Low-loss,high-purity (TeO<Subscript>2</Subscript>)<Subscript>0.75</Subscript>(WO<Subscript>3</Subscript>)<Subscript>0.25</Subscript> glass

By melting a mixture of high-purity oxides in a platinum crucible under flowing purified oxygen, we have prepared (TeO₂)_0.75(WO₃)_0.25 glass with a total content of 3d transition metals (Fe, Ni, Co, Cu, Mn, Cr, and V) within 0.4 ppm by weight, a concentration of scattering centers larger than 300 nm in size below 10² cm⁻³, and an absorption coefficient for OH groups (λ ∼ 3 μm) of 0.008 cm⁻¹. The absorption loss in the glass has been determined to be 115 dB/km at λ = 1.06 μm, 86 dB/km at λ = 1.56 μm, and 100 dB/km at λ = 1.97 μm. From reported specific absorptions of impurities in fluorozirconate glasses and the impurity composition of the glass studied here, the absorption loss at λ ∼ 2 μm has been estimated at ≤100 dB/km. The glass has been drawn into a glass-polymer fiber, and the optical loss spectrum of the fiber has been measured.     

Effect of secondary heat treatment on the spectroscopic properties of Na<Subscript>2</Subscript>O-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

We have studied the optical absorption and luminescence spectra of 45Na₂O · xNb₂O₅ · (55 − x)P₂O₅ glasses containing 5, 10, 20, 25, 30, and 35 mol % Nb₂O₅. The results indicate that the absorption band around 26000 cm⁻¹, responsible for the yellow color of the glasses, is due to the [Nb^(5+)--O⁻] center and disappears upon secondary heat treatment. Heat treatment of europium-doped glasses increases the concentration of Eu³⁺ centers in an asymmetric environment, which is accompanied by an increase in luminescence efficiency. The reason for this is that the Eu³⁺ ions are located outside the niobate subsystem of the glass matrix. The europium in the glasses studied acts as a protector ion.     

Liquid-phase epitaxy of NdAl<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> and Yb-doped YAl<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript>

Epitaxial layers of NaAl₃(BO₃)₄ (NAB) and YAl₃(BO₃)₄〈Yb〉 (YAB〈Yb〉) containing up to 10 at % Yb have been grown by liquid-phase epitaxy on YAB substrates. Their growth kinetics have been studied at relative supersaturations of the high-temperature solution from 2 × 10^?2 to 16 × 10^?2. The ytterbium concentration in YAB〈Yb〉 has been shown to vary little during the epitaxial process. Near the edges of the substrate, the surface morphology of the layers is complicated by vicinals, which have a spiral form in the case of YAB〈Yb〉. On \(\{ 10\overline 1 1\} \) YAB substrates, homogeneous single-crystal NAB films have been grown.     

Structural,optical and non-linear investigation of Eu<Superscript>3+</Superscript>: Al(NO<Subscript>3</Subscript>)<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> sol-gel glass

Optical absorption and fluorescence spectra of Eu³⁺ ions in Al(NO₃)₃-SiO₂ sol-gel glass have been investigated using the Judd- Ofelt theory. JO intensity parameters (ω _λ ) and subsequent radiative properties for⁵ D ₀ ↔⁷ F _1,2,4,6 transitions are determined. The lifetime (τ_r) of⁵ D ₀ state is computed and along with JO parameters are compared with their corresponding values in other glasses prepared by conventional technique. A structural analysis, using IR and XRD spectra and non- linear parametrization of the silica gel glass is carried out. The study reveals the glass to be a very good third order non- linear amorphous optical material.     

Emission analysis of Pr<Superscript>3+</Superscript> &; Ho<Superscript>3+</Superscript>: Ca<Subscript>4</Subscript>GdO(BO<Subscript>3</Subscript>)<Subscript>3</Subscript> powder phosphors

Emission spectral results of Pr³⁺ & Ho³⁺ ions doped Ca₄GdO(BO₃)₃ powder phosphors are reported here. XRD, SEM and FTIR measurements have been carried out for them. The emission spectrum of Pr³⁺: Ca₄GdO(BO₃)₃ has shown an emission transition ¹D₂ → ³H₄ at 606 nm with λ_exci = 480 nm (³H₄ → ³P₀) and Ho³⁺: Ca₄GdO(BO₃)₃ phosphor has shown an emission transition ⁵S₂ → ⁵I₈ at 549 nm with λ_exci = 447 nm (⁵I₈ → ⁵F₁). Emission performances of these two phosphors have been explained in terms of energy level diagrams.     

