Tungsten Tellurite Glasses Research Articles

2.7 μm emission properties of Er3+ doped tungsten–tellurite glass sensitized by Yb3+ ions

With a 980nm laser diode (LD) pumped, the sensitized effect of Yb3+ ions on 2.7μm emission properties and energy transfer mechanism in Yb3+/Er3+ co-doped tungsten–tellurite glass were investigated in present paper. Based on absorption spectra, Judd–Ofelt parameters and radiative transition probabilities were calculated and analyzed. The emission spectra were tested and the optimized concentration ratio of Yb3+ to Er3+ ions was found to be 3:0.5 with a largest calculated emission cross-section (6.05×10−21cm2) corresponding to Er3+:4I11/2→4I13/2 transition. When the concentration ratio of Yb3+ to Er3+ ions was 4:0.5, 1.5μm and 2.7μm emission decreased while up-conversion increased. The decreased 1.5μm and 2.7μm emission were induced by the saturation of Er3+:4I13/2 level. In brief, the advantageous spectroscopic characteristics indicated that Yb3+/Er3+ co-doped tungsten–tellurite glass may be a promising candidate for application of 2.7μm emission.

Effect of preliminary oxidation annealing on properties of porous silicon impregnated with a tungsten-tellurite glass activated by Er and Yb

The effect of preliminary oxidation annealing of porous silicon (PS) on photoluminescence (PL) under laser pumping at wavelengths of 532 and 980 nm, EPR, and transverse current transport in structures based on PS with a fused tungsten-tellurium glass (TTG) doped with Er and Yb has been studied. It has been shown that such annealing and the presence of silicon nanocrystals (nc-Si) in PS promote multiple PL enhancement for both Er ions in TTG and nc-Si in PS at wavelengths of 750 and 1540 nm, respectively. As TTG is fused into PS, P b -centers of nonradiative recombination are suppressed, while retaining discrete electron tunneling through nc-Si grains in PS.

M-line spectroscopic, spectroscopic ellipsometric and microscopic measurements of optical waveguides fabricated by MeV-energy N+ ion irradiation for telecom applications

Irradiation with N+ ions of the 1.5–3.5MeV energy range was applied to optical waveguide formation. Planar and channel waveguides have been fabricated in an Er-doped tungsten–tellurite glass, and in both types of bismuth germanate (BGO) crystals: Bi4Ge3O12 (eulytine) and Bi12GeO20 (sillenite). Multi-wavelength m-line spectroscopy and spectroscopic ellipsometry were used for the characterisation of the ion beam irradiated waveguides. Planar waveguides fabricated in the Er-doped tungsten–tellurite glass using irradiation with N+ ions at 3.5MeV worked even at the 1550nm telecommunication wavelength. 3.5MeVN+ ion irradiated planar waveguides in eulytine-type BGO worked up to 1550nm and those in sillenite-type BGO worked up to 1330nm.

MeV Energy $\hbox{N}^{+}$-Implanted Planar Optical Waveguides in Er-Doped Tungsten-Tellurite Glass Operating at 1.55 $\mu\hbox{m}$

We report on the fabrication and characterization of planar waveguides in an Er-doped tungsten-tellurite glass by implantation of 3.5 MeV N+ ions. Implantations were carried out in a wide fluence range of 1·1016 ÷8 ·1016 ions/cm2. Waveguides were characterized by m-line spectroscopy and spectroscopic ellipsometry. Irradiation-induced refractive index modulation saturated around a fluence of 8 ·1016 ions/cm2. Waveguides operating at 1550 nm were obtained in that material using 3.5 MeV N+ ion implantation.

Tm^3+ and Tm^3+-Ho^3+co-doped tungsten tellurite glass single mode fiber laser

We investigated the ~2 μm spectroscopic and lasing performance of Tm(3+) and Tm(3+)-Ho(3+) co-doped tungsten tellurite glass single mode fibers with a commercial 800 nm laser diode. The double cladding single mode (SM) fibers were fabricated by using rod-in-tube method. The propagation loss of the fiber was ~2.5 dB/m at 1310 nm. The spectroscopic properties of the fibers were analyzed. A 494 mW laser operating at ~1.9 μm was achieved in a Tm(3+) doped 20 cm long fiber, the slope efficiency was 26%, and the laser beam quality factor M(2) was 1.09. A 35 mW ~2.1 μm laser output was also demonstrated in a 7 cm long of Tm(3+)-Ho(3+) co-doped tungsten tellurite SM fiber.

