Spectroscopy and crystal-field analysis of Cr4+-doped transparent silicate glass-ceramics

We report transparent Cr⁴⁺-doped SiO₂–Al₂O₃–ZnO–Li₂O–K₂O glass-ceramics with broadband infrared luminescence. After heart-treatment, Li₂ZnSiO₄ crystallite was precipitated in the glasses, and its average size increased with increasing heat-treatment temperature. Racah parameters of Cr⁴⁺–Li₂ZnSiO₄ glass-ceramics have been calculated, and it was confirmed from absorption spectra that the energy levels of Cr⁴⁺-doped glass-ceramics are close to the cross point ¹E and ³T states. No infrared emission was detected in the as-made glass samples, but the broadband infrared emission centered at 1210 nm with the full width at half maximum (FWHM) of more than 250 nm was observed by exciting the glass-ceramics with excitation of an 808 nm laser diode. In order to analyze the located crystal field of Cr⁴⁺ ions, the emission spectra are fitted by multi-peak Gauss fitting. It is seen that the fluorescence spectra are fitted into two Gaussian bands at around 1195 and 1263 nm with band widths of 208 and 278 nm, respectively. The two Gaussian bands at around 1195 and 1263 nm have about the same decay rate, and hence they would probably originate from the same luminescent centers. The observed infrared emission could be attributed to Cr⁴⁺ ions at low-field sites in Li₂ZnSiO₄ glass-ceramics.     

The luminescence of Pr3+ ions doped in Y4Al2O9 by sol–gel synthesis

The Pr³⁺-doped Y₄Al₂O₉ powders were synthesized by sol–gel method. Powder X-ray diffraction and SEM techniques were used to check for Y₄Al₂O₉ powders. The Li⁺ co-doping with Pr³⁺ has an influence on the sintering temperature and morphology of the Y₄Al₂O₉ powders produced from the gel. The emission spectra under different excitations, e.g., the 488 nm line of an argon-ion laser, X-ray and UV light, were investigated. The luminescence intensity of Y₄Al₂O₉:Pr³⁺ could be increased with Li⁺ co-doping. Luminescence properties of Pr³⁺ ions in the two samples have some difference. In the Y₄Al₂O₉:Pr³⁺, the emission at 490 nm from ³P₀ is dominant, while, the Y₄Al₂O₉:(Pr³⁺ + Li⁺) system was characterized by a red emission at 607 and 610 nm corresponding to the ¹D₂ → ³H₄ inner transition of Pr³⁺ ions; and these two emissions show different excitation band from the 4f5d state.     

Glass composition dependence of luminescence due to Ge2+ center in germanate glasses

Germanate glasses were prepared by the melt-quenching method using an assembled hot-thermocoupler equipped in a sample chamber of a fluorescence spectrometer, and subsequently their luminescence and excitation spectra were measured. In the GeO₂ glass, luminescence bands due to the Ge²⁺ center appeared at the central wavelengths of 300 and 395 nm, their excitation bands being at 250 and 330 nm, respectively. In the (100 − x)GeO₂ − xM_mO_n glasses, for M_mO_n = B₂O₃ (x ≦ 50), SiO₂ (x ≦ 40), and Al₂O₃ (x ≦ 2), the luminescence intensity and therefore the amount of the Ge²⁺ center increased with increasing the content of M_mO_n, where M^(2n/m)+ ions (B³⁺, Si⁴⁺, and Al³⁺) have lower basicities than a Ge⁴⁺ ion. Contrarily, for M_mO_n = Li₂O (x ≦ 30), Na₂O (x ≦ 20), K₂O (x ≦ 20), CaO (x ≦ 20), SrO (x ≦ 3), BaO (x ≦ 15), ZnO (x ≦ 20), Ga₂O₃ (x ≦ 10), Sb₂O₃ (x ≦ 20), Bi₂O₃ (15 ≦ x ≦ 25), TiO₂ (x ≦ 3), and Nb₂O₅ (x ≦ 10), the luminescence intensity and the amount of the Ge²⁺ center rapidly decreased with increasing the amount of additives and disappeared, where M^(2n/m)+ ions (Li⁺, Na⁺, K⁺, Ca²⁺, Sr²⁺, Ba²⁺, Zn²⁺, Ga³⁺, Sb³⁺, Bi³⁺, Ti⁴⁺, and Nb⁵⁺) have higher basicities than a Ge⁴⁺ ion.     

