Co-doped Silica Glass Research Articles

Enhanced radiation resistance of Er3+/Yb3+ co-doped high-phosphorus silica glasses and fibers via phase-interface engineering

Enhanced radiation resistance of Er3+/Yb3+ co-doped high-phosphorus silica glasses and fibers via phase-interface engineering

Dy-Al-Ce codoped silica: a promising yellow laser glass with enhanced resistance to X-ray-induced photodarkening

To develop Dy doped silica glass with a higher irradiation resistance, which can be adapted to high power violet or blue LD pumped yellow laser fibers, the designed Dy-Al-Ce codoped silica glasses, 0.05Dy2O3-1.5Al2O3-xCe2O3-(98.45-x)SiO2 (x = 0, 0.05, 0.1, 0.25, 0.5), were prepared by the sol-gel method. Their excitation spectra, emission spectra and emission decay curves associated with the yellow emission from 4F9/2 to 6H13/2 of Dy were determined before and after the X-ray irradiation of 1000 Gy. The relation between these spectra and Ce-codoping concentrations is discussed, including the sensitization from Ce to Dy, the reverse energy transfer from Dy to Ce, and especially the X-ray-induced photodarkening, which is detrimental to the 576 nm yellow emission of Dy. The centers that cause the photodarkening are analyzed by electron paramagnetic resonance and radiation induced absorption spectra. It is found that Ce can effectively suppress the Al-oxygen hole center induced by the X-ray across the entire concentration range of Ce-codoping, but a new photodarkening center is generated at higher concentrations of Ce-codoping. Finally, the optimized Ce-codoping concentration of ∼0.1 mol% is used to achieve a promising yellow laser glass of Dy-Al-Ce codoped silica with enhanced irradiation resistance, resulting in its X-ray-induced photodarkening that is only 6% - 14% of that in the Ce-undoped.

A novel fluorescent probe for the detection of Fe3+ ions with Eu3+/SnO2 nanocrystals Co-doped silica glasses

Detection of Fe3+ ions is of paramount importance for environmental protection and human health. Herein, we reported a highly selective and sensitive fluorescence probe for the quantification of Fe3+ ions in aqueous solution with Eu3+/SnO2 nanocrystals co-doped silica glasses as the sensing unit. Due to the high stability of silica glasses and their efficient protection for emitting centers, the probe has good recyclability and can be applied in real water environment, indicating its potential for on-site sensing. The detection limit of Fe3+ ions is 7.54 nmol/L. Experiments were carried out to verify that the probe shows excellent cross interference with other metal ions. The detecting mechanism can be ascribed to the excitation/emission absorption and energy transfer of Fe3+ ions. Our work paves a novel way of semiconductor oxide nanocrystals for applications in optoelectronics.

Q-switched pulse generation by stimulated Brillouin scattering assisted four-wave mixing effect in erbium–bismuth co-doped multi-elements silica glass based optical fiber laser

We demonstrate Q-switched pulse generation at the 1562.5 nm region by using a 70 cm long erbium–bismuth co-doped alumina–germania–hafnium–yttria silica glass-based fiber as a gain medium in a simple ring resonator configured without saturable absorber and optical isolator devices. The Q-switching was obtained based on a stimulated Brillouin scattering assisted four-wave mixing effect in the gain medium, which induced the intensity modulation mechanism. The laser produced a multi-wavelength output comb centered at 1562.6 nm with a peak-to-peak spacing of about 0.09 nm due to nonlinear effects. Stable Q-switched operation of a hafnia–bismuth–erbium co-doped fiber laser was obtained at a pump power range of 129–319 mW with the repetition rate varying from 45.9 kHz to 89.3 kHz and the pulse width ranging from 8.8 µs to 3.58 µs. A maximum pulse energy of 26.9 nJ at an average output power of 2.4 dBm was achieved. This demonstrates a new passive technique based on a highly nonlinear gain medium for realizing Q-switched all-fiber laser sources.

