Spectroscopic investigations of Eu<Superscript>3+</Superscript> and Tb<Superscript>3+</Superscript>: Cadmium lead boro tellurite glasses

This paper reports on the preparation and spectral properties of europium (Eu³⁺) and terbium (Tb³⁺) ions doped cadmium lead boro tellurite (CLBT) glasses. For reference glasses, physical properties have been evaluated. From the [measurements of X-ray diffraction (XRD), glass amorphous nature of these [glasses has been studied. From the emission spectra of Eu³⁺: CLBT glasses, five [transitions (⁵ D ₀ → ⁷ F ₀, ⁷ F ₁, ⁷ F ₂, ⁷ F ₃ and ⁷ F ₄) at 579, 591, 613, 652 and 701 nm are observed with λ_exci = 392 nm (⁷ F ₀ → ⁵ L ₆) and in the case of Tb³⁺: CLBT glasses, four emission transitions ⁵ D ₄ → (⁷ F ₆, ⁷ F ₅, ⁷ F ₄ and ⁷ F ₃) are observed at 489, 543, 584 and 621nm respectively monitered with λ_exci = 376 nm (⁷ F ₆ → ⁵ G ₆).     

Crystallization and luminescence properties of Eu<Superscript>2+</Superscript> doped diopside glass ceramics

Eu²⁺ doped glass ceramics have been prepared and characterized. The crystallization and optical properties of the glass ceramics were studied by XRD, SEM, and fluorescence spectra. The precipitated crystalline phase in the glass ceramics was prismatic diopside (CaMgSi₂O₆) and plate-like cristobalite (β-SiO₂). As the heat treatment time increases, the content of crystals increases gradually. Fluorescence measurements showed that Eu²⁺ ions entered into the diopside crystalline phase and induced a much stronger emission in the glass ceramics than that in the corresponding glass. With increase of Eu²⁺ content, concentration quenching was observed.     

X-ray Fluorescence of Eu<Superscript>3+</Superscript> Ions in Glassy and Polycrystalline Lithium Tetraborate

The X-ray-luminescence spectra of glassy and polycrystalline lithium tetraborate Li₂B4O₇ activated by europium oxide Eu₂O₃ are studied in the spectral range of 200 to 800 nm. The luminescence observed in the wavelength region of 570 to 720 nm is caused by intraconfiguration f–f electron transitions between the levels of the first excited multiplet ⁵D and the main multiplet ⁷F of the Eu³⁺ ion.     

Roles of doping ions in persistent luminescence of SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript>: Eu<Superscript>2+</Superscript>,<Emphasis Type="Italic">RE</Emphasis><Superscript>3+</Superscript> phosphors

The polycrystalline Eu²⁺ and Dy³⁺ codoped strontium aluminates SrAl₂O₄: Eu²⁺,Dy³⁺ were prepared by a solid-state reaction. The UV-excited photoluminescence, persistent luminescence, and thermoluminescence of the SrAl₂O₄: Eu²⁺,Dy³⁺ phosphors with different compositions and ion doping was studied and compared. The results showed that the Eu²⁺ ion doped in SrAl₂O₄: Eu²⁺,Dy³⁺ phosphors is not only the UV-excited luminescent center but also the persistent luminescent center. The Dy³⁺ ion introduced into SrAl₂O₄: Eu²⁺ crystal matrix can hardly yield any luminescence under UV excitation but acts as an electron trap with a suitable depth for persistent luminescence. The Dy³⁺ codoping would effectively enhance the persistent luminescence and thermoluminescence. Different codoping RE ³⁺ ions have a different effect on persistent luminescence. Only the RE ³⁺ ions (for example, Dy³⁺ and Nd³⁺), which have suitable optical electronegativity, can form suitable electron traps and effectively improve the persistent luminescence of SrAl₂O₄: Eu²⁺. Based on the above observations, a persistent luminescence mechanism, electron transfer model, was proposed and illustrated. The text was submitted by the authors in English.     

