Predictable tendency of Bi NIR emission in Bi‐doped magnesium aluminosilicate laser glasses

Because of superbroad luminescence in the range of near infrared (NIR), Bi‐doped glasses and fibers have received more attentions recently for the applications in super broadband optical fiber amplifiers or new wavelength lasers. As the luminescence comes from the transitions between naked 6p orbitals of bismuth, it is very susceptible to slight changes of local field around Bi. Therefore, it is always very challenging to predict NIR emission of bismuth in advance. Here, we found bismuth NIR emission shows predictable tendency in ternary glass system of MgO–Al₂O₃–SiO₂. The emission peak shifts red along the content of magnesium upon the excitation of 484 nm, which follows a single exponential growth equation. In the meantime, the full width at half maximum (FWHM) is broadened while the lifetime keeps decreasing. Glass structure analysis on basis of FTIR, ²⁷Al NMR, ²⁹Si NMR spectra reveals that these changes correlate to integrity of glass network, the increased disorder of local field around bismuth and the enhanced interaction between bismuth and host, which are perhaps due to the linear increase of nonbridging oxygen, and the enhanced Si–O asymmetric stretching vibrations along with magnesium, respectively. Electron probe microanalysis shows good homogeneity of Si, Al, Mg, Bi, and O distribution within the samples, and yoyo experiments of heating and cooling between 30°C and 300°C reveal the good resistance of such doped glasses to thermal degradation. This makes the glasses promising in applications of fiber devices even under extreme condition such as at higher temperature. The finding in this work should be helpful for the design of Bi‐doped laser glasses in future.     

Tunable luminescence from bismuth‐doped phosphate laser glass by engineering photonic glass structure

Because of ultra‐broadband near‐infrared (NIR) emission bismuth‐activated glasses and fibers offer a new promising platform for novel photonic devices such as new type of optical amplifiers and broadly tunable fiber lasers. Yet, challenge remains to manipulate the NIR emission behavior of bismuth (Bi) in photonic glasses for efficient Bismuth‐doped fiber and fiber lasers. Here, by engineering phosphorus and aluminum's topology, broadly tunable NIR emission has been realized in Bismuth‐doped phosphate laser glass. Structural and optical analyses on ²⁷Al magic‐angle spinning nuclear magnetic resonance (MAS NMR), ³¹P MAS NMR, fourier transform infrared (FTIR) and static emission spectra suggest that polymerization of glass network can be improved by proper addition of aluminum into the system, which can be evidenced by partial conversion of Q² to Q³ species of phosphorus and the shift of P–O–P asymmetric stretching vibration toward lower frequency, and this turns out beneficial to Bi NIR emission. Embedding aluminum tetrahedra into phosphorus glass network can reduce the local crystal field around bismuth and therefore lead to the blueshift of Bi emission. This work presents new insights into the luminescent behavior of Bi ions in phosphate glass and it helps the design and fabrication of Bismuth‐doped glasses and fibers in future.     

Efficient Enhancement of Bismuth NIR Luminescence by Aluminum and Its Mechanism in Bismuth‐Doped Germanate Laser Glass

As a new member of laser glass family, bismuth‐doped glasses have received rising interests due to the application of fiber amplifiers and laser sources in the new spectral range for the next‐generation optical communication system. For practical application of the glasses, it must be considered on how to improve the luminescence efficiency. Here, we demonstrate that addition of aluminum can enhance the bismuth near‐infrared luminescence by more than 10 000 times, which is right followed by the discussion on the mechanism on why this can happen. We believe this work can be helpful for designing bismuth‐doped multiple component laser glasses with high efficiency. In addition, because of high susceptibility of bismuth to local field change, it can be used as probe ion to envision glass structures. Using bismuth as a luminescent structural probe, we can see the modifier ions of Bi⁺ are not completely randomly distributed inside germanate glass and they prefer the residence around tetrahedral AlO₄ sites.     

