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.     

Blue Upconversion Emission in Germanate Glass Co-Doped with Yb3+/Tm3+ Ions

In the paper, the upconversion luminescence of 70GeO₂–30[Ga₂O₃–BaO–Na₂O] glass system co-doped with Yb³⁺/Tm³⁺ ions was investigated. Strong blue emission at 478 nm corresponding to the transition ¹G₄ → ³H₆ in thulium ions was measured under the excitation of 976-nm diode laser. The dependence of the upconversion emission upon the thulium ion concentration was studied to determine the optimal conditions of energy transfer between energy levels of active dopants. The most effective energy transfer Yb³⁺ → Tm³⁺ was obtained in glass co-doped with molar ratio of dopant 0.7 Yb₂O₃/0.07 Tm₂O₃. The increase in thulium concentration more than 0.07 mol% results in the reverse energy transfer from Tm³⁺ → Yb³⁺, which leads to rapid quenching of the luminescence line at the wavelength 478 nm. In germanate glass co-doped with 0.7Yb₂O₃/0.07Tm₂O₃, the longest lifetime of ¹G₄ level equal 278 μs was achieved. The presented results indicate that elaborated germanate glass co-doped with Yb³⁺/Tm³⁺ ions is a promising material that can be used to produce fiber lasers and superluminescent fiber sources generating radiation in the visible spectrum.     

Effect of BaF2 Content on Luminescence of Rare‐Earth Ions in Borate and Germanate Glasses

Rare‐earth‐doped oxyfluoride germanate and borate glasses were synthesized and next studied using spectroscopic methods. Influence of fluoride modifier on luminescence properties of rare earths in different glass hosts was examined. The excitation and emission spectra of Pr³⁺ and Er³⁺ ions in the studied glasses were registered. The emission spectra of Pr³⁺ ions in germanate and borate glasses are quite different and depend strongly on the glass host. In samples doped with Er³⁺ ions emission bands located around 1530 nm corresponding to the main ⁴I_13/2→⁴I_15/2 laser transition were registered, independently of the glass host. Quite long‐lived near‐infrared luminescence of Er³⁺ ions was observed for germanate glasses with low BaF₂ content, while in borate glass systems influence of barium fluoride on luminescence lifetimes is not so evident. The Judd–Ofelt calculations were used in order to determine quantum efficiencies of excited states of rare‐earth ions in germanate and borate glasses.     

Enhanced luminescence in Tb3+-doped germanate glass ceramic scintillators containing CaF2 nanocrystals

Tb³⁺-doped germanate glass ceramics containing CaF₂ nanocrystals were prepared by melt quenching method with subsequent heat treatment. Their microstructures were investigated by XRD and TEM techniques. Their optical properties were studied by the transmittance, the photoluminescence, and the X-ray excited luminescence (XEL). The luminescence intensity in the glass ceramics under 377 nm light and X-ray excitations is significantly enhanced. The maximum integrated XEL intensity of the glass ceramics is about 50% of that of the commercial Bi₄Ge₃O₁₂ (BGO) scintillating crystal. The results indicate that Tb³⁺-doped germanate glass ceramic could be a promising scintillating material used in X-ray detection for slow event.     

Fabrication,tunable fluorescence emission and energy transfer of Tm3+-Dy3+ co-activated P2O5–B2O3–SrO–K2O glasses

A growing demand for white light-emitting diodes (W-LEDs) gives rise to continuous exploration of functional fluorescence glasses. In this paper, Tm³⁺/Dy³⁺ single- and co-doped glasses with composition (in mol%) of 30P₂O₅–10B₂O₃–23SrO–37K₂O were synthesized using the melt-quenching method in air. The physical properties, glass structure, luminescence characteristics and energy transfer mechanism of the glasses were systematically studied. As glass network modifiers, Tm³⁺ and Dy³⁺ ions can densify the glass structure. Excitation wavelength and doping concentration of Tm³⁺/Dy³⁺ ions have a direct impact on the emission intensities of blue and orange light as well as the color coordinate of the as-prepared glasses. A white light very close to standard white light can be obtained under 354 nm excitation when the content of Tm³⁺ and Dy³⁺ is 0.2 mol% and 1.0 mol%, respectively. The results of the emission spectra and decay curves reveal the existence of energy transfer from Tm³⁺ to Dy³⁺. The analytic results based on the Inokuti-Hirayama model indicate that the electrical dipole-dipole interaction may be the main mechanism of energy transfer. Moreover, Tm³⁺/Dy³⁺ co-activated glass phosphor has good thermal stability and chrominance stability and it is a promising candidate for white LEDs and display device.     

