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.     

Nd3+/Sm3+ codoped NaLa(WO4)2 glass ceramic: A novel optical heater

Transparent Nd³⁺/Sm³⁺ codoped tungstate silicate glass ceramics were prepared and used for the photothermal conversion process. XRD patterns, TEM image and the enhanced Raman signals confirm the appearance of the tetragonal scheelite NaLa(WO₄)₂ nanocrystals in the vitreous phase. In comparison to the precursor glass, the enhancement of photoluminescence of Nd³⁺ ions in the glass ceramics attributes to the enrichment of Nd³⁺ ion in the precipitated low phonon-energy tetragonal scheelite NaLa(WO₄)₂ nanocrystals. The rapid reduction of photoluminescence of Nd³⁺ ions in the Nd³⁺/Sm³⁺ codoped glass ceramics demonstrates that a strong energy transfer from Nd³⁺ to Sm³⁺ takes place, which provides more non-radiative relaxation channels and is beneficial for the improving the photothermal conversion efficiency. Under the irradiation of 808 nm laser diode, a significant temperature rise is observed in the Nd³⁺/Sm³⁺ codoped glass ceramics and may be used as a good optical heater.     

Distribution of Nd3+ ions in oxyfluoride glass ceramics

It has been an open question whether Nd³⁺ ions are incorporated into the crystalline phase in oxyfluoride glass ceramics or not. Moreover, relative research has indicated that spectra characters display minor differences between before and after heat treatment in oxyfluoride glass compared to similar Er³⁺-, Yb³⁺-, Tm³⁺-, Eu³⁺-, etc.-doped materials. Here, we have studied the distribution of Nd³⁺ ions in oxyfluoride glass ceramics by X-ray diffraction quantitative analysis and found that almost none of the Nd³⁺ ions can be incorporated into the crystalline phase. In order to confirm the rationality of the process, the conventional mathematical calculation and energy-dispersive spectrometry line scanning are employed, which show good consistency. The distribution of Nd³⁺ ions in oxyfluoride glass ceramics reported here is significant for further optical investigations and applications of rare-earth doped oxyfluoride glass ceramics.     

Selective excitation in transparent oxyfluoride glass-ceramics doped with Nd3+

Transparent oxyfluoride nano-glass-ceramics have been prepared by melting-quenching and doped with five different Nd³⁺ concentrations (0.1–2 mol%) to obtain the most efficient ⁴F_3/2 → ⁴I_11/2,13/2 emission. It was observed by differential thermal analysis (DTA) that the addition of Nd³⁺ does not affect the crystallization mechanism which corresponds to a diffusion-controlled volumetric process that starts from a constant number of nuclei. Nevertheless, the presence of the dopant affects the kinetics due to the progressive increase of T_g on increasing the Nd³⁺ content. LaF₃ crystals with a size between 9 and 12 nm are obtained after heat treatments at T_g + 20–80 °C as confirmed by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HR-TEM). Energy dispersive X-ray (EDX) analysis shows the incorporation of Nd³⁺ ions into the LaF₃ nano-crystals. Judd-Ofelt analysis from the absorption spectra further demonstrate the incorporation of Nd³⁺ ions into the fluoride phase and the most relevant parameters such as radiative lifetime and stimulated emission cross-section are calculated. A detailed optical characterisation clearly shows that Nd³⁺ ions in the glass-ceramics are incorporated in both crystalline and amorphous phases. Low temperature site-selective emission and excitation spectra, together with the different lifetime values of the ⁴F_3/2 state depending on the excitation and emission wavelengths, allow emission from Nd³⁺ ions in the LaF₃ nanocrystals to be identified and correlated with the structural properties. As the Nd³⁺ concentration is increased beyond 0.1 mol%, a stronger quenching of lifetime is observed for Nd³⁺ ions residing in LaF₃ crystals than for those dispersed in the glass matrix. This strong concentration quenching is explained by the much higher concentration of Nd³⁺ ions in the crystalline phase with respect to that in the glass matrix.     