Improving luminescence behavior and glass stability of tellurium-doped germanate glasses by modifying network topology

Broadband near-infrared (NIR) luminescent materials are of great interest for their potential application in optical communication, remote sensing, imaging, and homeland security. Tellurium (Te) doped glasses were recently recognized as such a promising candidate due to their broadband NIR emission (700–1700 nm). However, the achievement of Te-doped glasses with high luminescence efficiency and glass stability (GS) remains a daunting challenge. Here, the luminescence behavior and GS of Te-doped germanate glasses are manipulated by tailoring the glass network topology. Te NIR luminescence is enhanced by tailoring topological cages in germanate glass network structure through varying glass network modifiers. Meanwhile, the GS of potassium germanate glass is significantly enhanced due to increased network connectivity caused by the co-introduction of alkaline earth oxides. Finally, NIR luminescence intensity of the glass was further enhanced by optimizing the doping concentration of TeO₂. The findings here could contribute to designing Te-activated glasses with improved performance for application in optical amplifiers and tunable fiber lasers.     

Manipulating Bi NIR emission by adjusting optical basicity,boron and aluminum coordination in borate laser glasses

Bismuth‐doped (Bi) glasses and fibers have raised considerable attention for broadband emission and tunable fiber lasers in the near infrared (NIR) region. However, they suffer from low efficiency and it remains challenging to enhance Bi NIR emission. Here, we propose a facile way to enhance and tune the Bi NIR emission by adjusting optical basicity and modulating the boron and aluminum coordination in borate glasses. We find that BO₄ and AlO₅ species favor Bi NIR emission, right followed by the analyses of static emission spectra, the Fourier transform infrared (FT‐IR), and nuclear magnetic resonance (NMR) spectroscopy. Furthermore, abnormal Bi NIR luminescence phenomenon and boron anomaly were observed, which are attributed to the synthetic effect of B and Al coordination transformation. Besides, we find that BO₄ tetrahedron plays a major role in enhancing Bi NIR emission at low Al content, while AlO₅ hexahedron group will dominate at high Al concentration. Our investigation may give an insight into the luminescent behaviors of Bi in borate glasses and contribute to improving the performance of Bi‐doped fiber and fiber lasers in future.     

New strategy to enhance the broadband near‐infrared emission of bismuth‐doped laser glasses

Bismuth‐doped glasses and fibers with broadband near‐infrared (NIR) emission have garnered much attention on account of their potential applications in new fiber lasers and broadband amplifiers. Yet the realization of high gain from Bi‐doped fibers and highly efficient NIR emission from Bi‐doped glasses are still a stubborn puzzle. The enhancement of Bi NIR emission is normally based on modifying the glass composition and topology, which will change the structure of the glass over a wide range and alter the thermal or mechanical properties of the glass simultaneously, making it more complicated for the designing and fabricating of Bi fibers with good performance. Here, we find that a trace addition of Si₃N₄ can efficiently enhance the Bi NIR emission without changing the glass structure significantly, right followed by spectral and structural analysis. ²⁷Al NMR measurement reveals that the short‐ to medium‐range order of this glass is unchanged. The EPMA measurement confirms the homogeneity of fabricated glass. The great enhancement and red‐shift under blue light excitation may originate from the conversion of Bi active centers to low valence. Our results indicate that the trace addition of nitride could be a facile and maneuverable way to control the valence of active ions in glasses, which may contribute to improving the performance of photonic glasses.     

