Doped Oxyfluoride Glass Ceramics Research Articles

Enhanced luminescence of Eu3+ doped β-PbF2 oxyfluoride glass ceramics for a new optical thermometry by charge compensation and local lattice symmetry breaking

Eu3+ doped β-PbF2 oxyfluoride glass ceramics (GCs) were synthesized via conventional melt-quenching method. The micro-morphology and luminescence properties of the fabricated GCs were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and photoluminescence (PL) spectra. A new temperature sensing mechanism based on fluorescence intensity ratio (FIR) between 5D0 → 7FJ (1, 2, 3, 4) and 5D0 → 7F0 transitions of Eu3+ ion was proposed. Such new mechanism is due to strong thermal coupling of 7FJ (J = 0, 1, 2, 3, 4) states because of their small energy gap. With the increase of temperature, more and more population reaches high states 7FJ (J = 1, 2, 3, 4) from 7F0 state through thermalization process leading to different temperature-dependent transitions of 5D0 → 7FJ (J = 0, 1, 2, 3, 4). Furthermore, lattice distortion around Eu3+ ions caused by co-doped K+ ions resulting in distinct enhancement of emission of Eu3+ ion and violent splitting of 7FJ (J = 2, 3, 4) states. Meanwhile, narrowing of energy gap between 7FJ (J = 0, 1, 2, 3, 4) states resulting from the violent splitting of 7FJ (J = 2, 3, 4) states facilitated thermalization process between 7FJ (J = 0, 1, 2, 3, 4) states and then enhanced sensitivity of temperature measurement was obtained. We believe that this preliminary study will provide an important advance in exploring other innovative optical thermometry.

Effect of concentration of Er3+ on up-conversion luminescence in NaYF4 embedded oxy-fluoride glass-ceramics under 1550 nm excitation

Oxy-fluoride glass-ceramics (GC) has advantages such as low phonon energy of fluorides and the excellent physical and chemical properties of oxides. Here we report the synthesis of a series of transparent oxy-fluoride GCs with various doping contents of Er3+ (0.2 mol%-10 mol%) synthesized under different temperatures, and their UCL properties under the excitation of 1550 nm laser. We found that Er3+-doped glass matrix with NaYF4 fluoride nanocrystals demonstrated greatly enhanced UCL compared with as-prepared glass. The samples showed red light emission with 3 mol% Er3+ as the optimal doping content. The wavelength of UCL could be fine-tuned by the temperature of heat treatment, and 893 K seems to be the optimal temperature. We also studied the photoelectric conversion characteristics of the optimal Er3+ doped oxy-fluoride GCs with a polycrystalline silicon solar cell under the excitation of a 1550 nm laser as a possible strategy to effectively improve the photo-electric conversion efficiency of solar cells.

Structure and luminescence of Pr3+-doped oxyfluoride glass-ceramics containing Na5Y9F32: Pr3+ nanocrystals

Oxyfluoride glass-ceramics have become a focal point of recent research, positioned to advance significantly in areas such as LED illumination and optical data storage, etc. This study successfully prepared Pr3+-doped fluorosilicate glass and glass-ceramics embedded Na5Y9F32 nanocrystals. The introduction of Pr2O3 into the glass matrix disturbs the network structure, leading to a reduction in the band gap from 3.66 eV to 3.42 eV. When subjected to 443 nm light excitation, the 1.0 mol% Pr3+-doped glass-ceramics crystallized at 690 °C for 1.0 h exhibit the most potent luminescence, displaying seven emission peaks resulting from the radiative transition of Pr3+ ions, manifesting yellowish-pink hues. Furthermore, when stimulated by a 450 nm LD, the glass-ceramics display a distinct emission peak at approximately ∼247 nm, attributed to the electron transitions of 4f5d → 3H4 for Pr3+ ions. The luminescent properties of these glass-ceramics embedded with Na5Y9F32 nanocrystals illustrate potential applications in up-conversion and down-conversion luminescence.