Photocurrent and Optical Transmission Spectra of Sn- and Pb-Doped (As<Subscript>2</Subscript>S<Subscript>3</Subscript>)<Subscript>0.3</Subscript>(As<Subscript>2</Subscript>Se<Subscript>3</Subscript>)<Subscript>0.7</Subscript> Glass Films

The photocurrent and optical transmission spectra of thin (As₂S₃)_0.3(As₂Se₃)_0.7 glass films doped with Sn and Pb are reported. The strongest photoresponse is offered by the films doped with 0.010– 0.015 at % Sn or Pb. Low doping levels are shown to have a significant effect on the peak-response wavelength and band gap of the films.     

Manifestation of Nd ions on the structure,Raman and IR spectra of (TeO<Subscript>2</Subscript>-MoO-Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>) glasses

The structure of [80TeO₂ + (20–x)MoO + xNd₂O₃] glasses, with x = 0, 4, 6, 10 and 12 mol%, is studied in this work. Raman scattering in the spectral range (−2000 to 3500 cm⁻¹) and IR absorption spectra have been measured for crystalline TeO₂ and glasses, and their assignments were discussed and compared. Many vibrational modes were found active in both Raman and IR and their assignments for crystalline TeO₂ and for the glasses were discussed in relation to the tetragonal structure of crystalline α -TeO₂. Nd₂O₃ was found to completely eliminate diffuse scattering and enhance the Raman scattering intensity. Anti-stokes Raman bands in the range −1460 cm^{− 1} to −1975 cm^{− 1} were observed for both (30Li₂O + 70B₂O₃+ xNd₂O₃) glasses and [80TeO₂ + (20−x)MoO + xNd₂O₃] glasses and were attributed to some emission processes due to the doping of the glasses with Nd₂O₃.     

Gamma rays interactions with Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-doped Na<Subscript>2</Subscript>O–CdO–P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses assessed by collective optical and FT infrared absorption spectroscopy

Undoped and Bi₂O₃-doped glasses from the system Na₂O–CdO–P₂O₅ were prepared and studied through investigating their optical and FTIR spectra before and after gamma irradiation beside measuring their thermal expansion properties. Optical spectra reveal distinct UV absorption with additional peaks upon introducing Bi₂O₃ added with different concentrations from 1 to 7.5%. The UV absorption of the undoped sample is related to trace iron impurities while the extended UV absorption peaks are correlated with absorption of Bi³⁺ ions. FTIR spectra show condensed phosphate groups (Q², Q³ units) beside the sharing of bismuth ions in their vibrational sites. Gamma irradiation causes limited changes in the UV spectra but involves the generation of an induced visible band in the undoped glass. These changes are assumed to be due to some suggested photochemical reactions on the trace iron impurities and the formation of an induced visible (POHC) band on the phosphate network. Careful inspection of the selected deconvoluted spectra for the undoped glass and doped (7.5 wt%) supports the introduced assumptions. The thermal expansion parameters are correlated with the type of bonding of bismuth ions within the network structure.     

Preparation of apatite-type La<Subscript>9.33</Subscript>(SiO<Subscript>4</Subscript>)<Subscript>6</Subscript>O<Subscript>2</Subscript> electrolyte by urea-nitrates combustion

Apatite-type La_9.33(SiO₄)₆O₂ powders have been prepared by urea-nitrates combustion at low temperature. Process parameters of combustion and characteristics of electrolyte were studied and optimized. Gelation time of precursor has been shortened distinctly by introducing an appropriate solvent system. Molar ratio of nitric acid to lanthanum oxide dependence of the nature of the phases has first been characterized. Well-crystallized La_9.33(SiO₄)₆O₂ powders with an average size of 30.5 nm were obtained at a calcining temperature as low as 800°C for 12h. Dense ceramic with a relative density of 96% was prepared by sintering the green compact of these nanopowders at 1400°C for 3 h. The sintering body exhibited a high ionic conductivity of 4.38 × 10⁻³ S/cm at 700°C.     

