Transition Metal Fluoride Glasses Research Articles

Structural properties and luminescence of rare-earth ions in transition-metal fluoride glasses

The fluorescence of rare-earth ions RE3+ = Pr3+, Er3+ and Tm3+ has been compared in the transition-metal fluoride glass (36 mol% PbF2–24 mol% ZnF2–35 mol% GaF3–5 mol% YF3–2Al mol% F3) doped with either REF3 or RECl3. For the phonon-sensitive radiative transition, the lifetime is prolonged at low RECl3 concentrations because the phonon energy and/or electron coupling are reduced. For Pr3+, the doping with PrCl3 increases the lifetime by 50% with respect to PrF3 doping. These results suggest that the Cl− ions remain in the coordination sphere of the RE3+ ions in the ReCl3-doped glass after melting.

CP-MAS [formula omitted] with [formula omitted] decoupling NMR spectroscopy: medium range investigation in fluoride materials

The isotropic chemical shift of 207 Pb is used to perform structural investigations of crystalline fluoride compounds (PbF 2, Pb 2ZnF 6, PbGaF 5, Pb 3Ga 2F 12 and Pb 9Ga 2F 24) and transition metal fluoride glasses (TMFG) of the PZG family (PbF 2–ZnF 2–GaF 3). Using 207 Pb Cross Polarisation Magic Angle Spinning (CP-MAS) NMR with 19 F decoupling, it is shown that the isotropic chemical shift of 207 Pb varies on a large scale (1000 ppm) and that the main changes of its value are not due to the nearest neighbour fluorines but may be related to the number of next nearest neighbour (nnn) Pb 2+ ions. In this way, it is demonstrated that 207 Pb chemical shift is an interesting probe to investigate medium range order in either crystalline or glassy fluoride systems. The 207 Pb δ iso parameter has been linearly correlated to the number of nnn Pb 2+ ions.

From 1D to 3D fluorine octahedron networks in transition metal fluoride glasses: a 19F MAS NMR study

The sensitivity of the 19F isotropic chemical shift to the environment of the fluorine atom is used to investigate transition metal fluoride glass (TMFG) networks. The glass compositions were chosen in order to vary the initial constituents and check their influence on the octahedron network connectivity: PbF 2–ZnF 2–InF 3 (PZI), PbF 2–BaF 2–InF 3 (PBI) glasses and alkali fluoride glasses such as PbF 2–LiF–GaF 3, PbF 2–NaF–GaF 3, PbF 2–KF–GaF 3. NMR experiments give evidence for different fluorine atom sites. From the chemical shift values, it is shown that these fluorines may be classified into three categories: shared and unshared fluorines between two MF 6 octahedra and free fluorines which are not implied in these MF 6 octahedra. From the relative intensities of the corresponding NMR lines, the proportions of these different fluorines in the glasses are obtained and the connectivity of the MF 6 octahedra which constitute the networks is deduced. It is shown that the octahedra are corner shared and the dimensionality of the network varies from nearly 1D to 3D according to the glass composition. Furthermore, it appears that the structure of the alkali fluoride glasses is quite different from the other ones: the transition metal ions Zn 2+ and Ga 3+ or Zn 2+ and In 3+ are statistically distributed in the PZG (previously investigated) and PZI glasses, respectively when disconnected 3D domains of LiF 6/NaF 6/KF 6 and GaF 6 octahedra with Pb 2+ in interstitial positions are found in alkali fluoride glasses.