Infrared to visible upconversion luminescence in Ho3+ doped oxyfluoride glass ceramics

Infrared to visible upconversion luminescence in Ho3+ doped oxyfluoride glass ceramics

Spark plasma sintering and optical properties of Tm3+ and Tm3+ /Yb3+ doped NaLaF4 transparent glass-ceramics

Tm3+ doped oxyfluoride glass-ceramics (GCs) containing NaLaF4 nanocrystals (NCs) have been obtained by spark plasma sintering (SPS). First, the precursor glasses were melted and then milled and sieved to a suitable particle size. Glass powder pellets were sintered by spark plasma sintering under vacuum conditions. The SPS processing parameters (temperature, pressure, and holding time) were optimized to obtain transparent glass-ceramics. The times of SPS processing are considerably shorter compared with those for the preparation of these GCs by conventional thermal treatment. All glass-ceramics contain nanocrystals of the β- NaLaF4 phase with an average crystal size of 20 nm, but the more highly doped samples (2Tm3+ and 0.5Tm3+/2Yb3+) show evidence of the presence of another phase corresponding with α-NaLaF4. The luminescence properties of the near infrared (NIR) emissions of Tm3+ for different concentrations reveal the presence of concentration quenching of the 3H4 and 3F4 levels. The analysis of the decay from the 3H4 level with increasing concentration is consistent with a dipole-dipole quenching process assisted by energy migration, whereas the self-quenching of the 3F4→3H6 emission can be attributed to fast diffusion. Energy transfer between Yb3+ and Tm3+ ions is confirmed by the NIR and upconverted (UC) emissions after Yb3+ excitation at 975 nm. No UC emission is observed under 791 nm excitation of Tm3+ ions.

The effect of melt-homogenization and heat-treatment on the optical properties of the rare earth doped oxyfluoride glass-ceramics

We prepared four Er3+-Yb3+ co-doped oxyfluoride precursor glass (PG) samples with the same chemical composition at different melt-homogenization temperatures (Thomo), respectively, at the same melt-quenching rate. We investigated the effect of Thomo and heat-treatment (HT) on the crystallization, structure, and optical properties of the four samples. The results show that the structural heterogeneity in the PG sample increases with lowering Thomo, and this promotes phase-separation, and hence, formation of Ba2LaF7 crystals. Consequently, the light transmittance of PG samples is decreased, but the up-conversion (UC) luminescence is enhanced. Moreover, the crystallinity of the four PG samples was increased by HT, and this altered the light transmittance, and greatly enhanced the UC luminescence. The mechanism of these discovered phenomena was discussed in terms of structure and crystal evolution. This work provides an effective way to optimize the optical and photonic performances of the rare earth doped oxyfluoride glass-ceramics.

Optical Properties of Transparent Rare-Earth Doped Sol-Gel Derived Nano-Glass Ceramics.

Rare-earth doped oxyfluoride glass ceramics represent a new generation of tailorable optical materials with high potential for optical-related applications such as optical amplifiers, optical waveguides, and white LEDs. Their key features are related to the high transparency and remarkable luminescence properties, while keeping the thermal and chemical advantages of oxide glasses. Sol-gel chemistry offers a flexible synthesis approach with several advantages, such as lower processing temperature, the ability to control the purity and homogeneity of the final materials on a molecular level, and the large compositional flexibility. The review will be focused on optical properties of sol-gel derived nano-glass ceramics related to the RE-doped luminescent nanocrystals (fluorides, chlorides, oxychlorides, etc.) such as photoluminescence, up-conversion luminescence, thermoluminescence and how these properties are influenced by their specific processing, mostly focusing on the findings from our group and similar ones in the literature, along with a discussion of perspectives, potential challenges, and future development directions.

Photonic properties of novel Yb3+ doped germanium-lead oxyfluoride glass-ceramics for laser cooling applications

In recent years, our research group has developed and studied new rare-earth doped materials for the promising technology of solid-state laser cooling, which is based on anti-stokes fluorescence. To the best of our knowledge, our group is the only one in Canada leading the research into the properties of nanoparticles, glasses and glass-ceramics for optical refrigeration applications. In the present work, optical properties of 50GeO2-30PbF2-18PbO-2YbF3 glass-ceramics for laser cooling are presented and discussed as a function of crystallization temperature. Spectroscopic results show that samples have near infrared photoluminescence emission due to the 2F5/2–2F7/2 Yb3+ transition, centered at ~1016 nm with an excitation wavelength of 920 nm or 1011 nm, and the highest photoluminescence emission efficiency occurs for heat-treatment for 5 h at 350°C. The internal photoluminescence quantum yield varies between 99% and 80%, depending on the temperature of heat-treatment, being the most efficient under 1011 nm excitation. The 2F5/2 lifetime increases from 1.472 to 1.970 ms for heat treatments at 330°C to 350°C, respectively, due to energy trapping and the low phonon energy of the nanocrystals. The sample temperature dependence was measured with a fiber Bragg grating sensor, as a function of input pump laser wavelength and processing temperature. These measurements show that the heating process approaches near zero for an excitation wavelength between 1020 and 1030 nm, which is an indication that phonons are removed effectivelly from the glass-ceramic materials, and they can be used for optical laser cooling applications. On the other hand, the temperature increase as a function of input laser power into samples remains constant between 920 and 980 nm wavelength excitation, a temperature variation of 36 K/W (temperature of 58°C/W) was attained under excitation at 950 nm, showing a possible use for biomedical applications to be explored.1)

