Bismuth-doped Germanate Glass Research Articles

Low-temperature sintering of bismuth-doped glass with high fluorescence properties from mesoporous silica SBA-15

A kind of bismuth-doped silica glasses have been produced successfully by spark plasma sintering at 1070 °C using bismuth-doped SBA-15 powders. The samples were detected by X-ray diffraction, UV–vis–NIR, photoluminescence, fluorescent decay curve and X-ray photoelectron spectroscopy. The results showed that the samples possess favorable near-infrared fluorescence and the 0.9 mol% sample is the best one among these glasses. The emission peaks at ~1180, ~1150 and ~1250 nm can be observed when excited by 500, 700 and 800 nm. The average lifetimes of 0.9 mol% under 500, 700 and 800 nm excitation are 189.87, 311.46 and 132.16 μs. Furthermore, the value of the important optical parameter σemτ is 5.79 × 10−24 cm2s at 800 nm excitations, which is 36.8% and 9.2% larger than bismuth-doped germanate glasses and phosphate glasses that have been reported. These emission peaks could be decomposed into three bands at ~1150, ~1240 and ~1440 nm via Gaussian decomposition. Based on the results of this work, it is concluded that the NIR emission peaks at ~1150, ~1240 and ~1440 nm correspond to Bi0, Bi+ and (Bi2)2-, respectively. This glass with excellent luminescence properties could offer a practical material to improve the performance of broadband fiber amplifiers and tunable lasers.

Bismuth-doped glass microsphere lasers

In this work, a hybrid structure consisting of a multicomponent germanate glass microsphere containing bismuth as a gain medium is proposed and presented. The bismuth-doped germanate glass microspheres were fabricated from a glass fiber tip with no precipitation of the bismuth metal. Coupling with a fiber taper, the bismuth-doped microsphere single-mode laser was observed to lase at around 1305.8 nm using 808 nm excitation. The low threshold of absorbed pump power at 215 μW makes this microlaser appealing for various applications, including tunable lasers for a range of purposes in telecommunication, biomedical, and optical information processing.

Bismuth-doped germanate glass fiber fabricated by the rod-in-tube technique

Bismuth (Bi)-doped laser glasses and fiber devices have aroused wide attentions due to their unique potential to work in the new spectral range of 1 to 1.8 μm traditional laser ions, such as rare earth, cannot reach. Current Bi-doped silica glass fibers have to be made by modified chemical vapor deposition at a temperature higher than 2000°C. This unavoidably leads to the tremendous loss of Bi by evaporation, since the temperature is several hundred degrees Celsius higher than the Bi boiling temperature, and, therefore, trace Bi (∼50 ppm) resides within the final product of silica fiber. So, the gain of such fiber is usually extremely low. One of the solutions is to make the fibers at a temperature much lower than the boiling temperature of Bi. The challenge for this is to find a lower melting point glass, which can stabilize Bi in the near infrared emission center and, meanwhile, does not lose glass transparency during fiber fabrication. None of previously reported Bi-doped multicomponent glasses can meet the prerequisite. Here, we, after hundreds of trials on optimization over glass components, activator content, melting temperature, etc., find a novel Bi-doped gallogermanate glass, which shows good tolerance to thermal impact and can accommodate a higher content of Bi. Consequently, we successfully manufacture the germanate fiber by a rod-in-tube technique at 850°C. The fiber exhibits similar luminescence to the bulk glass, and it shows saturated absorption at 808 nm rather than 980 nm as the incident power becomes higher than 4 W. Amplified spontaneous emissions are observed upon the pumps of either 980 or 1064 nm from germanate fiber.

Thermal degradation of ultrabroad bismuth NIR luminescence in bismuth-doped tantalum germanate laser glasses.