Superposition model for [formula omitted] isotropic chemical shift in ionic fluorides: from basic metal fluorides to transition metal fluoride glasses

Experimental measurements of 19 F isotropic chemical shifts on a large set of mainly ionic fluoride compounds (from simple metal fluorides to transition metal fluoride glasses) obtained by MAS NMR at 15 kHz spinning rate are simultaneously investigated. First, Ramsey's theory of the chemical shift with molecular orbitals obtained by Lödwin's orthogonalisation method is used to evaluate the isotropic part of the 19 F chemical shift in ionic fluorides for which the crystallographic structure and the atomic radial wavefunctions are known. Then, assuming that the paramagnetic part of the 19 F shielding in a given material is simply the summation of the paramagnetic contributions due to all the cations in the neighbourhood of the considered fluorine, a superposition model of the 19 F isotropic chemical shift is developed. Finally, this empirical approach is applied to complex fluoride compounds of unknown structure and it is demonstrated that it allows to obtain reliable structural informations. More generally, it can be applied to all the ionic fluorides.

Investigation of fluorine octahedron connectivities in transition metal fluoride glasses by solid-state magic-angle-spinning nuclear magnetic resonance spectroscopy

High-resolution magic-angle-spinning (MAS) NMR spectroscopy is used to investigate the structural properties of some transition metal fluoride glasses ( - - ) related to the fluorine network. Several glass compositions are investigated in order to vary the ratios. MAS NMR experiments are carried out on certain crystalline compounds selected as being the initial constituents or recrystallization compounds of glassy phases, or because they have some specific particular connectivities of the fluorine octahedron network (e.g. ). It is shown that three types of fluorine are involved in the glass network: free fluorines which are not connected to transition metal ions, and shared and unshared fluorines belonging to and octahedra. Quantitative information on these three different fluorine sites, their relative ratios in the glassy networks, and the degree of cross-linking of the fluorine octahedra is obtained. Our results prove the validity of the previously adopted assumption according to which the glass network is built up from corner-sharing fluorine octahedra centred on transition metal ions.

The local field distribution of in transition metal fluoride glasses investigated by electron paramagnetic resonance

The EPR spectra of in two transition metal fluoride glasses (PZG and PBI) have been extensively studied as functions of temperature, concentration and microwave frequency (S, X, K and Q bands). The marked changes observed in the EPR spectra with temperature and concentration imply the existence of pairs of ions. The spectra of isolated ions were obtained at low temperature for samples with low doping concentration. Isolated ions are characterized by a fine-structure -parameter distribution within the range . The simulations of these spectra are computed with a Czjzek fine-structure parameter distribution (this solution prohibits the existence of axial symmetry sites). It indicates a decrease of the number of geometrical constraints compared to those for and (octahedral coordination in a fluoride medium), in agreement with the higher coordination numbers. -ion sites are found to be more distorted in PZG than in PBI, suggesting that the glass network has an influence on the polyhedron distortion amplitude.

Short-range order quantification in transition metal fluoride glasses (TMFG) through EPR spectra simulation

Cr3+ and Fe3+ EPR spectra in transition metal fluoride glasses (TMFG), pyrochlore CsZnGaF6 and amorphous GaF3 are found to be very similar. Then, it is inferred that the constituent octahedra of all these disordered fluoride compounds are characterized by closely related distortions. Two short-range structural models, based on CsZnGaF6 and GaF3, are worked out with the aim of characterizing octahedra in TMFG. The CsZnGaF6 model is developed using structural information on this compound. Amorphous GaF3 structure is simulated by using molecular dynamics calculations starting from rhombohedral GaF3. From the M-F distance and bonding angle distributions obtained from these two models, the Cr3+ and Fe3+ fine-structure parameter distributions are calculated with the help of the superposition model and finally the corresponding EPR spectra are computed. A good agreement is obtained simultaneously for the two local paramagnetic probes, which leads to a quantification of the short-range order in TMFG: constituent octahedra are only slightly distorted. It is interesting to note that the distributions of fine-structure parameters are very similar to the Czjzek ones previously used to simulate Cr3+ and Fe3+ spectra in TMFG.

