Aluminosilicate Oxyfluoride Glass Research Articles

Reduction mechanism and energy transfer between Eu3+ and Eu2+ in Eu-doped materials synthesized in air atmosphere

Abstract This article critically examines the reduction mechanisms and energy transfer processes between trivalent europium ions (Eu3+) and divalent europium ions (Eu2+) in materials synthesized in an air atmosphere. It also encompasses various materials and conditions, including a critical analysis of the reduction mechanism and energy transfer between Eu3+ and Eu2+ in Eu-doped materials. Specific investigations include exploring the reduction process in BaMgSiO4:Eu, focusing on factors influencing the reaction. The article also covers low-temperature self-reduction, addressing conditions and mechanisms such as the charge compensation model and laser-induced reduction. Additionally, it explores the influence of charge compensation on luminescent properties, emphasizing enhancements in red emission. Investigations into the role of oxygen vacancies in the reduction of Eu3+ and their implications on material properties are presented. This article further digs into abnormal reduction processes and the formation of defect centers in Eu3+-doped pollucite, proposing a substitution defect model for the self-reduction of europium ions in silicate Ba(Eu)MgSiO4 phosphors. Unusual reduction phenomena, such as reduction via boiling water in Yb2Si2O7:Eu3+ phosphors, and reductions in various glass systems, including porous glass, ZnO–B2O3–P2O5 glasses, aluminoborosilicate glasses, europium-doped Li2B4O7 glass, and aluminosilicate oxyfluoride glass (AOG), are also thoroughly examined.

Spectral properties and self-reduction of Eu3+ to Eu2+ in aluminosilicate oxyfluoride glass.

Eu-doped aluminosilicate oxyfluoride glass prepared via a melt-quenching method was investigated using X-ray diffraction, absorption spectroscopy, X-ray fluorescence spectrometry, photoluminescence spectroscopy and fluorescence decay curves. We found that the reduction of Eu3+ to Eu2+ ions occurred in the glass prepared in air. The emission spectra showed that the intensity of 4f65d → 4f7 transition of Eu2+ ions varied with increasing incident beam wavelength. Meanwhile, the fluorescence lifetimes of Eu3+: 5D0 → 7F2 monitored at 617 nm in the glass change with the variation of excitation wavelength. The energy transfer between Eu2+ and Eu3+ and the emission mechanisms of Eu2+ ions in the glass were also discussed.

Highly resolved and refreshable X-ray imaging from Tb3+doped aluminosilicate oxyfluoride glass scintillators

A glass scintillator with high spatial resolution of 20 lp mm−1and refreshable X-ray imaging is designed. The practical tests also reveal the great potential for applications in X-ray imaging.

Optical properties of ytterbium doped oxyfluoride glass-ceramics - Concentration and temperature dependence studies for optical refrigeration applications

Oxyfluoride glass-ceramics (GCs) doped with lanthanides have recently attracted much attention as a novel optoelectronic material candidate for optical refrigeration. In this study, the optical properties of highly transparent (~90% in the near infrared region) ytterbium doped germanate and aluminosilicate oxyfluoride glass ceramics with different rare earth ion concentrations varying from 0.5 to 3.0 mol % synthesized by the conventional melt quenching technique have been investigated to determine and compare their potential for optical refrigeration applications. The photoluminescence (PL) emission spectra at different temperatures (25°C–200 °C) were measured using different excitation wavelengths varying from 920 nm to 1030 nm in order to understand the behaviour of Stokes and anti-Stokes emission in all the glass-ceramics. The influence of ytterbium content is studied and found to substantially affect the PL emission and quantum yield and thus affect the cooling/heating characteristics. The highest intensity of anti-Stokes emission from the GC samples was observed in the composition containing 1.5 mol % or 2.0 mol % of Yb3+. Experiments monitoring the sample temperature at varying excitation wavelength between 1020 and 1030 nm demonstrates that the 1.5 mol % or 2.0 mol % Yb3+ concentrations are the most suitable for laser cooling applications.

