Oxyfluoride Glass Ceramics Research Articles

The effect of lithium fluoride on the thermal stability and thermoluminescence properties of borosilicate glass and glass-ceramics

The oxyfluoride glass and glass-ceramics from the LiF-B2O3-SiO2 system are developed. The stable glass can be produced in the range of 20–40 mol% LiF. The effect of LiF admixture on the thermal stability of the glass as well as the thermoluminescence (TL) properties such as glow curves shape is studied. The results show that the increase of lithium fluoride content in the borosilicate glass causes efficiency enhancement of the thermoluminescence signal. We have clearly stated that the process of controlled crystallization of the oxyfluoride glasses can lead again to increased intensity of the TL process. The glass-ceramics with 40 mol% LiF reveals similar level of TL signal to commercially used doped LiF material and can be considered as active material for alpha and beta radiation detectors.

Enhanced luminescence in Tb3+-doped glass-ceramic scintillators containing LiYF4 nanocrystals

Tb3+ ions single-doped transparent oxyfluoride glass-ceramics (GC) containing LiYF4 nanocrystals were prepared via a conventional high-temperature melt quenching way and subsequent further thermal-treatment. The microstructure and related luminescent properties of the composite materials were studied in detail. It was confirmed by XRD and TEM techniques that the precipitated particles in the glass phase of the GC590-4h sample were LiYF4 nanocrystals having a size of approximately 26 nm. Compared to the PG sample, the luminescence intensity of the GCs at 378 nm light excitation was significantly enhanced and the corresponding lifetime was prolonged. This is because the Tb3+ ions are preferentially enriched in the precipitated low-phonon-energy LiYF4 nanocrystals, which can effectively induce the reduction of non-radiative transitions. It is worth noting that the emission intensity of Tb3+ single-doped GCs containing LiYF4 nanocrystals at 545 nm (5D4→7F5) is also greatly improved (under X-ray excitation). The obtained results indicate that Tb3+ single-doped LiYF4 GC may have the potential to be a novel scintillator applied to X-ray detection for the slow event.

Eu3+ ion distribution in oxyfluoride glass nanocomposites

Assessment of activator distribution in lanthanide doped nanocomposites is an important and challenging task. Oxyfluoride glass ceramics have been chosen as a model system to characterize incorporation efficiency of Eu3+ ions in CaF2 nanocrystals using a combination of X-ray diffraction (XRD) and electron paramagnetic resonance (EPR) techniques. Lattice constant changes induced by size mismatch of Eu3+ and Ca2+ ions have been used to evaluate Eu3+ content in CaF2. The distortion of CaF2 lattice due to incorporation of europium ions can be detected from EPR investigations via Gd3+ paramagnetic probe spectra. It is shown that ratio of different symmetry CaF2:Gd3+ centres and linewidth of EPR transitions can be used to monitor europium content in the crystalline phase of glass ceramics.

Structural evolution of luminescence nanoparticles with rare-earth ions in the oxyfluoride glass ceramics

The structure of up-conversion luminescent nanoparticles in oxyfluoride glass ceramics doped with rare-earth ions has been studied by using small-angle neutron scattering and atomic force microscopy. The formation of rather large amorphous nanoparticles with an average size of about 30 nm was found for the initial system. At temperature treatment above 380°С with increased processing time, the initial large nanoparticles divide into the smaller ones with the average sizes in the range of 14–20 nm. It is assumed that this process corresponds to crystallization of the lead fluoride component with the formation of up-conversion luminescence centers. The structural parameters, morphology and size distributions of both amorphous and crystalline nanoparticles have been obtained.

