 353 cm−1 (Eg), 486 cm−1 (Eg), 641 cm−1 (Eg). The assignment was supported by the polarized Raman spectrum. Meanwhile, the symmetry coordinates of MgTiO3 primitive cell were analyzed and employed to expand the Raman-active modes.

Long Wavelength Extension of the Excitation Band of LiEuMo2O8 Phosphor with Bi3 + Doping

Bi-doped red phosphor series LiEu 1-x Mo 2 O 8 :xBi were prepared by solid-state reactions which present bright red luminescence (615 nm) dominated by a 5 D 0 → 7 F 2 transition of Eu 3+ . With Bi 3+ doping, the excitation bands of the phosphors extend to longer wavelength (from 350 to 380 nm), and the excitation efficiency for optimized Bi 3+ content is dramatically increased, which favors the phosphors for the white-light ultraviolet light emitting diode applications. The luminescent model for the phosphors studied in this work is proposed. Because the 6p level of Bi 3+ is immerged in the conduction band (CB), the excitation 6s → 6p of Bi 3+ is overlapped by the excitation 6s → CB, which results in extension of the excitation band. The absorbed energy by the excitation 6s → CB can be effectively transferred to Eu 3+ , but the 6p → 6s emission of Bi 3+ disappears.

Influence of Rare Earth Sc and La to the Luminescent Properties of FED Blue Phosphor Y 2SiO5 : Ce

Luminescent properties of Sc 3+ and La 3+ doped (Y 0.995 Ce 0.005 ) 2 SiO s phosphors were studied. In the Sc 3+ doped system (Y 0.995-x Sc x Ce 0.005 ) 2 SiO 5 , the solid solution extends to x = 0.65, but in the La 3+ doped system (Y 0.995-x, La x Ce 0.005 ) 2 SiO 5 , the solid solution range is not over the La 3+ content of x = 0.05. For La 3+ doped samples, the photoluminescence (PL) increases about 30% and cathodoluminescence (CL) increases about 10%. Additionally the color saturation is also improved with La 3+ doping. The mechanisms for these improvements are discussed. For the Sc 3+ doped samples, both PL and CL, clearly decrease. These phosphors may be useful in field emission displays TEED).