Generation of Emission Centers for Broadband NIR Luminescence in Bismuthate Glass by Femtosecond Laser Irradiation

Bismuth-doped glasses have recently received significant interest as potential material for ultrabroadband optical amplification in the telecommunication spectral bands, as well as as gain material for fiber lasers. However, the nature of the active centers that are responsible for the observed near-infrared (NIR) luminescence is still highly debated. In order to probe the mechanism that leads to NIR emission in bismuth-containing glasses, femtosecond (fs) laser irradiation was used. It is shown that local absorption properties in the visible spectral range can be altered in initially transparent bismuthate glasses after fs laser irradiation. Induced absorption centers exhibit the well-known broadband optical emission peaking at ∼1250 nm when excited with a 785 nm diode laser. Absorption and emission intensities increase with increasing average pulse energy. These observations are interpreted as a photo-induced reduction reaction of Bi³⁺ to Bi⁺ species, while the previously discussed formation of Bi-clusters by ion diffusion is excluded due to the very short interaction time that results from the use of fs laser. Bi⁺ species are, therefore, proposed as the major origin of NIR emission from Bi-doped glasses.     

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.     

若干无机/有机复合光功能材料及相关器件研究进展

在无机基质中光学均匀掺杂有机光添生物质以获得复合光功能材料是近年来的研究热点,复合光功能材料的溶胶－凝胶低温合成技术为其在非线性光学、固态可调谐染料激光器、发光显示、光致变色、光化学烧孔等领域的应用提供了可能。本文对无机／有机复合光功能材料的制备技术、结构与性能的表征手段,及其作为发光、激光、波导、波分复用、光致变色器件在光通信中的应用等研究进展作了评述。     

Transparent luminescent bulk nanocomposites of polysiloxane embedded with CdS nanocrystallines by a direct dispersion process

Transparent luminescent bulk nanocomposites of polysiloxane (PSO) embedded with semiconductor nanocrystals (NCs) have been fabricated by the direct dispersion of CdS NCs in alkyl-(poly)siloxane (APS) followed by co-polymerization. The non-polar characteristics of the APS precursor are compatible with the CdS NC surface (oleylamine), which allows the direct dispersion of the CdS NCs without the need of any surfactant exchange. Chemical crosslinking of the NC-APS dispersion via hydrosilylation between Si-H and the vinyl group in APS immobilizes the CdS NCs in the polysiloxane network. Net-shaped three-dimensional bulk transparent polysiloxane/CdS NC composites were obtained by liquid casting of the NC-precursor dispersion and chemical crosslinking. The PSO/CdS NC composites show visible luminescence under ultraviolet excitation and the luminescent color is tunable from blue to red by controlling the NC concentration in the composite. Photoluminescence spectral analyses reveal the origin of the luminescence as being from the defect emission of the CdS NCs (550-900 nm) and an emission from the PSO matrix (380-550 nm). The luminescent spectra covered a wide range from the ultraviolet to the near-infrared region. The luminescence of the PSO/CdS NC nanocomposites was stable without any apparent degradation after exposure to air for a long time. This simple direct dispersion process is feasible for the fabrication of luminescent nanocomposites with useful optical properties for potential applications in optics and photoelectron devices.     

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.     

Simultaneous control of the chemical state and local environment of Cr dopant in glass for extended emission

Control of the chemical state and local environment of Cr dopant in glass through self‐limited nanocrystallization is presented. Interesting wavelength‐tunable and ultra‐broadband near‐infrared luminescence with the full width at half maximum of about 380 nm from obtained Cr‐activated glass‐ceramics are demonstrated. The results indicate that the presented method may be an effective means of fabricating multifunctional optical gain materials and wideband fiber light sources.     