Er-doped silica fiber laser made by powder-based additive manufacturing

The pursuit of advanced fiber laser technologies has driven research toward unconventional manufacturing techniques. In this work, we present an erbium-doped fiber laser made using powder-based additive manufacturing. An Er3+/Al3+ co-doped silica glass rod was printed using laser powder deposition and then used as the core material in a fiber preform. The fiber drawn from the preform exhibited the complete, desired functionality linked to Er3+ doping. To demonstrate this, a standing wave laser cavity was formed with the feedback attained from the cleaved ends of the manufactured fiber. The high quality of the fiber is showcased through a low background loss, single-mode operation, a 9.4% laser slope efficiency, and an output of 4.5 mW, limited by the available pump power. This proof-of-concept opens up promising areas for rapid fabrication and development of high-performance fibers and fiber lasers.

Boosting Nd3+ emission in Nd/Al/Y co-doped silica glass by mid-range localized environmental manipulation

Improving the repetition frequency of high-energy lasers is vital to promote the development and application of high-energy lasers, and its key lies in finding the laser gain media with excellent thermal shock resistance and high emission cross-section. Rare-earth ion (RE3+)-doped silica glass, whose thermal shock parameter is 1.5 times higher than that of yttrium aluminum garnet (YAG) crystals, is expected to satisfy this criterion after enhancing the emission intensity of RE3+. Nevertheless, modulating the spectral properties of RE3+ in rigid silica glass networks poses a significant challenge. Herein, we propose a mid-range localized environmental manipulation approach, which dramatically changes the microscopic symmetry of RE3+ from amorphous to the desired crystal structures for emission enhancement. As a representative, Nd/Y/Al co-doped silica glasses were prepared and heat-treated for different durations to form different mid-range localized environments, which were demonstrated by transmission electron microscopy, electron paramagnetic resonance tests, and Judd-Ofelt theory analysis. The results show that Nd3+ enters the YAG structure in favor of its emission enhancement. After optimizing the mid-range local environment of Nd3+ to balance fluorescence enhancement with fluorescence quenching and Rayleigh scattering, the emission intensity increases by 300%. Our work suggests that the mid-range localized environmental manipulation approach is extremely promising for promoting the development of high-energy and high-repetition-rate lasers. Furthermore, this approach can be generalized to adjust the emission characteristics of other RE3+-doped glasses and fibers.

Ga-hybridization-mediated broadband optical amplification in Bi-activated photonic glass and fiber.

A Ga hybridization strategy is proposed for simultaneously enhancing the near-infrared activity and extending the bandwidth of Bi-activated photonic glass. Systematic studies on the near-infrared optical responses of Ga/Bi and Al/Bi co-doped silica glasses are performed. It is interesting to note that Ga/Bi co-doped glasses have a similar near-infrared emission center to Al/Bi co-doped glass, while the former is more effective in improving near-infrared activity. The different luminescence mechanisms of Ga/Bi and Al/Bi co-doped silica glasses are elucidated, and the corresponding microstructure-optical response relationship is discussed. In addition, the Ga/Bi co-doped silica optical fiber is successfully prepared, and the principal fiber amplifier device is fabricated. Furthermore, amplified spontaneous emission and broadband on-off gain are realized. The results suggest that Ga-hybridized Bi-activated photonic glass is a promising gain material for broadband fiber amplifiers.

Spectroscopic analysis of Nd/Al co-doped silica glass fabricated by laser additive manufacturing

In this work, Nd/Al co-doped silica glass was prepared by laser additive manufacturing. The doping concentrations of Nd3+ and Al3+ ions were measured to be 1.36 wt% and 1.71 wt%, respectively. A long fluorescence lifetime 664 μs in silica glass was achieved. Based on the measured absorption spectrum, the Judd-Ofelt (J-O) parameters of Nd3+ ions in matrix were calculated by J-O theory, which are Ω2=7.57×10−20cm−2,Ω4=8.01×10−20cm−2,Ω6=3.17×10−20cm−2, respectively. The value of Ω4/Ω6 is 2.53, indicating that Nd/Al co-doped silica glass has good spectral quality. The results demonstrate that Nd/Al co-doped silica glass manufactured by the laser additive manufacturing possesses excellent optical properties, which can be used in high-energy laser and amplification devices and promote the development of Nd-doped fiber lasers in the future.

Broadband L+ near-infrared luminescence in bismuth/germanium co-doped silica glass prepared by the sol–gel method

Ge-ODC plays a pivotal role in promoting the formation of BAC-Ge and L+ band emission centered around 1680 nm.

