Investigation of 2.0 μm emission in Tm and Ho co-doped oxyfluoride tellurite glass

This paper reports 2.0 μm emission properties of Tm³⁺/Ho³⁺ co-doped oxyfluoride tellurite glass exited by 808 nm laser diode (LD). Mid-infrared transmittance property of glass was investigated by Fourier transform infrared (FTIR) spectrometer. The real chemical composition of investigated glass was identified by X-ray photoelectric spectroscopy (XPS). Thermal stability of the glass was determined by differential thermal analysis (DTA) measurement. The Judd-Ofelt parameters, spontaneous radiative transition probabilities, branching ratios and radiative lifetime of Ho³⁺ were calculated based on the absorption spectra by using Judd-Ofelt theory. Results indicate that the maximum 2.0 μm emission intensity attributed to the ⁵I₇→⁵I₈ transition of Ho³⁺ was achieved at 1.5 mol% Tm₂O₃ and 1 mol% Ho₂O₃ concentrations in oxyfluoride tellurite glass. OH⁻ absorption at 3000 cm⁻¹ was greatly depressed by introduction of 10 mol% F⁻. The maximum absorption and stimulated emission cross-section of Ho³⁺ near 2.0 μm are 7.0×10⁻²¹ cm² at 1950 nm and 8.8×10⁻²¹ cm² at 2048 nm, respectively. The calculated radiative lifetime of 4.4 ms for ⁵I₇→⁵I₈ transition and large stimulated emission cross-section of the Tm³⁺/Ho³⁺ co-doped oxyfluoride tellurite glass indicate that the glass has a potential application in efficient 2.0 μm laser.     

Line patterning with large refractive index changes in the deep inside of glass by nanosecond pulsed YAG laser irradiation

Nanosecond (∼100 ns) pulsed (10 Hz) Nd:YAG laser operating at the wavelength (λ) of 1064 nm with pulse energies of 0.16-1.24 mJ/cm² has irradiated 10Sm₂O₃·40BaO·50B₂O₃ glass. It is demonstrated for the first time that the structural modification resulting the large decease (∼3.5%) in the refractive index is induced by the irradiation of YAG laser with λ=1064 nm. The lines with refractive index changes are written in the deep inside of 100-1000 μm depths by scanning laser. The line width is 1-13 μm, depending on laser pulse energy and focused beam position. It is proposed that the samarium atom heat processing is a novel technique for inducing structural modification (refractive index change) in the deep interior of glass.     

Effect of Ce codoping on Er-doped bismuth-germanate glass and fiber under 980 nm excitation

Er³⁺/Ce³⁺ codoped bismuth-germanate glasses with the composition of Bi₂O₃-GeO₂-Ga₂O₃-Na₂O were prepared by the conventional melt-quenching method. The absorption spectra, fluorescence spectra, upconversion emission and lifetimes of Er³⁺ ions were measured, and the effects of Ce³⁺-doping on the spectroscopic properties of 1.53 μm band fluorescence of Er³⁺ ion were investigated based on the analysis of energy transfer between Er³⁺ and Ce³⁺ ions. The results indicate that the 1.53 μm band fluorescence intensity can be improved evidently with the Ce³⁺-doped concentration under the excitation of 980 nm. Meanwhile, the theoretical simulation based on the population rate equation and light power propagation equation indicates that the C + L band signal gain can also be improved dramatically by introducing Ce³⁺ ions into the Er³⁺-doped bismuth-germanate glass fiber. Therefore, it is necessary to introduce Ce³⁺ ions when Er³⁺-doped bismuth-germanate glass with low phonon energy is applied to the 1.53 μm band broad Er³⁺-doped fiber amplifier (EDFA).     

Enhanced 1.53-μm and lowered upconversion luminescence in Er-doped Ga2O3-GeO2-Bi2O3-Na2O glass by codoping rare earths