Structure and luminescent properties of oxyfluoride glass-ceramics with YF3:Eu3+ nanocrystals derived by sol-gel method

In this paper, the transparent oxyfluoride glass-ceramic materials containing YF3:Eu3+ nanocrystals were fabricated via controlled ceramization of precursor xerogels at relatively low temperature T = 350 °C. The formation of YF3 nanocrystalline phase from Y(CF3COO)3 was verified based on X-ray diffraction (XRD) measurements as well as high-resolution transmittance electron microscopy (HR-TEM). Based on IR-ATR spectroscopy the functional groups inside sol-gel structures were identified. The optical properties of Eu3+ ions in fabricated sol-gel samples were investigated based on photoluminescence excitation and emission spectra as well as luminescence decay analysis of the 5D0 excited level. Upon excitation at near-UV illumination, λexc = 393 nm, the series of 4f6-4f6 photoluminescence bands of Eu3+ ions in reddish-orange light area were recorded. The Stark splitting of photoluminescence bands, double-exponential character of decay curves and long-lived emission for fabricated glass-ceramic samples clearly evidenced the partial substitution of Y3+ by optically active Eu3+ ions in precipitated YF3 nanocrystals. Indeed, it was identified that applied annealing conditions resulted in significant, almost 34-fold prolongation of luminescence lifetime from 0.24 ms (Eu3+ ions in xerogel host) up to 8.14 ms (Eu3+ ions incorporated into YF3 nanocrystals). It was also observed a clear correlation between identified phonon energies from IR measurements and luminescence behavior of Eu3+ ions.

A structure model for phase separated fluoroaluminosilicate glass system by molecular dynamic simulations

Oxyfluoride glass and glass ceramics have been widely used in optical devices with Ln3+ doping. Especially, fluoride phase separation is considered as the initial stage of nanocrystallization that can help to realize the controllable crystallization and also provide the low phonon energy environment in oxyfluoride glass. Therefore, a structure model to describe this phase separated glass system is in great help for designing optical materials with high luminescence. In this study, large-scale molecular dynamics (MD) simulations were performed to understand the structural heterogeneity and make attempt to propose a structure model for fluoroaluminosilicate glass. The simulation results reveal immiscible behaviors of the fluoroaluminosilicate glass that separate into fluoride-rich phase and aluminosilicate-rich residual matrix, which have structural features analogous to fluoride and aluminosilicate glass, respectively. Besides, Al3+ plays an essential role to inter-connect oxygen and fluorine ions on the oxide-fluoride phase interface, maintaining the stability of the glass system.

From structure to luminescence investigation of oxyfluoride transparent glasses and glass-ceramics doped with Eu3+/Dy3+ ions

Glasses and glass-ceramics with nominal composition 73 TeO2– 4BaO– 3Bi2O3–18SrF2-2RE2O3 (where RE = Eu, Dy) have been synthesized by conventional melt-quenching technique and subsequent heat treatment at 370 °C for 24 h in air atmosphere. Various Eu3+ to Dy3+ molar ratio have been applied to investigate luminescence properties in both glass and glass-ceramic matrices. Especially, white light emission through simultaneous excitation of Eu3+ and Dy3+ has been studied in detail. Influence of crystalline SrF2 phase on luminescence kinetics has been determined by luminescence decay time measurements. Presence of crystalline SrF2 phase has been confirmed by X-ray diffraction technique XRD and transmission electron microscopy TEM. X-ray photoelectron spectroscopy XPS and Fourier-transform infrared spectroscopy FTIR have been applied to get further insight into structural properties of glass and glass-ceramic materials. Color tunable white light emission has been obtained using UV excitation. Influence of the SrF2 crystallization on luminescence properties of prepared materials have been described in detail. Moreover, luminescence properties and especially emission color dependence on the Eu3+ to Dy3+ molar ratio have been exhaustively studied. Color-tunable white light emission has been observed as a result of simultaneous radiative transition of both, Eu3+ and Dy3+ ions when applying UV excitation. Judd – Ofelt and other optical parameters have been calculated based on luminescence emission spectra. Achieved results confirm that tellurite glass-ceramics containing SrF2 nanocrystals are good hosts for RE3+ ions and they can be considered as new phosphors for white light emitting diodes WLEDs.