First-principles study of local structure and optical properties of Yb/F co-doped silica glass for optical fiber applications

We calculate the geometric and optical properties of Yb/F co-doped silica glass which is the main component of optical fiber, by using first-principles. In the non-coplanar open-loop model (NCOL), by using the Bader charge method, our results revealed that the valence electrons of Yb ion are 1.89, which is extremely close to the Yb2+ ion. The absorption peaks, respectively, located at 3.2 eV (390 nm) and 4 eV (330 nm), which are close to typical Yb2+ characteristic absorption obtained from the experimental test. The absorption peaks correspond to the transitions from 1S0–2F7/2 T2g-1 and 1S0 to 2F5/2 T2g-3. Incorporation of F element and the formation of open-loop ring structure may make the Yb3+ ion more likely transform to Yb2+ ion. The NCOL model provides theoretical guidance for the experimental preparation of Yb-doped silica fiber.

Influence of GeO2 Content on the Spectral and Radiation-Resistant Properties of Yb/Al/Ge Co-Doped Silica Fiber Core Glasses.

In this study, Yb/Al/Ge co-doped silica fiber core glasses with different GeO2 contents (0–6.03 mol%) were prepared using the sol–gel method combined with high-temperature sintering. The absorption, fluorescence, radiation-induced absorption, continuous-wave electron paramagnetic resonance spectra, and fluorescence decay curves were recorded and analyzed systematically before and after X-ray irradiation. The effects of GeO2 content on the valence variations of Yb3+/Yb2+ ions, spectral properties of Yb3+ ions, and radiation resistance of Yb/Al/Ge co-doped silica glasses were systematically studied. The results show that even if the GeO2 content of the sample is relatively low (0.62 mol%), it can inhibit the generation of Yb2+ ions with slight improvement in the spectral properties of Yb3+ ions in the pristine samples and effectively improve its radiation resistance. Direct evidence confirms that the generation of trapped-electron centers (Yb2+/Si-E’/Al-E’) and trapped-hole centers (Al-OHC) was effectively inhibited by Ge co-doping. This study provides a theoretical reference for the development of high-performance, radiation-r esistant Yb-doped silica fibers.

Spectroscopic analyses of Er3+/Yb3+ co-doped laser sintering silica glasses

In this study, the laser sintering technique was used to obtain Er3+/Yb3+ co-doped silica glasses for up-conversion (UC) luminescence for the first time. Further, structural analysis of the glass sample was conducted via XRD, SEM and EDS measurements. Based on the measured absorption spectrum, important spectroscopic parameters including three intensity parameters Ωt (t = 2, 4 and 6), theoretical and experimental line strengths, spontaneous transition probabilities, branching ratios and radiative lifetimes, were calculated using the Judd-Ofelt (J-O) theory. The UC properties of Er3+/Yb3+ co-doped silica glasses were investigated upon the excitation of a 976 nm laser. It has been experimentally confirmed that the green and red UC luminescences corresponding to the radiative transitions of Er3+: 2H11/2 → 4I15/2 (green), 4S3/2 → 4I15/2 (green) and 4F9/2 → 4I15/2 (red) were achieved. This result is consistent with those of the J-O theoretical analysis. Additionally, the energy transfer mechanism between Er3+ and Yb3+, which is responsible for the UC process, was discussed based on their dependence on the pump power. The obtained results indicated that the Er3+/Yb3+ co-doped silica glasses manufactured using the laser sintering technique can be promising for the application of short-wavelength lasers.

Insights into the photodarkening mechanism of Tb3+/Al3+ co-doped silica glasses

In this work, Tb3+/Al3+ co-doped and Al3+ single doped silica glasses are taken as the research objects, and X-ray is used as the simulated light source to study the photodarkening mechanism. Detailed optical properties of the glasses before and after X-ray irradiation and the results of electron paramagnetic resonance (EPR) indicate that the photodarkening effect is attributed to the valence changes of Tb3+ ions and the energy transfer between Tb3+ ions and related defects. In addition, this work revealed the relationship between valence changes behavior of Tb3+ ions and various defects in glass matrix materials, deepening the understanding of the photodarkening mechanism in Tb3+ doped oxide glass. We envisage that our finding provides a depth-theoretical support for the synthesis of Tb3+-doped oxide matrix glass fibers with excellent optical and anti-photodarkening performance.