Spectroscopic properties and energy transfer (ET) in Ga₂O₃-GeO₂-Bi₂O₃-Na₂O (GGBN, glass doped with Er³⁺ and rare earths (RE³⁺; RE³⁺=Ce³⁺, Tb³⁺) have been investigated. Intense 1.53-μm emission with the peak emission cross-section achieved to 7.58×10⁻²¹ cm² from Er³⁺-doped GGBN glass has been obtained upon excitation at 980 nm. Effects of RE³⁺ (RE³⁺=Ce³⁺, Tb³⁺) codoping on the optical properties of Er³⁺-doped GGBN glass have been investigated and the possible ET mechanisms involved have also been discussed. Significant enhancement of the 1.53 μm emission intensity and decrease of upconversion (UC) fluorescence with increasing Ce³⁺ concentration have been observed. The incorporation of Tb³⁺ into Er³⁺-doped GGBN glass could significantly decrease the UC emission intensity, but meanwhile decrease the 1.53 μm emission intensity due to the ET from Er³⁺:⁴I_13/2 to Tb³⁺:⁷F₂. The results indicate that the incorporation of Ce³⁺ into Er³⁺-doped GGBN glass can effectively improve 1.53-μm and lower UC luminescence, which makes GGBN glass more attractive for use in C-band optical fiber amplifiers.     

Spectroscopic investigation of Tm:TeO2-WO3 glass

We studied the spectroscopic characteristics of telluride glass with the host composition (0.85)TeO₂-(0.15)WO₃, containing 0.25 and 1.0 mol% thulium oxide (Tm₂O₃). By analyzing the absorption spectra with the Judd-Ofelt theory, the average radiative lifetimes of 305±7.5 μs and 1.95±0.02 ms were determined for the ³F₄ and ³H₄ levels, respectively. Measured fluorescence lifetime of the ³F₄ level decreased from 218 to 51 μs for the 0.25 and 1.0 mol% Tm₂O₃ doped samples, respectively, indicating the effect of boosted non-radiative decay at higher doping concentrations. A similar trend was observed for the ³H₄ level, where the fluorescence lifetime decreased from 1.86 ms to 350 μs at these concentrations. The quenching of the 1460 nm (³F₄→³H₄) emission in favor of the 1800 nm (³H₄→³H₆) emission due to cross relaxation was further evident in the fluorescence spectra of the samples. The calculated stimulated emission cross sections (3.73±0.1×10⁻²¹ cm² at 1460 nm and 6.57±0.07×10⁻²¹ cm² at 1808 nm) reveal the potential importance of the Tm³⁺:(0.85)TeO₂-(0.15)WO₃ glass for applications in fiber-optic amplifiers and fiber lasers.     

The multiferroic properties of Bi(Fe0.95Co0.05)O3 films

Bi(Fe_0.95Co_0.05)O₃ films were prepared on conductive indium tin oxide (ITO)/glass substrates by chemical solution deposition. Well saturated polarization hysteresis loop has been observed with a remnant polarization value of about 22 μC/cm² at room temperature. Weak ferromagnetism with saturation magnetization of about 3 emu/cm³ was observed at room temperature. The clear observation of both room temperature ferroelectric and ferromagnetic properties suggests the potential multiferroic applications of Bi(Fe_0.95Co_0.05)O₃.     

Near-infrared emissions and quantum efficiencies in Tm-doped heavy metal gallate glasses for S- and U-band amplifiers and 1.8 μm infrared laser

Intense 1.8 μm and efficient 1.48 μm infrared emissions have been recorded in Tm³⁺-doped alkali-barium-bismuth-gallate (LKBBG) glasses with low phonon energies under the excitation of 792 nm diode laser. The maximum emission cross-sections for 1.8 and 1.48 μm emission bands are derived to be 6.26×10⁻²¹ and 3.34×10⁻²¹ cm², respectively, and the peak values are much higher than those in Tm³⁺-doped ZBLAN glass. In low-concentration doping, the full-widths at half-maximum (FWHMs) of the two emission bands are 223 and 122 nm, and the quantum efficiencies of the ³F₄ and ³H₄ levels are proved to be ∼100% and 86%, respectively. When the doping concentration increases to 1 wt%, the quantum efficiency of the ³H₄ level is reduced to 60% due to the cross-relaxation processes in high-concentration doping. Efficient 1.8 μm infrared emission in Er³⁺/Tm³⁺-codoped LKBBG glass has also been achieved under the excitation of 970 nm diode laser, and the probability and the efficiency of non-radiative energy transfer from Er³⁺ to Tm³⁺ are as high as 354 s⁻¹ and 58.4%, respectively. Efficient and broad 1.8 and 1.48 μm infrared emission bands indicate that Tm³⁺-doped LKBBG glasses are suitable materials in developing S- and U-band amplifiers and 1.8 μm infrared laser.     

