Verres fluores au tetrafluorure de zirconium proprietes optiques d'un verre dope au Nd3+

Glass formation has been observed in the ZrF₄BaF₂NaF system around the composition 50 % ZrF₄, 25 % BaF₂, 25 % NaF. A Nd³⁺ doped glass obtained by dissolving NdF₃ in the previous material has been studied. Absorption spectra in the region ${}^4\text{I}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{→}{}^2\text{P}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, I.R. fluorescence spectra and lifetime measurement of the ${}^4\text{F}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ level show a good protection of Nd³⁺ against the fluorescence quenching.     

Transfert d'energie entre les ions Ce3+ et Tb3+ dans GdAlO3

Energy transfer from the Ce³⁺ to the Tb³⁺ ion has been studied in a host GdAlO₃ structure. The maximum fluorescence intensity of Tb³⁺ is observed for the composition Gd_0.96Ce_0.02Tb_0.02AlO₃. The energy transfer from Ce³⁺ to Tb³⁺ is explained by a dipole-dipole type coulombic interaction.     

Sur le mecanisme de substitution des cations Sn4+ et Fe2+ dans la magnetite

The distribution of Fe²⁺ and Fe³⁺ in Fe_3?xSn_xO₄ solid solution has been established from saturation magnetization measurements. From these results it may be suggested that Fe²⁺ in A site destabilizes Fe³⁺ in A site at the expense of Fe²⁺ in B site.     

Mise en evidence d'un transfert d'energie de type Gd3+ → Tb3+ dans les phases Sr2Gd1−xTbxGaO5

Energy transfer from optically excited Gd³⁺ ions to Tb³⁺ ions is reported in Sr₂Gd_1?xTb_xGaO₅. It is illustrated by the comparison of the emission and excitation spectra of Sr₂GdGaO₅ and of Sr₂Gd_0,995Tb_0,005GaO₅ between 77 and 300 K.     

Mise en evidence d'un transfert d'energie Gd3+ → Eu2+ dans les phases RbGd3F10 dopees a l'europium divalent

The α and β Rb_1?xEu_xGd₃F_{10+ x} phases are efficient U.V. phosphors. Emission consists of narrow f-f lines. Energy transfer between Gd³⁺ and Eu²⁺ ions is reported.     

Interactions magnetiques hyperfines et quadrupolaires combinees pour les ions d'impuretes 119Sn2+ dans Cr2O3

Hyperfine magnetic interactions have been observed for the first time for Sn²⁺ ions introduced as doping agents in a magnetically ordered oxide (¹¹⁹Sn: Cr₂O₃). Mössbauer resonance at low temperature shows for ¹¹⁹Sn²⁺ the simultaneous presence of hyperfine magnetic and quadrupole interactions, which have the same order of magnitude at 77 K. From the spectra, the following parameters have been determined: tranfered hyperfine magnetic field: H_Sn²⁺ (77 K = 38 ± 1kOe, sign and value of the quadrupole interaction constant: eV_zzQ = + 3,6 ± 0,3 mm/s, asymmetry parameter: η = 0,15 ± 0,05, polar (θ) and azimutal (?) angles: $\text{θ ? ? ? 90°}$, and chemical shift: $\text{δ}\text{BaSnO}{}_3\text{= + 2,89 ± 0,02}\text{mm}\text{/}\text{s}$. The investigation shows that Sn²⁺ is localized at the surface of the Cr₂O₃ grains.     

Proprietes cristallographiques et dielectriques de deux nouvelles familles d'oxyfluorures contenant des ions Li+ et K+ et de structure derivee du type chiolite

Two new material series of formulas Na_5?xA_xW₃O₉F₅ (0 ? x ? 0.75; A = Li, K) with a chiolite related structure have been obtained by substituting sodium in Na₅W₃O₉F₅ either by lithium or by potassium. They have all a ferroelectric and ferroelastic behavior. The Curie temperature decreases slightly in both families as x increases. The size and quality of the crystals synthetized as well as the detected physical properties suggest potential applications in non linear properties.     