Adjustable white luminescence and high thermal stability in Eu2+/Eu3+/Tb3+/Al co-doped aluminosilicate oxyfluoride glass

In this paper, Eu2+/Eu3+/Tb3+/Al co-doped aluminosilicate oxyfluoride glass samples were synthesized via melt-quenching method in air atmosphere. Their structural and optical properties were systematically investigated through X-ray diffraction patterns, X-ray photoelectron spectroscopy, absorption spectra and photoluminescent spectra. The proportion of Eu2+ and Eu3+ can be controlled effectively by using various amounts of Al powder, which results in an adjustable luminescence in the glass samples. By combining the orange-red emission of Eu3+ and blue broad emission of Eu2+ as well as green emission of Tb3+, a white light emission with quantum yields of 30.0% was generated. At 513 K, the emission intensity of the optimal G-0.5Eu0.2Al4Tb glass remains about 93.1% of its initial intensity at 303 K. Our research exhibits the potential application of Eu2+/Eu3+/Tb3+/Al co-doped aluminosilicate oxyfluoride glass samples in white light-emitting diode devices.

Transparent Aluminosilicate Oxyfluoride Glass Ceramics Containing Upconversion Luminescent CaF2 Nanocrystals: Glass-to-Crystal Structural Evolution Studied by the Advanced Solid-State NMR Spectroscopy

Oxyfluoride glasses in the systems (55 – x)SiO2–(15 + x – z)Al2O3–zLa2O3–10CaO–20CaF2–yErF3 (x = 0, 5, 10, 15; y = 0.5, 1, 1.5; z = 0, 2, 5 mol %) were prepared by conventional melt-quenching metho...

Influence of Optical Basicity on Cu+ Luminescence in Aluminosilicate Oxyfluoride Glasses

Cu+-activated aluminosilicate oxyfluride glasses were successfully synthesized by melt quenching method in air with adding Al powder as reducing agent. Their luminescent properties were studied systematically via optical absorption, excitation and emission spectra. Upon UV irradiation, a blue-emitting band of Cu+ with relatively low optical basicity is observed. By increasing optical basicity of glass, obviously red shifts of excitation (290→313 nm) and emission (435→470 nm) peaks can be obtained. Through enhancing Cu+ content, excitation and emission bands present further redshifts, which shift from 313 to 338 nm and from 470 to 560 nm, respectively. It is proposed that the absorption band and emitting color of Cu+-doped glass could be tuned by changing the optical basicity of glass and Cu+ concentration. The highest quantum yield can reach 62.5%. More importantly, investigation of the thermal stability displays that over 91% of the room temperature luminescent intensity still preserves at 200 °C. These results infer that Cu+-activated aluminosilicate oxyfluride glasses may be utilized for UV converted W-LEDs.

Tuning Mn2+ luminescence in oxyfluoride glasses via Sc3+ doping

Mn-doped aluminosilicate oxyfluoride glasses containing various concentrations of Sc3+ ions were fabricated by a traditional melt-quenching method. Tunable Mn2+ luminescence from green to red was achieved with increase of Sc3+ doping content. A series of structural and spectroscopic characterizations evidenced that the Sc3+ dopants can induce the conversion of partial green-emitting [MnO4] tetrahedrons into red-emitting [MnO6] octahedrons in the glasses. This is attributed to the high cation-field-strength feature of Sc3+ ions in glass, which enables them to capture O2− from [SiO4] and [AlO4] tetrahedrons. Accordingly, it was demonstrated that the Mn2+ luminescence can be easily controlled by modifying lanthanide dopants (such as La3+, Y3+, Lu3+ and Sc3+) with distinct cation field strengths in the oxyfluoride glasses.

Photoluminescence and Structural Characterization of RE‐Doped Sodium Aluminosilicate Oxyfluoride Glass and Nanocrystalline Glass‐Ceramics as a Function of γ‐Irradiation Dose

Dy3+ and Eu3+‐doped oxyfluoride glass and glass nanocomposites are subjected to low and high dose of γ‐irradiation, i.e., 100 Gy and 1 kGy, respectively. The photoluminescence spectra show changes in electric to magnetic dipole ratios signifying variations in local structural environment. Glass‐ceramics depict the tendency of crystallization or the ordering of structure with increasing γ‐irradiation dose. The results are further supported with X‐ray diffraction and scanning electron microscopy (SEM) measurements. The formation of nanometer size fluoride particles in the pristine glass and glass‐ceramics after γ‐irradiation has been observed from SEM studies. Fourier transform infrared (FTIR) study reveals the restructuring of aluminosilicate network under γ‐irradiation.

