2 μm spectroscopic investigation of Tm3+-doped tellurite glass fiber

TmF₃ doped TeO₂–ZnO–La₂O₃ (TZL) glasses and fibers have been prepared by the conventional melt-quenching and suction casting methods, respectively. 2 μm emission properties and energy transfer mechanisms of the TZL glasses and fibers have been analyzed and discussed. The oscillator strength, Judd–Ofelt parameters, radiative transition probability and radiative lifetime of Tm³⁺ have been calculated based on the absorption spectra and Judd–Ofelt theory. The maximum emission cross-section of Tm³⁺ is 6.9 × 10^?21 cm² near 2 μm. Emission spectra have been obtained from both TZL fibers and bulk glass when excited with a 794 nm pump. The results of 2 μm emission spectra indicate that the line width of Tm³⁺ measured in fibers is narrower than that in the bulk glass sample. The peak position of the emission spectra shifts to longer wavelength with increment of the fiber length.     

Fabrication and characterization of Er3+-doped GeO2–PbO and GeO2–PbO–Bi2O3 glass fibers

Glass fibers were drawn from GeO₂–PbO–Bi₂O₃ and GeO₂–PbO melts previously doped with Er³⁺. From the differential thermal analysis curve, the glass transition temperature was determined to be 420 °C, and no crystallization peak was observed in the temperature range of that analysis, indicating stability with regard to devitrification. Raman spectroscopy was performed to characterize the structure of the glasses, which exhibited large transmission windows (0.5–5.0 μm) and large refractive indices (∼2.0). Infrared to visible upconversion of Er³⁺ was observed in the fibers. The visible emissions were related to the upconverted green emissions at about 530 nm (²H_11/2 → ⁴I_15/2) and 550 nm (⁴S_3/2 → ⁴I_15/2), and red emission at 668 nm (⁴F_9/2 → ⁴I_15/2) under 980 nm excitation. The infrared transition (⁴I_13/2 → ⁴I_15/2) was peaked at 1.53 μm. The results obtained suggest that the fibers exhibit the same structures as the parent glasses and can be used in upconversion fiber optical devices.     

Fine embossing of chalcogenide glasses: First time submicron definition of surface embossed features

Fine micro- and nano-structures were fabricated in the surface of chalcogenide glasses by hot embossing. A Perkin Elmer Thermomechanical Analyser (TMA 7) and an in-house designed and built vacuum pressing rig were employed for embossing and the process parameters of embossing were optimised empirically. The moulds used were a silicon-on-insulator (SOI) wafer presenting 300 nm–2 μm scale features and a silicon wafer containing 1–10 μm wide and ∼10 mm long channels. We report typical results of surface embossing four samples of bulk Ge₁₅As₁₅Se₁₇Te₅₃ glasses. The applied pressure ranged from ∼5 to 500 kPa and the temperature was set to be 60–70 °C higher than the glass transition temperature (T_g), as measured by differential thermal analysis. With the increase of pressure, and use of a vacuum environment, the quality of embossing structure has been improved. Under the optimum pressing conditions, 300 nm feature scale structures were successfully replicated from the mould opening the possibility of using hot embossing to fabricate nano-photonic devices. Due to its relative simplicity, hot embossing offers the potential to produce photonic integrated circuits and components based on novel inorganic compound glasses at low-cost, high-volume, and for a wide wavelength range.     

Production and properties of high purity TeO2− WO3−(La2O3, Bi2O3) and TeO2− ZnO−Na2O−Bi2O3 glasses

TeO₂–WO₃ (TW), TeO₂–WO₃–La₂O₃ (TWL), TeO₂–WO₃–La₂O₃–Bi₂O₃ (TWLB) and TeO₂–ZnO–Na₂O–Bi₂O₃ (TZNB) glasses were produced by high-purity oxide mixtures melting in platinum or gold crucible at 800 °C in the atmosphere of purified oxygen. The total content of Cu, Mn, Fe, Co and Ni impurities was not more than 0.1–0.5 ppm wt in the initial oxides and glasses. The stability of TZNB glasses to crystallization, characterized by (T_x ? T_g) value more than 150 °C, was demonstrated by DSC measurements at heating rate 10 K/min. In the case of La₂O₃-containing glasses the thermal effects of both crystallization and fusion of the crystallized phases were not observed. The hydroxyl groups absorption coefficients of pure tellurite glasses at the maximum of the absorption band (λ ~ 3 μm) were in the region of 0.012–0.001 cm^?1. The optical absorption losses, measured by the laser calorimetry method at λ = 1.56 and 1.97 μm, did not exceed 100 dB/km.     