Highly fluorine and ytterbium doped polarization maintaining large mode area photonic crystal fiber via the sol-gel process

Highly Yb-doped silica glass with low refractive index for fabrication of Yb-doped large-mode-area photonic crystal fiber (LMA PCF) is in favor of decreasing fiber length and thus increasing the threshold of nonlinear effects in pulse laser amplification. Accordingly, fluorine incorporation in highly Yb-doped silica glass is vitally important to compensate the sharp increase in refractive index caused by ytterbium and aluminum ions. In this work, the fluorine doping concentration in Yb/Al/P/F co-doped silica glass was significantly improved by a modified sol-gel method combined with high temperature sintering. The effects of fluorine doping on glass structure have been investigated in details by Raman spectra, nuclear magnetic resonance (NMR) and advanced pulse electron paramagnetic resonance (EPR) measurements. The incorporation of fluorine yields Si-F bonds and Yb-F bonds formation and leads to the mild change in spectroscopic properties. An optimized silica core glass rod with high Yb (0.77 wt.%) and fluorine (0.8 wt.%) doping concentration, low refractive index and acceptable optical quality was prepared. Based on the highly fluorine and ytterbium doped silica core glass, a polarization maintaining (PM) photonic crystal fiber with 40 µm core was prepared and the pump absorption coefficient at 976 nm was ∼6.5 dB/m. An average amplified power of 103 W was achieved from a 2-m-long PCF with the bend diameter of 23 cm. The slope efficiency (with respect to pump power) was 52% with laser beam quality factor M2 of 1.46.

Effect of co-dopants on the spectral property of Yb3+ doped silica glasses at 1018 nm

To enhance the laser performance of Yb3+-doped silica fiber for 1018-nm tandem-pumped technology, three series of Yb–Al, Yb-Al-P, and Yb–P co-doped silica glasses with a large size, high homogeneity, and precise composition control were prepared using a sol-gel method combined with high-temperature sintering technology. In addition, the effects of Al3+ and P5+ co-dopants on the absorption and emission properties of Yb3+-doped silica glasses at 1018 nm were investigated systematically. The normalized spectral characteristics of the glass samples with different doping series at 1018 nm were compared horizontally, and the results showed that the normalized emission intensity of the Yb-P-doped silica glass series samples at 1018 nm was significantly better than that of the other series. The emission subpeak was located near 1018 nm when the content of doped P was 5 mol%, and the position of the subpeak gradually blue-shifted as the content of the doped P increased. Using Raman spectroscopy combined with ultra-low temperature electron paramagnetic resonance (4K), the coordination environment of Yb3+ was accurately resolved at the atomic scale. In Yb3+-doped silica glasses, the coordination environment of Yb3+ was extremely different from the introduction of Al3+ and P5+, which is consistent with the influence of Al3+ and P5+ on the spectral properties of Yb3+ at 1018 nm.

Laser properties of Nd3+/Yb3+ co-doped glass fiber around 1 µm

The interest in N d 3 + / Y b 3 + co-doping was initially motivated by the discovery of N d 3 + → Y b 3 + energy transfer in 1964, which profoundly influenced the motivation for subsequent research. Here, however, we propose a new mechanism based on an 808 nm and 975 nm dual-pumping scheme, in which the effect of N d 3 + → Y b 3 + energy transfer process is negligible. Gain spectrum modulation and its application in tunable dual-wavelength lasers around 1 µm were demonstrated in a 30-cm-long N d 3 + / Y b 3 + co-doped silica glass fiber. In addition, interesting laser efficiency improvements, thermal performance improvements, and even photodarkening resistance behavior were observed. This work broadens the knowledge of N d 3 + / Y b 3 + co-doping and may provide useful insights for exploring co-doping with rare-earth ions.

Spectroscopic and luminescent properties of Nd3+-Al3+ co-doped silica glass prepared by spark plasma sintering

The Nd3+-Al3+ co-doped silica glass has drawn much attention due to the stability and efficient lasing emissions, while the high preparation temperature and residual hydroxyl groups restrict the further improvement of optical performance. In this work, transparent Nd3+-Al3+ co-doped glasses have been synthesized by spark plasma sintering at 980°C within 10 mins. Besides, adopting mesoporous powders as raw materials is beneficial to the homogeneous dispersion of ions in the glass. The transmittance, structure and luminescent properties were systematically investigated. The Judd-Ofelt intensity parameters were obtained to analyze the Al3+ co-doping effects. The PL intensity strongly depends on the ions concentration and the best value is obtained when the Nd3+ concentration is 1.0 mol% and ratio of Nd:Al is 1:7. In addition, the calculated emission cross section is 2.12, which is larger than the majority of previously reported values, suggesting that as-prepared silica glasses are candidates for laser host materials.