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.     

Immobilization of simulated An3+ into synthetic Gd2Zr2O7 ceramic by SPS without occupation or valence design

To simplify the immobilized process of nuclear waste, synthetic Gd₂Zr₂O₇ ceramic was employed to immobilize simulated An³⁺ (Nd³⁺) by spark plasma sintering (SPS) without any ion occupation or valence design. Sintering and characterization of immobilized simulated An³⁺ with various doping amounts were carried out. The effects of Nd₂O₃ content on the phase composition, active modes, micro-graph and density of the sintered ceramics were investigated. When the Nd₂O₃ doped amount reached up to 50 mol%, the raw peak of Nd₂O₃ existed. The sintered ceramics kept a single fluorite phase when Nd₂O₃ solubility achieved to 40 mol%. The sintered ceramics presented a well crystalline phase and the elements distributed evenly. In addition, as the Nd₂O₃ doped amount increase, the density and Vickers hardness values of Nd₂O₃ doped sample decrease.     

Efficient adsorption and in-situ ceramics immobilization of simulated trivalent actinides (Nd) by amino-functionalized mesoporous zirconia-silica

It is of great significance to develop a kind of adsorbent which can adsorb and in-situ immobilize radionuclides from aqueous solution. Herein, new amino-functionalized mesoporous zirconia-silica (ZNSi) composites were prepared and applied to adsorb and in-situ immobilize the simulated trivalent actinides (Nd) from aqueous solution. The obtained ZNSi composites exhibited high Nd adsorption capacity (31.14 mg/g) owing to the formation of Nd(OH)₃ via the reaction between Nd³⁺ and OH⁻ derived from the protonation of amino groups. The spent adsorbents with adsorbed Nd³⁺ were successfully changed to stable ZrSiO₄-based glass ceramics by simple sintering treatment. The ZrO₂ and Nd contents had great effect on the phase composition, microstructure evolution and aqueous stability of the obtained ZrSiO₄-based glass ceramics waste forms. The immobilized Nd showed excellent aqueous stability (10⁻⁷ g m⁻² d⁻¹) due to the crystal lattice immobilization of ZrSiO₄. Owing to the efficient adsorption and in-situ immobilization ability, the obtained ZNSi could be potential materials for radioactive wastewater treatment.     

Efficient Energy Transfer and Enhanced Near‐IR Emission in Cu+/Nd3+‐Activated Aluminophosphate Glass

The development of photonic materials for efficient energy conversion and high‐power solid‐state lasers is currently pursued given the wide range of applicable technologies and the possibility to help meet global energy demands in laser fusion power plants. In this work, Cu⁺ ions successfully incorporated in aluminophosphate glass are recognized as near‐ultraviolet (UV) sensitizers of Nd³⁺ ions resulting in remarkable near‐infrared (IR) ⁴F_3/2 → ⁴I_11/2 emission at 1.06 μm. Optical absorption, solid‐state ³¹P nuclear magnetic resonance, Raman, and photoluminescence spectroscopies characterizations are employed and assessment methods for material optical and structural properties are proposed. The spectroscopic data indicates an efficient (>50%) nonradiative energy transfer where the Cu⁺ ions first absorb photons broadly around 360 nm, and subsequently transfer the energy from the Stokes‐shifted emitting states to resonant Nd³⁺ energy levels. Then, the Nd³⁺ electronic excited states decay and the upper lasing state ⁴F_3/2 is populated, leading to enhanced near‐IR emission. It is suggested that the physico‐chemically robust Cu⁺/Nd³⁺ codoped aluminophosphate glass is a suitable candidate as solid‐state laser material with enhanced pump range in the near‐UV part of the spectrum and for solar spectral conversion in photovoltaic cells.     

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.     

