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A new TeO2-Ga2O3-BaO (TGB) glass system has been explored to achieve high-efficient luminescence at 2 μm region. The glasses are characterized by wide infrared transmittance range, excellent thermal stability, high density and refractive index, and low maximum phonon energy. Judd-Ofelt analysis reveals high spontaneous emission probabilities of Tm3+ and Ho3+ in this glass host. As a result, intense emissions near 1.8 and 2 μm were realized in the Tm3+-doped and Nd3+/Ho3+ co-doped TGB glasses, respectively. The emission cross-sections of Tm3+ and Ho3+ are 1.024 × 10−20 cm2 and 0.829 × 10−20 cm2 with maximum gain coefficients of 4.51 and 1.55 cm−1, respectively. The combined results indicate that the TGB glass system is a potential host for obtaining high-efficient 2 μm luminescence.

Despite great advances in glass science and technology, the debate on the predominant feature of the glass structural model, especially the structure-property relationship, has lasted for more than half a century. Recently, the phase diagram approach has shown to be an effective method for investigating the physical properties of glass but it is restricted to the binary glass systems. Herein, the phase diagram approach was popularized to a series of ternary glass systems with a quantitative prediction of their structure and physical properties, including the density, refractive index, thermal expansion coefficient, elastic modulus and shear modulus. Furthermore, the structure-property relationship of ternary glass and the borate anomaly are reasonably described via the phase diagram approach. Detailed error analysis for the predicted results is also performed. The good agreement between the calculated results and experimental data indicates that the phase diagram approach is a promising method for investigating the structure and physical properties of glasses, providing a novel insight into the study of glass science and technology.

We report our experimental and numerical results on the chaotic dynamics of a ball bouncing on a vertically vibrating plate. It is demonstrated that if the trajectories between collisions are classified according to the rescaled flight time, the chaotic attractor for the bouncing motion of the ball degrades into a regular structure composed of discrete energy levels in the phase space, and the motion states corresponding to these trajectories evolve into separate “microstates” populated on these levels. The probabilities of level transitions and the selection rules for the transitions are discussed. Then, the probability distribution of the energy dissipated during each collision is analyzed. It is found that there are discrete dissipation peaks in the energy dissipation spectrum. The origination of these dissipation peaks is analyzed from the perspective of level transitions.

Sodium and potassium germanate glasses and their corresponding crystals are investigated by X-ray diffraction, Raman spectroscopy, and Fourier transforms infrared spectroscopy. Highly coordinated species of Ge are found in germanate glass. In the K2O-GeO2 glass system, three Ge structural units (4-, 5-, and 6-fold) coexist in the glass structure when the content of K2O ranges between 11 and 20 mol%, while only two Ge species (4- and 6-fold) are left with a further increase of K2O content. It is interesting to note that K2O·8GeO2 crystal, which is prepared by the solid state sintering method or crystallized from potassium germanate glass (K2O

In this study, we have researched the internal behavior in segmented proton exchange membrane fuel cells (PEMFCs) with three different flow fields during cold start process. The change of internal current density and temperature in fuel cells with different flow fields could be obviously shown by the printed circuit board (PCB) technology, and the study shows that the flow field is significant for enhancing the cold start ability and durability. Single serpentine flow field has the best cold start performance, while triple channel serpentine flow field has the best uniformity. It is found that without a robust temperature rising tendency, the cell temperature reaching 0 °C does not definitely mean a successful cold start because the cell temperature might drop down 0 °C again. Polarization curves show that there is almost no performance degradation after successful cold start, but the cell degrades quickly after the failed cold start at −7 °C and −10 °C. Based on these characteristics, we optimized the rapid cold start strategy by using electric heating and make it possible to start up the PEMFC at temperatures down to −20 °C within about 11 min.