Formation of slab waveguides in eulytine type BGO and CaF2 crystals by implantation of MeV nitrogen ions

Ion implantation, compared with other waveguide fabrication methods, has some unique advantages. It has proved to be a universal technique for producing waveguides in most optical materials. The authors of the present article reported fabrication of channel and slab waveguides in an Erbium-doped tungsten tellurite glass by implantation of MeV energy N+ ions. The present article reports successful adaptation of the same technique to the fabrication of slab waveguides in eulytine type bismuth germanate (BGO) and CaF2 crystals. This is the first report on successful waveguide fabrication in these materials using 3.5MeVN+ ions at implanted fluences between 5×1015 and 4×1016ions/cm2. Spectroscopic ellipsometric measurements revealed the existence of guiding structures in both materials. M-line spectroscopic measurements indicated guiding effect in the as-implanted BGO up to 1550nm and up to 980nm in the as-implanted CaF2. Ion implantation induced the appearance of three peaks in the UV/Vis absorption spectrum of CaF2, that can be attributed to colour centres.

Photoluminescence of porous silicon saturated with tungsten-tellurite glass with rare-earth metal impurities

It has been shown that the presence of silicon nanoparticles in a layer of porous silicon saturated with tungsten-tellurite glass causes an increase in the photoluminescence quantum efficiency of erbium (1530 nm) by an order of magnitude in the case of long-wavelength excitation and an enhancement of the ytterbium photoluminescence (980 nm) by almost 50 times and erbium photoluminescence by 25 times in the case of short-wavelength pumping. This luminescence enhancement is explained by the formation of additional channels of transfer of external excitation by silicon nanocrystallites in porous silicon to impurity ytterbium and erbium ions in tungsten-tellurite glass.

Upconversion luminescence in Tm 3+/Yb 3+co-doped lead tungstate tellurite glasses

This work reports the upconversion luminescence properties of Tm 3+/Yb 3+ ions in lead tungstate tellurite (LTT) glasses. Judd–Oflet intensity parameters have been obtained from the absorption band intensities of Tm 3+ singly-doped and Tm 3+/Yb 3+ co-doped LTT glasses. The spontaneous emission probabilities, radiative lifetimes and branching ratios for 1G 4 and 3H 4 emission levels of Tm 3+ have been determined. Upconversion luminescence has been observed by exciting the samples at 980 nm (Yb 3+: 2F 7/2→ 2F 5/2) at room temperature. Four upconversion emission bands corresponding to the 1G 4→ 3H 6 (477 nm), 1G 4→ 3F 4 (651 nm), 1G 4→ 3H 5 (702 nm) and 3H 4→ 3H 6 (810 nm) transitions have been identified. The relative variation in the intensities of upconversion bands, the different channels responsible for upconversion spectra and the effect of Yb 3+ ions concentration on the upconversion luminescence of Tm 3+ ions have also been discussed.

Structures and Third-Order Optical Nonlinearities of BiO1.5-WO3-TeO2 Glasses

We investigated third-order optical nonlinearities (χ(3)) by femto-second Z-scan technique for various compositions of bismuth–tungsten–tellurite glasses (xBiO1.5–20WO3–(80–x)TeO2; x=0–15) as well as their Raman scattering spectra. It was revealed that a small additive of BiO1.5 (5 mol%) in WO3–TeO2 glass was capable of improving a real part of χ(3). However, an excess amount of BiO1.5 decreased the nonlinearity, resulting from TeO4–to–TeO3+1 transformation with an increase in BiO1.5. We shall attempt to explain the improvement on a basis of a two-phases model for WO3–TeO2 glasses.

Absorption and emission spectral studies of Sm 3+-doped lead tungstate tellurite glasses

The present work reports the effect of concentration on photoluminescence properties of Sm 3+ ions doped lead tungstate tellurite (LTTSm) glasses by using the absorption, emission and decay measurements. The Judd–Ofelt theory has been used to evaluate the three Judd–Ofelt intensity parameters ( Ω 2,4,6) and calculated oscillator strengths ( f c). LTTSm glasses exhibited intense reddish–orange emission when excited with 477 nm wavelength. Concentration quenching has been noticed beyond 1.0 mol% of Sm 3+ ion concentration. The decay curves of 4G 5/2 level exhibited single exponential behavior for all the concentrations and the measured lifetimes are found to depend strongly on Sm 3+ concentration. From the emission characteristic parameters of 4G 5/2 level, it is concluded that the LTTSm glasses could be useful for photonic devices like visible lasers, fluorescent display devices and optical amplifiers.

