Er3+-doped antimony-silica glass and fiber for broadband optical amplification

In this paper, the synthesis, structure, and optical analysis of Er³⁺-doped antimony-silica glass system are reported. The hybridization of Si with Sb ions is found to be favorable for reducing the phonon energy of the glass system. The optical properties, including the emission intensity and bandwidth, can be simultaneously improved. Notably, the full width at half maxima (FWHM) of near-infrared emission from Er³⁺ can be broadened from 61 to 82 nm. Furthermore, the antimony-silica glass fiber is successfully prepared, and the luminescence and gain performance of the fiber are characterized. The antimony-silica glass exhibits excellent fiber-forming ability, and the obtained fiber shows excellent gain performance. The results suggest that antimony-silica glass is a promising gain material for fiber amplifier and laser.     

Tunable and high-color-rendering white light emissions in full visible spectral range in Ag-aggregates/Sm3+ co-doped germanate glass fluorophors

To achieve a tunable and high-color-rendering white light emission in full visible spectral range, the Ag-aggregates/Sm³⁺ co-doped germanate glass fluorophors were prepared by a melt-quenching method. Under the excitation of different wavelengths, the intense broadband emissions covering full visible spectral range from blue to red were gained in the germanate glasses only containing Ag-aggregates. From the optical spectral analyses, it was found that with increasing the excitation wavelengths, the emission peak position exhibits red-shift. However, the red component in the emission spectra is still of relative lack for realizing high quality white light, therefore Sm³⁺ was introduced as co-dopant to supply the red spectral component. In this way, a series of chroma-tunable and full-color-emitting white lights with color coordinates from (0.26, 0.25) to (0.30, 0.32) were successfully realized based on adjusting the excitation wavelengths and Sm³⁺ concentration. Particularly, the color rendering index (CRI) up to 97.6 was achieved. Furthermore, the luminescence thermal stability of Ag-aggregates/Sm³⁺ co-doped germanate glass fluorophors was investigated based on the Arrhenius model, and the corresponding ΔE values for Ag aggregates and Sm³⁺ emissions were confirmed to be 0.25 and 0.19 eV, respectively. In addition, a temperature sensing model was established based on the luminescence intensity ratio of Ag-aggregates to Sm³⁺, and the thermochromatic property of Ag-aggregates/Sm³⁺ co-doped germanate glasses was also evaluated. It was found that the luminescence color coordinates of Ag-aggregates/Sm³⁺ co-doped glass fluorophors always lie in the white light region when the sample temperature increases from 301 to 693 K, thus indicating that Ag-aggregates/Sm³⁺ co-doped glass fluorophors have potential application in solid-state lighting sources as a single-component white lighting material.     

Photorefractive properties of polyphosphazenes containing carbazole-based multifunctional chromophores

A series of amorphous polyphosphazenes containing carbazole-based multifunctional chromophores were synthesized. These polymers show low glass transition temperature (20-65 °C) and can easily be fabricated into optically transparent films with long-term stability. As an unambiguous evidence of photorefractive effect, preliminary two-beam-coupling experiments were performed at 633 nm under room temperature. All of these single-component polymers exhibited photorefractive performance without external electric field or prepoling, and gain coefficient of 91 cm⁻¹ was observed in a polymer with the lowest glass transition temperature. The influence of the alkylene spacer length between the side group and the polymer backbone on the glass transition temperature, chromophore loading, as well as the optical gain was discussed. The steady-state photorefractive performance of a polyphosphazene with the shortest alkylene spacer was enhanced significantly by adding a photoconductive plasticizer N-ethyl-carbazole to lower the glass transition temperature and a gain of 198 cm⁻¹ and a diffraction efficiency of 46% were achieved at zero electric field.     

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.     

Intense emission at 2.9 μm from Yb3+/Ho3+ co-doped TeO2–Ga2O3–ZnO tellurite glasses

Mid-infrared lasers have important applications in infrared countermeasures, sensing, environmental monitoring, biomedicine, and many military and civilian fields. In this work, an intense emission at 2.9 μm from Yb³⁺/Ho³⁺ co-doped TeO₂-Ga₂O₃-ZnO (TGZ) glass was reported. The 2 μm, 1.2 μm and visible emissions were also performed to understand the competitive luminescent mechanism. With the increase in Yb³⁺ concentration, all the emissions of Ho³⁺ increased, whereas the emission of Yb³⁺ decreased due to the phonon-assisted energy transfer from Yb³⁺ to Ho³⁺. The lifetimes of optimized 3 mol% Yb₂O₃ and 1 mol% Ho₂O₃ co-doped TGZ glass, which has the maximum emission intensity, are 548 μs and 1.7 ms at 2.9 and 2 μm, respectively. The Judd–Ofelt intensity parameters, absorption, and emission cross sections were calculated to evaluate the mid-infrared fluorescence properties of this new glass matrix material. The gain coefficients show that the 2 and 2.9 μm laser gain can be realized by small pump energy, indicating that this glass is a promising medium for the mid-infrared optical fiber laser.     