Because of ultra-broadband luminescence in 1000-1700 nm and consequent applications in fiber amplifier and lasers in the new spectral range where traditional rare earth cannot work, bismuth-doped laser glasses have received rising interest recently. For long-term practical application, thermal degradation must be considered for the glasses. This, however, has seldom been investigated. Here we report the thermal degradation of bismuth-doped germanate glass. Heating and cooling cycle experiments at high temperature reveal strong dependence of the thermal degradation on glass compositions. Bismuth and tantalum lead to the reversible degradation, while lithium can produce permanent irreversible degradation. The degradation becomes worse as lithium content increases in the glass. Absorption spectra show this is due to partial oxidation of bismuth near-infrared emission center. Surprisingly, we notice the emission of bismuth exhibits blueshift, rather than redshift at a higher temperature, and the blueshift can be suppressed by increasing the lithium content.

Precise frequency shift of NIR luminescence from bismuth-doped Ta2O5–GeO2glass via composition modulation

Bismuth-doped glasses have received much attention in the last decade due to their broadband near-infrared (NIR) emission. Their optical properties are sensitive to composition and there are a few reports that qualitatively describe the dependence of these properties on their compositions. Yet the actual role of bismuth, as the matrix composition changes, remains fundamentally unclear. In this work, we investigate optical properties of bismuth-doped germanate glasses with different compositions and interpret their dependences in terms of their microscopic structure using Raman and Fourier transform infrared (FTIR) spectra. Beyond qualitative descriptions, quantitative empirical prediction laws are established on the grounds of the relationships between compositions, structures and properties of bismuth-doped germanate glasses. These findings enable precise predictions of the frequency shift of NIR luminescence from bismuth-doped glasses and a better understanding of the nature of bismuth NIR luminescent centers.

IR luminescence in bismuth-doped germanate glasses and fibres

We have studied the optical properties of lightly bismuth doped (≤0.002 mol %) germanate glasses prepared in an alumina crucible. The glasses are shown to contain bismuth-related active centres that have been identified previously only in bismuth-doped fibres produced by MCVD. With increasing bismuth concentration in the glasses, their luminescence spectra change markedly, which is attributable to interaction between individual bismuth centres.

Multifunctional tunable ultra-broadband visible and near-infrared luminescence from bismuth-doped germanate glasses

Here, we present three facile approaches to achieve wavelength tunable luminescence in the same host material with single dopant, i.e., by modulating doping level, preparation temperature, and atmosphere. Based on these methods, ultra-broadband tunable near-infrared luminescence with the largest full width at half maximum of about 500 nm covering the whole windows of optical communication has been obtained in bismuth-doped germanate glasses. Wavelength tunable luminescence is also observed with the change of excitation wavelength. Systematical strategy was followed to approach the physical origin of the near-infrared luminescence and we proposed that three different bismuth active centers contribute to the near-infrared luminescence in the germanate glasses. A comprehensive explanation for the tunable luminescence is given, combining the concentration, energy transfer, and chemical equilibrium of these active centers in the glasses. With the increase of melting temperatures and the increase of reducing extent of the preparation atmosphere, bismuth species transform from Bi3+ to Bi2+, Bi+, Bi0 and bismuth clusters, and then to bismuth colloid. Of particular interest is that red tunable luminescence was also observed by modulating doping level, preparation atmosphere, and excitation wavelength. Besides, the trapped-electron centers in germanate glasses can interact with bismuth species of high valence states leading to the formation of bismuth active centers of low valence states and the decrease of trapped-electron centers. This tunable ultra-broadband luminescence is helpful for a better understanding of the origin of the near-infrared luminescence in Bi-doped glasses and may have potential applications in varieties of optical devices.

Broadband optical amplification near 1300 nm in bismuth-doped germanate glass

In this paper, we present the broadband optical amplification in bismuth-doped germanate glass, at the second telecommunication window when excited with 808 nm and 980 nm laser diodes, respectively. The amplification range is from 1272 nm to 1348 nm wavelength, which is within the O-band of silica fiber communication. This bismuth-doped glass can be used as ultra broadband amplification material for wavelength-division-multiplexing (WDM) at the second telecommunication window.