Splitting and broadening of the emission bands of Y2O3:Eu3+,Nd3+ and its dependence on Nd3+ concentration and annealing temperature

Although Eu³⁺ ion-doped Y₂O₃ has been extensively used as red phosphors, their color rendering needs to be improved for high-quality illumination and displaying. Here, we show that the emission spectra of Y₂O₃:Eu³⁺ red phosphors can be broadened by the doping of Nd³⁺ ion so that the color rendering capability of Y₂O₃:Eu³⁺ was remarkably enhanced. Y₂O₃:Eu³⁺ and Y₂O₃:Eu³⁺,Nd³⁺ colloidal spheres were synthesized by wet chemical procedure and high-temperature treatment. The fluorescence measurement under the 254 and 380 nm ultraviolet excitation indicates that the 612 nm red emission peak of Eu³⁺ can be splitted into two ones by the doping of Nd³⁺ ion, of which the full width at half maximum (FWHM) is broadened from 4.2 nm to 9.6 nm. By varying the concentration of Nd³⁺ ion, it was determined that the optimal doping concentration of Nd³⁺ ion is of 3 mol% for realizing the strongest emission intensity. The further increase of Nd³⁺ ion exceeding 3 mol% would lead to a concentration quenching phenomenon. The analysis based on XRD spectra and the simplified energy diagram suggested that the doped Nd³⁺ ion not only monitored the growth dynamics, but also took an efficient energy transfer and a cross relaxation process to generate intense emission from Eu³⁺ ion in both of C₂ and S₆ sites, instead of preferable one type of Eu³⁺ site (C₂ or S₆) in the Nd³⁺ undoped sample.     

Conversion de l'energie cinetique des particules α et β− en energie lumineuse par un monocristal de ThBr4

Irradiation of ThBr₄ single crystals by energetic electrons and ∝ particles gives rise to an emission over a broad band at 405 nm. This emission has been studied in terms of the nature and energy of both particles and with beam intensity. The radioluminescence conversion efficiency is about 6 ± 2% for electrons at 250 keV and 2 ± 1 % for ∝ particles at5MeV. ThBr₄ is as well as other “phosphor”.     

Influence de l'addition de cuivre sur les proprietes structurales et physiques de VO2

Magnetic susceptibility, DTA, X-ray diffraction and EPR of Cu_xV_1?xO₂ samples have been studied. A new Q-phase stable at low temperature is reported. Analogies with M^III_xV_1?xO₂ phases (M^III = Al, Cr, Fe) are discussed.     

Effet JAHN-TELLER cooperatif et spectre optique de l'ion Cu2+ dans quelques chromites

Phase diagrams of Cu_1?xM_xCr₂O₄ (M²⁺ = Ni²⁺, Zn²⁺, 0,5(Li⁺+Ga³⁺)) are established by X-ray diffraction at high temperature and some cationic distributions deduced from neutron diffraction.The ligand field reflectance spectra of tetrahedrally coordinated Cu²⁺ in different oxidic host structures (I41/amd and Fd3m) are analysed at different temperatures (300 – 600 K). The evolution of electronic spectra may be correlated with the disparition of cooperative JAHN-TELLER effect. The quadratic distortion ($\text{c}\text{a}\text{< 1}$) in mixed nickel-copper chromites (0,5 < x ? 0,8) is mainly due to Ni²⁺; but, electronic spectra at high température in the range 4000 – 12000 cm^?1 discloses a certain contribution of Cu²⁺ ions to JAHN-TELLER distortion.     

高质量自调Q激光晶体Cr4+,Nd3+:Gd3Ga5O12的生长

用固相合成、共沉淀等方法合成了Cr4+,Nd3+GGG晶体的单相多晶材料.讨论了共沉淀法和固相合成法合成GGG单相的技术参数.用合成的单相多晶原料生长了高质量的Cr4+,Nd3+GGG单晶.通过测晶体的光谱性质发现Cr4+,Nd3+GGG晶体在400nm和520nm附近存在Cr3+离子的强的吸收峰.在808nm附近存在Nd3+离子宽的吸收带,能与InGa二极管激光有效的耦合;在1100附近有Cr4+的较强的吸收带,可实现对Nd3+的自调Q输出.Cr4+,Nd3+GGG晶体的荧光光谱与NdGGG晶体的一样,发光中心也位于1062nm,但其强度约为NdGGG的1/5～1/6.Cr4+,Nd3+GGG晶体是一种非常有潜力的自调Q激光晶体,可以实现大功率激光器的小型化和全固化.     