Ultrafast nonlinear optical properties of Bi2O3-B2O3-SiO2 oxide glass

The ultrafast nonlinear optical properties of Bi₂O₃-B₂O₃-SiO₂ oxide glass were investigated using a femtosecond optical Kerr shutter (OKS) at wavelength of 800 nm. The nonlinear response time of this Bi₂O₃-doped glass was measured to be <90 fs. The nonlinear refractive-index n₂ was estimated to be 1.6 × 10⁻¹⁴ cm²/W. Measurements for the dependence of Kerr signals on the polarization angle between the pump and probe beams showed that the Kerr signals induced by 30-fs pulse laser arose mainly from the photoinduced birefringence effect.     

Comparative investigation on spectroscopic properties of Er between Ce-doped and B2O3-added bismuth glasses

The comparative investigation on the spectroscopic properties of Er³⁺ in low phonon energy Bi₂O₃-GeO₂-Ga₂O₃-Na₂O glasses codoped with Ce³⁺ ion and added with B₂O₃ component, respectively, is presented. With increasing Ce₂O₃ content from 0 to 0.8 mol% or B₂O₃ content from 0 to 15 mol%, the lifetime of Er³⁺:⁴I_11/2 level decreases dramatically from 607 to 283 μs or to 197 μs, and the upconversion fluorescence is quenched in both glass samples. The nonradiative energy transfer from Er³⁺:⁴I_11/2→Ce³⁺:²F_5/2 or the enhanced multiphonon relaxation process together with the energy transfer between Er³⁺ and OH⁻ groups are, respectively, responsible for the results. Meanwhile, the lifetime of ⁴I_13/2 level remains almost unchanged in Er³⁺/Ce³⁺-codoped glasses whereas it decreases rapidly in B₂O₃-added cases. As a result, Er³⁺/Ce³⁺ codoping improves the 1.5 μm fluorescence emission intensity, however, B₂O₃ addition has a negative effect on it. The research results indicate that the Er³⁺/Ce³⁺-codoped bismuth glasses will be preferable for obtaining efficient 980 nm pumped EDFA.     

Fe fine particles encapsulated by titanium oxides with high magnetization for biomedical application

Iron (Fe) fine particles encapsulated by titanium oxide (TiO₂) were synthesized through a solid-phase reaction. The structure of Fe cores and TiO₂ shells consisted of α-Fe and rutile TiO₂, respectively. The average particle size was 0.8 μm, in which a Fe particle with a diameter of ∼750 nm was encapsulated by a TiO₂ shell with a thickness of ∼100 nm. The Fe particles had a high saturation magnetization of 127 Am²/kg and low coercivity of 1.6 kA/m. They also exhibited excellent corrosion resistance, similar to Fe₃O₄ in a soaking test.     

Effect of Ce on the spectroscopic properties in Er doped TeO2-GeO2-Nb2O5-Li2O glasses

The Ce³⁺ ion was introduced into Er³⁺ doped TeO₂-GeO₂-Nb₂O₅-Li₂O (TGNL) glass to improve the 1.5 μm fluorescence characteristics. As increasing of Ce³⁺ concentration, the lifetime of Er³⁺:⁴I_11/2 level is shortened form 360 to 225 μs, while the Er³⁺:⁴I_13/2 level remains unchanged. Accordingly, the upconversion fluorescence (blue, green and red) was quenched. Improved 1.5 μm emission is obtained and the reason is ascribed to the increase of nonradiative rate between the ⁴I_11/2 and ⁴I_13/2 level of the Er³⁺ ions.     

Bulk and surface properties of spinel Co3O4 by density functional calculations

DFT calculations are employed to bulk and surface properties of spinel oxide Co₃O₄. The bulk magnetic structure is calculated to be antiferromagnetic, with a Co²⁺ moment of 2.631 μ_B in the antiferromagnetic state. There are three predicted electron transitions O(2p) → Co²⁺(t_2g) of 2.2 eV, O(2p) → Co³⁺(e_g) of 2.9 eV and Co³⁺(t_2g) → Co²⁺(t_2g) of 3.3 eV, and the former two transitions are close to the corresponding experimental values 2.8 and 2.4 eV. The naturally occurring Co₃O₄ (1 1 0) and (1 1 1) surfaces were considered for surface calculations. For ideal Co₃O₄ (1 1 0) surfaces, the surface relaxations are not significant, while for ideal Co₃O₄ (1 1 1) surfaces the relaxation of Co²⁺ cations in the tetrahedral sites is drastic, which agrees with the experiment observation. The stability over different oxygen environments for possible ideal and defect surface terminations were explored.     