This study presents the design and principle of a current-pulsed power supply (CPPS) for the tearing mode (TM) feedback control of the J-TEXT tokamak. CPPS is a new method of stabilizing large magnetic islands and accelerating mode rotation through the use of modulated magnetic perturbation. In this application, continuous magnetic perturbation pulse trains with frequency of 1 kHz to kHz, amplitude of 0.25 G, and duty ratio of 20%–50% are required generating via in-vessel magnetic coils. A modified topology based on buck chopper is raised to satisfy the demands of inductive load. This modified topology is characterized by high frequency, rapid rising and falling edges, and large amplitude of current pulses. Appropriate RCD snubber circuit is applied to protect the Insulated Gate Bipolar Transistor (IGBT) switch device. Equipment with peak current that reaches 1 kA, frequency that ranges from 1 kHz to 3 kHz, and rising and falling time within 100 μs was constructed and applied to physical experiment.

Glass has become an indispensable and essential material with broad applications ranging from household appliances to building materials, photovoltaic cells, optical communications, and others. However, one of the major stumbling blocks to its optimal use is that the structure-property relationship has not been thoroughly characterized in the past few decades. In this paper, we present a method to predict the physical properties, including the density, refractive index, thermal expansion coefficient, elastic modulus and shear modulus, of a series of oxide and non-oxide glass systems via the phase diagram approach. The good agreement of the predicted values with experimental data shows that the phase diagram approach is useful and widely applicable for forecasting a variety of physical properties of glasses. Furthermore, compositions in the borate, germanate, and chalcogenide glass systems with anomalistic properties are carefully investigated and analyzed. Our results demonstrate that the phase diagram approach is an effective method for investigating the physical properties of glass, guiding the theoretical research and practical applications.

Tensile yield strength of extruded Mg–5.3Zn–0.5Ca–0.5Ce/La (weight percent) alloy is remarkably increased to 316 MPa from 163 MPa, via the warm rolling process. The tension twinning can be activated after low-strain (5–21%) rolling, and the dynamic recrystallization occurs with increasing rolling reduction. The dislocations are gradually accumulated within the original grains during the rolling, and the number fraction of low angle grain boundary is increased. The coarse secondary phases are gradually broken into small pieces, due to the increased rolling deformation. The weak fiber texture with 10 1 0 parallel to extrusion direction in the extruded alloy is modified to the typical 0002 10 1 0 texture after rolling, and the yield strength is notably improved, because of the multiple strengthening effects (grain refinement, work hardening, dispersion and texture). A good balance between strength (> 310 MPa) and ductility (~ 9.5%), has been achieved through the warm rolling.

Electron cyclotron extraordinary-wave decay into two upper hybrid waves in an inhomogeneous magnetized plasma is studied theoretically and numerically. The analytic expressions for the local coupling constant and convective amplification factor of two-plasmon decay (TPD) are obtained. It shows that the TPD threshold intensity is very high (about 15 MW) with the linear density profile in a tokamak plasma. However, within the nonmonotonicity density profile, the power threshold of TPD can significantly be reduced more than one order of magnitude (about 1.2MW). The comparison of the numerical and simulation results of the local coupling constant shows that they agree well with each other.

Recent J-TEXT research has highlighted the significance of the role that non-axisymmetric magnetic perturbations, so called three-dimensional (3D) magnetic perturbation (MP) fields, play in a fundamentally 2D concept, i.e. tokamaks. This paper presents the J-TEXT results achieved over the last two years, especially on the impacts of 3D MP fields on magnetohydrodynamic instabilities, plasma disruptions and plasma turbulence transport. On J-TEXT, the resonant MP (RMP) system, capable of providing either a static or a high frequency (up to 8 kHz) rotating RMP field, has been upgraded by adding a new set of 12 in-vessel saddle coils. The shattered pellet injection system was built in J-TEXT in the spring of 2018. The new capabilities advance J-TEXT to be at the forefront of international magnetic fusion facilities, allowing flexible study of 3D effects and disruption mitigation in a tokamak. The fast rotating RMP field has been successfully applied for avoidance of mode locking and the prevention of plasma disruption. A new control strategy, which applies pulsed RMP to the tearing mode only during the accelerating phase region, was proved by nonlinear numerical modelling to be efficient in accelerating mode rotation and even completely suppresses the mode. Remarkably, the rotating tearing mode was completely suppressed by the electrode biasing. The impacts of 3D magnetic topology on the turbulence has been investigated on J-TEXT. It is found that the fluctuations of electron density, electron temperature and plasma potential can be significantly modulated by the island structure, and a larger fluctuation level appears at the X-point of islands. The suppression of runaway electrons during disruptions is essential to the operation of ITER, and it has been reached by utilizing the 3D magnetic perturbations on J-TEXT. This may provide an alternative mechanism of runaway suppression for large-scale tokamaks and ITER.

