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Bismuth telluride (Bi2Te3) has attracted much attention in the field of thermoelectrics since it is one kind of commercial room-temperature thermoelectric material. Herein three kinds of Bi2Te3 thermoelectric fibers with internal tensile stress are fabricated utilizing an optical fiber template method. The effects of internal stress on the microstructure and the electrical transportation of Bi2Te3 thermoelectric fibers are investigated. The Bi2Te3 cores in the fibers are highly crystalline and possess a tensile nanosheet structure with preferential orientation as evidenced by X-ray diffraction and Raman studies. Tensile stress can enhance electrical properties of the fibers. And a paper cup generator covered with 20 pieces of optimized fibers provides a μW-level output power. It is inferred that tensile stress tuning can be an effective tool for the material optimization of thermoelectric performance.

Er3+ has been considered one of the most suitable sensitive ions of Ho3+ to generate 2 μm emission. In this work, luminescent properties and energy transfer mechanism of Er3+/Ho3+ co-doped lead silicate glass were systematically investigated under 980 and 1550 nm excitations, respectively. Based on the absorption spectra, the Judd-Ofelt intensity parameters, absorption and emission cross sections, and gain coefficient were calculated. The emission cross section of Ho3+: 5I7 → 5I8 transition is as large as 8 × 10−21 cm2. And the calculated maximum gain coefficient is 3.48 cm−1 at 2010 nm. In addition, the energy transfer efficiency between Er3+: 4I13/2 level and Ho3+: 5I7 level can reach 89.3% when the samples were pumped by a 980 nm laser diode. An intense 2 μm emission was obtained upon excitation of 1550 nm due to the large absorption cross section of Er3+ at 1550 nm and efficient energy transfer from Er3+: 4I13/2 level to Ho3+: 5I7 level. These results suggest that the Er3+/Ho3+ co-doped lead silicate glass has great potential for application as a mid-infrared laser material.

In this work, strong yellow emission was obtained in Dy3+ doped multi-component phosphate glass due to its high asymmetry and covalency of the local field and high phonon energy. The internal quantum efficiency was measured to be 39.27% and the figure of merit was calculated to be 210.53 pm2 × μs. What is more, silicate-clad Dy3+ doped multi-component phosphate core glass fiber was successfully drawn by using a rod-in-tube method, which has a strong fluorescence emission in yellow spectra band. The Dy3+ doping concentration is 2.6 wt.%, which is much larger than that of Dy3+ doped (0.2 wt.%) ZBLAN fiber. These results suggest that the silicate-clad Dy3+ doped multi-component phosphate glass fibers are potential host matrices for yellow laser.

Tin selenide (SnSe) exhibits high thermoelectric (TE) performance, which is a promising TE candidate for thermal-electrical energy conversion. In this work, Sn-Se alloy core borosilicate glass-clad fibers with ∼94 μm core and ∼220 μm cladding in diameter were fabricated by a molten core drawing method. X-ray diffraction (XRD) showed the core to be highly crystalline and consist of SnSe and SnSe2 poly-crystal grains. Based on EPMA measurement, there exists an inter-diffusion process between the core and cladding ions during the fiber drawing. The Seebeck coefficient of the Sn-Se core is −151 μV/K. The electrical conductivity of the Sn-Se core is as high as 6.2 × 103 S/m, which is close to that of SnSe single crystals. The demonstration of fibers with TE core materials and the integration with the conventional fiber fabrication technique represents the first step in providing the building blocks for fiber-integrated TE devices.

In4Se3 exhibits high thermoelectric performance as a typical example of semiconductors, which is a promising thermoelectric candidate for energy conversion applications. Here, InSe alloy core thermoelectric fibers with glass cladding were fabricated by a reactive molten core drawing method. The as-drawn fiber core was found to be InSe crystals as evidenced by X-ray diffraction. The In4Se3 crystals were obtained in the fiber core by annealing the as-drawn fibers. The Seebeck coefficient of the In4Se3 core fibers (−347 μV/K) was enhanced by ∼85% compared with that of the as-drawn InSe core fibers (−189 μV/K). This work constitutes a proof-of-concept that thermoelectric materials can be incorporated into fibers, which have promising applications in fiber-based thermoelectric devices.