Proprietes de l'ion Cu2+ dans la structure de AgCuPO4-β

AgCuPO₄-β (high temp.) crystallizes with orthorhombic symmetry, space group: Pbca, z=8 and unit-cell parameters: a=7.500(1), b=15.751(2), $\text{c}\text{=5.702(1)}\text{A}\text{?}$. Its structure has been solved and refined to R=0.046 for 664 independent reflexions. The framework is built up with PO₄ tetrahedra, AgO₅ pyramids and CuO₅ bipyramids. The Jahn-Teller effect of Cu²⁺ and magnetic properties are discussed.     

Determination structurale et proprietes de conduction d'un nouveau compose de type hollandite: K1,8(Li2,45Sb5,55)O16; mise en evidence d'une surstructure d'ordre 3

The crystal structure of a synthetic hollandite phase K_1,8(Li_2,45Sb_5,55)O₁₆ has been refined by the full matrix least-squares method using 940 three-dimensional reflexions to a final R value of 0.046. The K atoms are randomly distributed on the special positions 2b (0 0 $\text{1}\text{2}$) and 4e (0 0 ±z) with z = 0.340(4).A long-exposure rotation photograph along the c axis shows diffuse X-ray scattering between the layer line. After a thermal treatment the X-ray diffraction pattern shows weak but sharp reflexions that could be indexed by tripling the short axis. The structural studies indicate an ordering of the large K atoms within the channels.The ionic conductivity of this phase has been investigated on a single crystal by hyperfrequences method. The potassium ion conductivity is the ordre of magnitude of 10^?3 (ohm cm^?1) at 30°C along the c axis.     

Intercalation d'ions alkylammonium et d'alkylamines a longues chaines dans les gels de V2O5

C_nH_2n+1N⁺(CH₃)₃ ions and C_nH_2n+1NH₂ amines with n ranging from 1 to 18 have been intercalated into the lamellar structure of V₂O₅ gels. Alkyl chain orientation in the interfoliar space has been deduced from the basal d-spacing evolution with the chain length : the chains are parallel, then tilted and finally perpendicular to the host lamellae as the chain length increases. Their monolayer disposition is also demonstrated. The large adaptability of the host structure proceeding from its gel state, leads to fast reaction at room temperature, especially with small polar heads such as -NH₂ (less than an hour). Contrary to usual intercalates, due to the gel state, only a mean composition can be defined. It has been found to correspond to 0.3–0.4 intercalated species per V₂O₅ : this is in good agreement with the upper limit (0.5) deduced from sterical considerations based upon a full filling of the interfoliar space. Thermal decomposition of alkyl chains restricts the stability of these intercalates to 160°C. More likely of the cationic exchange type with trimethylammonium ions, intercalation mechanism appears more complex with amines, involving probably also a host-guest charge transfer.     

Luminescent properties of GdAl3(BO3)4:Ln3+ (Ln3+:Eu3+, Tb3+, Dy3+) nano-phosphors

GdAl₃(BO₃)₄:Ln³⁺ (Ln³⁺:Eu³⁺, Tb³⁺, Dy³⁺) nano-phosphors were prepared by sol–gel method. The structure properties of the phosphors are characterized by XRD, and GdAl₃(BO₃)₄:Ln³⁺ nano-phosphors have average sizes around 40 nm. The doping concentrations of Eu³⁺, Tb³⁺ and Dy³⁺ ions in GdAl₃(BO₃)₄ nano-phosphors are from 1 to 9 mol% for Eu³⁺ ions, from 2 to 12 mol% for Tb³⁺ ions and from 1 to 5 mol% for Dy³⁺ ions, respectively. The luminescent properties of rare-earth ions doped GdAl₃(BO₃)₄ nano-phosphors are analyzed by the photoluminescence spectra, which prime doping concentration of Eu³⁺, Tb³⁺, and Dy³⁺ ions are at 5, 12 and 3 mol%, respectively. The energy transfers in the luminescent processes of rare-earth ions doped GdAl₃(BO₃)₄ nano-phosphors are discussed.     

Etude spectroscopique par la technique d'affinement de raie de fluorescence de verres fluorophosphates dopes a Eu3+

Sodium aluminium fluorophosphate glasses doped with Eu³⁺ have been studied with the fluorescence line narrowing technique. Eu³⁺ is located in two types of sites. The more ionic is probably surrounded by fluorine ions with an O_h symmetry. The more covalent corresponding to an oxyfluoride environment has a C_2v symmetry. A nonradiative energy transfer from ionic to covalent sites may be detected.