Fabrication of double-cladding Ho3+/Tm3+ co-doped Bi2O3–GeO2–Ga2O3–BaF2 glass fiber and its performance in a 2.0-μm laser

A novel double-cladding Ho³⁺/Tm³⁺ co-doped Bi₂O₃–GeO₂–Ga₂O₃–BaF₂ glass fiber, which can be applied to a 2.0-μm infrared laser, was fabricated by a rod-tube drawing method. The thermal properties of the glass were studied by differential scanning calorimetry. It showed good thermal stability and matching thermal expansion coefficient for fiber drawing when T_x−T_g > 193°C and the maximum difference of the thermal expansion coefficient is 3.55 × 10⁻⁶/°C or less. The 2.0-μm luminescence characteristics were studied using the central wavelength of 808 nm pump light excitation. The results show that when the concentration ratio of Ho³⁺/Tm³⁺ reaches 0.5 mol%:1.0 mol%, the maximum fluorescence intensity was obtained in the core glass, the emission cross section reached 10.09 × 10⁻²¹ cm², and the maximum phonon energy was 751 cm⁻¹. In this paper, a continuous laser output with a maximum power of 0.986 W and a wavelength of 2030 nm was obtained using an erbium-doped fiber laser as a pump source in a 0.5 m long Ho³⁺/Tm³⁺ co-doped glass fiber. In short, the results show that Ho³⁺/Tm³⁺ co-doped 36Bi₂O₃–30GeO₂–15Ga₂O₃–10BaF₂–9Na₂O glass fiber has excellent laser properties, and it is an ideal mid-infrared fiber material for a 2.0-μm fiber laser with excellent characteristics     

Effect of introduction of TiO2 and GeO2 oxides on thermal stability and 2 μm luminescence properties of tellurite glasses

In this paper, Tm³⁺ doped pure tellurite glass, TiO₂ modified tellurite glass and TiO₂/GeO₂ co-modified tellurite glasses were prepared. The effects of the introduction of TiO₂ and GeO₂ oxides on the thermal, structural, optical properties of tellurite glasses were compared and analyzed intensively. Besides, the Judd-Ofelt intensity parameters and absorption and emission cross sections were calculated. DTA curves indicated the thermal stability of pure tellurite glass enhance obviously by GeO₂ modification. The introduction of TiO₂ and GeO₂ oxides in tellurite glasses arise a series of variation on the absorbance, luminescence peak position and fluorescence intensity which have been explained and analyzed in detail. Based on the analysis, the addition of TiO₂ in tellurite glass contributes to the improvement of 2 μm fluorescence performance, and the introduction of GeO₂ has great advantages in enhancing the thermal stability of glass.     

The mutual influence between rare earth element doping and femtosecond laser-induced effects in Ga-As-Sb-S chalcogenide glass

Femtosecond laser-induced damage thresholds (LIDTs) of Ga_0.8As_29.2Sb₁₀S₆₀ glasses doped with gradient Tm³⁺ concentrations and the effects of laser-induced damage on the glass' luminescence properties were studied in this work. Tm³⁺ doping in the glass considerably decreased the LIDT, from 3394.8 to 1881.8 mJ/cm², when the Tm³⁺ concentration increased from 0 to 5000 ppmw. This was related to the absorption of Tm³⁺ around the femtosecond laser's wavelength and microstructural changes caused by the Tm³⁺ doping. On the other hand, the femtosecond laser changed the glass matrix's elemental distribution and microstructure. Although the laser damaged the glass, the luminescence properties were barely affected. Based on the changes, femtosecond laser damage mechanism of chalcogenide glass doped with rare earth element was firstly proposed.     

Quantitative prediction of the structure and luminescence properties of Nd3+ doped borate laser glasses

Although great advance has been made in glass science, predicting luminescence properties of laser glass poses a significant challenge for scientists due to the complex relationship between the composition, structure, and properties of the rare earth ions doped laser glasses. The development of high-performance laser glass usually relies on intuition and trial-and-error. Recently, with the proposal of the materials genome engineering, the “glass genome” has also attracted much attention. Here, the structure of the Nd³⁺ doped B₂O₃-Li₂O laser glasses was analyzed using Fourier transform infrared spectra and nuclear magnetic resonance, revealing that the glass contains similar glass-forming ion-centered coordination polyhedron structure groups to the neighbor congruent glassy compounds. The structure and properties of glass largely depend on the neighbor congruent glassy compounds. Therefore, the structure and luminescence properties of Nd³⁺ doped B₂O₃-Li₂O and B₂O₃-MgO-Li₂O laser glasses can be quantitatively predicted via the neighbor congruent glassy compounds. The predictive values are in good agreement with the experimental data, which indicates that our approach is an effective way to predict the structure and luminescence properties of Nd³⁺ doped borate laser glasses.     

