Shubin Wang

Preparation of Y3Al5O12:Eu phosphors by citric-gel method and their luminescent properties

Abstract By using metal nitrates as starting materials and citric acid as complexing agent, Y3Al5O12 (YAG) and Y3Al5O12:Eu (1 mol%) (YAG:Eu) powder phosphors were prepared by a citrate–gel method. The formation process of YAG and YAG:Eu were investigated by means of XRD, TG–DTA and FT-IR spectra. The purified crystalline phases of YAG and YAG:Eu were obtained at 800 °C. The crystalline YAG:Eu phosphors showed an orange–red emission with 5 D 0 – 7 F 1 (591 nm) as the most prominent group, whose intensity was dependent on the pH value of the starting solution, citric acid content and firing temperature. It has been found that the suitable pH and citric acid/metal ratio are 3 and 2 for obtaining the highest emission intensity, respectively. The emission intensity increases steadily with increasing the annealing temperature from 800 to 1200 °C, and nearly remains constant after 1200 °C. Furthermore, great differences were observed for the lifetimes and the charge transfer band of Eu3+ in crystalline and amorphous states of YAG.

Patterning and luminescent properties of nanocrystalline Y2O3:Eu3+ phosphor films by sol–gel soft lithography

Nanocrystalline Y2O3:Eu3+ phosphor films and their patterning were fabricated by a Pechini sol-gel process combined with a soft lithography. X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG-DTA), atomic force microscopy (AFM), optical microscopy, UV/vis transmission and photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting films. The results of XRD indicated that the films began to crystallize at 500 degreesC and the crystallinity increased with the elevation of annealing temperatures. Uniform and crack free non-patterned phosphor films were obtained, which mainly consisted of grains with an average size of 70 nm. Using micro-molding in capillaries technique, we obtained homogeneous and defects-free patterned gel and crystalline phosphor films with different stripe widths (5, 10, 20 and 50 mum). Significant shrinkage (50%) was observed in the patterned films during the heat treatment process. The doped Eu3+ showed its characteristic emission in crystalline Y2O3 phosphor films due to an efficient energy transfer from Y2O3 host to them. Both the lifetimes and PL intensity of the Eu3+ increased with increasing the annealing temperature from 500 to 900 degreesC, and the optimum concentrations for Eu3+ were determined to be 5 mol%.

Luminescent properties of rare-earth-doped CaWO4 phosphor films prepared by the Pechini sol-gel process

CaWO4 phosphor films doped with rare-earth ions (Eu3+, Dy3+, Sm3+, Er3+) were prepared by the Pechini sol–gel process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy, thermogravimetric and differential thermal analysis, atomic force microscopy, and photoluminescence spectra, as well as lifetimes, were used to characterize the resulting powders and films. The results of the XRD analysis indicated that the films began to crystallize at 400°C and that the crystallinity increased with elevation of the annealing temperature. The doped rare-earth ions showed their characteristic emissions in crystalline CaWO4 phosphor films due to energy transfer from WO42− groups to them. Both the lifetimes and PL intensities of the doped rare-earth ions increased with increasing annealing temperature, from 500 to 900°C, and the optimum concentrations for Eu3+, Dy3+, Sm3+, Er3+ were determined as 30, 1.5, 1.5, 0.5 at.% of Ca2+ in CaWO4 films annealed at 900°C, respectively.

VUV-UV excited luminescent properties of calcium borophosphate doped with rare earth ions

The VUV-UV spectra of rare earth ions activated calcium borophosphate, CaBPO5:RE (RE = Ce3+, sm(3+), Eu2+, Eu3+, Tb3+ and Dy3+) were determined. The bands at about 155 nm in the VUV excitation spectra are attributed to the host lattice absorptions. The bands at 166 and 190 nm for the sample CaBPO5:Sm have been considered as related to the f-d transition and the charge transfer band (CTB) of Sm3+ ions, and the band at 169 nm for the sample CaBPO5:Dy is assumed to be connected with the f-d transition of the Dy3+ ions in CaBPO5. The partial reduction of Eu3+ CaBPO5:Eu prepared by high temperature solid state reaction in air is confirmed by the VUV-UV spectra

Preparation, patterning and luminescent properties of oxyapatite La9.33(SiO6)4O2:A(A = Eu3+, Tb3+, Ce3+) phosphor films by sol–gel soft lithography