The origin of the heterogeneous distribution of bismuth in aluminosilicate laser glasses

As one kind of novel and burgeoning laser materials, bismuth‐doped silicate glasses have aroused increasing attention for the super broadband near‐infrared (NIR) emission. However, the large optical scattering loss, resulting from optical heterogeneity in glass color and refractive index, limits their further applications in telecommunication system. Thus, it is urgent to uncover the essence of heterogeneity in Bi‐doped silicate glasses and subsequently improve glass optical performance. It will give us some hint to homogenize the glass component and Bi active centers so as to boost the development of Bi‐based glass materials. Here, taking 1 typical Bi‐doped calcium aluminosilicate glass as an example, we revealed the origin of the optical heterogeneities in glass color and refractive index through the NIR emission spectra, electron probe microanalyzer (EPMA) of elements and X‐ray photoelectron spectroscopy (XPS) of Bi 4f_5/2, Bi 4f_7/2, and Al 2p. The inhomogeneous distribution of Bi and aluminum components is responsible for the heterogeneity in this glass system. In addition, we found that tetrahedral coordinated aluminum favors the existence of Bi NIR centers, consequently resulting in enhanced Bi NIR emissions. Furthermore, based on our results and the role of Al³⁺ in glass network, we demonstrate the homogenizing of glass component by finely tuning glass composition. This work will enrich the understanding of Bi‐doped laser glass and provide a guideline for the design of component‐derived Bi‐doped silicate glasses and fibers with efficient NIR emission and high optical quality.     

Erbium doped Bi2O3-B2O3 glass-ceramics containing Bi3B5O12 and CaF2 nanocrystallites for 1.53 μm fiber lasers

Trivalent erbium ions doped Bi₂O₃-B₂O₃ transparent glass ceramics containing CaF₂ were prepared and characterized through X -ray diffraction, scanning electron microscopy, Fourier transform infrared absorption, optical absorption, and near infrared emission for 1.53 μm fiber lasers. The glass ceramics obtained by applying thermal treatment at 575 °C for 5 h and 575 °C for 10 h contain Bi₃B₅O₁₂ and CaF₂ crystallites. The Judd-Ofelt theory was applied to evaluate various spectroscopic and laser characteristic properties. The NIR emission corresponding to the ⁴I_13/2 → ⁴I_15/2 (∼1.53 μm) transition was studied by exciting the samples at 514.5 nm laser radiation. The stimulated emission cross-sections of ∼1.53 μm luminescence were also obtained applying the Mc Cumber theory. The experimental results confirm that the transparent glass ceramic obtained at a thermal treatment of 575 °C for 10 h is more suitable to design fiber lasers for diverse applications in the fields of industry, medicine and scientific research.     

Ultra-broadband and thermally stable NIR emission in Bi-doped glasses and fibers enabled by a metal reduction strategy

Bismuth (Bi)-doped glasses with broadband near-infrared (NIR) emission have been drawing increasing interest due to their potential applications in tunable fiber lasers and broadband optical amplifiers. Yet, the implementation of highly efficient and ultra-broadband Bi NIR emission covering the whole telecommunication window remains a daunting challenge. Here, via a metal reduction strategy to simultaneously create a chemically reductive environment during glass melting and enhance the local network rigidity, a super broadband (FWHM ≈ 600 nm) NIR emission covering the entire telecommunications window with greatly enhanced intensity was achieved in Bi-doped germanate glasses. More importantly, due to the excellent thermal stability, the super broadband Bi NIR emission can be well retained after the glass was drawn into an optical fiber. Furthermore, the transmission loss of 0.066 dB/cm at 1310 nm and an obvious broadband amplified spontaneous emission spectrum spanning a range of 1000–1600 nm were observed in this fiber. This work can strengthen our comprehension of the complicated Bi NIR luminescence behaviors and offer a feasible and universal way to fabricate tunable fiber lasers and broadband optical amplifiers based on Bi-doped multicomponent glasses.     

Wavelength Tailorability of Broadband Near‐Infrared Luminescence in Cr4+‐Activated Transparent Glass‐Ceramics

Four Cr⁴⁺‐activated transparent glass‐ceramics containing different species of silicate nano‐crystals (Zn₂SiO₄, Mg₂SiO₄, Li₂ZnSiO₄, and Li₂MgSiO₄) were successfully prepared. Absorption spectra, photoluminescence spectra, lifetime decay curves, and quantum yield of these transparent glass‐ceramics were measured. According to the crystal field strength of Cr⁴⁺‐incorporated tetrahedral sites, the broadband near‐infrared (NIR) luminescence of Cr⁴⁺ can be tailored from 1130 to 1350 nm and the lifetime of Cr⁴⁺ luminescence can be prolonged from 6 to 100 μs. Quantum yield in the transparent glass‐ceramics containing Li₂ZnSiO₄ nano‐crystals reached at 17%, which is the highest value of NIR luminescence in transition‐metal‐activated glass materials.     