Electron paramagnetic resonance determination of the local field distribution acting on Cr3+ and Fe3+ in transition metal fluoride glasses (TMFG)

Cr3+ and Fe3+ ions are used as paramagnetic probes of the local order in diamagnetic transition metal fluoride glasses (TMFG). EPR observations are made at S, X, K and Q band frequencies at different temperatures. It follows from the frequency dependence of the spectra that Cr3+ and Fe3+ ions are characterized by a continuous fine-structure parameter distribution in the range 0.06-0.55 cm-1 for Cr3+ and 0.04-0.33 cm-1 for Fe3+. The simulations of these spectra are computed with a fine-structure parameter distribution P(h20, lambda ) whose expression is determined by analogy with the distribution of electric field gradient P(Vzz, eta ) developed by Czjzek considering amorphous solids with random ionic coordination. An excellent agreement between observed and calculated spectra is obtained whatever the frequency band.

Vapour-phase deposition of rare-earth-doped PZG glasses

Physical vapour deposition has been used in transition metal fluoride glasses (TMFG) systems to prepare fluoride glass films doped with various active ions (3d transition or rare-earth). Active planar waveguides have been realized with PZG doped films on flat ZBLAN or CaF2 substrates.

Short range ordering in transition metal fluoride glasses as shown by EPR

Electron paramagnetic resonance (EPR) spectra of Fe3+ ion in crystalline powdered CsZnGaF6 and in transition metal fluoride glasses provide evidence of common features related to their disordered structures. From structural extended X-ray absorption fine structure data, the spin Hamiltonian parameter (b20 and b22) distribution of Fe3+ in CsZnGaF6 may be computed and allows us to build the corresponding EPR spectrum accurately. The main features of this distribution are comparable with Czjzek's as used to reconstruct the EPR spectrum of Fe3+ in PZG glass. It leads to some quantification of the local disorder in PZG glass.

Spectroscopic and laser properties of Nd3+ in fluoride glasses

Abstract In the last few years an increasing interest has arisen in the study of heavy-metal fluoride glasses related to passive and active optical applications materials. Up to now all glass lasers have used trivalent lanthanides as active ions. Neodymium-doped glasses are by far the most widely investigated systems. The spectroscopic properties of Nd3+ are dependent upon the chemical composition of the host glass. In this work we present a brief review of the optical properties of Nd3+ ions in heavy metal and transition metal fluoride glasses. This includes radiative and nonradiative transition probabilities, emission cross-sections, peak wavelengths and linewidths of the 4 F 3 2 → 4 I 11 2 laser transition, and Nd-Nd energy transfer. This is followed by a short discussion on the site-selective spectroscopy of Eu3+ in zirconium-barium-lanthanum and barium-indium-gallium fluoride glasses. Finally, we report a study of the laser properties of Nd3+ doped fluoride glass BlGaZLuTMn (30BaF2-l8InF3-l2GaF3-20ZnF2-9LuF3-6ThF4 -4MnF2-lNdF3 mol% composition) pumped by flashlamps. As far as we know this is the first time laser action has been obtained in bulk in this glass. From these studies the influence of site-dependent effects on the time-resolved stimulated emission properties of Nd3+ ions is also discussed.

Temperature-dependent concentration quenching of Nd3+ fluorescence in fluoride glasses

The optical properties and temperature-dependent concentration quenching of Nd3+ fluorescence have been investigated in heavy-metal and transition-metal fluoride glasses using steady-state and time-resolved laser spectroscopy. Judd-Ofelt parameters were derived from the absorption spectra and used to calculate the 4F3/2 to 4I11/2 stimulated-emission cross-section and the 4F3/2 radiative lifetime. From the thermal behaviour of lifetimes, a T3 dependence for the non-radiative Nd-Nd relaxation processes has been found in the 15-100 K temperature range for the three families of fluoride glasses investigated, which is in agreement with a two-site non-resonant process.