Tunable upconversion emission in Er3+/Yb3+ co-doped oxyfluoride glass ceramics containing NaYF4 nanocrystals by the incorporation of Li+ ions

Rare earth doped glass materials with efficient tunable upconversion emission are a challenging field of research in the development of advanced optical devices. In this paper, tunable upconversion emission was realized by incorporating Li+ ions in Er3+/Yb3+ co-doped oxyfluoride glass ceramics containing NaYF4 nanocrystals. The prepared glass ceramics samples experience significant enhancement of luminescence intensity (up to 15 times) under 980 nm excitation. Meanwhile, a composite yellow emission with adjustable CIE chromaticity coordinates was achievable by altering the doping concentration of Li+ ions. The XRD analysis, absorption spectra and Judd-Ofelt theoretical calculations consistently revealed that these phenomena were associated with the Li+ caused shrinkage/expansion of NaYF4 crystal cells, which offers the possibility of emission tuning. The relevant luminescence mechanism was discussed in detail. Furthermore, it may pave new avenue for optimizing novel oxyfluoride glass ceramics applied in various optoelectronic fields.

Upconversion luminescence in transparent oxyfluoride glass ceramics containing hexagonal NaErF4

Transparent oxyfluoride glass ceramics containing hexagonal NaErF4 nanocrystals were synthesized by a heat treatment of a precursor glass obtained by the melt quenching technique. Combined X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis revealed the formation of single phase nanocrystals in the glass ceramics. The enhancement of intensity and spectral change of upconversion luminescence (UCL) confirmed the presence of Er3+ ions in the crystalline phase of the glass ceramics. Dominant energy transfer processes were identified using the rate equation formalism. Time-resolved site-selective spectroscopy studies at low temperatures were employed to elucidate the local structure of Er3+ ions in the glass ceramics and microcrystalline NaErF4. The origin of multi-site formation in hexagonal NaErF4 lattice is discussed.

Fluorine losses in Er3+ oxyfluoride phosphate glasses and glass-ceramics

Er3+ doped phosphate glasses with the composition 75NaPO3-25CaF2 (mol%) were prepared at different melting temperatures to demonstrate the importance to quantify the fluorine content when preparing oxyfluoride glasses. Indeed, increasing the melting temperature from 900 to 1000 °C leads to a small reduction in the fluorine content from 9.4 at % to 8.8 at % as quantified using EPMA. Whereas this loss of fluorine can be suspected from small changes in the thermal properties of the glass, it increases significantly the glass crystallization tendency in this glass system. This means that a heat treatment of the as-prepared glass should be performed when evaporation of fluorine during the glass melting is suspected. Sample preparation for the characterization of the spectroscopic properties of the glasses is discussed here as well; bulk glasses should be used when measuring the spectroscopic properties of oxyfluoride glasses, which are known to be hygroscopic. It is shown, in this work, that a heat treatment of the glass within the investigated glass system leads to transparent glass-ceramics with volume precipitation of Er3+ doped CaF2 crystals with strong upconversion.

Transparent Sol-Gel Oxyfluoride Glass-Ceramics with High Crystalline Fraction and Study of RE Incorporation.

Transparent oxyfluoride glass-ceramic films and self-supported layers with composition 80SiO2-20LaF3 doped with Er3+ have been successfully synthesized by sol-gel process for the first time. Crack-free films and self-supported layer with a maximum thickness up to 1.4 µm were obtained after heat treatment at the low temperature of 550 °C for 1 min, resulting in a LaF3 crystal fraction of 18 wt%, as confirmed by quantitative Rietveld refinement. This is the highest value reported up to now for transparent oxyfluoride glass-ceramics prepared by sol-gel. This work provides a new synthesis strategy and opens the way to a wide range of potential applications of oxyfluoride glass-ceramics. The characterization by a wide range of techniques revealed the homogeneous precipitation of LaF3 nanocrystals into the glass matrix. X-ray absorption spectroscopy and electron paramagnetic resonance confirmed that the Er3+ ions are preferentially embedded in the low phonon-energy LaF3 nanocrystals. Moreover, photoluminescence (PL) measurements confirmed the incorporation of dopants in the LaF3 nanocrystals. The effective concentration of rare-earth ions in the LaF3 nanocrystals is also estimated by X-ray absorption spectroscopy.