Optical properties of Eu 3+ions in lead tungstate tellurite glasses

Lead tungstate tellurite (LTT) glasses doped with different concentrations of Eu 3+ ions have been prepared by the conventional melt quenching method. From the absorption spectrum, it has been observed that the bands originated both from the ground ( 7F 0) and the first excited ( 7F 1) states. Judd-Ofelt intensity parameters Ω 2 and Ω 4 have been evaluated from the 5D 0 → 7F 2 and 5D 0 → 7F 4 emission transitions respectively. The evaluated J-O intensity parameters have been used to calculate different radiative and laser characteristic parameters of the 5D 0 excited level. The large magnitudes of stimulated emission cross-section ( σ e) and branching ratio ( β R) obtained for 5D 0 → 7F 2 (0.62 μm) transition suggests that the LTTEu20 glass could be more suitable for lasing action in the visible region. The measured lifetime of 5D 0 excited state increases with increase of Eu 3+ concentration due to increasing asymmetry around the Eu 3+ ions.

Watt-level ∼2μm laser output in Tm^3+-doped tungsten tellurite glass double-cladding fiber

We report, for the first time to the best of our knowledge, a watt level cw fiber laser at ~2 μm from a piece of 40-cm-long newly developed highly thulium-doped (3.76 × 10(20) ions/cm(3)) tungsten tellurite glass double cladding fiber pumped by a commercial 800 nm laser diode. The maximum output power of the fiber laser reaches 1.12 W. The slope efficiency and the optical-optical efficiency with respect to the absorbed pump are 20% and 16%, respectively. The lasing threshold is 1.46 W, and the lasing wavelength is centered at 1937 nm.

Enhanced Green Emission from Er2WO6 Nanocrystals Embedded Composite Tellurite Glasses

A series of tungsten-tellurite glasses activated with different concentrations (0-1.5 mol%) of Er(3+) has been synthesized. The structural properties of the best luminescent sample and the optical properties of its Er(3+) ions, are studied both immediate after its preparation as well as after its ageing. On ageing the glass suffers structural reorganization and generates Er(2)WO(6)-nanocrystals in the matrix, which greatly enhances the normal and upconversion green luminescence efficiency of Er(3+). The nanocrystal aided enhancement of normal and upconversion luminescence of Er(3+) of the glass has been attributed to the crystal field effects of the new environment of Er(3+) in the nanocrystals. A phenomenon of preferential enhancement of red upconversion luminescence at the cost of green upconversion luminescence of Er(3+) at its higher concentrations in the glass has been observed and the related photo-physics is proposed. The material shows the prospect of being used as NIR solar concentrator.

Optical absorption and structure of impurity Ni 2+ center in tungstate–tellurite glass

Absorption spectra of Ni 2+ ions in 22WO 3–78TeO 2 tungstate–tellurite glass were studied and Ni 2+ extinction coefficient spectral dependence was derived in the 450–2700 nm wavelength range. Computer modeling of the glass structure proved Ni 2+ ions to be in trigonal-distorted octahedral environment in the tungstate–tellurite glass. Tanabe–Sugano diagram for such an environment was calculated and good description of the observed spectrum of Ni 2+ ion was obtained. Basing on both absorption spectral range width and the extinction coefficient, nickel should be considered among the most strongly absorbing impurities in the tellurite glasses.

Crystallization kinetics of the tungsten–tellurite glasses

The crystallization kinetics of the (1 − x)TeO 2– xWO 3 (where x = 0.10, 0.15, and 0.20, in molar ratio) glass system was studied by non-isothermal methods using differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. DSC measurements were performed at different heating rates to study crystallization kinetics of the first crystallization reactions of the glasses. XRD analysis of tungsten–tellurite glasses heat-treated above the first crystallization temperatures revealed that the first crystallization peaks attributed to the α-TeO 2 and γ-TeO 2 crystalline phases for 0.90TeO 2–0.10WO 3 and 0.85TeO 2–0.15WO 3 samples and α-TeO 2 and WO 3 crystalline phases for the 0.80TeO 2–0.20WO 3 sample. Avrami constants, n, calculated from Ozawa equation, were found between 1.14 and 1.44. The activation energies, E A , for the first crystallization reactions were determined by using the modified Kissinger equation as 379 kJ/mol, 288.1 kJ/mol and 228.8 kJ/mol, for 0.90TeO 2–0.10WO 3, 0.85TeO 2–0.15WO 3 and 0.80TeO 2–0.20WO 3 glasses, respectively.

Three-color nonlinear optical mixing for the determination of the refractive index dispersion of a tellurite glass

We determine the refractive index dispersion of a quaternary tungsten-tellurite glass over a broad spectral range from 0.4 to 3 μm from the wavelength dependence of the phase matching conditions for third-order nonlinear optical frequency conversion. We discuss the optimum phase-matching geometries for this task and obtain the wavelength-dependence of the refractive index to within three significant digits by a least-squares fit of a Sellmeier-type equation to the phase-matching data.