Optical and thermoluminescence properties of R2O–RF–B2O3 glass systems doped with MnO

Alkali fluoroborate glass systems containing manganese cations have been thoroughly investigated in order to obtain information about the structural role of manganese in such glass hosts. The amorphous phase of the prepared glass samples R₂O–RF–B₂O₃:MnO (with R = Li and Na) was confirmed from their X-ray diffraction. From the infrared spectra of these glass systems it was concluded that the glass structure contains two group of bands; one due to trigonal BO₃ units and the second due to the tetrahedral BO₄ units. As manganese was introduced, replacing lithium or sodium, it acts as a network modifier and the intensity of the second group of bands increases at the expense of the first group of bands. The optical absorption spectra of R₂O–RF–B₂O₃:MnO exhibited two conventional absorption bands; one due to Mn²⁺ ions and the other due to Mn³⁺ ions. The ESR spectra of these glasses showed a six-line hyper-fine structure centered at g = 2.01 (due to Mn²⁺ ions) and another signal at g = 4.3 (due to Mn³⁺ ions). The intensity of optical absorption bands and the ESR signal due to Mn²⁺ ions decreases with increasing MnO concentration indicating the conversion of Mn²⁺ ions into Mn³⁺ ions in the glass network. The thermoluminescence studies on these glass systems showed a quenching of TL output with increase in the concentration of MnO. All the obtained results were discussed on the basis of the glass structure and the conversion of Mn²⁺ into Mn³⁺ ions with increasing concentration of MnO in the glass systems.     

Magnetic resonance study of the crystallization behavior of InF3-based glasses doped with Cu2+, Mn2+ and Gd3+

The crystallization of fluoroindate glasses doped with Gd³⁺, Mn²⁺ and Cu²⁺ heat treated at different temperatures, ranging from the glass transition temperature (T_g) to the crystallization temperature (T_c), are investigated by electron paramagnetic resonance (EPR) and ¹⁹F nuclear magnetic resonance (NMR). The EPR spectra indicate that the Cu²⁺ ions in the glass are located in axially distorted octahedral sites. In the crystallized glass, the g-values agreed with those reported for Ba₂ZnF₆, which correspond to Cu²⁺ in a tetragonal compressed F⁻ octahedron and to Cu²⁺ on interstitial sites with a square-planar F⁻ co-ordination. The EPR spectra of the Mn²⁺ doped glasses exhibit a sextet structure due to the Mn²⁺ hyperfine interaction. These spectra suggest a highly ordered environment for the Mn²⁺ ions (close to octahedral symmetry) in the glass. The EPR spectra of the recrystallized sample exhibit resonances at the same position, suggesting that the Mn²⁺ ions are located in sites of highly symmetric crystalline field. The increase of the line intensity of the sextet and the decrease of the background line in the thermal treated samples suggest that the Mn²⁺ ions move to the highly ordered sites which contribute to the sextet structure. The EPR spectra of the Gd³⁺ doped glasses exhibit the typical U-spectrum of a s-state ion in a low symmetry site in disordered systems. The EPR of the crystallized glasses, in contrast, have shown a strong resonance in g ≈ 2.0, suggesting Gd³⁺ ions in environment close to cubic symmetry. The ¹⁹F NMR spin–lattice relaxation rates were also strongly influenced by the crystallization process that takes over in samples annealed above T_c. For the glass samples (doped or undoped) the ¹⁹F magnetization recoveries were found to be adjusted by an exponential function and the spin–lattice relaxation was characterized by a single relaxation time. In contrast, for the samples treated above T_c, the ¹⁹F magnetization-recovery becomes non-exponential. A remarkable feature of our results is that the changes in the Cu²⁺, Mn²⁺, Gd³⁺ EPR spectra and NMR relaxation, are always observed for the samples annealed above T_c.     

