EPR investigations of calcium phosphate glasses containing manganese ions

Glasses of the xMnO·(100−x)[yP₂O₅·CaO] systems, with y=1, 2, 3 and 0≤x≤50 mol% MnO were prepared and investigated by means of electron paramagnetic resonance (EPR). The local order in diamagnetic vitreous matrices could be revealed by the Mn²⁺ paramagnetic ions used in EPR experiments. In each systems corresponding to a particular value of y, the effect of increasing the MnO content in the samples was investigated. The structure of our glasses shows an evolution depending of MnO content from structural units involving Mn²⁺ ions in well defined vicinities, to structural units containing clustered manganese ions. The changes of the linewidth and the intensity of the resonance line centered at g_eff≈2.0 when the content of manganese ions are increasing revealed this evolution.     

Optical characterization of the phosphate glasses containing pair transition ions

The paper deals with optical and electronic properties of the aluminophosphate glasses containing Fe–Mn and Fe–Cr ion pairs in different concentration. The influence of the mixed alkali ions over the electronic properties has been investigated. The optical behavior (optical transmission) of the glass samples has been studied by UV-VIS spectroscopy and the refractive index dependency on wavelength has been discussed. The transmission spectra show features specific for the doping transition ions (TM), revealing different oxidation states of iron (Fe²⁺/Fe³⁺), manganese (Mn²⁺/Mn³⁺) and chromium (Cr³⁺/Cr⁶⁺) in the vitreous network. Mössbauer spectroscopy offers information regarding the TM oxidation states, redox processes and the iron coordination symmetry in the vitreous network. In the case of Fe–Mn doped glasses, the percentage of Fe²⁺ is about 40% and a doubled iron content leads to an increasing of Fe²⁺ percentage up to 53%. The replacing of lithium ions by natrium ions (mixed alkali effect) provides an increasing of the Fe²⁺ percentage up to 56%. The occurrence of the tetrahedral or octahedral symmetry of Fe²⁺ ions bonded by O^2? ions depends on the transition ion nature and Li⁺/Na⁺ ratio. Infrared absorption spectra of the pair transition ions-doped aluminophosphate glasses reveal optical phonons specific for the phosphate glass matrix.     

Raman and optical absorption spectroscopic investigation of Yb-Er codoped phosphate glasses containing SiO_2

Yb-Er codoped Na2O-Al2O3-P2O5-xSiO2 glasses containing 0 - 20 mol% SiO2 were prepared successfully. The addition of SiO2 to the phosphate glass not only lengthens the bond between pS＋ and non-bridging oxygen but also reduces the number of P=O bond. In contrast with silicate glass in which there is only four-fold coordinated Si4＋, most probably there coexist [SiO4] tetrahedron and [SiO6] oetahedron in our glasses. Within the range of 0 - 20 mol% SiO2 addition, the stimulated emission cross-section of Era＋ ion only decreases no more than 10%. The Judd-Ofelt intensity parameters of Er3＋, Ω2 does not change greatly, but Ω4 and Ω6 decrease obviously with increasing SiO2 addition, because the bond between Er3＋ and O2- is more strongly eovalently bonded.     

Laser beam induced optical aberrations in phosphate and fluoride phosphate glasses

Designing pulsed laser amplifiers requires detailed knowledge about beam distortions at the amplifying medium. Time resolved experiments have been performed on fluoride phosphate and pure phosphate glass in order to study optical aberrations induced by pump beam irradiation. By means of a probe beam tunable in wavelength, it was possible to discriminate between thermally induced variations of the optical path and beam narrowing effects due to the radial gain distribution. The experimental results were analyzed theoretically regarding Fresnel diffraction. A quite different response was found for the two types of glass despite their similar nominative properties. PACS 42.60.Jf; 42.60.By; 42.15.Fr     

Manifestation of europium ions in photoinduced absorption of lanthanum–gallium-sulfide-oxide glasses

 Illumination of Eu-doped lanthanum–gallium-sulfide-oxide glasses by doubled-frequency coherent laser pulses of Nd-YAG lasers at power densities 20–120 MW/cm² has shown an occurrence of photoinduced changes of fundamental absorption edge. Moreover, the total absorption was changed up to 25% in the transparent spectral range. Different rare-earth impurities cause different spectral shifts of absorption edge. Among them europium ions demonstrated the highest photoinduced changes. This may be caused by a relatively large polarizabiity of these ions compared to other rare earth ions. This opens a rare possibility to use the investigated sulfide glasses for recording of dynamic holograms.     

Subsurface damage of Nd-doped phosphate glasses in optical fabrication

We present a destructive method for detecting and measuring subsurface damage of Nd-doped phosphate glasses. An instrument based on the dimple method - a destructive method - was developed. Subsurface damage depth produced in each fabrication procedure was obtained. We extend the surface roughness-subsurface damage relation to Nd-doped phosphate glasses. The constant ratio of subsurface damage and surface roughness was obtained as well. We also analyse the relation of abrasive size and subsurface damage experimentally. From a measurement of the surface roughness or abrasive size, one can obtain an accurate estimate of the damage layer thickness that must be eliminated by polishing or subsequent grinding operations.     