Mechanism for broadening and enhancing Nd3+ emission in zinc aluminophosphate laser glass by addition of Bi2O3

Nd³⁺-doped phosphate laser glasses have been attracting much attention and widespread investigation due to their high solubility of rare earth (RE) ions, excellent spectroscopic properties, and large damage threshold. However, the narrow NIR emission bandwidth (less than 30 nm) of these Nd³⁺-doped phosphate glasses limits their further application toward ultrahigh power field and efficient fiber laser in new region. Here, we demonstrate the broadening and enhancing of Nd³⁺ NIR emission in laser glass of zinc aluminophosphate through tuning the glass structure and covalency of Nd-O bond without limiting the radiative properties of Nd³⁺. The maximum bandwidth of 1.05 μm emission is broadened to 50 nm, which is comparable to that of Nd³⁺-doped aluminate laser glasses. Simultaneously, the lifetime of ⁴F_3/2 level is elongated nearly by two times. Structural and optical properties of prepared glasses were discussed systematically to reveal the mechanism. Detailed analysis on optical spectra and glass structure indicates that the bandwidth is affected by not only the covalency of Nd-O but also the compactness of glass structure. Our results could enrich our understanding about the relationship between local glass structure and luminescence behaviors of active centers, and may be helpful in designing new RE-doped laser glass systems.     

Surface modification and fabrication of white-light-emitting Tm3+/CdS quantum dots co-doped glass fibers

Due to the widely tunable band gap and broadband excitation, CdS quantum dots (QDs) show great promise for yellow-light luminescence center in white-light-emitting devices. The light intensity of the CdS QD-doped glass was enhanced by doping the Tm³⁺ ions due to the higher absorption rate. The influence of Tm³⁺ ions on the surface structure of CdS QDs was enormous according to the first-principles calculations. Doping Tm³⁺ ions change the surface state of CdS QDs, which will fix the QDs emission peaks and enhance the luminescence of CdS QDs at a lower heat-treatment temperature. White-light emission was obtained by tuning the relative concentration between Tm³⁺/CdS QDs. However, there is a fundamental challenge to fabricate QD-doped glass fibers by rod-in-tube method since uncontrollable QDs crystallization is hard to avoid. Herein, a white-light-emitting borosilicate glass fiber was fabricated by the “melt-in-tube” method using a special designed Tm³⁺/CdS QDs co-doped borosilicate glass with low-melting temperature as fiber core. After heat treatment, ideal white-light emission was observed from the fiber under excitation at single wavelength (359 nm). This finding indicates that Tm³⁺/CdS QDs co-doped glass fiber with white-light-emitting devices has potential application as gain medium of white-light-emitting sources and fiber lasers.     

Enhanced broadband NIR emission in glass–ceramic fibers containing Nd3+/Yb3+ co-doped YCa4O(BO3)3 disordered nanocrystal

Demands are increasing for ultrashort pulse laser in industrial applications, where the gain bandwidth of most optical fiber material is not wide enough, and developing a wide bandwidth gain medium is challenging. Glass–ceramic fibers containing Nd³⁺/Yb³⁺ co-doped YCa₄O(BO₃)₃ nanocrystals were fabricated by the molten core method and successive heat treatment. After a careful heat treatment, Nd³⁺/Yb³⁺ co-doped YCa₄O(BO₃)₃ nanocrystals were precipitated in the fiber core. Enhanced broadband near-infrared (NIR) emission from 850 to 1150 nm (bandwidth: ∼252 nm) was obtained in the glass–ceramic fiber compared to that of precursor fiber. These results suggest that the Nd³⁺/Yb³⁺ glass–ceramic fibers are promising for broadband NIR optical amplifications and lasers.     

Polychromatic tunable luminescence of Eu3+ doped CsPbBr3 quantum dot glass ceramic induced by mechanical crystallization

Nowadays, inorganic perovskite quantum dots (QDs) glass has become a hot topic in the field of new optical materials. In this work, the Eu³⁺ doped CsPbBr₃ QDs phosphate glass has been successfully prepared. Different from the traditional heat treatment method, the CsPbBr₃ QDs were prepared by mechanical crystallization. When the QDs glass was ground at different times, due to the synergistic effect of red emission (Eu³⁺) and green emission (CsPbBr₃ QDs), the prepared QDs glass can produce the red-yellow-green polychromatic luminescence phenomenon. Benefit from the dual-emission centers of CsPbBr₃ QDs and Eu³⁺ which do not interfere with each other, the relative sensitivity of the temperature sensing is up to 2.11% K^-1, proving that the prepared Eu³⁺ doped QDs glass has practical application in the field of temperature sensing. The glass material obtained in this way not only has tunability and favorable sensitivity but also provides an effective way for the preparation of QDs.     