Spectroscopic and photoluminescence properties of Dy 3+-doped lead tungsten tellurite glasses for laser materials

Lead tungsten tellurite (LTT) glasses doped with different Dy 3+ ion concentrations have been prepared and characterized through optical absorption, photoluminescence and decay measurements. The glassy nature of the LTT host has been confirmed through the XRD measurements. The three phenomelogical intensity parameters Ω λ ( λ = 2, 4, 6) have been determined from the absorption spectral intensities using the Judd–Ofelt (J–O) theory. The hypersensitivity of 6H 15/2 → 6F 11/2 transition based on the magnitude of Ω 2 parameter has also been discussed. By using the J–O intensity parameters several radiative properties such as spontaneous transition probabilities ( A R ), fluorescence branching ratios ( β R ) and radiative lifetimes ( τ R ) have been determined. The effect of Dy 3+ ion concentration on the emission intensities of 4F 9/2 → 6H J′ ( J′ = 15/2, 13/2, 11/2 and 9/2) transitions has also been reported.

Effect of rare-earth dopants on the thermal behavior of tungsten–tellurite glasses

In the present study, the effect of rare-earth element addition on the thermal behavior of tungsten–tellurite glasses was investigated by running detailed differential thermal analyses. The glasses were prepared with the compositions of (1 − x)TeO 2– xWO 3, where x = 0.10, 0.15 and 0.20 in molar ratio and all three samples were doped with 0.5 and 1.0 mol% of Nd 2O 3, Er 2O 3, Tm 2O 3 and Yb 2O 3. By applying different glass preparing methods, the effect of melt-quenching techniques on the thermal behavior of tellurite glasses was also investigated and almost the same thermal behavior was observed for all attempts. Therefore, the glass samples were obtained by heating high purity powder mixtures to 800 °C in a platinum crucible with a closed lid, holding for 30 min and quenching in water bath. In general, the addition of rare-earth elements to undoped samples affected the thermal behavior of tungsten–tellurite glasses by shifting the glass transition and exothermic reaction temperatures to higher values and increasing the thermal stability. Moreover, the introduction of rare-earth dopants significantly decreased the temperature values of the first endothermic peaks corresponding to the eutectic reaction; whereas a slight decrease was observed in the second endothermic peak temperatures representing the liquidus reaction. Addition of rare-earth elements with higher atomic number (Er 2O 3, Tm 2O 3 and Yb 2O 3) resulted in peak splitting of the eutectic reaction.

Mid-infrared luminescence and energy transfer characteristics of Ho 3+/Yb 3+ codoped lanthanum–tungsten–tellurite glasses

Ho 3+/Yb 3+ codoped lanthanum–tungsten–tellurite (TWL) glasses are prepared by melt-quenching method. The Judd–Ofelt intensity parameters ( Ω t t = 2, 4, 6), radiative transition rates, radiative lifetimes, and branching ratios of Ho 3+ are calculated based on the absorption spectrum to evaluate the spectroscopic properties of Ho 3+ in TWL glass. The mid-infrared emission of the samples are investigated under the excitation of 980 nm LD. The absorption, emission cross-sections and gain coefficient of Ho 3+: 5I 7 → 5I 8 are calculated. The energy transfer processes of Yb 3+–Yb 3+ and Yb 3+–Ho 3+ are analyzed, the results show that the Yb 3+ ions can transfer their energy to Ho 3+ ions with large energy transfer coefficient, and a maximum efficiency of 84%.

Energy transfer and 1.8 μm emission in Tm 3+/Yb 3+ codoped lanthanum tungsten tellurite glasses

Tm 3+/Yb 3+-codoped lanthanum tungsten tellurite (TWL) glasses are prepared by melt-quenching method and the thermal stability of the glasses is analyzed. To evaluate the spectroscopic properties of Tm 3+ in TWL glass, the Judd–Ofelt intensity parameters ( Ω t t = 2, 4, 6), radiative transition rates, radiative lifetimes, and branching ratios of Tm 3+ are calculated based on the absorption spectrum. The 1.8 μm emission of the samples are investigated under the excitation of 980 nm LD. Large product of emission cross-section and lifetime ( σ em τ R) of Tm 3+: 3F 4 → 3H 6 is obtained, and the maximum gain coefficient at around 1835 nm is 3.6 cm −1. The energy transfer processes of Yb 3+–Yb 3+ and Yb 3+–Tm 3+ are analyzed, the results show that the Yb 3+ ions can transfer their energy to Tm 3+ ions with a large energy transfer coefficient, and a maximum efficiency of 89%.