Photoluminescence from germanate glasses containing silicon nanocrystals and erbium ions

We report the first observation of photoluminescence enhancement in Er³⁺ doped GeO₂–Bi₂O₃ glasses containing silicon nanocrystals (Si-NCs) excited by a laser operating at 980 nm. The growth of ≈200% in the intensity of the Er³⁺ transition ⁴S_3/2→⁴I_15/2 (545 nm) and of ≈100% for transitions ²H_11/2→⁴I_15/2 (525 nm), ⁴F_9/2→⁴I_15/2 (660 nm), and ⁴I_5/2→⁴I_13/2 (1530 nm) was observed in comparison with a reference sample that does not contain Si-NCs. The results open a new road for obtaining efficient Stokes and anti-Stokes emissions in germanate composites doped with rare-earth ions.     

Laser spectroscopy of Nd and Dy ions in lead borate glasses

The spectroscopic and laser properties of Nd³⁺ and Dy³⁺ ions in lead borate glass were studied. Luminescence spectra recorded in the near-infrared and visible ranges correspond to ⁴F_3/2-⁴I_J/2 (J=9, 11, 13) transitions of Nd³⁺ and ⁴F_9/2-⁶H_J/2 (J=11, 13, 15) transitions of Dy³⁺, respectively. Luminescence decay curves were analyzed as a function of activator concentration. Luminescence quenching is observed, which is due to Ln-Ln interaction increasing. Several spectroscopic parameters relevant to laser potential of Ln³⁺ ions (Ln=Nd, Dy) in lead borate glass were determined. The relatively large values of the quantum efficiency and the room-temperature emission cross-section for the ⁴F_3/2-⁴I_11/2 transition of Nd³⁺ at 1061 nm and the ⁴F_9/2-⁶H_13/2 transition of Dy³⁺ at 573 nm imply that Ln-doped lead borate glasses can be considered as promising solid-state materials for laser applications.     

Evolution of the spectral characteristics upon annealing of lithium borate glasses containing europium and aluminum

The spectral and structural characteristics of lithium borate glasses containing europium and aluminum have been investigated upon annealing at different temperatures. It has been found that the spectral characteristics of the studied system change nonmonotonically with an increase in the annealing temperature. After annealing at a temperature of 600°C, the luminescence spectra of the glasses exhibit broad structureless bands that are specific for the amorphous phase containing Eu³⁺ ions. Then, after annealing at T = 700°C, narrow lines appear in the wavelength ranges 585–595 and 610–620 nm, which correspond to the luminescence of the Eu(BO₂)₃ and EuAl₃(BO₃)₄ borates. A further increase in the annealing temperature (T = 800–900°C) leads to the disappearance of europium aluminum borate. In the luminescence spectra of these samples, there are narrow bands in the wavelength range λ = 585–595 nm, which are typical of europium metaborate. Finally, at a temperature of 1050°C, these bands disappear and narrow lines appear again in the wavelength range 610–620 nm, which are characteristic of the EuAl₃(BO₃)₄ borate. Thus, the temperature annealing makes it possible to purposely change the spectral characteristics of the studied system in the wavelength range 590–615 nm.     

Optical and luminescence spectroscopy of zinc gallate phosphors codoped with manganese and europium ions

Zinc gallate compounds codoped with manganese and europium ions were synthesized using the high-temperature solid-state reaction method. All samples were “characterized” by X-ray diffraction measurements, ultraviolet reflection spectroscopy, and photoluminescence spectroscopy. Structural investigations confirmed that incorporation of europium ions in zinc gallate host leads to distortion of the spinel unit cell and increase in lattice parameter. Manganese ions show the intense excitation in the region of band-to-band transitions. Zinc gallate spinel compounds codoped with manganese and europium ions exhibit emission in the whole spectral region. Among the manganese and europium activator emissions in the “green” and “red” spectral regions, the “blue” emission of spinel matrix was observed. Photoluminescence excitation spectra of europium ions and reflection spectra show similar results in the near-ultraviolet region of the spectra. The optimal concentration of europium activator was determined. Europium doping level leads to redistribution of excitation and emission intensities of zinc gallate codoped samples. The possible energy transfer mechanisms between matrix, manganese, and europium ions are discussed. Overlapping of excitation bands of all types of luminescence gives a possibility to obtain emission in the whole visible spectral range. The Commission Internationale de l’Eclairage chromaticity diagrams confirmed a possible application of the studied zinc gallate spinel compounds codoped with manganese and europium ions for the development of ultraviolet and near-ultraviolet phosphors with flexible emission color in the visible spectral range.     

Identification of the relative distribution of rare-earth ions in phosphate glasses

The relative distribution of rare-earth ions R3+ (Dy3+ or Ho3+) in the phosphate glass RAl(0.30)P(3.05)O(9.62) was measured by employing the method of isomorphic substitution in neutron diffraction. It is found that 7.9(7) R-R nearest neighbors reside at 5.62(6) A in a network made from interlinked PO4 tetrahedra. Provided that the role of Al is explicitly considered, a self-consistent account of the local matrix atom correlations can be developed in which there are 1.68(9) bridging and 2.32(9) terminal oxygen atoms per phosphorus.     

