F. Guillen

Mechanochromic and Thermochromic Luminescence of a Copper Iodide Cluster

The mechanochromic and thermochromic luminescence properties of a molecular copper(I) iodide cluster formulated [Cu(4)I(4)(PPh(2)(CH(2)CH=CH(2)))(4)] are reported. Upon mechanical grinding in a mortar, its solid-state emission properties are drastically modified as well as its thermochromic behavior. This reversible phenomenon has been attributed to distortions in the crystal packing leading to modifications of the intermolecular interactions and thus of the [Cu(4)I(4)] cluster core geometry. Notably, modification of the Cu-Cu interactions seems to be involved in this phenomenon directly affecting the emissive properties of the cluster.

Luminescent properties of Eu3+-activated lithium rare earth borates and oxyborates

Abstract The luminescence characteristics of Eu 3+ in the borates Li 6 Y(BO 3 ) 3 and Li 3 La 2 (BO 3 ) 3 and the recently discovered oxyborates LiLa 2 O 2 BO 3 , LiLn 6 O 5 (BO 3 ) 3 (Ln=Y,Gd) and Li 2 Lu 5 O 4 (BO 3 ) 3 have been investigated and compared to those in the borates LnBO 3 (Ln=La,Y) and the oxyborates “Ln 3 BO 6 ” (Ln=La,Gd). The probability of electric dipole f–f transitions is generally markedly higher in oxyborates than in borates. This is ascribed to the highly anisotropic environment of rare earth ions and the low position of the charge transfer states. Consequently, the Eu 3+ -activated oxyborates are characterized by a deeper red emission and faster decay.

Crystal growth and optical properties of new neutron detectors Ce/sup 3+/:Li/sub 6/R(BO/sub 3/)/sub 3/ (R=Gd,Y)

An efficient new scintillator that contains lithium, gadolinium, and boron, all three of which possess large neutron capture cross-section isotopes for highly exothermic reactions, has been recently developed. The homologous yttrium material was also investigated. These compounds of composition Li/sub 6/R(BO/sub 3/)/sub 3/ (R=Gd, Y) can be activated by Ce/sup 3+/. The synthesis of powders was carried out by high-temperature solid-state reaction from the starting materials LiOH, H/sub 2/O, H/sub 3/BO/sub 3/, Gd/sub 2/O/sub 3/, or Y/sub 2/O/sub 3/, and Ce(NO/sub 3/)/sub 3/, 6H/sub 2/O of purity /spl ges/99.99%, under a flow of argon/H/sub 2/ (5%). Under ultraviolet excitation, they show a broadband emission peaking at 390 nm. The gadolinium emission lies near the maximum of a 4f-5d Ce/sup 3+/ absorption band, so efficient Gd/sup 3+/-Ce/sup 3+/ transfer occurs. Ce/sup 3+/:Li/sub 6/R(BO/sub 3/)/sub 3/ (R=Gd, Y) crystals were grown by the Czochralski method in a resistance heating furnace using a conical vitreous carbon crucible of 150 cm/sup 3/ under deoxygenated pure argon. Monocrystalline boules as large as 3 cm diameter and 6 cm length have been obtained. The interest of these new materials is the high scintillation efficiency-as much as six times that of Li-glass scintillators for the Gd material. Moreover, these scintillators offer the ability to tailor their response to the neutron spectrum by varying the isotopic composition of the key constituents [lithium, gadolinium (yttrium), boron].

Investigations of the MSAl2S3 systems (M = Ca, Sr, Ba) and luminescence properties of europium-doped thioaluminates

Abstract Solid state-investigation of the MSAl 2 S 3 systems ( M = alkaline earth ) shows the existence of the following thioluminates CaAl 2 S 4 , SrAl 2 S 4 , Sr 2 Al 2 S 5 , BaAl 4 S 7 , BaAl 2 S 4 , Ba 2 Al 2 S 5 , Ba 4 Al 2 S 7 and Ba 5 Al 2 S 8 . All are isostructural with homologous thiogallates. When substituted for M, divalent europium shows an emission in all host lattices. Compared with thiogallates, wider bandgaps and higher energies of the 5d emitting level are characteristics favourable to the thermal stability of the emission; the increase in quenching temperature is particularly pronounced for M-rich hosts.

Charge transfer excitation of the Nd3+, Sm3+, Dy3+, Ho3+, Er3+ and Tm3+ emission in CaGa2S4

Abstract The excitation spectra of the Nd3+, Sm3+, Dy3+, Ho3+, Er3+ and Tm3+ emission in the sodium-compensated CaGa2S4 host lattice, a sulfide with wide band gap, contain an intense band below the absorption edge. Comparison of the energy of its maximum with thermodynamic data and correlations to Jorgensens refined spin-pairing theory predictions allow one to ascribe this band to a charge transfer transition ending onto 4f orbitals. The irregular variation within the rare earth series contrasts with the monotonic variation of the absorption edge in stoichiometric rare earth sulfides (e.g. NaLnS2), associated with interband transitions.