A new type of thermally sensitive fibers with an antimony selenide (Sb 2 Se 3 ) core and phosphate glass cladding is demonstrated. The fibers were fabricated by a molten core method and maintained overall diameters ranging from 250 to 800 μm and core diameters of 35–200 μm. A 2.8 cm long Sb 2 Se 3 core fiber, electrically contacted to external circuitry through fiber end facets, exhibited a four orders of magnitude change in conductivity after the whole fiber was heated from 25 to 195 °C. In addition, the fiber exhibited enhanced photoconductivity under illumination. These results indicate that Sb 2 Se 3 core multimaterial fibers have promising applications in temperature sensing, optical switches and photodetectors.

Highly rare earth ions (RE-ions) doping phosphate glass fiber makes it possible to obtain high gain and high output power per unit length. However, high concentrations of RE-ions will cause concentration quenching and crystallization during the conventional rod-in-tube fiber drawing process. In this work, highly Er 3 + /Yb 3 + co-doped multi-component phosphate glasses were prepared by the melt-quenching method. Through thorough investigation of 1.53 μm luminescent properties of the glasses, optimal RE-ions were ascertained. The Er 3 + and Yb 3 + doping concentrations reach as high as 13.77 × 10 20 and 2.295 × 10 20 ions/cm 3 , respectively. Then the silicate-clad highly Er 3 + /Yb 3 + co-doped phosphate core multimaterial fibers were successfully fabricated by a molten core method. The multimaterial fibers have a large refractive index difference and good interface between the phosphate glass core and silicate glass cladding. An intense 1.53 μm emission was obtained from the multimaterial fiber. The results indicate that the highly Er 3 + /Yb 3 + co-doped multimaterial fibers are promising in applications that require high gain and high power from a short piece of active optical fiber.

Yb3 +/Tm3 + co-doped fluorogermanate glasses have been prepared by the melt-quenching method. Their luminescent properties were investigated by absorption spectra, excitation and emission spectra, and dynamic luminescence decay curves. The energy transfer parameters were analyzed by the phonon sideband theory and the energy transfer mechanism between Yb3 + and Tm3 + was proposed. An efficient 1.8 μm luminescence with reduced up-conversion emission is achieved under excitation of 980 nm laser diode. It is found that the emission at 800 nm is the main path of energy loss in the up-conversion process and it can be lowered at a higher Tm3 + doping level. In addition, the forward energy transfer parameter from Yb3 + to Tm3 + is approximately two orders of magnitude greater than the backward one, supporting efficient 1.8 μm emission.

For the first time to the best of our knowledge phosphate glass-clad optical fibers comprising tellurium (Te) semiconductor core have been fabricated using a molten core approach. The cores were found to be highly crystalline and phase-pure as evidenced by X-ray diffraction (XRD) and corroborated by Micro-Raman spectrum. Elemental analysis across the core/clad interface suggests that there is some diffusion of oxygen and phosphorus into the core region and, conversely, diffusion of Te into the cladding region. Unfortunately, the propagation loss of the Te core fibers was too high to measure due to the significant scattering from the grain boundaries, oxygen and phosphor precipitates. However, the larger Raman gain, infrared and terahertz transparency of tellurium over silicon and germanium should make these fibers of significant value for fiber-based mid- to long-wave infrared, terahertz waveguides and Raman-shifted infrared light sources.

Elemental bismuth (Bi) exhibits a high magnetoresistance as a typical example of semimetal, which has significant application in information technologies. Silicate glass-clad Bi core fibers were fabricated by a molten core method and maintained core diameter of 100–150 µm and overall diameter of 300–450 µm. X-ray diffraction (XRD) and micro-Raman spectra showed the core to be highly crystalline with no observed secondary phases. Electro-probe micro-analyzer (EPMA) measurements confirmed a very well-defined core-clad interface. Demonstration of fibers with high magnetoresistance core materials and the potential integration with current state of the art technologies represents the first step in providing the building blocks for all-fiber sensors.