Optical properties of CeO<Subscript>2</Subscript> thin films

Cerium oxide (CeO₂) thin films have been prepared by electron beam evaporation technique onto glass substrate at a pressure of about 6 × 10⁻⁶ Torr. The thickness of CeO₂ films ranges from 140–180 nm. The optical properties of cerium oxide films are studied in the wavelength range of 200–850 nm. The film is highly transparent in the visible region. It is also observed that the film has low reflectance in the ultra-violet region. The optical band gap of the film is determined and is found to decrease with the increase of film thickness. The values of absorption coefficient, extinction coefficient, refractive index, dielectric constant, phase angle and loss angle have been calculated from the optical measurements. The X-ray diffraction of the film showed that the film is crystalline in nature. The crystallite size of CeO₂ films have been evaluated and found to be small. The experimental d-values of the film agreed closely with the standard values.     

Intense blue and violet luminescence in the (B<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript>):Eu<Superscript>2+</Superscript> system

Glassy-crystalline samples of compositions (B₂O₃-Al₂O₃-SiO₂):Eu²⁺ (3 at %) and (B₂O₃-2SiO₂):Eu²⁺ (3 at %) were obtained by sintering the initial powdered mixtures at 1300°C in air. Being excited by laser radiation at a wavelength of 325 nm, the former samples exhibit intense blue photoluminescence with a maximum at 434–448 nm, while the latter samples emit in the violet spectral interval with a maximum at 409 nm. An increase in the content of B₂O₃ leads to a shift of the emission maximum toward a shorter wavelength, while additional annealing at 1300°C C in vacuum shifts the spectrum toward longer wavelengths.     

Structure of WO<Subscript>3</Subscript>-TeO<Subscript>2</Subscript> glasses

WO₃-TeO₂ glasses have been studied by quantum-chemical simulation and Raman spectroscopy. The results have been used to develop a model for the network of tungstate-tellurite glasses. The model allows one to correlate the structure and optical properties (in particular, the position and intensity of Raman bands) of the glasses with their composition. The network of the glasses is shown to be made up, for the most part, of three types of structural groups: TeO₄ trigonal dipyramids, O=TeO₂ pyramids, and O=WO₅ octahedra. Any other structural units, in particular, WO₄ tetrahedra, are unnecessary. The model for the network of WO₃-TeO₂ glasses can be used to analyze the vibrational spectra of tungstate-tellurite glasses in a broad composition range. In particular, using this model we assigned the Raman spectra of the tungstate-tellurite glasses in the range 550–950 cm^?1.     

Ce and Eu activated Na<Subscript>2</Subscript>Zn<Subscript>5</Subscript>(PO<Subscript>4</Subscript>)<Subscript>4</Subscript>, a new promising novel phosphor

A new efficient phosphor, Eu²⁺/Eu³⁺ and Ce³⁺ activated Na₂Zn₅(PO₄)₄ has been synthesized by solid-state reaction technique at high temperature. X-ray powder diffraction analysis confirmed the formation of Na₂Zn₅(PO₄)₄ host lattice. Scanning electron microscopy indicated that the microstructure of the phosphor consisted of irregular fine grains with a size of about 0·5–2 μm. Photoluminescence excitation spectrum measurements of Ce³⁺ activated Na₂Zn₅(PO₄)₄ show that the phosphor can be efficiently excited by UV-Vis light from 280 to 310 nm to realize emission in the visible (blue) range due to the 5d-4f transition of Ce³⁺ ions which is applicable for scintillation purpose, whereas Eu²⁺/Eu³⁺ activated Na₂Zn₅(PO₄)₄ phosphor emits blue, green and red emission spectrum shows at 487 nm, 546 nm with a dominant peak at 611 nm respectively, due to Eu²⁺/Eu³⁺ ions which is promising candidate for solid state lighting. Therefore, newly synthesised, by low cost and easy technique prepared, novel phosphors may be useful as RGB phosphor for solid state lighting application.     

Extinction coefficient of Ni2+ in (TeO2)0.78(WO3)0.22 glass

The absorption spectra of (TeO₂)_0.78(WO₃)_0.22 glasses containing 0.01–1.0 wt % NiO have been measured at wavelengths from 450 to 2700 nm, and the spectral dependence of the extinction coefficient of Ni²⁺ in the glasses has been obtained. In the absorption bands centered at 810 and 1320 nm, the extinction coefficient is 20.2 ± 0.8 cm⁻¹ (870 ± 35 dB/(km ppmw)). According to the spectral range of its absorption and its extinction coefficient, nickel is a strongly absorbing impurity in tellurite glasses. The present results can be used to formulate sound nickel concentration limits in tellurite glasses for fiber-optic applications.     