Numerical instability occurs when coupled Maxwell equations and nonlinear two-fluid plasma equations are solved using finite difference method through parallel algorithm. Thus, a perfectly matched layer (PML) boundary condition is set to avoid the instability caused by velocity and density gradients between vacuum and plasma. A splitting method is used to first decompose governing equations to time-dependent nonlinear and linear equations. Then, a proper complex variable is used for the spatial derivative terms of the time-dependent nonlinear equation. Finally, with several auxiliary function equations, the governing equations of the absorbing boundary condition are derived by rewriting the frequency domain PML in the original physical space and time coordinates. Numerical examples in one- and two-dimensional domains show that the PML boundary condition is valid and effective. PML stability depends on the absorbing coefficient and thickness of absorbing layers.

The J-TEXT tokamak has been operated for ten years since its first plasma obtained at the end of 2007. The diagnostics development and main modulation systems, i.e. resonant magnetic perturbation (RMP) systems and massive gas injection (MGI) systems, will be introduced in this paper. Supported by these efforts, J-TEXT has contributed to research on several topics, especially on RMP physics and disruption mitigation. Both experimental and theoretical research show that RMP could lock, suppress or excite the tearing modes, depending on the RMP amplitude, frequency difference between RMP and rational surface rotation, and initial stabilities. The plasma rotation, particle transport and operation region are influenced by the RMP. Utilizing the MGI valves, disruptions have been mitigated with pure He, pure Ne, and a mixture of He and Ar (9:1). A significant runaway current plateau could be generated with moderate amounts of Ar injection. The RMP has been shown to suppress the generation of runaway current during disruptions.

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.

Orthogonal experiments of milling titanium alloy TA12 were done on the lifting workbench milling machine. The milling force signals were acquired through PIC-1712 Data Acquired Board. The main frequencies and energy distribution were got through analysis in SPTOOL of MATLAB. The signals were decomposed and reconstructed based on the main frequency of the milling force with wavelet toolbox. The influence of the milling velocity, axial depth of cut and radial depth of cut on the component milling force was got through range analysis. Through analyzing known that three factors had different influence on the component milling force.

Transparent glass-ceramics containing MF 2 (MF 3 ):Ho 3+ ,Tm 3+ (M = Ca, Ba, and La) nanocrystals have been prepared by melt quenching and subsequent thermal treatment. X-ray diffraction and transmission electron microscopy analysis confirmed the precipitation of MF 2 (MF 3 ) nanocrystals among the glass matrix. Energy-dispersive X-ray spectroscopy results evidenced the incorporation of Tm 3+ and Ho 3+ into the MF 2 nanocrystals. Intense 2.0 μm emission originating from the Ho 3+ : 5 I 7 → 5 I 8 transition was achieved upon excitation with 808 nm laser diode. A large ratio of the forward Tm 3+ → Ho 3+ energy transfer constant to that of the backward process indicated high efficient energy transfer from Tm 3+ ( 3 F 4 ) to Ho 3+ ( 5 I 7 ), and benefited from the reduced ionic distances of Tm 3+ –Tm 3+ and Tm 3+ –Ho 3+ pairs and low phonon energy environment with the incorporation of rare earth ions into the precipitated MF 2 nanocrystals. The results indicate that oxyfluoride glass-ceramic is a promising candidate for 2.0 μm laser.