Enhanced NIR photoemission from Bi-doped aluminoborate glasses via topological tailoring of glass structure

Bismuth (Bi)-doped laser glasses with broadband emission are of current interest in the fields of sensing, bio-imaging, and photonics. For practical applications, it must be considered how to improve the emission efficiency, in particular, for borate glasses with wide glass-forming range, low melting point, and excellent fiberizing ability. Herein, we experimentally demonstrate that addition of GeO₂ to aluminoborate glasses can effectively enhance Bi NIR emission by more than 300 times with prolonged decay time (~500 μs) and good homogeneity, which is, to our best knowledge, seldom achieved in Bi-doped borate multi-component glasses. The addition of second glass-former GeO₂, as revealed by detailed optical and structural analysis, leads to the facile regulation on local glass structure, forcing the conversion of aluminum species from AlO₅ and AlO₆ to AlO₄ and consequently pushes the conversion of Bi³⁺ to Bi⁺ and Bi⁰ and stabilizes Bi NIR centers, which finally results in highly enhanced Bi NIR emission. We believe these results could contribute to designing Bi-activated multi-component laser glass and fibers with efficient NIR photoemission.     

含Nb2O5和La2O3系统玻璃形成区

用新的玻璃形成区探索方法研究了La     

Novel gallate-based oxide and oxyfluoride glasses with wide transparency,high refractive indices,and low dispersions

The glass-forming region of a BaO-La₂O₃-Ga₂O₃ ternary system was confirmed and BaF₂-BaO-La₂O₃-Ga₂O₃ new oxyfluoride glasses were prepared by a containerless processing. We also analyzed the physical, thermal, and optical properties of new oxide and oxyfluoride glasses. The direct effects of the substitution of oxygen by fluorine and the effect of BaO and La₂O₃ on the refractive index and Abbe number were discussed on the basis of electronic polarizability and resonance wavelength of oscillator. The refractive indices increased with increasing La₂O₃ concentration because La₂O₃ increased the electronic polarizabilities. Abbe number increased with increasing BaO and fluorine concentration because of the decrease in resonance wavelength of oscillator. By the combination of the BaO, La₂O₃, and fluorine in the gallate glass system, we could obtain novel oxide and oxyfluoride glasses with high refractive index (1.81-1.95) and high Abbe number (31-55). The absorption edge in UV region shifted to the shorter wavelength and IR cut-off wavelength shifted to the longer wavelength with increasing fluorine. Therefore, wide transparent glass was obtained from 262 nm to 11.3 μm.     

High niobium oxide content in germanate glasses: Thermal,structural, and optical properties

Niobium alkali germanate glasses were synthesized by the melt‐quenching technique. The ternary system (90‐x)GeO₂–xNb₂O₅–10K₂O forms homogeneous glasses with x ranging from 0 to 20 mol%. Samples were investigated by DSC and XRD analysis, FTIR and Raman spectroscopy, and optical absorption. Structural and physical features are discussed in terms of Nb₂O₅ content. The niobium content increase in the glass network strongly modifies the thermal, structural and optical properties of alkali germanate glasses. DSC, Raman and FTIR analysis suggest niobium addition promotes NbO₆ groups insertion close to GeO₄ units of the glass network. XRD analysis also pointed out that samples containing high niobium oxide contents exhibit preferential niobium oxide‐rich phase after crystallization after heat treatment, which is similar to orthorhombic Nb₂O₅. Absorption spectra revealed high transmission range between 400 nm to 6.2 μm, added to a considerably decreased hydroxyl group content as the addition of niobium in the alkali germanate network. The niobium oxide‐rich phase crystallization process was studied and activation energy was determined, as well as nucleation and crystal growth temperatures and time for obtaining transparent glass‐ceramics.     

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.     