Thermal Stability and Spectral Properties of Tm<Superscript>3+</Superscript>-Yb<Superscript>3+</Superscript> CO-Doped Tellurite Glasses

Glasses of the system 75TeO₂–20ZnO–5La₂O₃–0.8Tm₂O₃–xYb₂O₃ were prepared by high temperature melt cooling method. Results of differential scanning calorimetry indicate that, all glass samples have excellent thermal stability. Judd–Ofelt strength parameters, spontaneous emission probabilities, fluorescence branching rations, fluorescence radiative lifetime of Tm³⁺ ions in tellurite glass were calculated. The impact of Yb³⁺ concentration on the fluorescence properties of Tm³⁺ ions in the S band under the pumping wavelength of 465 nm was investigated in a suggestion that, ³H₄ radiative lifetimes will be prolonged and the performance of optical amplifier gain of Tm³⁺ in tellurite glass co-doped with 0.5 mol % Yb³⁺ ions will be improved.     

Near-infrared luminescence enhancement in Yb3+/Ho3+ co-doped bismuth-tellurite glass by tailoring glass network

In this work, the glass network has been tailored by introducing the modifier WO₃ when a Ho³⁺/Yb³⁺ co-doped bismuth-tellurite glass composition was designed. The physical, absorption, emission, structure, and gain characteristics of the glasses with the different contents of WO₃ were investigated comprehensively based on various tests and analytical methods such as absorption spectra, fluorescence spectra, Raman spectra, and J-O theory. The results show that both the optical band gap and the bridge oxygen content are enhanced remarkably while the substitution of TeO₂ by WO₃, accelerating the transition from [TeO₃] to [TeO₄] units. Simultaneously, the value of Ω₆ reached the maximum of 2.26×10^-20 cm² when the WO₃ is equal to 10 mol%, indicating that the Stark splitting of Ho³⁺: ⁵I₇ energy level is the weakest. The optimal FWHM and the gain coefficient are 143.3 nm and 2.22 cm^-1, respectively. Furthermore, a blue shift of the central wavelength in absorption and emission peaks can be observed at the 2 μm band. As mentioned above, the bismuth-tellurite glass prepared is an ideal gain material that can realize a wider spectra span.     

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.     

Effect of residual chlorine on fluorescence emission of Dy3+ doped chalcogenide glasses with low gallium content

Chlorine or chlorides are usually used as a dehydrating agent for removing the O-H or S(Se)-H in the preparation of high-purity chalcogenide glasses. However, the residual chlorine in some rare-earth ions doped chalcogenide glasses was found to have a great negative impact on fluorescence emission. In this work, the effect of residual chlorine on the fluorescence emission of Dy³⁺ ions in serial (Ge)GaAsSbS glasses was studied quantitatively, and the reasons were discussed. Cl₂ gas and SbCl₃ were used as the source of chlorine and their residual contents were controlled by the post-distillation process and added content, respectively. The results can give some suggestions for how to eliminate the negative effects of chlorine and improve the glass’ optical gain properties.     

Self-crystallized Ba2LaF7:Nd3+/Eu3+ glass ceramics for optical thermometry

Eu³⁺/Nd³⁺-codoped Ba₂LaF₇ transparent bulk glass ceramics were successfully fabricated by glass self-crystallization. The structure and morphology of the sample were investigated by X-ray diffraction, transmission electron microscopy (TEM), high-resolution TEM, and selected area electron diffraction. The fluorescence intensity ratios of Nd³⁺ emission at 800 nm to the Eu³⁺ emission at 699 nm (⁵D₀ → ⁷F₄) were measured under 578.3 nm laser excitation in a wide temperature range from 290 to 740 K. A relatively good temperature sensing performance was obtained with a maximum relative sensitivity of 1.02% K⁻¹ at 420 K. Both the emission peaks for temperature sensing were located in the optical window of biological tissue, which is favorable for biomedical applications. The results indicate that Ba₂LaF₇:Nd³⁺/Eu³⁺ glass ceramics have a potential application as temperature probes.     