Effect of Al2O3 on the electrical properties of ZnO-Pr6O11-based varistor ceramics

The effect of Al₂O₃ on the electrical properties of ZnO-Pr₆O₁₁-based ceramics is investigated in this work. The average grain size of ZnO increased as the Al₂O₃ content increased from 10.3 to 13.5 μm. It was found that a sample doped with Al₂O₃ of 0.005 mol% showed the highest nonlinear current-voltage characteristics with a nonlinear exponent of 43.8 and a leakage current of 0.66 μA. When the Al₂O₃ content was increased, the donor concentration was increased from 0.51×10¹⁸/cm³ to 1.59×10¹⁸/cm³, but the barrier height was decreased from 1.01 to 0.87 eV. The best electrical stability against aging stress was obtained by doping Al₂O₃ of 0.001 mol%.     

Upconversion luminescence of Er/Yb-codoped natrium-germanium-bismuth glasses

The absorption and upconversion fluorescence spectra of a series of Er³⁺/Yb³⁺-codoped natrium-germanium-bismuth glasses have been studied. The transition probabilities, excited state lifetimes, and the branching ratios have been predicted for Er³⁺ based on the Judd-Ofelt theory. At room temperature, an upconversion efficiency of 6.1×10⁻² has been obtained for the green emission from the glass with 0.5 wt% Er₂O₃ and 3.0 wt% Yb₂O₃ pumped by 980 nm radiation with an intensity of 270 W/cm². And the “standardized” efficiency for green upconversion light is higher than that reported in lead-germanate, lead-tellurite-germanate, and silicate glasses. The results indicate that the Er³⁺/Yb³⁺-codoped natrium-germanium-bismuth oxide glass may be a potential material for developing upconversion optic devices.     

Exchange bias in thin-film (Co/Pt)3/Cr2O3 multilayers

We have fabricated exchange-biased Co/Pt layers ((0.3 nm/1.5 nm)×3) on (0 0 1)-oriented Cr₂O₃ thin films. The multilayered films showed extremely smooth surfaces and interfaces with root mean square roughness of ≈0.3 nm for 10 μm×10 μm area. The Cr₂O₃ films display sufficient insulation with a relative low leakage current (1.17×10⁻² A/cm² at 380 MV/m) at room temperature which allowed us to apply electric field as high as 77 MV/m. We find that the sign of the exchange bias and the shape of the hysteresis loops of the out-of-plane magnetized Co/Pt layers can be delicately controlled by adjusting the magnetic field cooling process through the Néel temperature of Cr₂O₃. No clear evidence of the effect of electric field and the electric field cooling was detected on the exchange bias for fields as high as 77 MV/m. We place the upper bound of the shift in exchange bias field due to electric field cooling to be 5 Oe at 250 K.     

Role of Al2O3 in upconversion and NIR emission in Tm and Er codoped calcium fluoro phosphorous silicate glass system

In this study, the principal role of Al₂O₃ on the features of the photoluminescence spectra of Tm³⁺ ion and upconversion phenomenon in Tm³⁺ and Er³⁺ codoped CaF₂−Al₂O₃−P₂O₅−SiO₂ glass system has been investigated. The concentration of Al₂O₃ is varied from 2 to 10 mol% while that of Er³⁺ and Tm³⁺ is fixed. IR and Raman spectral studies have indicated that there is a gradual increase in the degree of disorder in the glass network with increase in the concentration of Al₂O₃ up to 6.0 mol%. This is attributed to the presence of Al³⁺ ions in octahedral positions in larger proportions. When the glasses are doped with Tm³⁺ ions, the blue and red emissions were observed, whereas in Er³⁺ doped glasses blue, green and red emissions were observed. When the glasses are codoped with Tm³⁺ and Er³⁺ ions and excited at 790 nm, all the three emission lines were observed to be reinforced, especially in the glasses mixed with 6.0 mol% of Al₂O₃. The IR emission band detected at about 1.8 μm due to ³F₄→³H₆ transition of Tm³⁺ ions is also observed to be strengthened due to codoping. The reasons for enhancement in the intensity of various emission bands due to codoping have been identified and discussed with the help of rate equations for various emission transitions.     