Full color white light,temperature self-monitor,and thermochromatic effect of Cu+ and Tm3+ codoped germanate glasses

Lighting sources with full-color visible output are widely preferred in practical applications. In addition, modern lighting sources also tend to be intelligentized, and the intelligentization asks for smart luminescence materials. In this work, we attempt to develop novel full-color emitting material with temperature sensing and thermochromatic ability. To this end, the Cu²⁺ is successfully reduced to Cu⁺ which is incorporated into the germanate glasses. The glasses are prepared via a melt-quenching technique using graphite powders as reducing reagent. The supper-broadening of the excitation and the emission spectra of Cu⁺ in the germanate glasses are observed. Full-color emission is realized by introducing Tm³⁺ as co-dopant to provide the blue component in the spectra. The energy transfer behavior between Cu⁺ and Tm³⁺ is investigated, and it is found that these two luminescence centers are independently existent without energy transfer between them. The chromatic properties of the Cu⁺/Tm³⁺ co-doped glasses are tuned by Tm³⁺ concentration and excitation wavelength. The temperature sensing based on the fluorescence intensity ratio technique is demonstrated, and a constant sensitivity for the temperature detection is obtained. Moreover the thermochromatic property is also investigated, and it is found that the studied Cu⁺/Tm³⁺-doped glasses exhibit excellent thermochromatic performance.     

Quantitatively predicting the optical and spectroscopic properties of Nd3+-doped laser glasses

Predicting the properties of glass based on compositional and structural information is a fundamental issue with enormous practical and industrial significance for the study of laser glass. Here we address this problem and demonstrate the application of phase diagram method in predicting the spectroscopic properties of Nd³⁺-doped binary and ternary silicate, binary phosphate, and borate laser glasses from their initial congruently melting compounds. In particular, spectroscopic properties, such as effective linewidth (Δλ_eff) and fluorescence branching ratio (β) can be precisely predicted in all glass systems with an error less than 5%. Furthermore, a composition–structure–property database of Nd³⁺-doped ternary silicate glass system is established and preliminarily applied to the composition design and explanation of commercial glass. This study provides interpretable predictions of the optical and spectroscopic properties for Nd³⁺-doped laser glasses.     

Highly thermally stable single-component warm-white-emitting ZANP glass: Synthesis,luminescence, energy transfer,and color tunability

Luminescent glass demonstrates potential for applications as color converters in white-light-emitting diodes (W-LEDs). In this study, solution combustion synthesis combined with low-temperature melt quenching was employed as a novel route for preparing new white-light fluorescent glasses (rare-earth-doped ZnO–Al₂O₃–Na₂O–P₂O₅, ZANP). The developed solution combustion synthesis can considerably decrease the reaction temperature and time, with several advantages such as energy and time savings. X-ray diffraction and photoluminescence spectroscopy, as well as decay curves, CRI, and CCT, as well as the Commission Internationale de I′Eclairage (CIE) 1931 chromaticity coordinates, were assessed to examine the microstructure and photoluminescence properties of Tm³⁺/Dy³⁺ co-doped and Tm³⁺/Dy³⁺/Eu³⁺ tri-doped ZANP glasses for use in W-LEDs. Experimental results revealed that ZANP glass co-doped with Tm³⁺ and Dy³⁺ exhibits blue- and yellow-light emissions based on the energy transfer of dipole-dipole interaction between Tm³⁺ and Dy³⁺, which can realize the adjustment of color in a wide range. The emitting color coordinate (0.343, 0.344) of ZANP: 1.0Tm³⁺, 0.75Dy³⁺ approach ideal white light. Also, by the introduction of additional Eu³⁺ doping, ZANP:1.0Tm³⁺, 0.75Dy³⁺, 0.1%Eu³⁺ glass emit warm-white light (CCT = 3198?K) under an excitation of 361?nm. Moreover, the tri-doped ZANP glasses exhibit good thermal stability, where the luminous intensity at 498?K remains exceeding 50% of that at room temperature, and the color coordinate offset is only 2.87?×?10^?2 relative to room temperature.     

Optical Investigation of Ce3+‐Activated Borogermanate Glass Induced by Substitution of BaF2 for BaO

Transparent and colorless CeO₂‐activated borogermanate glasses, with the nominal molar composition of 25B₂O₃–40GeO₂–14Gd₂O₃–1CeO₂–(20?x) BaO–xBaF₂ (x = 0, 2.5, 5, 10, 15 and 20), were synthesized by a melt‐quenching method in air. Their optical investigation on the transmittance, photoluminescence (excitation and emission spectra), the luminescence decay curves, as well as the temperature‐dependent Ce³⁺ emission are studied systematically with the gradual substitution of BaF₂ for BaO. The room‐temperature photoluminescence results reveal that the emission intensity can be improved by about 2.5 times with the full substitution of BaF₂ for BaO. The blue shift of the cut‐off edge, excitation and emission spectra of Ce³⁺‐activated borogermanate glass, and the emission intensity of Ce³⁺ ions as a function of temperature range in 80–500 K are also discussed.     

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.     

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.