EPR structural investigations of transition metal fluoride glasses (TMFG)

Abstract The results of an EPR study of TMFG separately doped with Ti3+, Cr3+, Fe3+, Mn2+, Co2+ and Cu2+ ions are presented. These ions are octahedrally coordinated; for Ti3+ and Cu2+ the octahedra are tetragonally distorted. Spin-spin interactions give rise to a strong concentration and temperature dependence of the EPR spectra for Cr3+, Fe3+ and Mn2+; moreover, for these ions a zero field absorption is observed (consistent for Cr3+ with a large single crystal field parameter distribution).

Raman spectroscopy vibrational analysis of octahedrally coordinated fluorides: Application to transition metal fluoride glasses

An extensive Raman investigation of octahedrally coordinated single-crystal fluorides have been performed. The theoretical study of these phases, using group theory, gives the evidence of close relationship between metal oxidation number, connection schemes, and spectra features. The results of this study, when applied to the case of transition metal fluoride glasses, propose these glasses to be built up with octahedral entities predominantly linked by corners to form one-dimensional networks.

Energy transfer between manganese(II) and thulium(III) in transition-metal fluoride glasses

Lead zinc gallium fluoride glass containing 2 mole% TmF 3 is shown to luminesce from 1I 6 (35200 cm −1), 1D 2(28000), 1G 4 (21500) and 3H 4 (12800) to several lower J levels. When the 24 mole% ZnF 2 is replaced by MnF 2 in the absence of thulium, the (broad band) quartet-to-sextet (ground state) emission at 16800cm −1 has a mean lifetime of 1 ms. If 2 mole% TmF 3 is added to the latter glass, energy transfer decreases the lifetime to below 0.03 ms. The high critical radius R 0 (above 20 Å) is rationalized by Mn-Mn energy migration (concomitant with a lifetime shortened from 24 ms) to be compared with R 0≈ 8 Å for low Mn(II) concentration, almost identical with energy transfer between 1 mole% each of MnF 2 and NdF 3 previously studied in an analogous glass.

Photoelastic Characteristics of Fluorozirconate and Transition-Metal Fluoride Glasses

Photoelastic Characteristics of Fluorozirconate and Transition-Metal Fluoride Glasses

Energy transfer between manganese(II) and neodymium(III) in transition-metal fluoride glasses

Energy transfer between Mn(II) and Nd(in) in glasses of composition: 36 PbF 2, 24 ZnF 2, 35 GaF 3, 2 AlF 3, 3 YF 3, 4 LaF 3 in which manganese may replace all the zinc, and neodymium some lanthanum, is studied by dynamic and static methods. Both methods arrive at the same results indicating linear dependence of transfer probability on donor concentration. These results also demonstrate energy storage in the manganese-neodymium system having applications in Nd lasers.

ChemInform Abstract: POLARIZED RAMAN SCATTERING IN RARE EARTH FLUORIDE GLASSES

AbstractDie polarisierten Raman‐Spektren von Seltenerdmetallfluorid‐Gläsern, basierend auf BaF2 und ThF4 in Kombination mit ZnF2, YF3, YbF3, LuF3 und/ oder AIF , werden mit denen von Schwermetallfluorid‐Gläsern (ZrF4, HFF, in Kombination mit BaF2) verglichen.

Polarized Raman Scattering in Rare‐Earth Fluoride Glasses

The polarized Raman spectra of rare‐earth fluoride glasses based on BaF2 and ThF4, in combination with ZnF2, YF3, YbF3, LuF3, andlor AlF3, are reported and compared with those of other heavy‐metal fluoride glasses. The spectra of rare‐earth fluoride glasses, especially those containing large amounts of AlF3, have relatively broad and mostly depolarized features, suggesting that these glasses are more highly disordered than fluorozirconate and transition‐metal fluoride glasses.

Frequency and Temperature Dependence of Infrared Edge Absorption in Transition Metal Fluoride Glasses

Frequency and Temperature Dependence of Infrared Edge Absorption in Transition Metal Fluoride Glasses