Nanocrystalline (NC) metals and alloys always exhibit extremely high strength but quite limited ductility. This disappointing ductility might be caused by the preparation artifacts and the weak strain hardening ability of NC materials. In order to optimize the mechanical properties of NC metals and alloys , especially to enhance their ductility, and investigate the underlying deformation mechanism, nanocrystalline Ni, dual phase Ni-Co alloy and Cu were synthesized via electrodeposition and electro-brush deposition respectively, and then a series of mechanical tests were carried out. The results show that all the materials exhibit a combination of high strength and remarkable ductility. The high strength can be attributed to the “true” nanocrystalline grain sizes ranges from 15 to 30 nm. In addition, three factors are revealed to contribute to the enhanced ductility of these materials, respectively: (a) modified deformation mode (the tensile-relaxation cycle test) for nanocrystalline Ni, (b) high strain hardening and cooperative deformation for dual-phase Ni-Co alloy, and (c) high strain rate sensitivity for nanocrystalline Cu.

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.

Disruptions have the possibility of causing severe wall damage to large tokamaks like ITER. The mitigation of disruption damage is essential to the safe operation of a large-scale tokamak. The shattered pellet injection (SPI) technique, which is regarded as the primary injection method for ITER, presents several advantages relative to massive gas injection, including more rapid particle delivery, higher total particle assimilation, and more centrally peaked particle deposition. A dedicated argon SPI system that focuses on disruption mitigation and runaway current dissipation has been designed for the Joint Texas Experimental Tokamak (J-TEXT). A refrigerator is used to form a single argon pellet at around 64 K. The pellet will be shaped with a 5 mm diameter and a 1.5-10 mm length. Helium gas at room temperature will be used as a propellant gas for pellet acceleration. The pellet can be injected with a speed of 150-300 m/s. The time interval between injection cycles is about 8 min. The pellet will be shattered at the edge of the plasma and then injected into the core of plasma. The first experiments of SPI fast shutdown and runaway current dissipation have been performed.

Disruptions have the potential to cause severe damage to large tokamaks like ITER. The mitigation of disruption damage is one of the essential issues for the tokamak. Massive gas injection (MGI) is a technique in which large amounts of a noble gas are injected into the plasma in order to safely radiate the plasma energy evenly over the entire plasma-facing wall. However, the radiated energy during the disruption triggered by massive gas injection is found to be toroidally asymmetric. In order to investigate the spatial and temporal structures of the radiation asymmetry, the radiated power diagnostics for the J-TEXT tokamak have been upgraded. The multi-channel arrays of absolute extreme ultraviolet photodiodes have been upgraded at four different toroidal positions to investigate the radiation asymmetries during massive gas injection. It is found that the toroidal asymmetry is associated with plasma properties and MGI induced MHD activities.

The spectroscopic properties of Er3+-doped Sb2O3–B2O3 glass have been investigated for developing 1.55-μm broadband fiber amplifiers and tunable lasers. A broad 1.55-μm near infrared emission peaked at 1527 nm with a full width at half maximum (FWHM) of 91 nm has been obtained for 30Sb2O3–69B2O3–1Er2O2 glass upon excitation of a 980 nm laser diode. This broad luminescence locates in the region of 1440–1650 nm and covers the S, C and L bands. The emission cross-section of the 4I13/2→4I15/2 transition of Er3+ ions and the measured lifetime of the 4I13/2 level of Er3+ ions are 6.01×10−21 cm2 and 0.341 ms, respectively. Based on the electronic polarizability of the oxide ion and optical basicity estimated from the values of refractive index and molar volumes, the covalent bonding character in the local ligand environments around Er3+ in Sb2O3–B2O3 glasses increases with increasing Sb2O3 content. It is noted that the product of the emission cross-section and the FWHM of the glass, σe×FWHM, is as great as 567×10−28 cm3, which is comparable or higher than that of Er3+-doped tellurite- and germanate-based glasses.