Enhanced tunable mid-infrared emissions by controlling rare earth ion energy transfer processes in multifunctional multiphase solids

Owing to the increasing application of high-performance and multifunctional mid-infrared (MIR) optoelectronic devices, it is important to achieve a high emission efficiency and broadband tunable luminescence. In this study, nanocrystalline units with unique properties were integrated into an amorphous frame with high transmittance and infinite ductility to achieve an enhanced MIR emission. In the single active ion-doped system, owing to the combination of the lower phonon energy of the crystal, the fixed position of the crystal lattice, and the glass transparency, a substantial increase in the infrared fluorescence intensity was achieved. Particularly, an excellent 3 μm luminescence was realized by the stable composite material. In the co-doped system, a bottom-up strategy was adopted to achieve full coverage of the 2 μm MIR atmospheric window, and the results confirmed that the spatial distribution of the optically active nanocrystal units in the glass frame effectively controlled the energy transfer processes.     

Erbium-Ion-Doped Tellurite Glass Fibers and Waveguides—Devices and Future Prospective: Part II

Following on from Part I of this review article that focuses on the suitability of Er³⁺-doped tellurium oxide glass for optical amplification in fiber, this Part II article describes how the fiber gain data were then employed to engineer amplification in waveguides, which can be integrated with semiconductor pump sources. The gain characteristics and bandwidth of a phosphate modified tellurite waveguide formed on a GaAs substrate are discussed. The limiting structural compatibility of Er³⁺-doped tellurite glass with polydimethylsiloxane polymer for active–passive integration is overcome by adopting a nanoscale super-lattice approach for waveguide engineering.     

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.     

Mid-infrared luminesce of ZnS:Cr2+-glass composite and fiber

Cr²⁺-doped materials with mid-infrared (Mid-IR) broadband luminescence are of fundamental importance for various applications, such as solid-state lasers technology, biolabeling, optical telecommunication, and solar energy management. Especially, Cr²⁺-doped glass has been considered as one of important material candidates. The major challenge is the precipitation of crystals doped with Cr²⁺ ions in glass. So, “crystals in glass composite” is an effective method to solve this issue. Here, we describe a ZnS:Cr²⁺ in borophosphate glass composite (CZPB) which exhibits Mid-IR luminescence in the region from 1700 to 2900 nm with the full width at half maximum (FWHM) of about 690 nm. In addition, the materials can also be fabricated into fiber without obvious change in the characteristic luminescence band. The results provide new opportunities for the construction of the broadband fiber light source operating at Mid-IR waveband region.     

Crystallization control in Ni2+-doped glass-ceramics for broadband near-infrared luminesce

The research of doped photonic glass has recently attracted much attention owning to the significant applications in various fields, including lasers, photovoltaics, and optical amplification. In this work, we present the design, fabrication, and experimental implementation of a novel fluorosilicate photonic glass-ceramics with broadband luminescence. We demonstrate that precipitated nanocrystals can be tuned by changing the heat-treatment temperature. This proposal offers an excellent opportunity for controlling the local environment around Ni²⁺ dopant. Consequently, the broadband and flat emission covering a waveband from 1200 to 2400 nm with a bandwidth of 605 nm can be realized. The possible physical mechanism, which can be attributed to the gradual change of nanocrystals from K₂SiF₆ to KCdF₃ with the enhancement of the heat-treatment temperature, is also discussed.     

Effect of sol maturation on the preparation of luminescent ormosils

An UV‐polymerization approach was proposed to construct luminescence organic‐inorganic hybrid. Methacryloxypropyltrimethoxysilane (MAPTMS) was chosen as sol–gel precursor to prepare the host matrix and acrylic europium Eu(AA)₃ was used as guest dopants. Structural modifications during irradiation were evident in both the inorganic and organic domains of the hybrid material. The influence of condensation degree of the silicate network on the photopolymerization kinetics of organic moieties was investigated. It appeared that the sol maturation time was of vital importance to the phase homogeneity and optical transparency of materials. To get more efficient copolymerization and higher luminescence intensity of the target ormosils, two key processing factors including incorporation time and entrapping concentration are reported. Incorporation time when acrylic europium was introduced into the matrix during sol maturation is found to be helpful to overcome phase separation. The effect of entrapping concentration of europium(III) compound on the luminescence performance was further studied. Material synthesized by this approach has three advantages: optical transparency with little phase separation, organic and inorganic composite with interpenetrating network, covalent grafting of acrylic europium without luminescent species leakage. This “photopolymerization of molecular grafting” strategy is hopeful to offer a promising development for luminescent ormosil glasses. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45146.     

