In this study we present the production and characterization of Pb 2 P 2 O 7 -Nb 2 O 5 glasses and optical fibers. The dependence of Nb 2 O 5 content on thermal, structural and optical properties were investigated by thermal analysis (DSC), Raman spectroscopy, UV-Visible absorption, M-Lines and Z-scan techniques. Glass transition temperatures (T g ) increased linearly with Nb 2 O 5 content up to 60 mol %, while thermal stability against crystallization (T) reached a maximum value of 225 o C at 40 mol% of Nb 2 O 5 . Raman spectra showed a significant structural change by the insertion of NbO 6 octahedral units in the glass network. The increase of Nb 2 O 5 concentration shifts the glasses absorption edge to lower energies, and also increase the linear refractive indexes (n 0 ) due to the high polarizability of niobium atoms and formation of non-bridging oxygen. Similarly to n 0 , an increase in the positive values of nonlinear refractive indexes was observed using Z-Scan technique with increase of Nb 2 O 5 content, based on structural changes caused by the replacement of Pb 2 P 2 O 7 instead Nb 2 O 5 . The average of n 2 values at 500 -1500 nm raised from 2.2 × 10 -19 to 3.8 × 10 -19 m 2 /W, when the Nb 2 O 5 content was increased from 10 to 60 mol %. Lastly, a core-cladding preform was produced by suction method and the optical fiber drawn. The sample containing 40 mol% of Nb 2 O 5 was used for presenting the highest thermal stability against crystallization and n 0 values greater than 2 from green to near-infrared wavelengths. Multimode step index fiber with good core circularity and concentricity was produced and the optical losses were determined by cut-back method at visible and near-infrared ranges.3 IntroductionLead pyrophosphate glasses containing tungsten oxide in the binary system Pb 2 P 2 O 7 -WO 3 have already been investigated and shown interesting thermal and optical properties, resulting chemically stable, extremely high resistance against devitrification and high linear and nonlinear refractive indexes [1,2]. The optical properties were correlated with the specific phosphate glass network containing lead atoms and tungsten octahedrons. At high WO 3 contents the octahedrons WO 6 units linked together through W-O-W bonds to form highly polarizable clusters, which were pointed out to be responsible, in conjunction with lead atoms polarization, for high linear and nonlinear optical properties [2]. Besides the interesting optical properties, lead pyrophosphate glass present high vitrifying ability and unusual capability to dissolve large amounts of others glass formers, modifiers, or intermediate compounds without reduction of glass forming ability [3,4], as observed by the insertion of WO 6 inside the phosphate covalent network that form strong P-O-W bonds which are responsible to enhance the network connectivity [5]. Transparent phosphate glasses containing heavy metal oxides such as Bi 2 O 3 , Sb 2 O 3 , WO 3 , Nb 2 O 5 , and PbO are subject of intense studies and widely exploited as optical compone...

This work presents the production and characterization of a new prolific binary glass system based on SbPO 4-GeO 2. The dependence of GeO 2 content on thermal, structural and optical properties were investigated by means of thermal analysis, Raman, UV-Vis-NIR, infrared, M-lines and EPR spectroscopy. Glass transition temperatures remain constant around 410°C when GeO 2 content is increased, indicating that GeO 4 units are not responsible for increasing the connectivity of PO 4 units. Thermal stability linearly increases as a function of GeO 2 content, reaching a value around 400°C for glass containing 90 mol% of GeO 2. Raman spectroscopy was used to evaluate the glass structural changes when GeO 2 is incorporated from 30 to 90 mol% indicating a gradual change from a phosphate to a germanate glass skeleton. The optical window extends from 350 nm at UV region, up to 2.7 μm in the middle-infrared region limited by the multiphonon cutoff due to the strong OH absorption. M-lines technique shows that increasing GeO 2 content decreases the refractive index, mainly because the lower concentration of higher polarizable antimony atoms. EPR spectra of heat treated V 2 O 5 doped glasses, at different temperatures above the glass transition temperature, shows the characteristic eight-line hyperfine splitting spectrum. The spin Hamiltonian parameters obtained from the simulated spectra indicates that the paramagnetic tetravalent vanadium ions in the glasses exist as vanadyl form VO 2+ , located in axially distorted octahedral sites. For glasses treated at higher temperatures a second VO 2+ component appears in the EPR spectra and the analysis of the spin-Hamiltonian parameters suggests that these vanadyl ions are in more tetragonal distorted octahedral sites than those in the glass.

Recent advances in glass chemistry have led to new multifunctional optical glasses of great technological importance. Glasses containing high amounts of antimony have been studied for use in nonlinear optics, near-infrared transmission, and as hosts for rare-earth ions in photonic devices. This work describes a luminescence study of Er 3þ and Er 3þ /Yb 3þ co-doping in a new SbPO 4-GeO 2 binary glass system. Nearinfrared and visible up-conversion emissions were observed in the green and red regions, which are enhanced when the samples are co-doped with Yb 3þ. Near-infrared emissions have good quantum efficiency and full width half maximum of 61 nm. Visible up-conversion emissions are governed by two photons and described by excited state absorption, energy transfer and cross-relaxation processes.

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