The competition between infrared down-conversion (DC) and visible up-conversion (UC) is systemically studied in Tm3 + and/or Yb3 +/Tm3 + co-doped fluoride modified germanate glasses. Based on the absorption spectra, the Judd–Ofelt intensity parameters, absorption and emission cross-sections, figure of merit (FOM), and saturated gain coefficient are calculated and analyzed. An intense 1.8 μm emission is obtained upon 808 nm laser diode (LD) excitation in Tm3 + doped samples, while an efficient 1.8 μm emission is observed by 980 nm LD in Yb3 +/Tm3 + co-doped samples, along with visible UC emissions. It is found that 3F4 state of Tm3 + can be easily populated and then further excited to higher excited states through Yb3 + upon 980 nm LD. Our results suggest that these Tm3 + doped fluoride modified germanate glasses are of great significance for searching efficient mid-infrared laser materials.

Enhanced 1.8 μm emission from Tm 3+ by Yb 3+ sensitization and bubbling in tungsten tellurite glasses has been demonstrated under the excitation of a 976 nm laser diode. Radiative properties such as spontaneous emission probabilities, radiative lifetimes and fluorescence branching ratios along with absorption and emission cross sections have been calculated from the absorption spectra. The influences of Yb 3+ concentration, Tm 3+ concentration, and bubbling time on spectroscopic properties have been thoroughly investigated. It is found that with increasing the bubbling time to 35 min, OH − content deceases sharply while 1.8 μm emission intensity improves greatly and 3 F 4 level lifetime prolongs to 1.57 ms close to radiative time. After 35 min, they change very little due to almost reaching the dynamic balance. The strength of interaction between Tm 3+ and OH − is determined. The energy transfer mechanism between Yb 3+ and Tm 3+ is proposed by photoemission spectroscopy and lifetime measurement. The energy transfer coefficients have been analyzed by the extended spectral overlap method and hopping model. Large ratio of the forward energy transfer from Yb 3+ to Tm 3+ to the backward one (223) and high energy transfer efficiency (97%) from Yb 3+ to Tm 3+ ensure efficient 1.8 μm emission. Hence, Yb 3+ sensitization and the reduction of OH − content could be expected to open up a possibility to achieve high efficient 2.0 μm lasing from Tm 3+ under a 976 nm LD pump.

Silicate glasses containing PbS quantum dots (QDs) with narrow size distribution were prepared through heat treatment. Transmission electron microscopy (TEM) results show that spherical PbS QDs are densely dispersed in the glassy matrix. Using ZnS–PbO to replace PbS as precursor of PbS QDs, the size distribution of PbS QDs in glasses becomes more uniform. Tunable infrared luminescence from 1100 to 2200 nm has been obtained by controlling the glassy matrix and preparation parameters. Obvious optical amplification at communication windows of 1.55 μm and 1.33 μm is probed, and the PbS QDs doped glasses using ZnS–PbO as precursor exhibit larger optical amplification. The PbS QDs doped glasses with intense optical amplification are considered to be promising candidate as gain medium for broadband fiber amplifier and tunable fiber laser.

Serious up-conversion process (UCPE) of Er3+ in Er3+/Yb3+ codoped tellurite glass is one of the big challenges impeding Er3+ doped tellurite fiber amplifier towards full commercialization, though its gain bandwidth is much wider than Er3+ doped silica fiber amplifier. For solving or suppressing UCPE, it has been proposed to better introduce a third foreign ion with proper layout of energy level into this system, and thus, modulate energy transfer between them. Three rare earth ions, RE3+=Ce3+, Dy3+, and Tb3+, are selected in this paper, and it turns out that three of them can efficiently reduce the transition probability of UCPE, and Ce3+ rather than Dy3+ and Tb3+ can at the same time enhance the 1.53 μm emission of Er3+ originating 4I13/2→4I15/2. The underlying mechanism will be discussed based on both experimental and theoretical results.

