J.C. Cousseins

Red luminescence in Pr3+-doped calcium titanates

A strong single red emission band (λ max = 613 nm, FWMH = 450 cm -1 ) was observed at room temperature in Pr 3+ -doped calcium titanates. The evolution of the intensity of this luminescence was analysed in compensated and uncompensated samples (using Na + , Ag + or TI + as charge compensators) and also as a function of Pr concentration. Emission, excitation and reflectivity spectral repartitions were investigated at various temperatures, as well as the luminescence decays. The origin of the red luminescence is discussed.

Synthesis dependent luminescence efficiency in Eu3+ doped polycrystalline YBO3

The influence of the synthesis method on the luminescence efficiency of the orthoborate YBO 3 :Eu 3+ was studied by comparing the optical performances of samples prepared by three routes: solid state reaction (SR), wet process (WP) and sol-gel processing (SG). On the basis of X-ray powder diffraction, SEM micrographs and photoluminescence measurements, SG appears to be the most efficient method to prepare high quality compounds for practical applications. Such a conclusion is reinforced by the existence of an important gain in the luminescence efficiency using this procedure.

Improvement of the optical performances of Pr3+ in CaTiO3

Abstract Trivalent praseodymium-doped calcium titanates are red emitting phosphors upon UV photon excitation in the range 150–300 nm, with a luminescence appearing as a single peak centered at 613 nm. The intensity of this emission is investigated in different samples prepared either by a solid state or a sol–gel method. The study includes analyses of microstructure, sintering temperature, charge compensation and Pr concentration effects.

Molecular design of luminescent organic-inorganic hybrid materials activated by europium (III) ions

Abstract Luminescent hybrid materials consisting in rare-earth (Eu 3+ , Gd 3+ ) organic complexes covalently attached to a silica-based network have been obtained by a sol–gel process. Four dicarboxylic acids with different aromatic subunits (dipicolinic acid, 4-phenyl-2,6-pyridinedicarboxylic acid, 4-(phenylethynyl)-2,6-pyridinedicarboxylic acid and 2,6-Bis(3-carboxy-1-pyrazolyl)pyridine) have been chosen as ligands for Ln 3+ ions. They were grafted to 3-aminopropyltriethoxysilane (APTES) to give organically modified alkoxysilanes that were used as molecular precursors for the preparation of hybrid materials. Ln 3+ first coordination sphere, composition of the siloxane matrix and connection between the organic and inorganic parts have been characterized by infrared spectroscopy, by 13 C 29 Si solid-state NMR as well as by elemental analyses. UV excitation in the organic component resulted in strong emission from Eu 3+ ions due to an efficient ligand-to-metal energy transfer. As compared to reference organic molecules, hybrid samples exhibited similar emission properties under UV excitation in addition to mainly unchanged excited states lifetimes. However, by direct excitation of the Eu 3+ - 5 D 0 energy level, the presence of two different site distributions were evidenced in the four hybrid compounds. Emission features related to each of these site distributions and their respective attribution were investigated. Variations in the relative emission intensities were observed according to the nature of the organic chromophore. These variations were discussed in relation to the ATE (Absorption-Transfer-Emission) mechanism and to the relative energy positions of the ligand and the rare-earth ions respectively.

Luminescence of the orthoborate YBO3:Eu3+. Relationship with crystal structure

Abstract Pseudo-vaterite structure of YBO3 has been determined from X-Ray data taken from a single crystal. This orthoborate crystallizes in the P6 3 m space group. The structure exhibits two types of [YO8] polyhedra due to the existence of two environments for the yttrium ions. The Eu3+ luminescence in this compound corroborates fairly well the structural determination by identification of two crystallographic sites both showing a C3 symmetry.

Synthesis and optical features of an europium organic–inorganic silicate hybrid

Abstract An europium organic–inorganic silicate hybrid was synthesized by grafting a coordinative group (dipicolinic acid) to a silicate network precursor (3-aminopropyltriethoxysilane) via a covalent bonding. Sol–gel process and complexation were performed using different experimental conditions. The hybrid materials, in particular the Eu 3+ coordination mode, were characterized by infrared and luminescence spectroscopies. Morphology of the materials and TG analysis showed that grafted silica enhanced thermal and mechanical resistances of the organic part.

Preparation of fluorides at 80°C in the NaF-(Y, Yb, Pr)F3 system

Crystalline single-phase hexagonal fluorides with nominal compositions NaY 1–x–y Yb x Pr y F 4 (with 0≤x≤1 and y≤0.05) have been prepared by a coprecipitation technique without the need of any thermal treatment as a final step. Compared with the fluorides prepared by solid state chemistry, this protocol allows better control of the stoichiometry of the materials and improves the homogeneity of the grain size distribution. The influence of these structural and microstructural parameters and of the oxygen content on the optical performances of these fluorides is examined and discussed by comparison with the spectroscopic properties of solid state synthesized Pr 3+ -doped NaYF 4 fluorides.

Orthoborates processed by soft routes: correlation luminescence structure

Abstract YBO 3 and H–Ln BO 3 (Ln=La, Nd, Sm, and Eu) orthoborates have been prepared by an original sol–gel mineral process. This synthesis method over solid state reaction offers the possibility of obtaining high quality materials at low temperatures, without parasitic phases. Luminescent europium ions have been used as structural probes to investigate these orthoborate phases. Due to the purities of the different powders the symmetries of the europium ion in the different matrices have been determined unambiguously and a comparison between the luminescence results and the structural descriptions given in the literature has been realized.

Optical properties of Eu3+ activated Sr10F2 (PO4) 6 elaborated by coprecipitation

Abstract The compound Sr 10 F 2 (PO 4 ) 6 was synthesized by coprecipitation at 1200°C and characterized by X-ray diffraction, thermogravimetric analysis and IR spectroscopy. The Eu 3+ fluorescence spectra were recorded in this compound using either a tunable dye laser or a nitrogen laser. Whatever the excitation technique, the emission essentially arises from the 5 D 0 level of the Eu 3+ ion. The spectroscopic results are discussed in relation to the existence of different crystallographic sites for Eu 3+ in this host material.

Optical properties of Tb3+ in the diphosphate CsYP2O7

Abstract The luminescence of Tb 3+ ion in the diphosphate CsY 1− x Tb x P 2 O 7 (0 x ⩽ 1) is reported. A high concentration quenching of the emission from the 5 D 3 level due to a 5 D 3 → 5 D 4 cross-relaxation process is pointed out, well described by the Inokuti and Hirayama model in the case of a dipole-dipole interaction. On the other hand, a weak concentration quenching of the emission originating from the 5 D 4 level is observed. The luminescence dynamics showed that a fast diffusion occurs for the high Tb 3+ ion concentration, involving the 5 D 4 level; this process is moreover phonon-assisted.