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.     

Spectroscopic properties of Tm3+ doped TeO2-R2O-La2O3 glasses for 1.47 μm optical amplifiers

Upon excitation at 808 nm laser diode, an intense 1.47 μm infrared fluorescence has been observed with a broad full width at half maximum (FWHM) of about 124 nm for the Tm³⁺-doped TeO₂-K₂O-La₂O₃ glass. The Judd–Ofelt parameters found for this glass are: Ω₂ = 5.26 × 10^?20 cm², Ω₄ = 1.57 × 10^?20 cm² and Ω₆ = 1.44 × 10^?20 cm². The calculated emission cross-sections of the 1.47 μm transition are 3.57 × 10^?21 cm², respectively. It is noted that the gain bandwidth, σ_e × FWHM, of the glass is about 440 × 10^?28 cm³, which is significantly higher than that in ZBLAN and Gallate glasses, a high gain of 35.5 dB at 1470 nm can be obtained in a TKL glass fiber. TeO₂-R₂O (R = Li, Na, K)-La₂O₃ glasses has been considered to be more useful as a host for broadband optical fiber amplifier.     

1.5 μm Emission and infrared-to-visible frequency upconversion in Er+3/Yb+3-doped phosphoniobate glasses

Sodium phosphoniobate glasses with the composition (mol%) 75NaPO₃–25Nb₂O₅ and containing 2 mol% Yb³⁺ and x mol% Er³⁺ (0.01 ⩽ x ⩽ 2) were prepared using the conventional melting/casting process. Er³⁺ emission at 1.5 μm and infrared-to-visible upconversion emission, upon excitation at 976 nm, are evaluated as a function of the Er³⁺ concentration. For the lowest Er³⁺ content, 1.5 μm emission quantum efficiency was 90%. Increasing the Er³⁺ concentration up to 2 mol%, the emission quantum efficiency was observed to decrease to 37% due to concentration quenching. The green and red upconversion emission intensity ratio was studied as a function of Yb³⁺ co-doping and the Er³⁺–Er³⁺ energy transfer processes.     

Synthesis and bioactive properties of macroporous nanoscale SiO2–CaO–P2O5 bioactive glass

A macroporous nanoscale bulk bioactive glass (SiO₂–CaO–P₂O₅ system) was prepared by sol–gel co-template method. Porosimeter analysis showed that the as-synthesized bioactive glasses (BGs) had a porosity of 85% and exhibited a multimodal pore size distribution, nanopores (10–40 nm) and macropores (100 nm–10 μm). Morphological and structural characterizations showed the pores were interconnected with pore walls of about 250 nm in width and 1 μm in length. In vitro bioactivity test indicated that the as-synthesized bulk BGs exhibited faster apatite layer formation capability than the conventional sol–gel BGs. Additionally, the deposited layer was identified as hydroxycarbonate apatite, which is similar to the inorganic part of human bone.     