Crystallization and spectroscopic properties of Eu-doped CaF2 nanocrystals in transparent oxyfluoride glass-ceramics

Transparent oxyfluoride glass-ceramic in the system SiO₂–Al₂O₃–CaF₂–EuF₂ containing Eu-doped CaF₂ nanocrystals were produced by using the controlled crystallization of melt-quenched glass. X-ray diffraction and transmission electron microscopy data have revealed the formation of the CaF₂ nanocrystals of about 65 nm size. Photoluminescence spectra have shown an increase of the splitting of the luminescences associated to the Eu³⁺ ion along with annealing time which is consistent with the Eu³⁺ environment evolving from a glassy to a crystalline state.     

Synthesis and Crystal Structure of Mixed-valence Hexanuclear Manganase Oxide Complex,Hexakis(μ<Subscript>2</Subscript>-pivalato)-tetrakis(μ<Subscript>3</Subscript>-pivalato)-mono(pyridine)-tris(pivalic acid)-bis(μ<Subscript>4</Subscript>-oxo)dimanganese(III) tetramanganase(II)

Abstract  The complex, [Mn₆O₂(OOCCMe₃)₁₀(HOOCCMe₃)₃(py)], has a hexanuclear structure with a Mn₆O₂ core. This complex crystallizes in the monoclinic space group P2₁/n with a = 17.757(5) ?, b = 27.413(5) ?, c = 22.348(5) ?, β = 90.233(5)°, V = 9,040(4) ?³ and Z = 4. It contains a [Mn₆O₂]¹⁰⁺ core that can be described as two edge-sharing Mn₄ tetrahedra at the centre of each of which tetrahedron lies a μ₄-O²⁻ ion. All Mn atoms are six-coordinate and possess distorted octahedral geometry. Mn₄ exhibits butterfly arrangement with both μ₄-O atoms on the same side of the molecule. The complex is mixed-valence , and the Mn^III centers are assigned as the two central metal ions bridged by two O²⁻ ions. Index abstract  The complex, [Mn₆O₂(OOCCMe₃)₁₀(HOOCCMe₃)₃(py)], has a hexanuclear structure with a Mn₆O₂ core. This complex crystallizes in the monoclinic space group P2₁/n with a = 17.757(5) ?, b = 27.413(5) ?, c = 22.348(5) ?, β = 90.233(5)°, V = 9040(4) ?³ and Z = 4. It contains a [Mn₆O₂]¹⁰⁺ core that can be described as two edge-sharing Mn₄ tetrahedra at the centre of each of which tetrahedron lies a μ₄-O²⁻ ion. All Mn atoms are six-coordinate and possess distorted octahedral geometry. Mn₄ exhibits butterfly arrangement with both μ₄-O atoms on the same side of the molecule. The complex is mixed-valence , and the Mn^III centers are assigned as the two central metal ions bridged by two O²⁻ ions.      

High lithium ion conduction of sulfide glass-based solid electrolytes and their application to all-solid-state batteries

Sulfide glass-based solid electrolytes prepared by melt quenching and mechanical milling were reviewed. The sulfide and oxysulfide glass–ceramic electrolytes in the system Li₂S–P₂S₅–P₂O₅ with superionic Li₇P₃S₁₁ and Li_3.25P_0.95S₄ crystals exhibited high conductivity of over 10⁻³ S cm⁻¹ at room temperature and high electrochemical stability. Newly designed all-sulfide batteries 80SnS·20P₂S₅/80Li₂S·20P₂S₅/75Li₂S·25Cu were successfully fabricated; reversible charge–discharge capacities of more than 400 mAh g⁻¹ were observed after the second to 10th cycles. The operation of those all-sulfide lithium secondary batteries is a first step for the realization of the all-solid-state monolithic batteries.     