Near‐Infrared Broadband Photoluminescence of Bismuth‐Doped Zeolite‐Derived Silica Glass Prepared by SPS

Through the order–disorder transition process of zeolites, bismuth‐doped zeolite‐derived silica glasses with broadband near‐infrared (NIR) photoluminescence have been successfully prepared by spark plasma sintering (SPS). The samples were characterized by X‐ray diffraction, UV‐vis, photoluminescence, and fluorescence lifetime. The results showed that as‐prepared samples possessed favorable broadband NIR luminescence. The NIR emission (peaked at ~1140 nm) intensity decreased with increasing the bismuth doping concentration when excited by 500 and 700 nm. The tendency was different from the emissions (peaked at ~1240 nm) excited by 800 nm. In addition, the NIR fluorescence peaks of the fixed Bi concentration sample can be observed almost around 1140 or 1240 nm when excited by different wavelengths from 500 to 950 nm. These phenomena implied that the NIR emission peaked at different wavelengths may originate from different bismuth species. Three kinds of Bi active centers Bi⁺, Bi⁰, and (Bi₂)^2? were proposed to contribute to the NIR emission peaks at ~1140, 1240, and 1440 nm, respectively. Interestingly, a broadband NIR emission peaked at 1207 nm with a full‐width at half maximum of 273 nm was observed when excited by 600 nm, whose intensity was stronger than that excited by 800 nm. This property might be useful for broadband fiber amplifiers and tunable lasers.     

Experimental and theoretical studies on NIR luminescence of titanate-germanate glasses doped with Pr3+ and Tm3+ ions

Near-infrared (NIR) luminescence of Pr³⁺ and Tm³⁺ ions in titanate-germanate glasses has been studied for laser and fiber amplifier applications. The effect of the molar ratio GeO₂:TiO₂ (from 5:1 to 1:5) on spectroscopic properties of glass systems was studied by absorption, luminescence measurements, and theoretical calculations using the Judd–Ofelt theory. It was found that independent of the TiO₂ concentration, intense NIR emissions at 1.5 and 1.8 μm were observed for glasses doped with Pr³⁺ and Tm³⁺ ions, respectively. Moreover, several spectroscopic and NIR laser parameters for Pr³⁺ and Tm³⁺ ions, such as emission bandwidth, stimulated emission cross-section, quantum efficiency, gain bandwidth, and figure of merit, were determined. The results were discussed in detail and compared to the different laser glasses. Systematic investigations indicate that Pr³⁺-doped system with GeO₂:TiO₂ = 2:1 and Tm³⁺-doped glass with GeO₂:TiO₂ = 1:2 present profit laser parameters and could be successfully applied to NIR lasers and broadband optical amplifiers.     

Enhancement of ultrabroadband Bi NIR emission via fluorination for all wavelength amplification of optical communication

Bismuth (Bi)-doped photonic glasses and fibers with broadband near-infrared (NIR) photoemission have potential applications in tunable lasers and broadband amplifiers. Yet, when it comes to all wavelength amplification of optical communication, it remains challenging to achieve efficient Bi NIR emission in the technically relevant C- and L- bands (1530-1625 nm). Here, we propose a scheme by fluorination triggered enhancement of ultra-broadband Bi NIR emission in nitrided germanate glasses. Besides, compared to previous research, a unique and efficient Bi-activated ultra-wideband NIR emission with new emission bands peaked at ~924 and ~1520 nm under excitation of 450 nm are obtained in nitrided germanate glasses after fluorination. Moreover, the fluorination can modulate the local chemical environment by forcing the conversion of aluminum species from AlO₄ to AlO₅ and AlO₆ and consequently increase the flexibility of the glass network structure, which finally induces the conversion of Bi species and then manipulates the relative emission intensity of different Bi NIR centers. Thus, a flat and tunable emission spectrum covering the entire optical communication band is obtained by optimizing the fluoride amount. We believe this work is helpful to design the Bi-doped tunable fiber lasers and ultra-broadband amplifiers for all wavelength amplification of optical communication.     