Spectroscopic properties and energy transfer in Ga2O3– Bi2O3–PbO–GeO2 glasses codoped with Tm3+ and Ho3+

This paper reports on the spectroscopic properties and energy transfer in Ga₂O₃–Bi₂O₃–PbO–GeO₂ glasses doped with Tm³⁺ and/or Ho³⁺. From the optical absorption spectra of Tm³⁺, Judd–Ofelt intensity parameters, radiative transitions probabilities, fluorescence branching ratios, and radiative lifetimes have been calculated using Judd–Ofelt theory. The measured differential scanning calorimetry result shows that the glass exhibits excellent stability against devitrification with ΔT = 129 °C. The measured luminescence spectra show that the ³H₄ → ³F₄ transition of Tm³⁺ upon 808 nm laser diode excitation possess a broad full width at half-maximum of ∼126 nm. The maximum value calculated stimulated emission cross-section and the measured lifetime of ³H₄ level from the 1.47-μm transition are ∼4.73 × 10⁻²¹ cm² and ∼0.239 ms, respectively. It is noticed that codoping of Ho³⁺ could significantly enhanced the ratio of the intensity of 1.47–1.80 μm by energy transfer via Tm³⁺: ³F₄ → Ho³⁺: ⁵I₇.     

Laser spectroscopy of Nd3+-doped PbO–Bi2O3–Ga2O3–BaO glasses

We present spectroscopic results of PbO–Bi₂O₃–Ga₂O₃–BaO glass doped with different concentration of Nd₂O₃. These glasses have high refractive index (∼2.4) and large spectral transmission window. Measurements of absorption, emission and fluorescence lifetime are presented. From the calculations of the Judd–Ofelt parameters the radiative lifetimes, branching ratios and quantum efficiency of ⁴F_3/2 level are calculated. The highest emission intensity was measured for the sample doped with 0.5 wt% of Nd₂O₃ with emission cross-section of 2.6 × 10⁻²⁰ cm², at 1069 nm, fluorescence lifetime of 110 μs, quantum efficiency of 82% and effective linewidth of 34 nm. The results point out this glass system as good candidate to be used in the development of photonic devices operating in the near infrared spectral range.     

Compositional effects on fluorescence lifetime of Dy3+ ions embedded in chalcogenide Ge–As–S glasses containing very small amount of Ga and CsBr

We have investigated the fluorescence lifetimes of Dy³⁺: 1.3 μm emission in the chalcogenide Ge–As–S glasses with different compositions but identically containing 0.5 mol% Ga and 0.5 mol% CsBr. The measured lifetimes turn out to be sensitive not only to the concentrations of Ga and CsBr but also to compositional variations in the Ge–As–S host glasses. The lifetime is enhanced conspicuously in glass of the S-sufficient compositions, relative to the stoichiometric GeS₂–As₂S₃ composition, while this effect is not significant in the S-exact and S-deficient compositions. We employ Ga K-edge EXAFS analysis to support that the local structural environments of Ga in the modified chalcogenide glasses are closely correlated with the lifetime enhancement effect.     

Er3+-doped germanate glasses for active waveguides prepared by Ag+/K+ ↔ Na+ ion-exchange

Planar waveguides were prepared by Ag⁺/K⁺ ? Na⁺ ion-exchange on Er⁺³-doped GeO₂–ZnO–Na₂O–Li₂O glasses obtained by a melting–casting method. Optical parameters of the waveguides were measured at 543.5, 632.8, and 1550 nm by m-line technique as a function of the Ag⁺ ion-exchange time. The optimized planar waveguides show an effective diffusion depth (d) of 2.95 μm and well confined propagating TE₀ and TM₀ modes at 1550 nm. Spectroscopic properties as photoluminescence emission and emission decay time were evaluated for the erbium-doped planar waveguide, indicating that Ag⁺ ? Na⁺ ion-exchange enhance the photoluminescence emissions in the green and infrared regions from erbium ions. The glass system studied is promising to be applied as optical amplifiers in the C-telecom band. Green emission sensitized by Ag⁺ was also observed.     

Novel Bi-doped glasses for broadband optical amplification

Broadband infrared luminescence is observed in various Bi-doped oxide glasses prepared by conventional melting-quenching technique. The absorption spectrum of the Bi-doped germanium oxide glass consists of five broad peaks at below 370, 500, 700, 800 and 1000 nm. The fluorescence spectrum exhibits a broad peak at about 1300 nm with full width at half maximum (FWHM) of more than 300 nm when excited by an 808 nm laser diode. The fluorescence lifetime at room temperature decreases with increasing Bi₂O₃ concentration. Influence of the glass composition and melting atmosphere on the fluorescence lifetime and luminescent intensity is investigated. The mechanism of the broadband infrared luminescence is suggested. The product of stimulated emission cross-section and lifetime of the Bi-doped aluminophosphate glass is about 5.0 × 10^?24 cm² s. The glasses might be promising for applications in broadband optical fiber amplifiers and tunable lasers.     