Synthesis and characterization of new glasses based on Li<Subscript>2</Subscript>S-P<Subscript>2</Subscript>S<Subscript>5</Subscript>-Sb<Subscript>2</Subscript>S<Subscript>3</Subscript> system

There is great interest in sulfide glasses because of their high lithium ion conductivity. New sulfide glasses based on Li₂S-P₂S₅-Sb₂S₃ system have been synthesized by a classical quenching technique. A summary of thermal and structural characterization is presented. Electrical conductivities of the samples have been determined by Impedance Spectroscopy. The compositions of low lithium content (below 20% mol) have presented low electronic conductivities close to 10⁻⁸ S/cm at room temperature. The compositions of medium lithium content (30–50% mol) have presented mixed ionic-electronic behavior with predominant on ionic conductivity with a maximum values around 10⁻⁶ S/cm for samples up to 50% Li₂S at room temperature. Arrhenius behavior is verified between 25°C and T_g for all glasses with activation energies about 0.55–0.64 eV. A comparative study of conductivities with glasses belonging to the other chalcogenide systems has been undertaken.     

Mn-doped Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> nanocrystal with enhanced electrochemical properties based on aerosol synthesis method

Mn-doped Li₃V_2?x Mn _x (PO₄)₃ nanocrystals with enhanced electrochemical properties for lithium-ion batteries were synthesized by aerosol process successfully. The nanocrystals synthesized from aerosol-assisted spray process have an average particle size smaller than 500 nm, with some initial particle size of about 100 nm. The Mn-doped Li₃V₂(PO₄)₃ cathode materials show higher capacity and coulombic efficiency than pure Li₃V₂(PO₄)₃ materials. Especially, the Mn-doped Li₃V_1.94Mn_0.06(PO₄)₃ shows a capacity of 130 mAh/g in the voltage range of 3.0–4.4 V and a coulombic efficiency of 99.5 % at 1C. The results from XRD, SEM, HRTEM, and EIS suggested that lattice changes of Li₃V₂(PO₄)₃ due to Mn doping and the fine particles enabled by aerosol-assisted spray process can significantly reduce the charge-transfer resistance and improve the apparent Li⁺ diffusion coefficient of insertion/desertion in the electrodes, which were the critical reason of better electrochemical performance of Mn-doped Li₃V₂(PO₄)₃ cathode materials.     

Proton Conductivity and Thermal Properties of Ba(H<Subscript>2</Subscript>PO<Subscript>4</Subscript>)<Subscript>2</Subscript>

We have grown single crystals of barium dihydrogen phosphate and studied its thermal transformations during heating to 500°C and its electrotransport properties. Ba(H₂PO₄)₂ (Pccn) has been shown to undergo no phase transitions up to its dehydration temperature. The thermal decomposition of Ba(H₂PO₄)₂, accompanied by dehydration, involves two steps, with maximum rates at ~265 and 370°C, and results in the formation of barium dihydrogen pyrophosphate and barium metaphosphate, respectively. The total enthalpy of the endothermic dehydration events is–244.6 J/g. Using impedance spectroscopy, we have studied in detail the proton conductivity of polycrystalline and single-crystal Ba(H₂PO₄)₂ samples in a controlled atmosphere. Adsorbed water has been shown to have a significant effect on the proton conductivity of Ba(H₂PO₄)₂ up to 130°C. The proton conductivity of the Ba(H₂PO₄)₂ single crystals has been shown to be anisotropic. The conductivity anisotropy correlates with specific structural features of the salt. Higher conductivity values, 3 × 10^–9 to 2 × 10^–7 S/cm in the range 60–160°C, have been observed in the [100] crystallographic direction, exceeding the conductivity along [010] by an order of magnitude. The activation energy for proton conduction is 0.80 eV.     