Visible and Infrared Luminescence, Energy Transfer in Er/Yb Codoped Oxyfluoride Glass Ceramics

Visible and Infrared Luminescence, Energy Transfer in Er/Yb Codoped Oxyfluoride Glass Ceramics

Structural Origins of RF3/NaRF4 Nanocrystal Precipitation from Phase-Separated SiO2-Al2O3-RF3-NaF Glasses: A Molecular Dynamics Simulation Study.

Oxyfluoride glass-ceramics with RF3 or NaRF4 (R3+: rare earth elements) nanocrystals are considered as favorable hosts for luminescence applications. In this work, we utilized large-scale molecular dynamics (MD) simulations with effective partial charge potentials to study a series of oxyfluoride glasses that are of interest to the precipitation of RF3 or NaRF4 nanocrystals as previous experiment results suggested. The results show that phase separation exists in all glass compositions with fluoride-rich regions made up of R3+, Na+, and F- and oxide-rich regions consisting of aluminosilicate networks. These fluoride-enriched regions can serve as the precursor for RF3, cubic and hexagonal NaRF4, and NaF crystal precipitation. The results also confirm that the concentration of Na+ in the fluoride phase plays a key role in determining the crystal phases (RF3, NaRF4, or NaF) and crystal structure (cubic vs hexagonal NaRF4) to be precipitated. Consequently, this study shows that MD simulations with effective potentials can fill the gap in the structural understanding of oxyfluoride glass and provide insights into atomic scale information of the phase separation behavior that is useful in predicting the potential crystal types in oxyfluoride glass. When coupled with experimental validations, these simulations can expedite the exploration of novel luminescent oxyfluoride glass ceramics.

Tailoring up-conversion luminescence for optical thermometry in K+/Er3+ co-doped oxyfluoride glass ceramics

Abstract In this work, a strategy of K+ ions doping was visited with the aim of enhancing up-conversion luminescence (UCL) and sensitivity for optical thermometer of β-PbF2:Er3+ glass ceramics (GCs). Compared to K+-free β-PbF2:Er3+ GCs, the UCL intensity of green (521, 552 nm), red (668 nm), NIR (825 nm) emissions and absolute sensitivity (Sa) for optical thermometer of the β-PbF2:Er3+ GCs co-doped with 10 mol% K+ ions were increased by 176, 82, 18 and 1.5 times, respectively. Charge compensation and the distortion of the local symmetry around the Er3+ ions, when the K+ ions were introduced, were confirmed to be the origin of the enhancement. The results show that K+ ions simultaneous co-doping of β-PbF2:Er3+ glass ceramics (GCs) very effective way to integrate this material for advanced photonic applications.

Energy transfer behaviors and tunable luminescence in Tb3+/Eu3+ codoped oxyfluoride glass ceramics containing cubic/hexagonal NaYF4 nanocrystals

Abstract For glass ceramics, glass crystallization and doping activators into nanocrystalline phases are the key factors determining optical performance, including energy transfer (ET) process. Herein, we propose a strategy to verify ET behaviors based on glass crystallization, elaborately selecting phase-transformed NaYF4: Tb3+, Eu3+ nanocrystals embedded transparent glass ceramics as a typical example. The ET behaviors from Tb3+ to Eu3+ are clarified via photoluminescence spectra, time-resolved spectra and decay curves. Impressively, the corresponding ET process in cubic NaYF4 turns out to be more efficient than that in hexagonal, in spite of a disorder-to-order transformation from cubic to hexagonal. The reason for this abnormal ET efficiency is that dopants prefer to be partitioned into the cubic NaYF4 rather than the hexagonal one during glass crystallization. This work provides keen insights into the relationship between glass crystallization and ET behaviors, which can also feed back to helpfully guide the design and fabrication of glass ceramics with superior optical performance.