Silicate oxyapatite La-9.33 (SiO6)(4)O-2:A (A = Eu3+, Tb3+ and/or Ce3+) phosphor films and their patterning were fabricated by a sol-gel process combined with soft lithography. X-ray diffraction (XRD), Fourier transform infrared spectroscopy, atomic force microscopy, optical microscopy and photoluminescence spectra, as well as lifetimes, were used to characterize the resulting films. The results of XRD indicated that the films began to crystallize at 800degreesC and the crystallinity increased with the increase in annealing temperatures. Transparent nonpatterned phosphor films were uniform and crack-free, which mainly consisted of rodlike grains with a size between 150 and 210 nm. Patterned thin films with different bandwidths (20, 50 mum) were obtained by the micromoulding in capillaries technique. The doped rare earth ions (Eu3+, Tb3+ and Ce3+) showed their characteristic emission in crystalline La-9.33(SiO6)(4)O-2 phosphor films, i.e. Eu3+ D-5(0)-F-7(J) (J = 0, 1, 2, 3, 4), Tb3+ D-5(3,4)-F-7(J) (J = 3, 4, 5, 6) and Ce3+ 5d (D-2)-4f (F-2(2/5), F-2(2/7)) emissions, respectively. Both the lifetimes and PL intensity of the Eu3+, Tb3+ ions increased with increasing annealing temperature from 800 to 1100 degreesC, and the optimum concentrations for Eu3+, Tb3+ were determined to be 9 and 7 mol% of La3+ in La-9.33(SiO6)(4)O-2 films, respectively. An energy transfer from Ce3+ to Tb3+ was observed in the La-9.33(SiO6)(4)O-2:Ce, Tb phosphor films, and the energy transfer efficiency was estimated as a function of Tb3+ concentration.

Local structure and valences of samarium in SrB4O7:Sm and SrB6O10:Sm prepared in air

The coordination numbers for the samarium atoms and the Sm-O bond distances in SrB4O7:Sm and SrB6O10:Sm prepared in air were determined by means of Sm-L-3 edge EXAFS. The coordination. was found to be nine-folded for both these hosts and the bond distance was 2.40-2.42 Angstrom in SrB4O7:Sm and 2.42-2.44 Angstrom in SrB6O10:Sm. For SrB4O7:Sm the coordination number is coincident with that of the strontium. atoms suggesting the substitution of the samarium atoms at the strontium sites. The coordination number of the strontium atoms in SrB6O10 was also suggested to be nine assuming the same type of substitution. The valences of samarium were determined from the luminescent spectra. Both divalent and trivalent ions were present in both SrB4O7:Sm and SrB6O10:Sm, while the fraction of Sm2+ was higher in the former than in the latter. This difference has been assigned to the difference in rigidity between the B-O networks in these structures.

VUV and Eu-L3 edge XANES spectra of europium-doped strontium tetraborate prepared in air

Abstract VUV-UV and Eu-L3 edge XANES spectra were measured for europium-doped strontium tetraborate prepared by solid state reaction at high temperature in air. The VUV-UV spectra show that the host absorption band of SrB4O7 appears below 170 nm. The charge transfer band of Eu3+ doped in SrB4O7 is peaked at 272 nm. The 4f–5d transitions of Eu2+ consist of a band peaked at 310 nm with a shoulder at 280 nm and also include the bands peaked at 238 (weak) and 203 (strong) nm. The result of XANES spectrum at Eu-L3 edge of the synthesized sample indicates that Eu3+ and Eu2+ coexist in SrB4O7:Eu prepared in air, which is consistent with the results of the VUV-UV spectra.

The microstructure and tribological properties of copper surfaces implanted with carbon ions

Abstract Carbon ions were implanted into copper surfaces to a dose of 1×10 18 xa0ionsxa0cm −2 at 50xa0keV, and the as-implanted specimens were studied by Raman spectroscopy, selected area diffraction (SAD), transmission electronic microscopy (TEM) and high-resolution electronic microscopy (HREM). The Raman spectra indicate that diamond-like carbon (DLC) was formed on/in the copper surfaces. From HREM images, it is observed that the copper forms amorphous or nano grains and contains a large number of amorphous carbon and nanometre graphite clusters (

Structural and electrical properties of CVD diamond films doped by N+ implantation

Chemical vapor deposited (CVD) diamond films (DF) were prepared on P-type oriented Si substrates. The films were implanted with 140 keV N+ to doses of 5 x 10(14) similar to 1 x 10(16)cm(-2), respectively. Under the implantation, the DF becomes more and more disordered with each increasing dose. Scanning electronic microscopy (SEM) and Raman measurements reflect the amorphization process. Combining the electrical resistance measurements, it is clear that polycrystalline DF has a higher threshold dose of amorphization than that for bulk ones. The damages induced by implantation can be partially removed by annealing when the dose is below the critical value. Larger doses of implantation produce amorphous carbon which can transform into micro-polycrystalline graphite during annealing. Thus, the conductivity is increased dramatically. However, for smaller dose N+ implanted samples, while annealing was performed, the samples become comparable conductive for the activation of N dopants