2.5–5.5 μm mid-infrared emission from Ni2+-doped chalcohalide glass ceramics containing CsPbI3 perovskite nanocrystals

The development of mid-infrared (MIR) broadband tunable lasers urgently needs high performance laser gain materials. Transition metal (TM) ions doped glass ceramics are considered to be efficient MIR broadband laser gain media. However, it is difficult to achieve gain because of the large scattering loss and low luminescence efficiency. In this paper, GeS₂–Sb₂S₃–CsI–PbI₂ chalcohalide glass ceramics containing CsPbI₃ perovskite nanocrystals are fabricated by the melt-quenching method and subsequent heating treatment. The crystallization behavior of CsPbI₃ nanophase and MIR luminescence properties of Ni²⁺ dopant are systematically investigated. Evidently, spherical CsPbI₃ perovskite nanocrystals are precipitated and uniformly distributed in the glassy matrix, which can reduce the light scattering and make the chalcohalide glass ceramics have a high transparency. Moreover, an ultra-broadband MIR emission in the range of 2.5–5.5 μm is observed for the first time, to our best knowledge, from Ni²⁺-doped chalcohalide glass ceramics containing CsPbI₃ perovskite nanocrystals. The newly developed Ni²⁺-doped chalcohaldie glass ceramics could be promising gain media for MIR broadband tunable lasers.     

Glass-forming region and enhanced Bi NIR emission in sodium tantalum silicate laser glass

Bismuth (Bi)-doped glasses and fibers are of current interest as promising active media for new fiber lasers and amplifiers due to their 800-1700 nm near-infrared (NIR) emission. However, the optically active Bi centers in silica are easily volatilized during high-temperature fiber drawing, which results in low Bi doping concentration and low gain NIR luminescence. Here, we explored the glass-forming region in a model glass system of sodium tantalum silicate (Na₂O-Ta₂O₅-SiO₂) glass and attained suitable glass host for enhancing Bi NIR emission, right followed by detailed analysis on optical and structural characterization. Glass-forming region roughly lies in where Ta₂O₅ ≤ 30 mol%, SiO₂ ≥ 40 mol%, and Na₂O ≤ 40 mol%. Not only is glass-forming ability improved but also Bi NIR emission is enhanced (~60 times) by the introduction of Ta into glass network. Dissociated Na cations are restricted beside Ta, the high-field-strength element, so that the negative impacts of Na cations on glass formation and Bi NIR emission are weakened, which is responsible for the highly enhanced Bi NIR emission. This work helps us understand the glass-forming of tantalum silicate glass systems and luminescent behaviors of Bi. Hopefully, it could contribute to designing the Bi-doped laser glasses and high gain fibers with stable luminescent properties in future.     

Er~(3+)-Tm~(3+)共掺碲酸盐玻璃中近红外超宽带发光性质

研究了Er~(3+)-Tm~(3+)共掺TeO_2O-Nb_2O_5-Ln_2O_3(TKNL)碲酸盐玻璃的近红外发光光谱以及上转换光谱性质,该碲酸盐玻璃的起始析晶温度与玻璃转变温度之差△T为136℃,表明此玻璃具有良好的热稳定性,有利于拉制光纤。在808 nm半导体激光器的激发下在近红外波段观察到半高宽为185 nm的宽带近红外发光。通过对不同Tm~(3+)浓度以及不同激发波长下TKNL玻璃的近红外发光以及上转换发光的研究,探讨了Er~(3+)m~(3+)之间的能量传递机理。上述玻璃材料有望用作S和C波段光纤放大器的增益介质。     