Large negative refractive index modification induced by irradiation of femtosecond laser inside optical glasses

We report on the refractive index modification (Δn) and its cross sectional profile of the created lines inside the different types of optical glasses, containing BaO, TiO₂, or La₂O₃ as a metal oxide. The lines were fabricated by scanning a stage and focusing the femtosecond laser pulses, 800 nm wavelength, a 250 kHz repetition rate and 200 fs pulse duration, from the Ti:sapphire regenerative amplifier system. The Δn measurements were performed with the qualitative phase microscopy technique. As a result, it was found that the Δn and its sign are different depending on glass types. For example, in the glasses containing TiO₂, the Δn became smaller in the modified region and some of them showed relatively large decrease of the Δn, Δn < −0.01, with about 10 μm width. Such a glass material could be useful for the compact optics and optical devices.     

Temperature-dependent fluorescence characteristics of an ytterbium-sensitized erbium-doped tellurite glass

In this article, the 1.5 μm emission spectra corresponding to the ⁴I_13/2→⁴I_15/2 transition of Er³⁺ in tellurite glass are studied within the temperature from 8 to 300 K. The emission spectra of Er³⁺: ⁴I_13/2→⁴I_15/2 transition are also analyzed using a peak-fit routine, and an equivalent four-level system is proposed to estimate the stark splitting for the ⁴I_15/2 and ⁴I_13/2 levels of Er³⁺ in the tellurite glass. The results indicate that the ⁴I_13/2→⁴I_15/2 emission of Er³⁺ can exhibit a considerable broadening due to a significant enhance the peak a′, and b′ change, respectively, and the peaks of which are located at about 1507 and 1556 nm. A detailed study of temperature-dependent 1.5 μm emission spectra involving the change of the corresponding sub-bands shows that as the temperature decreases from 300 to 8 K, its line-shape becomes sharper and more intense (the full-width at half-maximum decreases from 59 to 38 nm). Temperature-dependent fluorescence intensities and the experimentally determined lifetimes are investigated; the results show that a decrease behavior of fluorescence intensities and lifetimes are observed for temperature from 8 to 300 K.     

Effect of ultrasonic irradiation on structure and electrochemical properties of LiMn2O4 thin films cathode material for Li-ion micro-batteries

Two kinds of spinel LiMn₂O₄ thin film for lithium ion micro-batteries were successfully prepared on polycrystal Pt substrates by spin coating methods, which were carried out under ultrasonic irradiation (USG) and magnetic stirring (MSG), respectively. The microstructures and electrochemical performance of LiMn₂O₄ thin films were characterized by thermogravimetry analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and galvanostatic charge-discharge measurements. It was found that the crystalline structure of USG samples grew better than that of the MSG samples. At the same time, higher discharge capacity and better cycle stability were obtained for the LiMn₂O₄ thin films of USG at the current density of 50 μAh/cm² between 3.0 and 4.3 V. The 1st discharge capacity was 57.8 μAh/cm²-μm for USG thin films and 51.7 μAh/cm²-μm for MSG thin films. After 50 cycles, 91.4% and 69% of discharge capacity could be retained respectively, indicating that ultrasonic irradiation condition during spin coating was more suitable for preparing spinel LiMn₂O₄ thin films with better electrode performance for lithium ion micro-batteries.     

Infrared absolute intensities of ozone in the 10 and 5 μm spectral range: New investigations

Infrared high resolution spectra of ozone ¹⁶O₃ have been recorded in the 10 and 5 μm spectral ranges in order to derive their absolute intensities with a best achievable accuracy. Spectra have been recorded with the home made stepping mode FTS of GSMA (Reims). In the two spectral regions, we use UV-IR crossed beam cell. The quantification of ozone is achieved using UV cross section at 253.65 nm. A check of this UV calibration is also performed using direct pressure measurements of quasi-pure samples of O₃. The intensities are derived from infrared spectra using multifit procedure already tested. In the 10 μm range, where 12 different spectra have been recorded, 65 well selected lines led to a good agreement (better than 0.3%) with the HITRAN 2008 (or 2004) values, confirming our previous work [De Backer-Barilly MR, Barbe A. Absolute intensities of the 10 μm bands of ¹⁶O₃. J Mol Spectrosc 305:2001;43-53]. In the 5 μm range, where 18 transitions are selected, we also note a correct agreement with HITRAN 2008, despite a slightly larger averaged value between (1.9%) experimental and theoretical (HITRAN). As conclusion, authors suggest the use of current HITRAN 2008 data for atmospheric retrievals.