This paper reports on cooperative energy transfer and upconversion luminescence properties of Tb3+/Yb3+- and Nd3+/Yb3+/Tb3+-codoped oxyfluoride glasses. Upon excitation with a 980 nm laser diode, an intense green upconversion luminescence along with weak ultraviolet (UV)–visible emissions has been observed in Yb3+/Tb3+-codoped oxyfluoride glasses. Power dependence of UV–visible upconversion luminescence intensity has been examined, revealing that a cooperative energy transfer mechanism from Yb3+ ions is responsible for the excitation of Tb3+ ions. Meanwhile, it is noticed that Tb3+ upconversion emission bands have also been clearly detected at 487, 542, 587 and 620 nm in Nd3+/Yb3+/Tb3+-codoped oxyfluoride glasses upon excitation with a 808 nm laser diode. The quadratic dependence of the upconversion luminescence on the pump-laser power indicates two-photon process for the population of Tb3+:5D4 state via Nd3+→Yb3+→Tb3+ energy transfer. However, no emission has been observed in the oxyfluoride glasses codoped with Yb3+/Tb3+ or Nd3+/Tb3+, respectively, upon excited at a 808 nm laser diode. A proposed upconversion mechanism involving energy transfer from Nd3+ to Yb3+, and then a cooperative energy transfer process from two excited Yb3+ to Tb3+ has been presented.

This paper reports on the optical spectroscopic properties and thermal stability of Er3+-doped antimony-borosilicate glasses for developing 1.5 microm optical amplifiers. Upon excitation at 980 nm laser diode, an intense 1.5 microm infrared fluorescence has been observed with the maximum full width at half maximum (FWHM) of 90 nm for Er3+-doped antimony-borosilicate glasses. The emission cross-section and the lifetime of the 4I13/2 level of Er3+ ions are 6.3 x 10(-21) cm2 and 0.30 ms, respectively. It is noted that the product of the emission cross-section and FWHM of the glass studied is as great as 567 x 10(-21) cm2 nm, which is comparable or higher than that of bismuthate and tellurite glasses.

This paper reports on frequency upconversion emission properties of Tm 3+ /Yb 3+ - and Ho 3+ /Yb 3+ -codoped Ga 2 O 3 –GeO 2 –Bi 2 O 3 –PbO glass upon excitation of 980 nm laser diode. The dependence of the upconversion emission intensity upon the excitation power has been examined and the involved mechanisms have also been discussed. An intense blue emission at 476 nm and two weak red emissions at 650 and 689 nm have clearly been observed in Tm 3+ /Yb 3+ -codoped samples, which are assigned to the 1 G 4 → 3 H 6 , 1 G 4 → 3 F 4 and 3 F 2,3 → 3 H 6 transitions of Tm 3+ ions. The cube-like dependence of the 476 and 650 nm emissions on the incident pump laser power, indicates three-photon contribute to the blue–red upconversion emissions, respectively. Meanwhile intense green and red emissions peaked at 545 and 660 nm in Ho 3+ /Yb 3+ -codoped samples, which are ascribed to the transitions of ( 5 F 4 , 5 S 2 ) → 5 I 8 and 5 F 5 → 5 I 8 transitions of Ho 3+ , have been confirmed that two photons contribute to these upconversion processes. The observed upconversion emission intensity as function of Yb 3+ concentration suggests that the presence of the Yb 2 O 3 plays a major role in enhancing the upconversion emission efficiency.

Er3+-doped tellurite glasses TeO2–GeO2–Nb2O5–Na2O–K2O–ZnO have been investigated for developing 1.5-μm fiber and planar amplifiers. Effects of GeO2 and Nb2O5 on the thermal stability and optical properties of Er3+-doped tellurite glasses have been discussed. It is noted that the incorporation of GeO2 or Nb2O5 increases the thermal stability of tellurite glasses significantly. Er3+-doped GeO2- and Nb2O5-modified tellurite glasses exhibit the stimulated emission cross-section as great as 10.7 × 10−21 cm2, which is significantly higher than that of silicate and phosphate glasses. In addition, the intensity of upconversion luminescence of the Er3+-doped GeO2- and Nb2O5-modified tellurite glasses decreased clearly with increasing GeO2 or Nb2O5 content. As a result, Er3+-doped tellurite glasses might be a potential candidate for developing laser or optical amplifier devices.