The effect of Nd3+ concentration on fabrication,microstructure, and luminescent properties of anisotropic S-FAP ceramics

Nd³⁺ doped strontium fluorophosphate (S-FAP), with chemical formula Sr₅(PO₄)₃F, nanopowders were prepared using the co-precipitation method. The prepared powders had no impurity phase with a grain size of about 30 nm and the doping limit of Nd³⁺ ions in strontium fluorophosphate is about 9 at.%. The morphology and particle size were determined by the doping concentration of Nd³⁺. Anisotropic Nd: S-FAP transparent ceramics with different Nd³⁺ doping concentrations were fabricated successfully by the simple hot-pressing method. The grain size of prepared S-FAP transparent ceramics decreased first and then increased with the increase of Nd³⁺ concentration. The 2 at.% Nd: S-FAP ceramic presented the highest optical transmittance at all wavelengths range. The characteristic transitions from the ground state to the excited states of Nd³⁺ ions were observed from the absorption spectra, and the absorption cross-section was calculated at 3.71 × 10^–20 cm². The influence of Nd³⁺ ion concentration on luminescence intensity and fluorescence lifetime was studied under 796 nm excitation. The strong emission of ⁴F_3/2→⁴I_9/2 transition in Nd: S-FAP was calculated by Judd–Ofelt (J-O) theory.     

Role of Nd3+ ions on the nucleation and growth of PbS quantum dots (QDs) in silicate glasses

The influence of Nd₂O₃ addition on the precipitation kinetics of lead chalcogenide (PbS) quantum dots (QDs) in silicate glasses was investigated. Energy dispersive X‐ray spectroscopy (EDS) indicated that the Nd³⁺ ions are preferentially located inside the PbS QDs rather than in the glass matrix. Changes in diameter (D) of PbS QDs exhibited smaller time dependencies (i.e., D≈t^{0.270‐0.286}) than that predicted by the classical Lifshitz–Slyozov–Wagner (LSW) theory. This is due to the limited concentrations of Pb²⁺ and S^2? ions and the large diffusion distance inside the glass matrix. In addition, extended X‐ray absorption fine structure (EXAFS) results indicated that the formation of PbS QDs was retarded due to the presence of Nd₂O₃ in the glasses, as the large NdO_x polyhedra interrupt the diffusion of Pb²⁺ and S^2? ions. We believe that these Nd³⁺ ions are primarily located in PbS QDs in the form of Nd–O clusters, and that the PbS QDs are built on top of these clusters.     

Effects of Al:Si and (Al + Na):Si ratios on the properties of the international simple glass,part I: Physical properties

Understanding composition-structure-property relationships of high-alumina nuclear waste glasses are important for vitrification of nuclear waste at the Hanford Site. Two series of glasses were designed, one with varying Al:Si ratios and the other with (Al + Na):Si ratios based on the international simple glass (ISG, a simplified nuclear waste model glass), with Al₂O₃ ranging from 0 to 23 mol% (0 to 32 wt%). The glasses were synthesized and characterized using electron probe microanalysis, X-ray photoelectron spectroscopy, small angle X-ray scattering, high-temperature oxide melt solution calorimetry, and infrared spectroscopy. Glasses were crystal free, and the lowest Na₂O and Al₂O₃ glass formed an immiscible glass phase. Evolution of various properties—glass-transition temperature, percentage of 4-coordinated B, enthalpy of glass formation—and infrared spectroscopy results indicate that structural effects differ based on the glass series.     