Luminescent properties and applications of Tb3+ doped silicate glasses with industrial scales

Tb³⁺ doped X-ray conversion glassy screen with an industrial scale (50 mm × 50 mm × 12 mm) was successfully fabricated, and its luminescent properties and applications in CCD imaging system were investigated. Results showed that Tb³⁺ doped silicate glasses mainly emit weak blue (400–460 nm) and strong green (480–570 nm) fluorescence. With the increase of Tb³⁺ ion concentration, the intensity of green emission increases, but that of blue emission decreases. Gd³⁺ ions can sensitize the luminescence of Tb³⁺ ions among silicate glasses. With the increase of CeO₂ concentration, the luminescent intensity of Tb³⁺ doped silicate glasses at 550 nm quickly decreases. However, the irradiation resistance of Tb³⁺ doped silicate glasses can be effectively improved by CeO₂ addition. The imaging quality of the luminescent glass screen is more excellent than that of Gd₂O₂S polycrystalline screens.     

The absorption and circular dichroism spectra of langasite family crystals doped with chromium ions

The absorption and circular dichroism spectra of langasite family crystals, La₃Ga₅SiO₁₄, La₃Ga₅GeO₁₄, Ca₃Ga₂Ge₄O₁₄, Sr₃Ga₂Ge₄O₁₄ (red), Sr₃Ga₂Ge₄O₁₄ (green), La₃Ta_0.5Ga_5.5O₁₄, and La₃Nb_0.5Ga_5.5O₁₄, which were doped with chromium ions, have been investigated in the range of 240–850 nm. It is shown that chromium ions are incorporated into the structure of the investigated crystals both in the octahedrally (Cr³⁺ ion in 1a octahedron) and tetrahedrally (Cr⁴⁺ ion in 2d tetrahedron) coordinated positions. The ion ratio Cr³⁺/Cr⁴⁺ changes in a wide range in the crystals studied.     

Glass formation in the MoO3–Nd2O3–La2O3–B2O3 system

In MoO₃–Nd₂O₃–B₂O₃ and MoO₃–Nd₂O₃–La₂O₃–B₂O₃ systems, glasses were obtained in the region between 20 and 30 mol% Ln₂O₃. A liquid-phase separation region was observed near the MoO₃–B₂O₃ side up to 20 mol% Ln₂O₃ (La, Nd). The amorphous phases were characterized by X-ray diffraction (XRD), differential thermal analysis (DTA), UV–VIS and infrared spectroscopy (IR). According to DTA data B₂O₃-rich glasses are stable up to 630 °C while glasses rich in MoO₃ are stable up to 430 °C. The glasses are transparent in the visible region. Structural models for the glasses network were suggested on the basis of IR spectral investigations. It was established that BO₃ (1380 cm⁻¹), BO₄ (1100–950 cm⁻¹) and MoO₄ (860 cm⁻¹) groups build up the glass network. MoO₆ units (band at 880 cm⁻¹) together with BO₃ units participate in the formation of the glass network with a high MoO₃ content (80–90 mol%).     

Czochralski growth and characterization of Dy: La3Ga5.5Nb0.5O14 single crystals

Dysprosium (Dy) doped La₃Ga_5.5Nb_0.5O₁₄ single crystals were grown by the traditional Czochralski method along z‐axis. The structure of the crystal has been studied by X‐ray powder diffraction method, and the unit‐cell parameters are calculated to be a=8.22070 Å, c=5.12533 Å and V=299.965 ų. The segregation coefficient of Dy³⁺ in La₃Ga_5.5Nb_0.5O₁₄ crystal was measured by X‐ray fluorescence analysis. For 1 mol% doping level in the melt, the distribution coefficient of Dy³⁺ was determined to be 0.341 wt%. Specific heat, thermal expansion and transmission spectrum of Dy: La₃Ga_5.5Nb_0.5O₁₄ single crystals have been measured. The fluorescence spectra of Dy³⁺: La₃Ga_5.5Nb_0.5O₁₄ crystals were measured at room temperature, and there were four emission transitions occurring at 479, 576, 662 and 754 nm, respectively. The fluorescent lifetimes measurement results show 1.0% Dy: La₃Ga_5.5Nb_0.5O₁₄ possesses shorter fluorescence decay time (303.4 μs) than does 1.0%Dy:LGS (436.12 μs). (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electrical and dielectric properties of Sb2O3–V2O5–K2O glasses