We investigate the spectroscopic properties of the 1.5-microm emission from the (4)I(13/2)--(4)I(15/2) transition of Er(3+) ions in bismuth-germanate-lead glasses for applications in broadband fiber amplifiers. The emission peak locates at 1532nm with a full width at half-maximum (FWHM) of approximately 65nm. The measured lifetime and the calculated emission cross-section of this transition are 3.3ms and 8.66x10(-21)cm(2), respectively. IR-to-green-upconversion occurs simultaneously upon excitation of the 1.5-microm emission with a commercially available 980nm laser diode. Effects of PbF(2) content on the thermal stability, structure and spectroscopic properties of Er(3+)-doped bismuth-germanate-lead glasses have been examined. We find that the substitution with PbF(2) provides a couple of potentials: shortening the UV cutoff band and decreasing the phonon energy of host glasses. Codoping of Yb(3+) significantly enhances both the green-upconversion and 1.5-microm emission intensity by means of a nonradiative Yb(3+)--Er(3+) energy transfer. Energy transfer processes and nonradiative phonon-assisted decays could account for the population of the (2)H(11/2) level, which is an emitting level of the green-upconversion of Er(3+). The results indicate the possibility towards the development of bismuth-germanate-lead based glasses as photonics devices.

This paper reports on the spectroscopic properties and energy transfer in Ga 2 O 3 –Bi 2 O 3 –PbO–GeO 2 glasses doped with Tm 3+ and/or Ho 3+ . From the optical absorption spectra of Tm 3+ , 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 Δ T = 129 °C. The measured luminescence spectra show that the 3 H 4 → 3 F 4 transition of Tm 3+ 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 3 H 4 level from the 1.47-μm transition are ∼4.73 × 10 −21 cm 2 and ∼0.239 ms, respectively. It is noticed that codoping of Ho 3+ could significantly enhanced the ratio of the intensity of 1.47–1.80 μm by energy transfer via Tm 3+ : 3 F 4 → Ho 3+ : 5 I 7 .

We report on 2.0-microm emission characteristic and energy transfer of Ho3+-doped tellurite glass sensitized by Tm3+ upon excitation of a conventional 808 nm laser diode. The Judd-Ofelt strength parameters, spontaneous radiative transition probabilities and radiative lifetime of Ho3+ have been calculated from the absorption spectra by using the Judd-Ofelt theory. Significant enhancement of 2.0-microm emission of Ho3+ has been observed with increasing Tm3+ doping up to 0.7 mol%. The energy transfer coefficient of the forward Tm3+--Ho3+ is approximately 17 times larger than that of the backward Tm3+--Ho3+ energy transfer. Our result indicates that the maximum gain of 2.0-microm emission, assigned to the transition of (5)I7--(5)I8 of Ho3+, might be achieved from the tellurite glass at the concentration of 0.5 mol% of Tm2O3 and 0.15 mol% of Ho2O3. The high gain coefficient and quantum efficiency (1.16) along with the large value of the product of the stimulated emission cross-section and the measured radiative lifetime (4.12 x 10(-27) m(2)s) of the Ho3+/Tm3+-codoped tellurite glasses might find potential applications in efficient 2.0-microm laser.