Thermodynamic assessment of the pseudoternary Na2O–Al2O3–SiO2 system

Vitrified high‐level radioactive waste that contains high concentrations of Na₂O and Al₂O₃, such as the waste stored at the Hanford site, can cause nepheline to precipitate in the glass upon cooling in the canisters. Nepheline formation removes oxides such as Al₂O₃ and SiO₂ from the host glass, which can reduce its chemical durability. Uncertainty in the extent of precipitated nepheline necessitates operating at an enhanced waste loading margin, which increases operational costs by extending the vitrification mission as well as increasing waste storage requirements. A thermodynamic evaluation of the Na₂O–Al₂O₃–SiO₂ system that forms nepheline was conducted by utilizing the compound energy formalism and ionic liquid model to represent the solid solution and liquid phases, respectively. These were optimized with experimental data and used to extrapolate phase boundaries into regions of temperature and composition where measurements are unavailable. The intent is to import the determined Gibbs energies into a phase field model to more accurately predict nepheline phase formation and morphology evolution in waste glasses to allow for the design of formulations with maximum loading.     

Crystallization study of rare earth and molybdenum containing nuclear waste glass ceramics

A glass-ceramic waste form is being developed for immobilization of waste streams of alkali (A), alkaline-earth (AE), rare earth (RE), and transition metals generated by transuranic extraction for reprocessing of used nuclear fuel. Benefits over an alkali borosilicate waste form are realized by the partitioning of the fission product fraction insoluble in glass into a suite of chemically durable crystalline phases through controlled cooling, including (AE,A,RE)MoO₄ (powellite) and (RE,A,AE)₁₀Si₆O₂₆ (oxyapatite). In this study, a simplified 8-oxide system (SiO₂-Nd₂O₃-CaO-Na₂O-B₂O₃-Al₂O₃-MoO₃-ZrO₂) was melted, then soaked at various temperatures from 1450 to 1150°C, and subsequently quenched, in order to obtain snapshots into the phase distribution at these temperatures. For these samples, small angle X-ray and neutron scattering, quantitative X-ray diffraction, electron microscopy, ²³Na nuclear magnetic resonance, Nd³⁺ visible absorption, and temperature-dependent viscosity were characterized. In this composition, soak temperatures of 1250°C were necessary to nucleate calcium molybdate (~10-20 nm in diameter). Further cooling produced oxyapatite and total crystallization increased with lower soak temperatures. Both Na and Nd entered the crystalline phases with lower-temperature soak conditions. Slow cooling or long isothermal treatments at ~975°C produced significantly higher crystal fractions.     

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.     

Retention analysis from vitrified low-activity waste and simulants in a laboratory-scale melter

The Waste Treatment and Immobilization Plant (WTP) will process and stabilize nuclear waste stored in tanks on the Hanford Site. At the WTP, the tank waste will be combined with glass-forming chemicals to make a melter feed slurry that can be vitrified in joule-heated melters. Technetium-99 (⁹⁹Tc), a long-lived radionuclide present in tank waste, is semi-volatile from a glass melt at elevated temperatures. A small laboratory-scale melter system has been designed by PNNL to operate under radioactive conditions, giving it the ability to vitrify actual tank waste and gain information about melter feed processability and the partitioning of components of interest. This study describes two runs performed in a duplicate system with non-radioactive simulants of Hanford tanks 241-AP-107 and 241-AN-105 to gain insight into the relationship between the retentions of ⁹⁹Tc and its non-radioactive surrogate Re while also investigating the effects of increasing the reducing agent such as sucrose during vitrification on processing and the retention of semi-volatile components in the glass product. The results from these runs align with the general trends of greater retention in the glass of Re compared to ⁹⁹Tc and the improved retention in the glass of Re with increased reducing agent.     