Visible up-conversion luminescence of CaWO<Subscript>4</Subscript>: Er<Superscript>3+</Superscript>,Yb<Superscript>3+</Superscript> and emission enhancement by tri-doping of Li<Superscript>+</Superscript> ions

Er³⁺,Yb³⁺ co-doped CaWO₄ polycrystalline powders were prepared by a solid-state reaction and their up-conversion (UC) luminescence properties were investigated in detail. Under 980 nm laser excitation, CaWO₄: Er³⁺,Yb³⁺ powder exhibited green UC emission peaks at 530 and 550 nm, which were due to the transitions of Er³⁺ (²H_11/2)→Er³⁺ (⁴I_15/2) and Er³⁺ (⁴S_3/2)→Er³⁺ (⁴I_15/2), respectively. Effects of Li+ tri-doping into CaWO₄: Er³⁺,Yb³⁺ were investigated. The introduction of Li⁺ ions reduced the optimum calcinations temperature about 100 °C by a liquid-phase sintering process and the UC emission intensity was remarkably enhanced by Li⁺ ions, which could be attributed to the lowering of the symmetry of the crystal field around Er³⁺ ions.     

Structure and Luminescence Properties of Eu<Superscript>3+</Superscript>-Doped Cubic Mesoporous Silica Thin Films

Eu³⁺ ions-doped cubic mesoporous silica thin films with a thickness of about 205 nm were prepared on silicon and glass substrates using triblock copolymer as a structure-directing agent using sol–gel spin-coating and calcination processes. X-ray diffraction and transmission electron microscopy analysis show that the mesoporous silica thin films have a highly ordered body-centered cubic mesoporous structure. High Eu³⁺ ion loading and high temperature calcination do not destroy the ordered cubic mesoporous structure of the mesoporous silica thin films. Photoluminescence spectra show two characteristic emission peaks corresponding to the transitions of ⁵D₀-⁷F₁ and ⁵D₀-⁷F₂ of Eu³⁺ ions located in low symmetry sites in mesoporous silica thin films. With the Eu/Si molar ratio increasing to 3.41%, the luminescence intensity of the Eu³⁺ ions-doped mesoporous silica thin films increases linearly with increasing Eu³⁺ concentration.     

Efficient manganese luminescence induced by Ce<Superscript>3+</Superscript>-Mn<Superscript>2+</Superscript> energy transfer in rare earth fluoride and phosphate nanocrystals

Manganese materials with attractive optical properties have been proposed for applications in such areas as photonics, light-emitting diodes, and bioimaging. In this paper, we have demonstrated multicolor Mn²⁺ luminescence in the visible region by controlling Ce³⁺-Mn²⁺ energy transfer in rare earth nanocrystals [NCs]. CeF₃ and CePO₄ NCs doped with Mn²⁺ have been prepared and can be well dispersed in aqueous solutions. Under ultraviolet light excitation, both the CeF₃:Mn and CePO₄:Mn NCs exhibit Mn²⁺ luminescence, yet their output colors are green and orange, respectively. By optimizing Mn²⁺ doping concentrations, Mn²⁺ luminescence quantum efficiency and Ce³⁺-Mn²⁺ energy transfer efficiency can respectively reach 14% and 60% in the CeF₃:Mn NCs.     

Structural and Activity Investigation into Al<Superscript>3+</Superscript>, La<Superscript>3+</Superscript> and Ce<Superscript>3+</Superscript> Addition to the Phosphomolybdate Heteropolyanion for Isobutane Selective Oxidation