Yb is a good candidate as a pump source because there are only two manifolds in the Yb energy level scheme, the F7/2 ground state and the F5/2 excited state, and thus concentration quenching and excited-state absorption should not affect the lasing or the excitation wavelength [1]. Extensive investigations have been of Yb-doped glasses, fibers, and crystals [2–5]. The relatively long fluorescence lifetime, as well as the broad absorption and emission bands, is more prominent for Yb-doped glasses than for crystals, making the glasses attractive for diode-pumped generation of ultra-short pulses, high-power ultra-short pulse amplification and tunable laser sources [6]. In addition, the ability to achieve high concentrations of Yb ions and low loss also triggered the rapid development of various Yb-doped glasses such as phosphate, borate, and silicate glasses. However, up to now, there are few systematic investigations of the optical properties of Yb-doped germanate glasses. In this work, the spectroscopic properties of germanate glasses with different concentrations of Yb ions and different thicknesses were investigated. Glasses with compositions (mol%) 10Na2O–60GeO2– 30PbO–xYb2O3 (x = 0.2, 0.6, 1.0, 1.4, and 2.0) were prepared using regent-grade powders Na2CO3, Pb3O4, and high purity GeO2 (>99.999%). Yb 3+ was introduced as Yb2O3 with 99.9% purity. Batches of 20 g were well mixed in appropriate proportions and melted at 1050 C in a covered alumina crucible in a SiC-resistance electric furnace. The liquids were held for 15 min and the homogenous bubble-free melts were cast on a stainless plate preheated at about 150 C. The samples were well annealed in a muffle furnace to reduce thermal stress. The annealed samples were cut using a low-speed diamond saw and polished with 5 lm diamond paste. Plates of dimensions 20 mm · 10 mm · 2 mm with two polished faces were used for optical measurements. The refractive index of the studied glass was measured using the Brewster angle method. The density of the sample was measured using the Archimedes’ liquidimmersion method on an analytical balance with a precision of 0.0001 g. Absorption spectra of the glass sample were recorded with a Perkin-Elmer-Lambda 900UV/VIS/NIR spectrophotometer in the range 850–1100 nm. Fluorescence measurements were performed with a 940 nm diode laser excitation and detected by a TRIAX550 spectrophotometer controlled by a computer. The infrared fluorescence lifetime was determined by modulating the pump laser diode drive current with a square-pulse duration of 40 ms at a repetition of 10 Hz. All the measurements were performed at room temperature. The important spectroscopic parameters required include the effective emission and absorption cross sections of the F5/2 fi F7/2 transition and the upper laser level lifetimes of Yb. The emission cross section can be determined by either the method of reciprocity or the Fuchtbauer–Ladenburg formula. On the basis of the reciprocity method described by McCumber [7], the emission cross section, remi can be calculated from the measured absorption cross section, rabs, i.e.

This paper investigated on the dehydration of Er 3+ -doped phosphate glasses using O 2 + CCl 4 bubble flow method. The influence of parameters of dehydration effect was studied systemically. It was found that the dehydration rate was rather rapidly at the initial stage of bubbling. Increasing gas flow rate and temperature could drive the dehydration process toward lower OH concentration in the melts. The dehydration process was carried out in open system and analyzed by thermodynamic theory of open system, which clarified the process of eliminating of OH groups from the glass melts with bubbling time and gas flow rate. A time-dependent empirical equation about reaction rate constant was derived, and the relationships between rate constant and bubbling flow rate, and temperature were also discussed. This analytical method could be applicable to the dehydration of glass melt using other dehydration agents.

We report on the blue-green-red up-conversion spectroscopic properties of Pr 3+ /Yb 3+ -codoped oxyhalide tellurite glasses upon excitation of a conventional 980 nm laser diode (LD). Significant enhancement of the blue-green-red up-conversion emission intensity has been observed with increasing PbCl 2 doping. The up-conversion intensity has a quadratic dependence on incident pump laser power, indicating a two-photon process. The population of the Pr 3+ upper 3 P 0 emitting level was accomplished through a combination of a ground state absorption, energy transfer and excitated state absorption. 1.3-μm emission in the second telecom window originated from Pr 3+ : 1 G 4 → 3 H 5 transition has also been investigated upon excitation at 980 nm LD. The measured peak wavelength and full width at half-maximum of the fluorescent are 1335 nm and ∼100 nm, respectively. An enhanced 1.3μm emission with increasing PbCl 2 doping has also been observed. Codoping of Yb 3+ significantly enhance both the blue-green-red up-conversion emission and 1.3-μm emission intensity by way of a nonradiative Yb 3+ : 2 F 5 →Pr 3+ : 1 G 4 energy transfer.