Tunable luminescence properties and energy transfer of single-phase Ca<Subscript>4</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>O: Dy<Superscript>3+</Superscript>, Eu<Superscript>2+</Superscript> multi-color phosphors for warm white light

The novel Ca_4?x(PO₄)₂O: xDy³⁺ and Ca_4?x?y(PO₄)₂O: xDy³⁺, yEu²⁺ multi-color phosphors were synthesized by traditional solid-state reaction. The crystal structure, particle morphology, photoluminescence properties and energy transfer process were investigated in detail. The X-ray diffraction (XRD) results demonstrate that the products showed pure monoclinic phase of Ca₄(PO₄)₂O when x < 0.1. The scanning electron microscopy (SEM) indicated that the phosphors were grain-like morphologies with diameters of ~ 3.7–7.0 μm. Under excitation of 345 nm, Dy³⁺-doped Ca₄(PO₄)₂O phosphors showed multi-color emission bands at 410, 481 and 580 nm originated from oxygen vacancies and Dy³⁺. Interestingly, Ca₄(PO₄)₂O: Dy³⁺, Eu²⁺ phosphors exhibited blue emission band at 481 nm and broad emission band from 530 to 670 nm covering green to red regions. The energy transfer process from Dy³⁺ to Eu²⁺ was observed for the co-doped samples, and the energy transfer efficiency reached to 60% when Eu²⁺ molar concentration was 8%. In particular, warm/cool/day white light with adjustable CCT (2800–6700 K) and high CRI (R_a > 85) can be obtained by changing the Eu²⁺ co-doping contents in Ca₄(PO₄)₂O: Dy³⁺, Eu²⁺ phosphors. The optimized Ca_3.952(PO₄)₂O: 0.04Dy³⁺, 0.008Eu²⁺ phosphor can achieve the typical white light with CCT of 4735 K and CRI of 87.     

Synthesis of Er<Superscript>3+</Superscript> and Er<Superscript>3+</Superscript> : Yb<Subscript>3+</Subscript> doped sol-gel derived silica glass and studies on their optical properties

Er₃₊ and Er₃₊ : Yb₃₊ doped optical quality, crack and bubble free glasses for possible use in making laser material have been prepared successfully through sol-gel route. The thermal and optical, including UV-visible absorption, FTIR etc characterizations were undertaken on the samples. The absorption characteristics of Er₃₊ doped samples clearly revealed the absorption due to Er₃₊ ions. On the other hand Yb₃₊ : Er₃₊ doped samples showed enhanced absorption due to² F _7/2 →² F _5/2 transition. The absorption and emission cross-section for² F _7/2 ↔² F _5/2 of Yb³⁺ were estimated. FTIR absorption spectra have clearly shown the reduction of the absorption peak intensity with heat treatment in the range 3700–2900 cm⁻¹. The 960 cm^-1 band also showed progressive decrease in the absorption band peak intensity with heat treatment. The result of the investigations with essential discussions and conclusions have been reported in this paper.     

Synthesis and photoluminescence study of narrow-band UVB-emitting LiSr<Subscript>4</Subscript>(BO<Subscript>3</Subscript>)<Subscript>3</Subscript>:Gd<Superscript>3+</Superscript>, Pr<Superscript>3+</Superscript> phosphor

A series of Pr³⁺, Gd³⁺ and Pr³⁺–Gd³⁺-doped inorganic borate phosphors LiSr₄(BO₃)₃ were successfully synthesized by a modified solid-state diffusion method. The crystal structures and the phase purities of samples were characterized by powder X-ray diffraction. Surface morphology of the sample was studied by scanning electronic microscopy (SEM). The optimal concentrations of dopant Gd³⁺ ions in compound LiSr₄(BO₃)₃ were determined through the measurements of photoluminescence (PL) spectra of phosphors. Gd³⁺-doped phosphors LiSr₄(BO₃)₃ show strong band absorption in UV spectral region and narrow-band UVB emission under the excitation of 276 nm was only due to ⁶P _J → ⁸S_7/2 transition of Gd³⁺ ions. The effect of Pr³⁺ ion on excitation of LiSr₄(BO₃)₃:Gd³⁺ was also studied. The excitation of LiSr₄(BO₃)₃:Gd³⁺, Pr³⁺ gives a broad-band spectra, which show very good overlap with the Hg 253.7 nm line. The photoluminescence spectra of LiSr₄(BO₃)₃ with different doping concentrations Pr³⁺ and keeping the concentration of Gd³⁺ constant at 0.03 mol have also been studied. The emission intensity of LiSr₄(BO₃)₃:Pr³⁺–Gd³⁺ phosphors increases with increasing Pr³⁺ doping concentration and reaches a maximum at 0.01 mol. From the photoluminescence study of LiSr₄(BO₃)₃:Gd³⁺, Pr³⁺ we conclude that there was efficient energy transfer from Pr³⁺→ Gd³⁺ ions in LiSr_4?x?y Pr _x Gd _y (BO₃)₃ phosphors.