Abstract  

Twelve phosphomolybdate compounds were synthesized via cationic exchange and were of the form: M _x H_3–3x [PMo₁₂O₄₀] (M = Al, La or Ce; 0 ≤ x ≤ 1). These compounds were analyzed by XRD and adsorption isotherm. Aluminum addition causes a primitive cubic phase, while lanthanum and cerium yield body-centered structures. La and Ce addition reduces surface area of phosphomolybdate structure. Temperature-programmed experiments for the selective oxidation of isobutane yielded methacrolein, 3-methyl-2-oxetanone (lactone), acetic acid (not with aluminous compounds), propene (only with aluminous compounds), carbon dioxide and water. The preference for propene rather than acetic acid formation with Al³⁺ may be due to the smaller cation size, or primitive cubic structure. These products form via two distinct reaction processes, labeled categories 1 and 2. Category 1 formation is associated with isobutane forming products on the surface, but reaction rate determined by bulk migration of charged particles. Category 2 formation is concerned with isobutane penetrating deep within the bulk of the substrate and forming products which subsequently desorb in a series of bell-shaped humps. Methacrolein forms via both category 1 and 2, whilst all other products form via category 2 exclusively. Kinetic analysis showed apparent activation barriers for category 1 methacrolein formation range from 67 ± 2 kJ mol⁻¹ to >350 kJ mol⁻¹, and occur in groups with small, medium and large activation barriers. The addition of +3 metal cations to the phosphomolybdate anion increase thermal stability, significantly decreasing deactivation; IR spectroscopy shows that the Keggin structure remains intact during temperature-programmed experiments with the Al, La and Ce salts.     

Spectral properties of Er<Superscript>3+</Superscript> in alkali-zinc-tellurite,barium-tellurite-molybdate,and fluoride glasses

Glasses of three compositions—TeO₂ · ZnO · N₂O (TZN), where N is Li, Na, or K; TeO₂ · MoO₃ · BaO (TMB); and ZrF₄ · BaF₂ · LaF₃ · AlF₃ · NaF (ZBLAN)—activated by Er³⁺ or Yb³⁺ and Er³⁺ ions were synthesized and investigated. For the ZBLAN glass, the brightest luminescence of Er³⁺ ions in the visible range was observed under excitation by the irradiation of a diode laser with the generation wavelength 0.98 μm. The TZN glass is not inferior in the intensity of luminescence with the wavelength 1.55 μm to the TMB glass, having phonons of higher energy than those for the TZN glass (940 and 740 cm⁻¹, respectively). A glass was prepared with a high content of molybdenum oxide. The possibility to increase the up-conversion efficiency in tellurite glasses is considered.     

Thermal Stability and Spectral Properties of Tm<Superscript>3+</Superscript>-Yb<Superscript>3+</Superscript> CO-Doped Tellurite Glasses

Glasses of the system 75TeO₂–20ZnO–5La₂O₃–0.8Tm₂O₃–xYb₂O₃ were prepared by high temperature melt cooling method. Results of differential scanning calorimetry indicate that, all glass samples have excellent thermal stability. Judd–Ofelt strength parameters, spontaneous emission probabilities, fluorescence branching rations, fluorescence radiative lifetime of Tm³⁺ ions in tellurite glass were calculated. The impact of Yb³⁺ concentration on the fluorescence properties of Tm³⁺ ions in the S band under the pumping wavelength of 465 nm was investigated in a suggestion that, ³H₄ radiative lifetimes will be prolonged and the performance of optical amplifier gain of Tm³⁺ in tellurite glass co-doped with 0.5 mol % Yb³⁺ ions will be improved.     

Dehydration of aldoximes on rare earth exchanged (La<Superscript>3+</Superscript>, Ce<Superscript>3+</Superscript>, RE<Superscript>3+</Superscript>, Sm<Superscript>3+</Superscript>) Na–Y zeolites: A facile route for the synthesis of nitriles

Rare earth exchanged Na–Y zeolites, H-mordenite, K-10 montmorillonite clay and amorphous silica-alumina were effectively employed for the continuous synthesis of nitriles. Dehydration of benzaldoxime and 4-methoxybenzaldoxime were carried out on these catalysts at 473 K. Benzonitrile (dehydration product) was obtained in near quantitative yield with benzaldoxime whereas; 4-methoxybenzaldoxime produces both Beckmann rearrangement (4-methoxyphenylformamide) as well as dehydration products (4-methoxy benzonitrile) in quantitative yields. The production of benzonitrile was near quantitative under heterogeneous reaction conditions. The optimal protocol allows nitriles to be synthesized in good yields through the dehydration of aldoximes. Time on stream (TOS) studies show decline in the activity of the catalysts due to neutralization of acid sites by the basic reactant and product molecules and water formed during the dehydration of aldoximes.     