Fabrication of inorganic–organic hybrid films for optical waveguide

Inorganic–organic hybrid guiding and buffer layers for optical waveguides were synthesized by the sol–gel process. An acid-catalyzed solution of 3-(trimethoxysilyl)propylmethacrylate and tetraethylorthosilicate was used as a precursor to produce thick films by spin-coating. Incorporation of a UV-sensitive functional group leads to the fabrication of the photo-patternable guiding layer. High-resolution patterned films with 8 μm linewidth were obtained using a conventional photo-lithography. Furthermore, the amount of phenyltrimethoxysilane added as a refractive index modifier varied in order to control the refractive index of the underlying buffer layer. The refractive index variations and structural changes of these inorganic–organic hybrid films as a function of the processing conditions were analyzed using the prism coupling technique and a Fourier transform infrared spectrometer. We have produced optically transparent films at above 500 nm with a propagation loss of 0.84 and 1.49 dB/cm at 1310 and 1550 nm, respectively.     

Influence of TiO2 on proton conductivity in fuel cell electrolytes based on sol–gel derived P2O5–SiO2 glasses

P₂O₅–TiO₂–SiO₂ based glasses have been prepared by a sol–gel process. The glasses were characterized by structural, thermal, nitrogen adsorption–desorption and conductivity measurements. The structural formation has been confirmed by the FTIR and NMR analysis. The proton conductivity of the glasses increased linearly with increase in temperature. Glasses with an average pore size less than 2 nm showed higher values of proton conductivity in humid atmosphere. The conductivity value increased from 6.47 × 10⁻⁴ S/cm to 3.04 × 10⁻² S/cm at 70% RH in the temperature range 30–90 °C. We observed in fuel cell measurements that the performance of the E1 electrode is superior to that of the other electrodes at the same operating condition. The power density shows a similar pattern to current density.     

Blue,green and red upconversions in Ho2O3-doped fluorophosphate glasses

Near infrared (NIR) to visible upconversions of a fluorophosphate glass of composition (mol%) 7Ba(PO₃)₂–32AlF₃–30CaF₂–18SrF₂–13MgF₂ doped with various concentrations (0.1, 0.3 and 1.0 mol%) of Ho₂O₃ have been investigated by exciting at 892 nm at room temperature. Three upconverted bands originated from the ⁵F₃ → ⁵I₈, (⁵S₂, ⁵F₄) → ⁵I₈ and ⁵F₅ → ⁵I₈ transitions have been found to center at 491 nm (blue), 543 nm (green) and 658 nm (red), respectively. These bands have been justified from the evaluation of the absorption, normal (down conversion) fluorescence and excitation spectra. The upconversion processes have been interpreted by the excited state absorption (ESA), energy transfer (ET) and cross relaxation (CR) mechanisms involving population of the metastable (storage) energy levels by multiphonon deexcitation effect. It is evident from the infrared reflection spectral (IRRS) analysis that the upconversion phenomena are expedited by the low multiphonon relaxation rate in fluorophophate glasses owing to their high intense low phonon energy of ∼600 cm⁻¹ which is very close to that of fluoride glasses (500–600 cm⁻¹).     

Broadband near-infrared emission from Bi–Er–Tm Co-doped germanate glasses

Bi–Er–Tm co-doped germanate glasses and Bi, Er, Tm singly doped glasses were prepared and characterized through absorption spectra, NIR emission spectra and decay lifetime. A super broadband near-infrared emission from 1000 nm to 1600 nm, covering the whole O, E, S, C, and L bands, was observed in the Bi–Er–Tm co-doped samples due to the result of the overlapping of the Bi related emission band (centered at 1300 nm), the emission from Er^{3+ 4}I_13/2 → ⁴I_15/2 transition (centered at 1534 nm) as well as the emission from Tm^{3+ 3}H₄ → ³F₄ transition (centered at 1440 nm), which is essential for broadly tunable laser sources and broadband optical amplifiers. The energy transfer process was also discussed at the end of the paper.     