Electric measurements, including temperature dependencies of direct electrical conductivity and temperature dependencies of complex electrical modulus, have been implemented using Sb₂O₃–V₂O₅–K₂O glass samples. These glasses absorb ambient humidity but their resistance to water attack depends on composition. The significant decrease of conductivity up to 100 °C can arise from water desorption. Cycling measurements of direct electrical conductivity versus temperature were also implemented. They show that the 30Sb₂O₃–30V₂O₅–40K₂O and 70Sb₂O₃–30K₂O glasses are irreversibly damaged with the formation of the hydrated layer. In addition, it was observed that the evolution of DC conductivity is ruled by Arrhenius relation, while activation energy decreases as Sb₂O₃ concentration increases.     

Ternary system Li2O–K2O–Nb2O5: Re-examination of the 30 mol% K2O isopleth and growth of fully stoichiometric potassium lithium niobate single crystals by the micro-pulling down technique

Potassium lithium niobate (KLN) single crystals have attractive properties for non-linear optical applications based on frequency conversion of laser diodes in the blue range. Especially, fully stoichiometric K₃Li₂Nb₅O₁₅ crystals would be capable of doubling a laser light in the near UV range. Using powder X-ray diffraction and DSC experiments, we have re-investigated the 30 mol% K₂O isopleth of the ternary system Li₂O–K₂O–Nb₂O₅ in order to explore the possibility of a limited existence field for this phase. From our results, it was shown that the stoichiometric KLN phase exists between 970 and 1040 °C, temperature at which it undergoes a non-congruent melting. From this conclusion, compositionally homogeneous a-axis oriented single crystals fibers of stoichiometric K₃Li₂Nb₅O₁₅ were successfully grown by the micro-pulling down technique with pulling rates in the range 0.3–0.7 mm min⁻¹. The crystal length was between 10 and 120 mm for an apparent diameter near 500 μm. The fibers, characterized by optical microscopy, X-ray diffraction and Raman spectroscopy, appeared free of macro-defects and of good quality and their stoichiometric composition was also confirmed.     

Structure and optical properties of chalcohalide glasses doped with Pr and Yb ions

Glasses of systems 100-y((GeS₂)₈₀(Sb₂S₃)_20−x(PbI₂)_x)yPr₂S₃, x = 0; 2; 5, 8; y = 0; 0.01; 0.1; 0.5 and 99.9-z((GeS₂)₈₀(Sb₂S₃)₁₈(PbI₂)₂)0.1Pr₂S₃zYb₂S₃, z = 0.05; 0.1; 0.15) were synthesized in high purity. Optically well transparent glasses were obtained for x  5 mol.% PbI₂, for y  0.1 mol.% Pr₂S₃ and for z  0.15 mol.% Yb₂S₃. The glasses were stable and homogeneous, as confirmed by X-ray diffraction and electron microscopy, with high optical transmittivity from visible (red) region up to infrared region (900 cm⁻¹). The density of the glasses was 3.26–3.33 gcm⁻³ for PbI₂ containing glasses. The glass transition temperature, T_g, was 320–336 °C. The optical absorption bands in rare-earth doped glasses corresponded to ³H₄–³F₄, ³H₄–³F₃, ³H₄–(³F₂ + ³H₆) f–f electron transitions of Pr³⁺ ions and to ²F_7/2–²F_5/2 f–f electron transitions of Yb³⁺ ions. Strong luminescence band with maximum near 1340 nm (electron transition ¹G₄–³H₅) was found in Pr₂S₃ doped glasses. The intensity of this band was rising with doping by Yb³⁺ ions. The possible mechanism of the luminescence enhancement is suggested.     