稀土离子掺杂的多组分玻璃光纤

稀土离子掺杂的多组分玻璃光纤在宽带光纤放大器与上转换光纤激光器中具有重要的应用。本文介绍了稀土离子掺杂多组分玻璃光纤宽带光纤放大器与上转换光纤激光器的工作机理,综述了其最新相关研究进展,并对目前研究中需进一步解决的问题及未来的发展提出了建议与展望。从当前的研究现状来看,碲酸盐玻璃和铋基玻璃应是今后宽带玻璃光纤放大器光纤基质材料的研究重点。对上转换光纤激光器基质材料而言,如何获得更好的具有低声子能量和优良物化性能的玻璃基质,还需进一步探索。     

Structural and optical properties of Ho2TeO6 micro-crystals embedded in tellurite matrix

In the present work, Ho³⁺ doped tellurite glasses and glass ceramics have been explored. Micro-sized Ho₂TeO₆ crystals have been successfully prepared in TeO₂ matrix using two step heat treatment method. Structural, thermal and optical properties have been investigated using different characterization techniques. Variations in above mentioned properties were observed to improve when these crystals grew in TeO₂ matrix. We have reported several anti-Stokes and Stokes emissions extended from UV to NIR region on excitation with 532 and 976 nm laser radiations. The unique structure of Ho₂TeO₆ crystal was expected to play a crucial role in enhancement of the optical properties of glass ceramics.     

Improving the NIR light‐harvesting of perovskite solar cell with upconversion fluorotellurite glass

Upconversion glasses are capable of converting the sub‐bandgap NIR light into photons of a particular wavelength which can be efficiently utilized by solar cells. Herein, the Yb³⁺/Er³⁺ co‐doped fluorotellurite upconversion glasses were prepared. The most intense upconversion luminescence (UCL) under 980‐nm LD excitation was obtained in the glass with Yb³⁺‐to‐Er³⁺ molar ratio of 10:1. The dependences of UCL on the pump power and temperature were investigated. The UCL can be mainly attributed to the two‐photon involved energy transfer processes and is very stable to the change in temperature even when heated up to 200°C. The subsequent implementation of the glass as upconverter for a MAPbI_3‐xCl_x‐based perovskite solar cell (PSC) resulted in an open circuit voltage of 0.83 V and a short circuit current density of 0.32 mA/cm². This application of upconversion glass for enhancing the NIR light harvesting offers a promising way to improve the photo‐electric conversion efficiencies of PSCs.     

Quantum-dots-precipitated rare-earth-doped glass for ultra-broadband mid-infrared emissions

Mid-infrared (MIR) fiber lasers have wide application prospects and great commercial value in the fields of medical operation, remote sensing and military weapon, etc. At present, Tm³⁺-doped glass can obtain broadband luminescence at 2 μm, the introduction of Ho³⁺ or Er³⁺ ions also shows a tunable MIR emission but with limited success. Herein, the rare-earth (RE) doped glass with quantum dots (QDs) precipitation is proposed for achieving ultra-broadband MIR emissions. The types and sizes of QDs are determined by the XRD and TEM, and their optical properties are further characterized by the absorption and emission spectra as well as the lifetime decay curves. It is found that the diameter of the QDs is gradually increased from 1.7 to 5.1 nm by increasing the heat-treated temperature from 490°C to 530°C, respectively. Interestingly, an ultra-broadband emission covering 1400-2600 nm is achieved from the heat-treated glass upon the excitation of 808 nm laser diode as a result of an overlapped emission from Tm³⁺ and PbS. All results suggest that these QDs-precipitated RE-doped glasses have important application prospects in ultra-broadband MIR laser glass, glass fiber, and fiber lasers.