Synthesis of zinc oxide nanostructures on graphene/glass substrate by electrochemical deposition: effects of current density and temperature

The electrochemical growth of zinc oxide (ZnO) nanostructures on graphene on glass using zinc nitrate hexahydrate was studied. The effects of current densities and temperatures on the morphological, structural, and optical properties of the ZnO structures were studied. Vertically aligned nanorods were obtained at a low temperature of 75°C, and the diameters increased with current density. Growth temperature seems to have a strong effect in generating well-defined hexagonal-shape nanorods with a smooth top edge surface. A film-like structure was observed for high current densities above -1.0 mA/cm² and temperatures above 80°C due to the coalescence between the neighboring nanorods with large diameter. The nanorods grown at a temperature of 75°C with a low current density of -0.1 mA/cm² exhibited the highest density of 1.45 × 10⁹ cm^-2. X-ray diffraction measurements revealed that the grown ZnO crystallites were highly oriented along the c-axis. The intensity ratio of the ultraviolet (UV) region emission to the visible region emission, I_UV/I_VIS, showed a decrement with the current densities for all grown samples. The samples grown at the current density below -0.5 mA/cm² showed high I_UV/I_VIS values closer to or higher than 1.0, suggesting their fewer structural defects. For all the ZnO/graphene structures, the high transmittance up to 65% was obtained at the light wavelength of 550 nm. Structural and optical properties of the grown ZnO structures seem to be effectively controlled by the current density rather than the growth temperature. ZnO nanorod/graphene hybrid structure on glass is expected to be a promising structure for solar cell which is a conceivable candidate to address the global need for an inexpensive alternative energy source.     

Phenothiazinyl- and 4-diethylaminophenyl-substituted diethylenes as fluorescent and hole-transporting molecular materials

A series of phenothiazinyl- and 4-diethylaminophenyl-substituted diethylenes were synthesized and characterised; their thermal, optical and photoelectrical properties were investigated. TGA showed that the compounds display high thermal stability, achieving 5% mass loss at temperatures up to 385 °C; DSC revealed that many of the compounds exhibited glass transition temperatures ranging from 20 to 124 °C. Dilute solutions of the diethylenes exhibited fluorescence emission in the green-blue region with an efficiency reaching 99%. Electron photoemission spectrometry and time of flight revealed ionization potentials of 5.34–5.52 eV; the room temperature hole drift mobility of one of the compounds molecularly doped in bisphenol Z polycarbonate exceeded 10^?5 cm²/Vs under a high electric field.     

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.     

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.     

Impact of Eu3+ Dopants on Optical Spectroscopy of Ce3+: Y3Al5O12‐Embedded Transparent Glass‐Ceramics

Transparent glass‐ceramics containing Ce³⁺: Y₃Al₅O₁₂ phosphors and Eu³⁺ ions were successfully fabricated by a low‐temperature co‐sintering technique to explore their potential application in white light‐emitting diodes (WLEDs). Microstructure of the sample was studied using a scanning electron microscope equipped with an energy dispersive X‐ray spectroscopy. The impact of co‐sintering temperature, Ce³⁺: Y₃Al₅O₁₂ crystal content and Eu³⁺ doping content on optical properties of glass‐ceramics were systematically studied by emission, excitation spectra, and decay curves. Notably, the spatial separation of these two different activators in the present glass‐ceramics, where Ce³⁺ ions located in YAG crystalline phase while the Eu³⁺ ones stayed in glass matrix, is advantageous to the realization of both intense yellow emission assigned to Ce³⁺: 5d→4f transition and red luminescence originating from Eu³⁺: 4f→4f transitions. As a result, the quantum yield of the glass‐ceramic reached as high as 93%, and the constructed WLEDs exhibited an optimal luminous efficacy of 122 lm/W, correlated color temperature of 6532 K and color rendering index of 75.     

Nd3+-doped glass-ceramic fiber fabricated by drawing precursor ceramic and successive heat treatment

Optical fibers have been formed by replacing precursor glass core with precursor ceramic core, in which drawing process, the precursor ceramic melted to fill the space of the core region while the clad glass was softened. Nd³⁺ doped LaNbO₄ nanocrystals were precipitated in the core after heat treatment. X-ray diffraction, Raman spectra, high-resolution transmission electron microscopy, electron paramagnetic resonance, optical microscope, and photoluminescence were used to characterize the obtained fiber. No crystallization, cracking, bubble, or undissolved substance is observed in the core region of precursor fiber. Nd³⁺ doped LaNbO₄ nanocrystals are precipitated in the core region after thermal treatment. Under the pumping source of 808 nm, three emission bands located at ～887 nm, ～1064 nm, and ～1337 nm are observed, which makes this GC fiber a promising material for the NIR fiber amplifier.