M. Haouari

Optical absorption and electron paramagnetic resonance study of -doped phosphate glasses

We report in this paper optical absorption and electron paramagnetic resonance (EPR) results obtained on -doped phosphate glasses. Optical absorption allowed us to evaluate the crystal-field parameters , B and C. Electron paramagnetic resonance measurements indicate that ions are located in sites with low symmetry and a relatively large zero-field splitting. Both electron paramagnetic resonance and optical absorption data show that the chemical bonds of ions with the ligands are rather covalent in nature but that the ionic contribution to those bonds decreases in the order: PBa > PBaK > PBaKMg. Furthermore, it is found from this study that the crystal-field strength increases in the order: PBa < PBaK < PBaKMg.

Spectroscopic Properties of Cr3+-Doped Phosphate Glasses

Emission spectroscopy of Cr 3+ -doped phosphate glasses has been studied. Different site distributions of the chromium ions having an environment with nearly octahedral symmetry could be identified on the basis of the luminescence decay characteristics and the time-resolved emission study. The low quantum yield in luminescence is attributed to an efficient multiphonon relaxation process deexciting rapidly ions submitted to the weaker crystal field.

Electron paramagnetic resonance study of five-coordinated Cu2+ in ethylenediammonium copper(II) diphosphate monohydrate

The results of an electron paramagnetic resonance study of a new product, namely ethylenediammonium copper(II) diphosphate monohydrate of chemical formula Cu(NH3(CH2)2NH3)P2O7.H2O, are presented. The X-ray diffraction has shown the existence of two types of copper(II) coordination polyhedron for each elementary mesh in this compound. Each polyhedron consists of a copper ion surrounded by five oxygenated ligands stoning from two P2O7 groups and a water molecule. Fair agreement between these results and those obtained by X-ray diffraction is observed. In particular the organization of oxygen atoms as pyramids with a square plane around the copper(II) ions is confirmed. The existence of two magnetically nonequivalent sites of copper per mesh is evidenced.

Effect of CdS nanocrystals on the photoluminescence of Eu3+-doped silicophosphate sol gel glass

In this work, we investigate the effect of co-doping with CdS nanoparticles on the photoluminescence properties of Eu3+ doped silicophosphate glass prepared via the sol gel method. Infrared spectroscopy (FTIR) revealed the insertion of phosphorus within the silicate network. XRD and TEM analyses revealed the presence of CdS nanoparticles dispersed in the glass matrix. Based on the optical study and the effective mass theory for spherical quantum dots, it was found that CdS nanocrystals have a gap of nearly 3.53 eV and a size of 2.42 nm. The enhancement of Eu3+ emission induced by CdS nanocrystals and thermal annealing was assigned to either an energy transfer via defect states or structural alteration of the glass network around the rare earth ions.

Use of MPA-capped CdS quantum dots for sensitive detection and quantification of Co 2+ ions in aqueous solution

Water soluble CdS quantum dots (QDs) were synthesized by a simple aqueous chemical route using mercaptopropionic acid (MPA) as a stabilizer. These QDs had a fluorescence emission band maximum at 540 nm with a FWHM ∼130 nm and a quantum yield of ∼12%. Transmission electronic microscopy images were used to determine the QD diameter of 8.9 ± 0.4 nm. From this value we calculated the molecular mass M(QD) = 1.17 × 106 g mol-1 and the extinction coefficient at the band edge (450 nm) ε450 = 4.7 × 106 cm-1 M-1, which allowed to determine the true molar concentration of 17 nM for spectroscopic measurements in solution. The fluorescence intensity of MPA-CdS QDs was quenched only in the presence of Co2+ ions, but not in the presence of thirteen other metal cations. The fluorescence quenching of MPA-CdS QDs appeared proportional to the Co2+ concentration in the range 0.04-2 μM. Based on a fluorescence peak position and a lifetime both independent from Co2+ concentration, the quenching mechanism of MPA-CdS QDs appeared static. Because the strong electronic absorption of Co2+ overlaps the emission of QDs, our results can be explained by Förster energy transfer from QD to the bound Co2+ cations.