Effect of the GeO2 content on the radiation resistance of Er3+ -doped silica glasses and fibers

In this work, Er/Al/Ge co-doped silica glasses with different GeO2 content (0–3 mol%), as well as Ge/Al co-doped silica glasses, are prepared by combining the sol–gel and high-temperature sintering methods. Further, the effects of the GeO2 content on the absorptions and emissions properties, and lifetimes of the glasses before and after 1KGy γ-ray irradiation are compared. The Er/Al/Ge co-doped silica fibers are prepared from a preform produced via modified chemical vapor deposition (MCVD) combined with nano sol-doping. The effects of Ge co-doping on the optical loss and amplifier gain of the Er-doped silica fibers (EDFs) before and after irradiation are also investigated. The related mechanism and species of the γ-ray radiation-induced color centers are revealed via radiation-induced-absorption (RIA) and continuous wave electron paramagnetic resonance (CW-EPR) spectroscopies. The results revealed that co-doping with GeO2 considerably improves the radiation resistance of the glass and exerts a slight effect on the spectral properties of the Er/Al/Ge co-doped silica glasses before irradiation. The RIA and CW-EPR spectra revealed that the aluminum–oxygen hole center (AlOHC) defects reduce with increasing GeO2 content because the intermediaries, the Ge-related oxygen-deficient centers (GeODC(I) and GeODC(II)), exhibit stronger abilities to trap the holes compared with the [AlO4/2]− group. This reduces the RIA level in the visible and near-infrared regions of the Er/Al/Ge co-doped silica glass. The irradiation experiment on the fiber further confirmed that the radiation resistance of EDFs can be considerably improved by Ge co-doping.

Manufacture and up-conversion luminescence of Er/Yb co-doped silica glass microstructure optical fiber based on the laser sintering technique

In this study, the laser sintering technique combined with the stack-capillary-draw method was used to manufacture Er3+/Yb3+ co-doped silica glass microstructure optical fiber for up-conversion (UC) luminescence for the first time. The obtained fiber, whose structure can be maintained well, shows no obvious element diffusion during the fiber-drawing process. The core glass is amorphous without any crystallization, and Er and Yb elements are uniformly distributed throughout the fiber core. Intense upconverted green and red emissions corresponding to (2H11/2, 4S3/2) → 4I15/2 and 4F9/2 → 4I15/2 transitions, respectively, together with an emission corresponding to 2H11/2 → 4I13/2 transition were observed upon the excitation of a 976-nm laser. The intensity of green and red UC luminescence shows a linear dependence on the excitation power which demonstrates that a two-photon absorption process is responsible for the UC process. The results demonstrated the laser sintering technique provides an alternative method to manufacture Er3+/Yb3+ co-doped fiber, which would promote the development of UC luminescent materials.

Tailoring of communication band luminescence for super broadband optical amplifier based on [formula omitted] co-doped nanoporous silica glass

We report on a series of Er3+/Yb3+/P5+ co-doped silica glass from nanoporous silica glass based on glass phase separation technology. The optical properties of the Er3+/Yb3+/P5+ co-doped glasses were investigated. Measurements showed that phosphorus can promote energy transfer from Yb3+ ions to Er3+ ions while suppressing the energy transfer from Er3+ ions to Yb3+ ions and efficiently suppressing the amplified spontaneous emission (ASE) from Yb3+ ions at 1030 nm. Additionally, the luminescence of Er3+ (I413/2→I415/2) was greatly extended under 976 nm laser excitation, and the full width at half maximum (FWHM) of Er3+ (I413/2→I415/2) was measured to be up to 72 nm and enables the luminescence peak redshifted. The emission cross section of Er3+ (I413/2→I415/2) was calculated to be 1.6*10−20cm2, one order higher than that of other silica glasses. It is suggested that the Er3+/Yb3+/P5+ co-doped silica glasses based on nanoporous silica glass present great potential for broadband amplification.