Formation of dipole nanoclusters in blood serum protein solutions containing europium and potassium ions

Aqueous solutions of major serum proteins (albumin and g-globulin) with small concentrations of potassium and europium ions were investigated with the use of photon-correlation spectroscopy and atomicforce microscopy. The coefficients of translation diffusion, as well as the effective radiuses of the scattering particles in the solutions as a function of pH and salt concentration, were obtained. It was found that protein dipole nanoclusters form in these solutions, which was confirmed by AFM methods as well.     

含磷酸胍基间作用的磷酸双乙酸胍晶体电子结构与光学性质研究

基于磷酸胍基间作用在L-精氨酸磷酸盐晶体特异性与生物化学功能中的重要角色,已制备了含有磷酸胍基的新晶体磷酸双乙酸胍.本文采用第一性原理计算了磷酸双乙酸胍晶体的电子结构与三个晶向上的光学性质,探讨了其中基团间作用与光学性质的关联.结果表明,磷酸双乙酸胍晶体能隙为4.77 eV,远小于磷酸二氢钾晶体,更易吸收光子,在胍基、羧基与磷酸根上发生电子跃迁.磷酸双乙酸胍晶体在[100]和[010]方向光学性质相近,[001]晶向上胍基N-2p在价带内电子跃迁产生强吸收,能量损失高且分布较窄,光学应用受到限制,该研究对理解和研究磷酸双乙酸胍晶体中基团间作用及其光学性质奠定了良好的基础.     

The optical absorption of hydroxyl ions associated with divalent calcium in NaCl

The measurements confirmed the association of Ca²⁺ and OH^– in NaCl: CaCl₂ + NaOH, which causes an increase and a shift +0·031 of the OH^– absorption at 2·8, the extinction of the OH^– UV-absorption at 184 nm and the occurrence of new absorption bands between 160 and 210 nm.The measurements were performed at the II. Physikalisches Institut of the University of Stuttgart.     

Preparation and properties of Ce-doped Na–Gd phosphate glasses

Rare earth-doped sodium–gadolinium phosphate glasses with increased luminescence efficiency are promising materials for the detection of neutrons, γ- and X-rays. Their main advantages are low cost, high radioluminescence light output, high quality and chemical durability. The glasses were prepared by a rapid quenching technique in air. The radioluminescence intensity maximum was achieved for a Ce concentration of 3 mol% and that of Gd around 30%. Glass transition temperatures were above 300°C for the tested samples and this guarantees that the glass can be utilised in a sufficiently broad temperature range. The glass-forming ability of this glass system is high. However, until now high-quality glass has been only prepared with a Gd concentration of 40 mol% in the starting batch. The glasses containing at least 30 mol% Gd were moisture resistant, while those with lower Gd concentrations were slightly hygroscopic.     

EPR and optical absorption studies of Fe ions in sodium borophosphate glasses

Electron paramagnetic resonance (EPR) and optical absorption spectral investigations have been carried out on Fe³⁺ ions doped sodium borophosphate glasses (NaH₂PO₄-B₂O₃-Fe₂O₃). The EPR spectra exhibit resonance signals with effective g values at g=2.02, g=4.2 and g=6.4. The resonance signal at g=4.2 is due to isolated Fe³⁺ ions in site with rhombic symmetry whereas the g=2.02 resonance is due to Fe³⁺ ions coupled by exchange interaction in a distorted octahedral environment. The EPR spectra at different temperatures (123-295 K) have also been studied. The intensity of the resonance signals decreases with increase in temperature whereas linewidth is found to be independent of temperature. The paramagnetic susceptibility (χ) was calculated from the EPR data at various temperatures and the Curie constant (C) and paramagnetic Curie temperature (θ_p) have been evaluated from the 1/χ versus T graph. The optical absorption spectrum exhibits bands characteristic of Fe³⁺ ions in octahedral symmetry. The crystal field parameter (Dq) and the Racah interelectronic repulsion parameters (B and C) have also been evaluated and discussed.     

Investigation on luminescence properties of Nd ions in alkaline-earth titanium phosphate glasses

Nd³⁺ ions doped alkaline-earth titanium phosphate glasses were prepared by using the conventional melt quenching method. Absorption spectra were recorded and oscillator strengths of the transitions were calculated using area under the absorption bands. The energy level analysis was carried out by using free-ion Hamiltonian model. The three host dependent Judd-Ofelt intensity parameters, Ω_λ (λ = 2, 4, and 6) were used to elucidate the structure of glassy matrix around Nd³⁺ ion as well as to determine the ⁴F_3/2 metastable state radiative properties such as radiative transition probabilities, branching ratios and radiative lifetimes. The decay curves of all the three glasses show single exponential behavior. The discrepancy between the experimental and calculated lifetimes of emitting level was attributed to multiphonon relaxation. The achieved high quantum efficiencies for the ⁴F_3/2 level indicate efficient laser emission at 1.06 μm in these glass systems.