Laura Muresan

Yttrium-tantalate-based phosphors for x-ray intensifying screen

The paper presents some aspects referring to the synthesis of niobium activated yttrium orthotantalate phosphor (YTaO4:Nb), utilizable in the manufacture of X-ray intensifying screens for medical diagnosis. The influence of some preparative conditions such as activator concentration and firing regime on the crystalline structure and luminescent characteristics are investigated. Photoluminescence spectroscopy, X-ray diffraction and FT-IR spectroscopy are used to evaluate the material quality.

Morpho-structural and luminescence investigations on yttrium silicate based phosphors prepared with different precipitating agents

AbstractYttrium silicate doped with cerium (Y2SiO5:Ce) was obtained from Y-Ce-Si based precursors prepared by the simultaneous addition of reagents (SimAdd) technique. The synthesis of the precursors was done in well controlled conditions using ammonium oxalate, ammonium carbonate or urea as precipitating agents. Results regarding the influence of precipitating agents on the morpho structural and photoluminescent characteristics of Y2SiO5:Ce are reported. The TG analysis in correlation with EGA, FT-IR and XRD investigations reveals the formation of oxalate, hydroxy-carbonate or hydroxy-nitrate based compounds, the same as the conversion of the precursors to well crystallized yttrium silicate. XRD patterns show that the precursors are amorphous except for the sample prepared with ammonium oxalate. Depending on the precipitation conditions, the phosphors phase composition varies from single phase (X2-Y2SiO5) to a mixture of phases (X2-Y2SiO5, X1-Y2SiO5, Y2O3). Under UV excitation, phosphors exhibit the specific blue emission of cerium with an intensity that varies from 175.8% (urea) to 96.0% (ammonium carbonate) and to 78.5% (ammonium oxalate). The emission intensity depends on the phase purity and order degree of the phosphors. PACS Classification codes:78.55 Hx, 81.20Fw

Studies on the synthesis of terbium-activated gadolinium oxysulphide phosphors

Terbium activated gadolinium oxysulphide phosphor (Gd2O2S: Tb) shows bright green luminescence and high efficiency under X-ray excitation. Phosphor utilization depends on powder characteristics and luminescent properties that are regulated during the synthesis stage. The paper prsents some of our results referring to the synthesis of Gd2O2S: Tb phosphor by solid state reaction route, from oxide precursors. The influence of flux composition and amount as well as the sulphide supplier concentration on phosphor properties was investigated in order to prepare efficient luminescent powders for the manufacture of X-ray intensifying screens for medical diagnosis.

Photo-and cathodoluminescence investigation of CaWO4:Eu,Tb phosphors

Rare earth activated phosphors are largely used in optoelectronic devices, X-ray intensifying screens and fluorescent lamps. Luminescent properties (color, efficiency, and decay parameters) and powder characteristics (particle morphology and size, crystalline structure) that are regulated during the synthesis process determine the phosphor utilization potential. Photoluminescence (PL) and cathodoluminescence (CL) investigations are used in order to evaluate the quality of phosphor based on europium and terbium activated calcium tungstate. CL and PL spectra as well as CCL-SEM pictures of some CaWO4: Eu,Tb samples are discussed in relation with some of their preparation parameters. The mutual interaction of the two activating ions is put in evidence.

The role of calcination temperature on structural and luminescence behaviour of novel apatite-based Ca2Y 8(SiO4)6O2: Ce3+,Tb3+ phosphors

A series of novel apatite-based Ca2Y8(SiO4)6O2 phosphors doped with Ce3+ and Tb3+ were synthesized by a solid-state reaction method at different calcination temperatures and times. The comparative results of thermal analysis (TG-DTA), FTIR, X-ray diffraction (XRD) and environmental scanning electron microscope (ESEM) reveal that the firing temperature for Ca 2Y 8 (SiO4)6O2:Ce3+, Tb3+ was optimized to be 1200°C. The systematic studies on the influences of thermal treatment conditions on photoluminescence (PL) and cathodoluminescence (CL) properties were also reported. The excitation spectra of Ca2Y8(SiO4)6O2:Ce3+, Tb3+exhibited one strong excitation band at 325nm. The PL and CL results indicated that the violet-blue emission intensities about 400nm from the Ce3+ and efficient green emission at 544nm from Tb3+ were highly dependent on the calcination conditions.