Jeanine Thery

Preparation, structure, optical, and magnetic properties of lanthanide aluminate single crystals (LnMAl11O19)

Rare‐earth aluminates having the general formula LnMAl11O19 with Ln3+ = La, Pr, Nd, Sm, Eu, Gd, and M2+ = Mg, Ni, Co, Mn, Fe have been synthetized. This paper is devoted to mixed compounds of the series La1−xNdx Mg Al11O19 of which large single crystals have been obtained by the flame fusion method. A full refinement of the pure lanthanum compound (x = 0) having a quasimagnetoplumbite structure has been performed (final R = 0.039). Spectroscopic investigations of the (La, Nd) aluminate have allowed the measurement of fluorescence yield and lifetime of Nd3+ in the host lattice as a function of the neodymium content. Additional results have been obtained on the magnetic anisotropy, from susceptibility measurements performed on the Nd3+ aluminate in the temperature range 4–300 K.

LNA: A new CW Nd laser tunable around 1.05 and 1.08 µm

We have investigated the CW laser properties of the lanthamide hexa-aluminate La 0.9 Nd 0.1 MgAl 11 O 19 at room temperature. When a 1 cm long crystal is pumped by an Ar+ laser (514 nm) or a Kr+ laser (752 nm), CW emission is obtained with slope efficiencies of 10 and 26 percent, respectively. A four-plate Lyot filter in the cavity forces the LNA crystal to oscillate in either of the two major bands centered al 10 820 A (tuning range 80 A) and 10 545 A (tuning range 35 A).

Structural investigation of K+ and Tl+ β-aluminas

Abstract Structures of K+ and Tl+ aluminas were investigated by single-crystal X-ray diffraction. In the final refinements, corresponding to R values of 0.034 and 0.058, respectively, the distribution of conducting ions was found to be similar to that of Na β-alumina. In K+ β-alumina clear evidence of additional electronic density in the spinel-like blocks is obtained and is interpreted as due to a Frenkel defect.

Growth by laser ablation of Y2O3 and Tm∶Y2O3 thin films for optical applications

Crystalline undoped and thulium doped yttrium oxide (Y2O3) thin films have been grown by the pulsed laser deposition (PLD) technique on various single-crystal substrates heated at 700 °C. X-Ray diffraction (XRD) analysis showed that the orientations of the films depended on the substrate and on the oxygen pressure. The crystalline quality of Y2O3 thin films, studied by rocking-curve measurements and by Rutherford backscattering spectroscopy (RBS) in channeling geometry, and the in-plane orientations between films and substrates, determined by X-ray asymmetric diffraction, were also found to depend on the same parameters. The recording of the visible fluorescence spectra of the thulium (Tm) doped Y2O3 thin films, as well as the measurements of the fluorescence lifetimes of the 1D2 and 1G4 thulium emitting levels, gave results very similar to those obtained on bulk crystals. Doping rates in Tm of 0.5 and 1% were found to limit Tm–Tm interactions inside the films and to give relatively high visible fluorescence intensities.

New Cr4+ activated compounds in tetrahedral sites for tunable laser applications

Abstract The three new Cr4+ doped matrices studied in this work exhibit only tetrahedrally coordinated lattice sites for the small cations and therefore will not incorporate Cr3+ ions. The Cr4+ doped compounds SrGa4O7 and Sr(Ga, Al)2O4 exhibit broad band IR fluorescence. But it appears difficult to combine easy crystal growth and good optical properties. If Cr4+:SrGa4O7 can be grown by Czochralski method, its fluorescence lifetime is very short (1 μs at 100 K). On the contrary for Cr4+:Sr(Ga, Al)2O4, the 100 K fluorescence lifetime can reach 35 μs (and 10 μs at 300 K), but the hexagonal-monoclinic structural transition prevents to grow good quality single crystals. Cr4+:Li2MgSiO4 is a remarkable compound. At 300 K it exhibits broad and intensive fluorescence peaking at ∼ 1.2 μm. The fluorescence lifetime exceeds 100 μs at 300 K and 400 μs at ∼ 50 K. This is the highest value reported so far, to our knowledge, for a Cr4+ activated material. The very long fluorescence lifetime and its temperature dependence are explained by the thermalization of the Cr4+ 3T2 and 1E levels, the 1E level being the lowest one. Crystal growth of Cr4+:Li2MgSO4 using the flux method is in progress.

Structural refinements on a sodium β-aluminogallate crystal and a parent Nd3+-exchanged crystal

Abstract X ray structural refinements are performed on a sodium β-aluminogallate single crystal and on the corresponding Nd 3+ -exchanged compound, which presents potential laser applications. In the hexagonal unit cells ( a = b = 5.667 A, c = 22.663 A, Z = 2 for the Na + compound and a = b = 5.644, c = 22.610 A for the Nd-exchanged compound), the study of ion distribution reveals a single position for the rare-earth active ion, a highly disordered distribution of sodium ions in the mirror-planes of the structure and a nonrandom localization of gallium in the available sites.

Structure of a sodium-neodymium aluminate with mixed β-alumina and magnetoplumbite structure

The structure of a mixed sodium-neodymium aluminate has been investigated on a single crystal. It reveals hexagonal symmetry (SG P6m2, Z = 1) and the unit cell (a = 5.57, c = 22.25 A) is described as an alternate stacking of half β-alumina unit cell and half magnetoplumbite unit cell. This leads to an ordering between the layers of large ions Na+ and Nd3+ in the c direction.

X‐ray diffuse scattering study of the low‐temperature microdomains in silver β‐alumina

A semiquantitative analysis of the X-ray diffuse scattering from β-alumina between 20 K and room temperature shows the change with temperature of the organization of the conducting ions. The earlier reported low-temperature superstructure never achieves long-range order. Both the size of the 2D domains and the order within the domains, as reflected by the occupation factors, saturate around 77 K. Above this temperature, the size decreases from its saturation value of 45 A to about 10 A at 400 K, with a parallel decrease of the order inside the domains. The occupation factors could be determined up to 220 K, and they extrapolate at room temperature to values close to the average occupation determined by conventional structure analysis.

Lanthanide ion exchange in sodium ß-aluminogallate Na1+x(Al1−yGay)11O17+x/2 single crystals 0

Abstract Large single crystals (5×5×1.5 mm 3 ) of sodium s-aluminogallate, with compositions Na 1+x ( Al 1−y Ga y ) 11 O 17+ x 2 (0.25 have been prepared at 1450–1600°C using a flux evaporation method. NaF flux was employed. Ga 3+ ions substitute for Al 3+ ions in the spinel blocks and the lattice parameters are found to be larger than those of s-alumina. Several lanthanide ions have been partially exchanged for sodium ions in these crystals using molten rare-earth salts while such an exchange does not occur in s-alumina. The distribution of these ions can be either homogeneous (Eu 2+ /Eu 3+ mixture) or inhomogeneous (Ce 3+ , Nd 3+ ). These materials could present interesting optical properties.

Short-range order in barium hexaaluminate (phase I) single crystals

Abstract Single crystals of barium hexaaluminate (phase I, barium β-alumina) with the composition Ba0.68Al11O17.18 have been obtained by zone melting. X-ray and electron diffuse scattering give evidence of local ordering between Ba and vacancies. This short-range order is simulated by a Monte Carlo-type routine and can be described as a two-dimensional superstructure a √3 × a√3, covering about 60A˚and limited by zones which contain vacancies or barium clusters.