Morphology and photoluminescence properties of phenolic epoxy resin coating on KH550-modified SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript>: Eu<Superscript>2+</Superscript>, Dy<Superscript>3+</Superscript> powder in the presence of triarylsulfonium hexafluoroantimonate

In this study, the amino silane coupling agent (KH550)-modified SrAl₂0₄: Eu²⁺, Dy³⁺ phosphor powder coated with phenolic epoxy resin (EOCN) in the presence of triarylsulfonium hexafluoroantimonate catalyst was prepared using the combination of organic–inorganic composite dip-coating and UV curing coating methods. The results of SEM, TEM, and FTIR showed that the organic coating was a layer of compact membrane with a thickness of 20–50 nm, which can be named silane-modified epoxy monomer generated by the KH550 and the EOCN. Furthermore, it was observed that afterglow and spectrum properties of the coated phosphor powder had good long-afterglow luminescence properties, and revealed two emission peaks at 435 nm and 520 nm under the same excitation wavelength of 360 nm, respectively. More interesting, the emitting color of the coated sample was located in the area of cyan light on CIE1931 chromaticity diagram, which led to a slight blue shift rather than the yellow–green color of the pure SrAl₂0₄: Eu²⁺, Dy³⁺ phosphor powder.     

Effects of adding B<Subscript>2</Subscript>O<Subscript>3</Subscript> as a flux on phosphorescent properties in synthesis of SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript>: (Eu<Superscript>2+</Superscript>, DY<Superscript>3+</Superscript> phosphor

SrAl₂O₄: (Eu²⁺, Dy³⁺) phosphor was prepared by solid state reaction. B₂O₅ as a flux was added in SrAl₂O₄:(Eu ²⁺, Dy³⁺) in order to accelerate a solid state reaction. In this paper, the effects of B₂O₃ on the crystal structure and the phosphorescent properties of the material have been evaluated. The synthesized phosphor exhibited a broad band emission spectrum peaking at 520 nm, and the spectrum peak showed little effect by the B₂O₃ contents. The maximum afterglow intensity of the SrAl₂O₄: (Eu²⁺, Dy³⁺) phosphor was obtained at the B₂O₃ content of 5%. Adding the B₂O₃ caused uniform distortion to the crystal structure of the phosphor and resulted in reducing the lengths of a and c axes and Β angle of the SrAl₂O₄ crystal. The uniform distortion was accompanied with crystal defects which can trap the holes generated by the excitation of Eu²⁺ ions. The afterglow characteristic of the SrAl₂O₄: (Eu²⁺, Dy³⁺) phosphor was thus enhanced.     

Theoretical studies of local structures and spin hamiltonian parameters for Cu<Superscript>2+</Superscript> in alkali barium borate glasses

The local structures and spin Hamiltonian parameters are theoretically studied for Cu²⁺ in alkali barium borate glasses 20A₂O ? 24.5BaO · 55B₂O₃ · 0.5CuO, where A = Li, Na and K by the quantitative calculations of these parameters for tetragonally elongated octahedral 3d ⁹ clusters. The [CuO₆]^10? clusters are subject to the local relative tetragonal elongation ratios 7.8, 8.1 and 8.4% in Li, Na and K barium borate glasses, respectively, owing to the Jahn–Teller effect. The increasing (Li < Na < K) local relative elongation ratio and decreasing cubic field parameter and covalency factor are discussed in a consistent way.     