Response of structure and mechanical properties of high entropy pyrochlore to heavy ion irradiation

Material with superior damage tolerance, chemical durability, and structure stability is of increasing interest in high-level radioactive waste management and structural components for advanced nuclear systems. In this paper, high-entropy (La_0.2Ce_0.2Nd_0.2Sm_0.2Gd_0.2)₂Zr₂O₇ with pyrochlore-type structure was synthesized through conventional solid-state method. The as-synthesized high-entropy oxide maintained crystalline after being irradiated by using Au³⁺ with 9.0 MeV energy at the fluence of 4.5 × 10¹⁵ ions·cm^-2, indicating its high tolerance to heavy-ion irradiation. The irradiation-induced order-disorder transition from pyrochlore structure to defective fluorite structure occurred in high-entropy (La_0.2Ce_0.2Nd_0.2Sm_0.2Gd_0.2)₂Zr₂O₇. After irradiation, no irradiation-induced segregation was observed at grain boundary. Moreover, the mechanical properties of high-entropy pyrochlore were improved. The heavy-ion irradiation resistance mechanisms of high-entropy pyrochlore were discussed in detail. Our work identified high-entropy (La_0.2Ce_0.2Nd_0.2Sm_0.2Gd_0.2)₂Zr₂O₇ can be a promising candidate for immobilization of high-level radioactive waste as well as advanced nuclear reactor system from the perspective of irradiation resistance.     

Corrosion behavior of Monofrax K-3 refractory in borosilicate-based model low activity waste glass melts

Owing to its good chemical and thermal durabilities at high temperatures, Monofrax K-3 refractory is widely used in nuclear waste vitrification as a lining material in melting vessels. However, the corrosion of K-3 refractory during the vitrification of nuclear waste is a serious problem because it affects the melter's safety, performance, and lifetime. Therefore, in the present study, we have focused on unearthing the impact of glass network formers, such as SiO₂, B₂O₃, and Al₂O₃, in a model nuclear waste glass composition on the corrosion of Monofrax K-3 refractory. The corrosion tests have been performed per ASTM C621 at 1150°C for 5 days. The dimensional measurements on corroded K-3 refractory suggest that Al₂O₃ and SiO₂ tend to reduce the refractory corrosion (neck loss), with the effect of Al₂O₃ being significant. A corroded region on the K-3 refractory at the melt–refractory interface is observed. The corrosion occurs via a coupling of the melt infiltration induced by a capillary effect and the dissolution of Al, Mg, and Fe components from K-3 into the melt through chemical reactions. A Cr-rich layer is retained on the glass contact surface of the corroded K-3 refractory.     

Preparation and fluorescence of Nd3+ doped poly(methyl methacrylate) fibre

Neodymium octanoate (NdOA) was synthesized from neodymium oxides and dissolved into poly(methyl methacrylate) (PMMA) forming a solid solution of Nd³⁺ doped PMMA (Nd-PMMA). Investigation of the absorption spectrum of Nd-PMMA showed that it was similar to that of Nd³⁺ doped silica glasses, but with about 5 nm of blue shift. The glass transition temperature (T_gs) of all the Nd-PMMA samples were about 10°C higher than that of pure PMMA for Nd³⁺ concentrations of 60–700ppm. The Nd-PMMA was used to draw a fibre. The emission output of the fibre at 585 nm was observed under a green source pumping at 532 nm by optimization of the Nd³⁺ concentration and the length of the fibre. Under 1 W pumping radiation, 60 μW output was obtained for the fibre with Nd³⁺ concentration of 70 ppm and length of 15 cm.     

A Unique Approach to Characterization of Sol‐Gel‐Derived Rare‐Earth‐Doped Oxyfluoride Glass‐Ceramics

Using the sol‐gel route Nd³⁺‐doped oxyfluoride glass‐ceramics were prepared. LiYF₄ and YF₃ crystals were deposited in the glass‐ceramics and their size, distribution, and amount ratio were varied by changing the compositions and heating temperatures. The incorporation of Nd³⁺ ions into both the fluoride crystals was confirmed by the high‐resolution elemental mapping of the glass‐ceramics. The incorporated Nd³⁺ ions showed up and down conversion photoluminescence whose properties were obviously different among the samples. The preliminary site analysis for Nd³⁺ ions was carried out using a unique approach associated with the Prony series approximation. Finally, the approach was found to be useful for the analysis of materials that are structurally complicating.