Search

International audience; The photoluminescence of two series of A- and B-site Eu3+ substituted (SrxBa1-x)(2)CaWyMo1-yO6 double perovskite phosphor materials, (SrxBa1-x)(1.96)Eu0.02K0.02CaWyMo1-yO6 and (SrxBa1-x)(2)Ca0.96Eu0.02Li0.02WyMo1-yO6 (x and y=0, 0.25, 0.50, 0.75, and 1), were studied systematically as a function of stoichiometry and crystal structure. The Eu3+ lattice sites controlled by co-doping with either K or Li were confirmed by Raman spectroscopy. The variation in integrated emission intensity and emission colour over the experimental matrix was examined using statistical tools, and the observed trends were rationalized based on the physical and electronic structure of the phosphors. Phosphors with Eu on B-site with maximum Sr content had remarkably higher emission intensities than all other materials, but the emission was more orange than red due to domination of the D-5(0) - F-7(1) (595 nm) transition of Eu3+. The relative intensities of the D-5(0) - F-7(2) (615 nm) and D-3(0) - F-7(1) transitions of Eu3+, and thus the red-shift of the emission, decreased linearly with increasing Sr content in the A-site Eu-substituted phosphors, and reached a maximum for Sr1.96Eu0.02K0.02CaW0.25Mo0.75O6. A maximum external quantum efficiency of 17% was obtained for the phosphor Sr2Ca0.7Eu0.15Li0.15W0.5Mo0.5O6 with Eu on B-site. (C) 2016 Elsevier Inc. All rights reserved.

Modified Pechini synthesis routes were developed for synthesis of the novel red phosphor materials NaLa(WO4)(MoO4):Eu3+ and Ba2CaMoO6:Eu3+. Phase pure NaLa(WO4)(MoO4):Eu3+ was obtained at calcination temperatures ≥600 °C using malic acid or tartaric acid as complexing agents. Phase pure Ba2CaMoO6:Eu3+ was attained using EDTA and citric acid, at calcination temperatures ≥800 °C. Choice of complexing agents were discussed on the basis of the solubility of the precursors, metal complex stability constants and conformations of the complexes. The powder properties were characterised using X-ray diffraction, thermal analysis and electron microscopy. Photoluminescence emission intensity was studied as a function of the complexing agents used and calcination temperature of the powders. Maximum emission intensity for NaLa(WO4)(MoO4):Eu3+ was obtained at a calcination temperature of 600 °C, whereas the maximum for Ba2CaMoO6:Eu3+ was obtained after calcination at 1100 °C. Both materials displayed desirable optical properties for use as phosphors in white light-emitting diodes. Phase pure NaLa(WO4)(MoO4):Eu3+ and Ba2CaMoO6:Eu3+ red phosphor materials were synthesised by the modified Pechini route, thus permitting lower calcination temperatures which resulted in increased emission intensity for NaLa(WO4)(MoO4):Eu3+.

International audience; Two series of A-site and B-site Eu3+ doped (SrxBa1-x)(2)CaWyMo1-yO6 double perovskite phosphor materials were prepared via a modified Pechini sol-gel route; (SrxBa1-x)(1.96)Eu(0.02)K(0.02)CaW(y)Mo(1-)yO(6) and (SrxBa1-x)(2)Ca0.96Eu0.02Li0.02WyMo1-yO6 (x and y=0, 0.25, 0.50, 0.75, 1). The Sr/Ba ratio was the main determinant for the crystal symmetry of the series, while variation in the W/Mo ratio did influence the crystal symmetry significantly. The crystal structure evolved with Sr/Ba ratio from cubic Frn (3) over barm for x=0, via tetragonal 14/m for x=0.25, to monoclinic P2(1)/n for x >= 0.5, as verified by Rietveld refinement of X-ray diffractograms as well as by Raman spectroscopy. The reported boundaries for the compositionally induced phase transitions are in very good agreement with reported optical properties. (C) 2015 Elsevier Inc. All rights reserved.