Epoxy silicone based matrix materials for two-photon patterning of optical waveguides

3D polymeric optical waveguides play an intrinsic role in a rapidly developing area of broadband communications. Advances in the field of electronics means there is a greater demand for higher speeds, larger data storage, smaller components and the improvement in the design of integrated optical circuits. Two-photon photopolymerisation (2PP) is a promising three-dimensional microfabrication technique, which can be used to produce structures in the sub-micron region. With the use of near-infrared (NIR) lasers, 3D optical waveguides can be fabricated in polymer-based matrix materials, based on the increase of the refractive index in the vicinity of the laser focus.The development of a new polysiloxane material, used in the study of the integration of optical interconnects on printed circuit boards is presented. The desirable properties of epoxy functional silicones crosslinked with diamines deem them suitable for such applications. An epoxy terminated polysiloxane; crosslinked with an aminopropyl disiloxane has been developed as a suitable material for the fabrication of optical waveguides by two-photon absorption (TPA). The material fulfils a number of requirements including a good refractive index contrast between the matrix material and inscribed waveguide, full flexibility and high thermal stability.The matrix material was characterised by Fourier transform infrared spectroscopy (FTIR) and thermal gravimetric analysis (TGA) The optical waveguides were characterised by phase contrast microscopy, and were directly integrated onto specially designed PCB’s by correctly positioning waveguide bundles between optoelectronic components using TPA, making it possible to detect transmitted photocurrents.     

Controllable ultra-broadband visible and near-infrared photoemissions in Bi-doped germanium-borate glasses

The design of functional materials with tunable broadband luminescence performance is still of great interest in the fields of lighting, solar cells, tunable lasers, and optical amplifiers. Here, via a melt-quenching method, a series of bismuth (Bi)-doped germanium-borate glasses with composition of 40GeO₂–25B₂O₃–25Gd₂O₃–10La₂O₃–xBi₂O₃ have been prepared, in which multiple Bi active centers can be stabilized simultaneously. Dual-modulating modes of visible (380-750 nm) and near-infrared (NIR) (1000-1600 nm) broadband photoemissions were effectively controlled under flexible excitation scheme. Photoluminescence (PL) spectra at low temperature 10-298 K were appropriately employed to interpret such an unusual wide visible emission band. To further illustrate the origin of NIR component, transmission electron microscopy (TEM) measurement was carried out. It is demonstrated experimentally that the visible emission mainly originates from the collective contribution of the ³P₁/³P₀¹S₀ transitions of Bi³⁺, while the broadband NIR luminescence should be related to the formation of low valent Bi⁺ and (or) Bi⁰ centers. This work may help to enhance the knowledge of the complex luminescence mechanism for the Bi species and it also enables such transparent glass materials to be a promising candidate for the multifunctional tunable light source.     

Chalcogenide glasses with embedded ZnS nanocrystals: Potential mid‐infrared laser host for divalent transition metal ions