Excitation and photoluminescence spectra of solid solutions based on lanthanum indate LaInO<Subscript>3</Subscript> of a perovskite structure doped with Nd<Superscript>3+</Superscript> and Cr<Superscript>3+</Superscript> ions

Using a solid-phase method, single-phase solid solutions of La_1–x Nd _x InO₃ (x = 0.007, 0.02, 0.05), LaIn0.99Cr0.01O3, and La_0.95Nd_0.05In_0.995Cr_0.005O₃ have been obtained and their excitation and photoluminescence (PL) spectra have been studied at room temperature. It is found that the intensity of excitation and PL bands for La_1–x Nd _x InO₃ solid solutions depends on the degree of the substitution of La³⁺ ions by Nd³⁺ ions. A solid solution with 0.02 < x < 0.05 possesses the largest intensity of the PL bands in IR wavelength range of 850–950, 1040–1100, and 1350–1370 nm. It is found that replacing 0.5% of In³⁺ ions in a solid solution of La^0.95Nd^0.05InO₃ by Cr³⁺ ions leads to a substantial increase in the intensity of all the PL bands by exciting with light of the wavelength of λ_exc = 490 nm and a decrease in the intensity of all the PL bands by an excitation with light of the wavelengths of λ_exc = 358, 532, and 585 nm.     

Optical properties of alkali and alkaline-earth lead borate glasses doped with Nd<Superscript>3+</Superscript> Ions

Spectroscopic and physical properties of Nd³⁺-doped alkali lead borate glasses of type 20R ₂O · 30PbO · 49.5B₂O₃ · 0.5Nd₂O₃ (R = Li and K) and alkaline-earth lead borate glasses 20RO · 30PbO · 49.5B₂O₃ · 0.5Nd2O3 (R = Ca, Ba, and Pb) have been investigated. Optical absorption spectra have been used to determine the Slater-Condon (F₂, F₄, and F₆), spin orbit ξ_4f, and Racah parameters (E₁, E₂, and E₃). The oscillator strengths and the intensity parameters Ω₂, Ω₄, and Ω₆ have been determined by the Judd-Ofelt theory, which, in turn, provide the radiative transition probability (A), total transition probability (A _T ), radiative lifetime (τ _R ), and branching ratio (β _R , %) for the fluorescent levels. The lasing efficiency of the prepared glasses has been characterized by the spectroscopic quality factor (Ω₄/Ω₆), the value of which is in the range 0.2–1.5, typical of Nd³⁺ in different laser hosts. A red shift of the peak wavelength is observed upon addition of alkali or alkaline-earth oxides to the lead borate glass. A higher value of the W₂ parameter for potassium-doped glass indicates a higher covalency for this glass matrix. The relative intensity of the peaks ⁴I_9/2 → ⁴F_7/2, ⁴S_3/2 has also been studied. The text was submitted by the authors in English.     

Er<Superscript>3+</Superscript>- and Tm<Superscript>3+</Superscript>-Containing Ultra-Transparent Oxyfluoride-Based Glass Ceramics for Wavelength Division Multiplexing Optical Amplifiers

Ultratransparent glass ceramics activated with thulium and erbium ions were fabricated. The precursor oxyfluoride glass was 32SiO₂ · 9AlO_1.5 · 31.5CdF₂ · 18.5PbF₂ · 5.5ZnF₂ · 3.5ReO_1.5 with Re = Tm or Er. Upon heat treatment, Er³⁺ and Tm³⁺ nucleate the growth of nanocrystalline β-PbF₂, which acts as a host for rare-earth ions. The spectroscopic properties of the thulium and erbium ions, studied via UV-VIS-NIR absorption and luminescence spectroscopy, show that most of the active ions are embedded in the crystalline phase. From the absorption measurement, we extracted the cross sections of Tm³⁺ ions embedded in the crystalline and glassy phases. The comparison between the experimental lifetimes before and after thermal treatment gave as a result that the ceramming process increases the quantum efficiency of the Tm³⁺ electronic transitions. In the case of Er³⁺-activated glass ceramics, the ⁴ I _13/2 ⇄ ⁴ I _15/2 telecom transition broadens and flattens.Original English Text Copyright © 2005 by Fizika i Khimiya Stekla, Tosello, Montagna, Mattarelli, Ferrari, Chaussedent, Monteil, Tikhomirov, Seddon.This article was submitted by the authors in English.