Redox reactions during temperature change in soda-lime–silicate melts doped with copper and iron or copper and manganese

Glasses with the base composition 16Na₂O · 10CaO · 74SiO₂ doped with copper and iron or copper and manganese were studied by high temperature UV–vis–NIR spectroscopy. The spectra exhibited distinct absorption bands attributed to the respective transition metal ions present (Cu²⁺, Fe²⁺, Fe³⁺, Mn³⁺). In glasses doped with only one polyvalent element, the absorption decreases linearly with increasing temperature, the absorption bands are shifted to smaller wave numbers and get broader. In glasses doped with two types of transition metals, the situation is the same up to a temperature of around 550 °C. At larger temperature, the Cu²⁺-absorption in glasses also co-doped with iron increases again, while in glasses doped with both copper and manganese the absorption is approximately the same as in glasses solely doped with copper. It is shown that this is due to redox reactions between polyvalent species. These reactions are frozen in at temperatures <550 °C.     

Highly enhanced f–f transitions of Eu3+ in La2O3 phosphor via citric acid and poly (ethylene glycol) precursor route

The luminescent material europium-activated La₂O₃ have been prepared by the citric acid and poly (ethylene glycol) (PEG) precursor route. Their structures and optical properties were characterized by FT-IR spectrum, X-ray diffraction (XRD), thermogravimetry-differential thermal analysis (TG-DTA), UV–vis spectroscopy, and photoluminescence (PL) spectra, respectively. The results show considerable enhancement of the photoluminescence, especially the Eu³⁺ f–f transition excitation lines and the charge transfer band (CT). The samples can exhibit strong red emission centered at 626 nm excited at either the CT band (300 nm) or the Eu³⁺ f–f transition (396 nm), suggesting the potential application as the red phosphors for ultraviolet light-emitting diodes (LEDs), which can be attributed to the ⁵D₀→⁷F₂ transition of Eu³⁺. The remarkable enhancement of color purity of red emission and the concentration quenching of Eu³⁺ in La₂O₃ were also observed with increasing Eu³⁺ doped concentration.     

New photoluminophore nanocomposite based on organic compound with Eu ions and copolymer styrene-butylmethacrilate

New nanocomposite (NC) material on the base of thenoyltrifluoroacetone (TTA) coordinated with trivalent europium ions and structured with phenantroline (Eu(TTA)₃Phen) and copolymer from styrene and butylmethacrylate (1:1) (SBMA) was prepared. The visible photoluminescence spectra of composites excited with N₂-laser (λ = 0.337 μm) at room and T = 78 K temperatures were studied. For the Eu(TTA)₃Phen/SBMA nanocomposite material emission bands located at 578, 590, 612, 675 and 705 nm can be attributed to the spin forbidden f–f transitions ⁵D₀ → ⁷F_i (i = 0,1,2,3 and 4), respectively. The more intensive luminescence band situated at 612 nm with the half width of 3 nm is connected to the Eu³⁺ ion electronic transition ⁵D₀ → ⁷F₂. It was shown that the maximum intensity of photoluminescence occurs at the concentration of 15% of the Eu(TTA)₃Phen in the SBMA polymer matrix.     

Photoluminescence properties of Sm3+-doped SFB glasses for efficient visible lasers

The photoluminescence properties of different concentrations of Sm³⁺ ions doped sodium fluoroborate (SFB) glasses of composition Na₂O–LaF₃–CaF₂–AlF₃–B₂O₃–SmF₃ have been investigated. The energy level analysis is carried out using free-ion Hamiltonian model. The Judd–Ofelt intensity parameters are used to evaluate the laser characteristic parameters such as spontaneous transition probability, radiative lifetime and fluorescence branching ratio for ⁴G_5/2 → ⁶H_J (J = 5/2, 7/2, 9/2 and 11/2) emission transitions of Sm³⁺ ion. The principal photoluminescence transitions of interest are identified by recording the emission spectra for different Sm³⁺ ion concentrations and measuring their emission cross-sections, integrated absorption cross-sections and optical gain parameters. The decay profiles from the ⁴G_7/2 excited manifold state to its lower lying energy levels have been recorded by monitoring the excitation and emission wavelengths at 402 and 600 nm, respectively. The dependence of effective fluorescence lifetime on the Sm³⁺ concentration is also discussed.