Chalcogenide glasses (ChGs) containing II‐VI chalcogenide (ChG) nanocrystals such as ZnS/Se have recently been intensively studied as promising mid‐infrared nonlinear optics and laser materials, yet preparation of pure‐phase II‐VI nanocrystals embedded in ChGs via controlled crystallization is still very challenging. In this study, a new system of ChGs and glass ceramics (GCs), viz., (100?x)As₂S₃–xZnSe (x = 0 ~ 30 mol%), is synthesized, and its physical and optical properties including density, molar volume, microhardness, glass transition temperature, glass network structure, transmission, and refractive index are comprehensively characterized. Significantly, it is initially demonstrated that pure ZnS nanocrystals can be precipitated in GCs simply by a thermal treatment process. The composition and thermal treatment temperature dependencies of crystallization are studied using X‐ray diffraction spectroscopy, and the morphology of the nanocrystals by high‐resolution transmission electron microscope. The ChG GCs with embedded ZnS nanocrystals retaining good transparency can be a potential host laser material for divalent transition metals (e.g., Cr²⁺/Fe²⁺, etc.), and thus used for ultrabroadband tunable continuous or ultra‐short‐pulsed mid‐infrared fiber lasers.     

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.     

Novel ultraviolet-opaque, visible-transparent and light-emitting ZnO-QD/silicone composites with tunable luminescence colors

Multifunctional, ultraviolet (UV)-opaque, visible-transparent and light-emitting materials with tunable luminescence colors are highly desirable for many applications in areas of ultraviolet shielding, light-emitting diodes and optical lenses etc. In this work, ZnO quantum dots (ZnO-ODs) with various sizes are first synthesized using a simple sol-gel route and novel multifunctional ZnO-QD/silicone composites with tunable luminescence colors are then prepared via a simple direct mixing method by uniformly dispersing ZnO-QDs in the silicone matrix. The structure and morphology of the ZnO-QD/silicone composites are characterized using high resolution transmission electron microscopy and attenuated total reflection Fourier transform infrared spectroscopy. UV-vis spectrometer and fluorescent photometer are used to study the optical properties of ZnO-QD/silicone composites. The results show that the ZnO-QD/silicone composites are opaque in the UV region, transparent in the visible region and also light-emitting with tunable luminescence colors from blue to yellow-green.     

树脂基复合材料中埋入大直径光纤性能的研究

本文依据国家有关的复合材料测试标准对树脂基复合材料埋入与不埋空心光纤进行了对比实验。实验结果表明大直径空心光纤埋入树脂基复合材料中对其性能的影响是比较小的,不会影响到树脂基复合材料工程结构中性能和使用。从而为复合材料的智能自诊断与自修复提供了一种研究的新方法。     

铋掺杂铝硅酸盐玻璃的超宽带近红外发光性质

采用高温熔融法制备了组分为50SiO_2-xAl_2O_3-(50-x)MgO-Bi_2O_3(x=5,10,15,20,摩尔比)的铋掺杂铝硅酸盐玻璃。研究了铋掺杂铝硅酸盐玻璃超宽带近红外发光性质,探讨了玻璃基质的光学碱度对铋离子宽带发光特性的影响。结果表明:在690nm和808nm的激发下,铋掺杂铝硅酸盐玻璃的红外荧光中心分别位于1106nm和1294nm;随光学碱度的增强,铋离子的红外发光强度减弱。并对铋离子超宽带发光的机理进行了探讨,认为其红外发光源于低价的Bi~+和Bi~(2+)。     

Two-wavelength excitation–driven robust operation of green up-conversion emission in Er3+-doped oxyfluoride glass–ceramic

Efficient optical modulation enables a significant improvement of optical conversion efficiency and regulation of optical response rate, showing great potential for optoelectronics applications. However, the weak interaction between photons poses a strong obstacle for manipulating photon–photon interactivity. Here, upon simultaneous excitation of 850 and 1550 nm, a fast–slow optical modulation of green up-conversion (UC) luminescence in oxyfluoride glass ceramics containing NaYF₄:Er³⁺ nanocrystals can be achieved. Compared with the sum of luminescence intensity excited by the two single-wavelengths, green UC luminescence excited by simultaneous two-wavelength presents an obvious increase by approximate six times. Interestingly, the response rate of green UC luminescence relies on the pump strategy of two-wavelength excitation, showing as high as two times of the fast–slow response difference. The fast–slow optical modulation of green UC luminescence under two-wavelength excitation is promising for emerging applications in all-optical switching.