Phase‐Selective Nanocrystallization of NaLnF4 in Aluminosilicate Glass for Random Laser and 940 nm LED‐Excitable Upconverted Luminescence

AbstractYb/Er doped hexagonal β‐NaLnF4 (Ln = Gd, Y, Lu) are regarded as the most efficient green upconversion (UC) materials. Unfortunately, β‐NaLnF4 is quite difficult to grow as monocrystal owing to cubic‐to‐hexagonal phase transition during cooling. As an alternative, herein a nanocrystallization controllable strategy to synthesize monodisperse whole‐family β‐NaLnF4 (from NaLaF4 to NaLuF4) embedded bulky glass ceramics is reported. A series of structural and spectroscopic characterizations indicate that Na content and Al/Si ratio are the most important factors to determine phase‐selective NaLnF4 crystallization in the aluminosilicate oxyfluoride glasses. Impressively, such nanocomposites are evidenced to be ideal hosts for upconversion luminescence of Yb3+/Er3+ dopants and as the proof‐of‐concept experiments, their applications in a random laser and incoherent LED‐excitable upconverting device as emitting media are demonstrated. It is expected that this study will provide a deep understanding for controllable crystallization in glass and extend the practical applications of glass ceramics in optoelectronic fields.

Luminescence and energy transfer in Dy3+/Eu3+ co-doped aluminosilicate oxyfluoride glasses and glass-ceramics

A series of oxyfluoride glasses with the composition SiO2–CaF2–Al2O3–CaO, doped with Dy2O3 (0.5–1 mol%) and Eu2O3 (0–4 mol%), have been prepared using the melt quenching method. The glass-ceramics have been obtained by heating the as-made glasses at 680 °C and 750 °C for 1 h. The glasses and the glass-ceramics were investigated using photoluminescence techniques in the near-UV and visible ranges, and differential thermal analysis (DTA) and x-ray diffraction (XRD) measurements were performed. The samples doped with 0.5 mol% Dy3+ were observed to have the highest luminescence intensity under 453 nm excitation compared to the samples doped with 1 mol% Dy3+ and the co-doped samples. The increased luminescence intensity could be caused by energy transfer between rare-earth (RE) ions and cross-relaxation of Dy3+ ions. Energy transfer from Dy3+ to Eu3+ ions in the glasses and the glass-ceramics was confirmed by excitation spectra and luminescence decay kinetics. The average luminescence lifetimes of the Dy3+ emission band at 575 nm under 453 nm excitation decrease with the addition of Eu3+ ions. Energy transfer in the glasses and the glass-ceramics was estimated to be in the range from 11% to 68%, depending on the RE ion concentration.

Electron paramagnetic resonance and photoluminescence investigation of europium local structure in oxyfluoride glass ceramics containing SrF2 nanocrystals

Different compositions of europium doped aluminosilicate oxyfluoride glass ceramics prepared in air atmosphere have been studied by electron paramagnetic resonance (EPR) and optical spectroscopy methods. X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements show presence of homogenously distributed SrF2 nanocrystals after the heat treatment of the precursor glass. Efficient Eu3+ incorporation in the high symmetry environment of glass ceramics is observed from the photoluminescence spectra. EPR spectra indicate Eu3+ → Eu2+ reduction upon precipitation of crystalline phases in the glass matrix. For composition abundant with Eu2+ in the glassy state such behaviour is not detected. Local structure around europium ions is discussed based on differences in chemical compositions.

Local structure of gadolinium in oxyfluoride glass matrices containing SrF2 and BaF2 crystallites

Gd3+ doped aluminosilicate oxyfluoride glasses and glass-ceramics containing SrF2 and BaF2 crystallites have been studied by differential thermal analysis (DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM), photoluminescence (PL) and electron paramagnetic resonance (EPR) spectroscopy techniques. A pronounced EPR fine structure emerges after the heat treatment of the glass matrix. EPR spectra simulations indicate the formation of cubic, tetragonal and trigonal Gd3+ centres in the studied compositions.