Luminescence properties of Ce3+-doped oxyfluoride aluminosilicate glass and glass ceramics

Ce3+-doped oxyfluoride aluminosilicate glasses and glass ceramics were prepared by a melt-quenching method with subsequent heat treatment, and their spectral and scintillation properties were measured and analyzed. The effects of Na+ ions and glass microcrystallization on the spectral and scintillation properties are discussed. Although Na+ ions were favorable for the formation of glass, their photoluminescence and radioluminescence intensity were relatively low. After microcrystallization, the photoluminescence and radioluminescence intensities of the sodium-free oxyfluoride aluminosilicate glass ceramics increased by 2.3 and 4 times, respectively. Microcrystallization of glass is an effective method to improve the scintillation properties.

Infrared-laser precipitation of Dy3+-Yb3+ codoped SrF2 nanocrystals in glass and upconversion luminescence

Oxyfluoride glass-ceramics containing SrF2nanocrystals have been prepared by a CO2 laser treatment on the glass prepared by high temperature melt quenching. The optimized scan speed and laser power produced nanocrystals with sizes of ~10 nm. Energy dispersive spectroscopy mapping analysis showed that Dy3+ and Yb3+ ions are highly populated inside the SrF2 nanocrystals. We also report a substantially enhanced down-converted visible emission from the 4F9/2 state of Dy3+ ions, including some violet emissions from the higher energy states under 365 nm excitation in the glass-ceramics, as compared to the as-made glass. Moreover, 980 nm laser diode excitation produced strong green and red emissions from the 4I15/2 state and blue and yellow emissions from the 4F9/2 state. A model has been proposed to interpret the upconversion emissions through the multistep-excitation of Dy3+ ions and energy transfers from, efficient sensitizers, Yb3+ ions to Dy3+ ions.

Optical, structural and luminescence properties of oxyfluoride phosphate glasses and glass-ceramics doped with Yb3+

The impact of Al2O3 and Y2O3 addition on the structure, Yb3+ luminescence and crystallization is investigated for glasses in the P2O5-SrO-Na2O system. Although the addition of Al2O3 and Y2O3 leads to a more connected phosphate network as evidenced using IR and Raman spectroscopies and increases the glass transition temperature, it does not affect strongly the site of the Yb3+. The addition of Al2O3 and Y2O3 slightly decreases the rate of the glass crystallization. Surface crystallization occurs upon heat treatment. Crystallization was confirmed by the presence of sharp peaks in the XRD patterns of the glasses. Independently of the glass composition, different crystalline phases precipitate in the glasses upon heat treatment. The precipitation of the Na1O7P2Yb1 crystal phase leads to an increase of the excited state 2F5/2 lifetime of Yb3+ and also of the bandwidth of the Yb3+ emission band centered at 1 μm.

Highly sensitive optical thermometers based on unconventional thermometric coupled levels of Tm3+ following a Boltzmann-type distribution in oxyfluoride glass ceramics

Two highly-sensitive innovative coupled levels of 3F2,3/1D2 and 3F2,3/1G4 governed by a Boltzmann-type distribution in Tm3+/Yb3+ co-doped β-PbF2 GCs were proposed.

Intense up-conversion emission from Er3+/Yb3+ ion co-doped transparent oxyfluoride glass-ceramics containing Y5O4F7 nanorods for optical thermometry

Formation of orthorhombic Y5O4F7:Er3+,Yb3+ nanorods in oxyfluoride glass-ceramics to realize intense up-conversion emission for application in optical thermometry.