Spectroscopic properties and energy transfer (ET) in Bi2O3(PbO)–GeO2–Ga2O3 (BPGG) glass doped with Tm3+ and/or Tb3+ have been investigated. It is noted that the Tm3+ single-doped BPGG glass exhibits broad 1.47-μm fluorescence peaked at 1465 nm with a full width at half-maximum (FWHM) of ∼134 nm. The incorporation of Tb3+ into Tm3+-doped BPGG glass could significantly decrease the 1.80 μm emission intensity and enhance the intensity ratio of 1.47-μm to 1.80-μm (I1.47/I1.80), which reveals that Tb3+ ion can be considered to be an effective sensitizer ion on improving the 1.47-μm emission. The products of FWHM × σ e p e a k and τ f × σ e p e a k for the 1.47-μm fluorescence are in the range of 5.66–6.63 × 10−26 cm3 and 8.76–10.02 × 10−25 cm2 s. Effects of Bi2O3 substitution for PbO on spectroscopic properties, such as 1.47-μm emission of Tm3+, Judd–Ofelt intensity parameters Ωt (t = 2, 4, 6), and the lifetime of the 3H4 level of Tm3+, have also been investigated.

The leucite crystallization kinetics via kalsilite from the hydrothermally-derived precursor was investigated by XRD and non-isothermal DTA. The leucite precursor was prepared by hydrothermal method from silica sol, aluminum nitrate and potassium nitrate. The crystallization of the precursor experienced two steps. Kalsilite crystallized at first, and then it reacted with the redundant SiO2 in the precursor and finally the leucite formed. On the DTA curve, the two exothermic peaks were corresponding to the two times of crystallization. Determined by the Kissinger equation, the activation energy of kalsilite crystallization and leucite crystallization via kalsilite was 103(SD 8) kJ/mol and 125(SD 4) kJ/mol respectively and both the crystallizations were nucleation and three-dimensional growth, which follows the diffusion-controlled mechanism with increasing nucleation rate.

This paper reports on the successful preparation and a detailed study on the up-conversion properties of Er3+ -doped TeO2-ZnO-PbCl2 oxylialide tellurite glasses. Three intense emissions centered at around 527, 549 and 666 nm have been clearly observed under 977 nm excitation and the involved mechanisms have been explained. The green emissions centered at 527 and 549 nin are due to the H-2(11/2 ->) I-4(15/2) and S-4(3/2) -> I-4(15/2) transitions, and the red up-conversion emission centered at 666 nm is associated with the F-4(9/2) -> I-4(15/2) transitions of Er3+ ions, respectively. The quadratic dependence of fluorescence on excitation laser power confirm that two-photons contribute to up-conversion of the green-red emissions. (c) 2005 Elsevier B.V. All rights reserved.

Three Er3+-doped tellurite glasses with compositions of 70TeO(2)-30ZnO, 70TeO(2)-20ZnO-10Nb(2)O(5) and 70TeO(2)-20ZnO-5BaO-5Nb(2)O(5) have been investigated for developing fiber and planar broadband amplifiers and lasers. The optical spectroscopic properties and thermal stability of Er3+-doped tellurite glasses have been discussed. The results show that the incorporation of Nb2O5 increases the thermal stability of Er3+-doped tellurite glasses significantly, Er3+-doped niobium tellurite glasses 70TeO(2)-20ZnO-10Nb(2)O(5) and 70TeO(2)-20ZnO-5BaO-5Nb(2)O(5) exhibit the good thermal stability (DeltaT > 150degreesC), the large emission cross-section (>10 x 10(-21) cm(2)) and broad full width at half maximum (similar to65 nm), will be preferable for broadband Er3+-doped fiber amplifiers. (C) 2004 Elsevier B.V. All rights reserved.