Des conducteurs ioniques pseudo-bidimensionnels: Li8MO6 (M = Zr, Sn), Li7LO6 (L = Nb, Ta) et Li6In2O6

Abstract The ionic conductivity of the pseudo-2D oxides Li 8 MO 6 (M = Zr, Sn), Li 7 LO 6 (L = Nb, Ta) and Li 6 In 2 O 6 has been measured and related to their structures. The ideal lattice consists of octahedral sheets [(Li 2 M)O 6 ] n , [(Li□L)O 6 ] n or [(In 2 □)O 6 ] n of CdI 2 -type, between which 6 Li + ions are inserted with a tetrahedral environment. As expected from the structures the highest lithium mobility is observed for Li 7 LO 6 phases and the smallest one for Li 8 MO 6 .

Energy transfer from Eu2+ to trivalent rare earth ions in BaY2F8

Abstract An efficient energy transfer from divalent europium to trivalent rare earth ions appears in the luminescence spectrum of BaY 2 F 8 when it is simultaneously doped with Eu 2+ and Ln 3+ ions (Ln = Tb, Ho, Er) as a consequence of a f-f emission of Eu 2+ .

Les oxydes doubles de plomb et de manganese

The investigation of the lead-oxygen-manganese system under an oxygen pressure of 1 atmosphere shows the existence of five ternary oxides with compositions Pb0.25MnO2, Pb0.25MnO2−x (x ⋍ 0.01), Pb0.43MnO2.18, Pb0.43MnO2.14 (Pb3Mn7O15) and Pb2MnO4. The structure of Pb3Mn7O15 has been solved; it consists of an ABAB packing of oxygen and lead atoms with the manganese atoms occupying octahedral sites. The ternary phases are catalysts for oxidation-reduction reactions, Pb0.43MnO2.18 having the largest activity. They are more stable in acidic solutions than the Ln1−xPbxMnO3 perovskites (where Ln is a rare earth).

CdWO3F2, a new luminescent fluorotungstate

Abstract Investigation of the system CdF2-WO3 shows the existence of a fluorotungstate formulated CdWO3F2 and structurally related to CuWO3F2. Under UV or X-ray excitation CdWO3F2 shows a broad emission band with a maximum at 525 nm at 300 K. Thermal quenching occurs above room temperature, confirming the beneficial effect of the presence of fluorine on the stability of the O-W charge-transfer emission.

Synthesis, structure and electronic properties of the cerium and potassium thiosilicate: KCeSiS4

Abstract The cerium and potassium thiosilicate KCeSiS 4 has been synthesized at 800 °C from Ce, Si, K 2 S and S precursors weighted in the K:Ce:Si:S = 1:1:1.15:4.3 ratio. This yellow, air stable compound crystallizes in the monoclinic space group P2 1 , (No. 4) with the cell parameters: a = 6.5201(3) A, b = 6.5982(3) A, c = 8.6920(5) A, β = 107.701(3) °, V = 356.23(3) A 3 and Z = 2. Refinement of 36 parameters by the Rietveld method, using 974 reflections led to R p (%) = 2.49, R wp (%) = 3.35 and χ 2 = 2.71. KCeSiS 4 , isostructural to KLnMQ 4 (Ln = La, Nd, Gd, Y; M = Si, Ge; Q= S, Se), consists of two-dimensional ∞ 2 [CeSiS 4 ] − anionic layers separated by K + ions. These layers are built upon [CeS 7 ] distorted monocapped trigonal prisms, sharing 2 edges and 2 corners with each other, and upon [SiS 4 ] tetrahedra linked to the ∞ 2 [CeS 4 ] 5− skeleton by edge and face sharing. From magnetic measurements, an effective magnetic moment μ eff (300 K) = 2.73(2) μ B was calculated in good agreement with the k (i) Ce (III) Si (IV) S 4 (−II) charge balance. From diffuse reflectance measurements, a band gap of 2.68(1) eV correlated to the occurrence of a 4 f → 5 d electronic transition was evidenced. Moreover, chromatic L/a/b coefficients, equal respectively to 88.37/−18.85/52.91, have been determined for the bright yellow colour of the compound. These parameters compare rather well with those of NiTiO 3 , a well known industrial pigment. The room temperature strong green luminescence at E = 2.45 eV( λ = 506.1 nm) of KCeSiS 4 has been investigated through emission and excitation spectroscopy in the UV-visible range.