On the influence of lead and cadmium fluoride content on thermal, optical and structural properties of oxyfluoride glass

This study reveals the effect of PbF2 and CdF2 addition on the aluminosilicate oxyfluoride glass network over a wide compositional range. The structure of glasses in SiO2–Al2O3–PbF2 and SiO2–Al2O3–PbF2–CdF2 system matrices was studied by using DTA, XRD, UV–VIS, density, Raman and FTIR spectroscopy. The observed shifts of absorption edge due to band gap variations with heavy metal fluoride (HMF) addition are compared with theoretical model of optical basicity and physical parameters derived from density. The variation in Tg, and stability factor are supported by Raman and FTIR results which show formation of NBOs and other super structural units with addition of HMF in the aluminosilicate network.

Visible to near-infrared down-conversion luminescence in Tb3 + and Yb3 + co-doped lithium–lanthanum–aluminosilicate oxyfluoride glass and glass-ceramics

Tb3+ and Yb3+ co-doped oxyfluoride glasses were fabricated in a lithium–lanthanum–aluminosilicate matrix (LLAS) by a melt-quench technique. Glass-ceramics were obtained by appropriate heat treatment of the as-prepared glasses. Visible to near-infrared down-conversion luminescence was studied for glass and glass-ceramic samples with different Yb3+ concentrations. It has been found that the luminescence intensity at 940–1020nm from Yb3+ ions increases while the emission lifetime of Tb3+ ions decreases in the glass-ceramic compared to that in the as-prepared glass, which indicates that the energy transfer efficiency increases in the glass-ceramics compared to that in the as-prepared glass. The down-conversion luminescence also increased for increasing Yb3+ concentration from 1mol% to 2mol%, but decreased for the sample with a high Yb3+ co-doping concentration of 8mol%, which is attributed to the concentration quenching.

Luminescent properties of Tb 3+ and Gd 3+ ions doped aluminosilicate oxyfluoride glasses

Tb 3+ and Gd 3+ ions doped lithium–barium–aluminosilicate oxyfluoride glasses have been prepared. The transmission, emission and excitation spectra were measured. It has been found that those Tb 3+-doped lithium–barium–aluminosilicate oxyfluoride glasses exhibit good UV-excited luminescence. The luminescence intensity of Tb 3+ ion increases for those (Tb 3+, Gd 3+)-codoped glasses. Energy transfer process from Gd 3+ ion to Tb 3+ ion is indicated.

Luminescence of Ce3+/Tb3+ ions in lithium–barium–aluminosilicate oxyfluoride glasses

Ce 3+ /Tb 3+ -doped lithium–barium–aluminosilicate oxyfluoride glasses have been prepared. Transmission and luminescent properties under UV excitation have been investigated. Luminescent properties were analyzed by measuring the excitation and photoluminescence spectra. Photoluminescence measurements indicate that the sample doped with Ce 3+ ion has a strong purplish-blue emission and that doped with Tb 3+ ion exhibits bright green emission at about 542 nm under UV excitation. The Ce 3+ ion strongly sensitizes the luminescence of the Tb 3+ ion in the (Ce 3+ , Tb 3+ )-codoped oxyfluoride glass.

Tb-doped Aluminosilicate Oxyfluoride Scintillating Glass and Glass-ceramic

AbstractTwo aluminosilicate oxyfluoride glass systems, a lead-cadmium-aluminosilicate oxyfluoride and a lithium-lanthanum-aluminosilicate oxyfluoride, doped with different TbF3 concentrations, have been fabricated and investigated. By appropriate heat treatment of the as-prepared glasses above, transparent glass-ceramics (TGC) were obtained. The glass-ceramics contain Tb:Pb(Cd)F2 or Tb:LaF3 nano-crystals in the glass-matrix. Differential scanning calorimetry, Raman scattering, and luminescence under both UV and β-particle excitation have been investigated on as-prepared glasses and glass-ceramics. It has been found that the terbium-doped lithium-lanthanum-aluminosilicate oxyfluoride glass exhibits good UV excited luminescence and β-induced luminescence. The luminescence yield increases for glass-ceramic compared to that of the as-prepared glass. The including of LaF3 in the glass-matrix is beneficial for a higher Tb-doping concentration and a high light yield. The light yield of lithium-lanthanum-aluminosilicate oxyfluoride glass and glass-ceramic is comparable to that of Schott IQI-301 product. However, the terbium-doped lead-cadmium-aluminosilicate oxyfluoride glass and glass-ceramic have a detrimental luminescence performance. The lead cations in the glass-matrix may create non-bridging oxygen defects, which are a strong source of charge traps, and correlated to a strong Raman “Boson” peak.