Synthesis and photoluminescence properties of ZnTiO_3:Eu^(3+) red phosphors via sol-gel method

ZnTiO3：Eu3＋ phosphors were synthesized with different concentrations of Eu3＋ doping through sol-gel method. The samples were calcined at different temperatures for 2 h in air. The synthesized powders were characterized by X-ray diffraction（XRD）, scanning electron microscopy-energy dispersive spectroscopy（SEM-EDS）, transmission electron microscopy（TEM）, Raman and photoluminescence spectroscopy. The XRD results showed that the Zn Ti O3：Eu3＋ phosphors doped with different concentrations of Eu3＋ ions calcined at 600 oC were of single phase, which indicated that the Eu3＋ ions had been successfully incorporated into the Zn Ti O3 host lattice and did not destroy the lattice structure of Zn Ti O3 host. The Raman spectrum, SEM and TEM also proved that the doping of Eu3＋ did not change the lattice structure of hexagonal Zn Ti O3 host. The photoluminescence（PL） of Eu3＋ ions with the main emission peak at 614 nm was observed to increase with Eu3＋ concentrations from 0.5 mol.% to 2.0 mol.% and decreased when the concentration was increased to 2.5 mol.%. The decrease in the PL intensity at higher Eu3＋ concentrations could be associated with concentration quenching effect. The CIE1931 chromaticity diagram（x, y） of Zn Ti O3：2.0 wt.%Eu3＋ phosphors were located in the red region（x=0.652, y=0.347）. The luminescence properties suggested that Zn Ti O3：Eu3＋ phosphors might be regarded as a potential red phosphor candidate for light emitting diodes（LEDs）.

Luminescence properties of Eu^(3+)-doped new scheelite-type compounds

The efficient new red emitting scheelite-type compounds, Eu3＋-doped （5 tool.%） Y（Zro.5Wo.5）O4, Lu（Zro.sWo,5）O4 and Y（Y1/3W2/3）O4, were successfully prepared. The crystal structure, photoluminescence and decay properties of the obtained phosphors were investigated. Shifts of the peaks in the XRD patterns were observed when y3＋ sites in the host were occupied by Lu3＋ or Zr/W sites were occupied by Y/W, As a result of the crystallographic occupancy of Eu3＋ located at the cation positions without inversion symmetry, under O---Zr/W and O---.Eu3＋ ligand-to-metal charge-transfer states （LMCT） excitation at 300 nm, the emission spectra of these compounds presented 5Do---7F2 transition for EH3＋ at 612 nm. The diagram of EU3＋ energy levels in these new scheelite-type compounds and the energy transfer processes were discussed.

Microstructure and luminescent properties of Eu^3+-activated MgGa2O4:Mn^2+ ceramic phosphors

Mn2+and the trivalent europium(Eu3+)-doped MgGa2O4 ceramics are characterized using a multi-experimental approach.The formation of spinel-structured ceramics is ascertained from X-ray diffraction(XRD)analysis.Morphology investigations with transmission electron microscopy(TEM)show irregularly shaped grains and grain boundaries with a homogeneous distribution of Eu3+ions.The inability of Eu activator to penetrate the bulk of ceramic grains is inferred from positron annihilation lifetime spectroscopy data.The Eu doping is shown to enhance the positron trapping rate due to the occupancy of vacancy-type defects at ceramic grains by Eu3+ions.Both Mn2+and Eu3+doped samples show a broad multi-color luminescence in 350–650 nm range under 240 nm and 270–300 nm excitations.Blue emission is concluded to originate from host defects,whereas green emission and narrow lines in the red region of the spectrum are attributed to Mn2+and Eu3+ions,respectively.High asymmetry around Eu3+ions can be concluded from the photoluminescence and positron annihilation lifetime spectra analysis.