Enhanced 2.0 μm emission and energy transfer in Yb3+/Ho3+/Ce3+ triply doped tellurite glass

Ce³⁺ induced enhancement of Ho³⁺ ~ 2.0 μm emission in Yb³⁺/Ho³⁺ codoped sodium–zinc–tellurite (TNZ) glass was achieved under 980 nm LD laser excitation. The spectroscopic studies show that the upconversion is remarkably reduced by the presence of Ce³⁺. The ~ 2.0 μm fluorescence intensity is nearly triply enhanced, and the energy transfer efficiency from Yb³⁺ to Ho³⁺ is improved from 16.1% to 42.6% by increasing the Ce³⁺ concentration from 0 to 0.8 mol%. The mechanism responsible for the upconversion reduction and ~ 2.0 μm emission enhancement in Yb³⁺/Ho³⁺/Ce³⁺ triply-doped TNZ glass is also discussed. Our results indicate that the Yb³⁺/Ho³⁺/Ce³⁺ triply-doped TNZ glass is a promising candidate material for improving the Ho³⁺ 2.0 μm fiber laser performance.     

Optical properties and infrared-to-visible upconversion in Er3+-doped GeO2–Bi2O3 and GeO2–PbO–Bi2O3 glasses

Luminescence properties and upconversion studies of germanate glasses in ternary GeO₂–PbO–Bi₂O₃ and binary GeO₂–Bi₂O₃ systems containing Er₂O₃ (0.1–1.0 wt%) are presented for the first time. The Judd-Ofelt parameters found for these glasses are: Ω₂ = 4.50 × 10⁻²⁰ cm², Ω₄ = 1.55 × 10⁻²⁰ cm² and Ω₆ = 0.69 × 10⁻²⁰ cm² for binary glasses and Ω₂ = 4.44 × 10⁻²⁰ cm², Ω₄ = 1.82 × 10⁻²⁰ cm² and Ω₆ = 0.39 × 10⁻²⁰ cm² for ternary glasses. The refractive index of these glasses is found to be ∼2. The transition ⁴I_13/2 → ⁴I_15/2 is peaked at ∼1.53 μm and shows a radiative lifetime around 5 ms. Both systems exhibit similar emission cross-section at 1.53 μm around 0.8 × 10⁻²⁰ cm². Upconverted green emission at ∼530 nm (²H_11/2 → ⁴I_15/2) and ∼550 nm (⁴S_3/2 → ⁴I_15/2) and red emission at ∼668 nm (⁴F_9/2 → ⁴I_15/2) are observed under 980 nm cw excitation. Our results suggest that these glasses are promising candidates for applications in photonics.     

Tm-doped aluminate glass fibers for S-band optical amplification

Thulium-doped fiber amplifiers (TDFAs) have been proposed as practical devices for the amplification of light signals in the so-called S-band (1460–1530 nm) of the transparency window of standard telecommunications fiber. As the quantum efficiency of the desired ³H₄ → ³F₄ luminescence of Tm³⁺ is adversely affected by non-radiative decay when high maximum phonon energy (MPE) host glasses are used, a practical TDFA requires an active fiber made from a glass with intermediate to low MPE. We have explored the possibility of using aluminate fibers for this application, as bulk samples of Tm-doped alkaline earth aluminate glass are characterized by a MPE of 780 cm⁻¹ and a quantum efficiency for the 1460 nm fluorescence of ∼35%. Despite the high devitrification tendency of aluminate glass, pure aluminate core fibers with minimum losses of ∼0.5 dB/m have been successfully fabricated by the rod-in-tube technique using viscosity- and expansion-matched alkaline earth aluminosilicate cladding glasses.