Luminescence of Er3+ doped oxyfluoride phosphate glasses and glass-ceramics

Glasses with the composition (75 NaPO3-(25-x) CaO-xCaF2) (in mol %) were prepared with 0.15 mol% of Er2O3. The effect of the glass composition and of heat treatment on the spectroscopic properties of the newly developed glasses is reported. With the progressive replacement of CaO by CaF2, the Er3+:4I13/2 lifetime and the intensity of the upconversion emission increase whereas the intensity of the emission at 1.5 μm decreases due to the decrease in the phonon energy in the as-prepared glasses. The glasses were heat treated at 20 °C above their respective glass transition temperature for 17 h to form nuclei and then at their crystallization temperature from 15min to 1 h to grow the nuclei into crystals. The heat treatment leads to the precipitation of crystalline phases, the composition of which depends upon the glass composition. As the Er3+:4I13/2 lifetime increases and the intensity of the upconversion increases for the glass with x = 0 after heat treatment, the Er3+ ions are expected to be incorporated into the phosphate-based crystals. However, as the shape of the emission band at 1.5 μm remains unchanged and the intensity of the upconversion decreases significantly after heat treatment of the glasses with x > 10, the crystals found in the glass-ceramics with x > 10 are thought to free of Er3+ ions. Although Er3+ ions entered in the CaF2 crystals precipitating in aluminosilicate glass, the Er3+ ions are believed to remain in the amorphous phosphate part of the glass-ceramic containing CaF2 crystals.

Effect of Melting Times on the Down-Shifting Properties in Ce3+-Doped Oxyfluoride Glass Ceramics for a-Si Solar Cells

We synthesize Ce3+-doped oxyfluoride glass ceramics (GCs) with different melting times employing the conventional melt-quenching method. We investigate the crystal structure and photoluminescence properties of Ce3+-doped GCs in detail in order to evaluate the effect of melting times on the downshifting properties. The photoluminescence properties revealed that the Ce3+ doped GCs have an intense emission band in the broad region from 480 to 600 nm under 427 nm excitation. We improve the energy-conversion efficiency of a-Si solar cells by 0.41%, from 5.02% to 5.43%, by incorporating the Ce3+-doped GCs with a melting time of 1.5 h. The above results indicate that Ce3+-doped GCs can be a promising candidate as downshifting materials for applications in a-Si solar cells.

Infrared-to-Visible Up-conversion in Er-Pr-Yb Triply Doped Oxyfluoride Glass Ceramics

We synthesized Er3+-Yb3+, Pr3+-Yb3+, and Er3+-Pr3+-Yb3+-doped oxyfluoride glass ceramics containing CaF2 nanocrystals by proper thermal treatments. Spectral characteristics of down- and up-converted emissions in three kinds of glass ceramics under 365-nm and 980-nm excitations were compared and explained by cross relaxations, excited-state absorptions, and energy-transfer processes between different ions. The huge reduction of up-conversion emission in the triply doped glass ceramics under 980-nm excitation compared to the Er3+-Yb3+ codoped one was explained by the split pump power and the direct energy transfer from Er3+ to Pr3+ ions. Increasing Yb3+ concentration from 2% to 10% in the triply doped glass ceramics showed more than quadratic enhancement of the absorbed power, and we explained it by the enhanced energy-transfer efficiency from Yb3+ to Er3+ ions. We also observed enhanced up-converted emissions of Er3+ and Pr3+ ions in three kinds of glass ceramics under simultaneous excitation at 980 nm and 1550 nm, and suggested detailed up-conversion mechanisms.

Phase transitions and upconversion luminescence in oxyfluoride glass ceramics containing Ba4Gd3F17 nanocrystals

Novel transparent Er3+ doped oxyfluoride glass-ceramics containing Ba4Gd3F17 nanocrystals were prepared by melt quenching followed by heat treatment of as-prepared glasses. The phase composition and microstructure were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Intense upconversion luminescence (UCL) was detected. Longer characteristic decay times and splitting of the luminescence bands compared to the precursor glass indicated the incorporation of erbium ions in the crystalline phase. The spectroscopic properties of glass ceramics were compared with single phase cubic and rhombohedral Ba4Gd3F17 ceramics. The unit cell parameters and atomic positions in the rhombohedral phase were calculated using Rietveld refinement. The local environment of Er3+ and the phonon energy of both polymorphs were analyzed using luminescence and Raman spectroscopy. In the glass ceramics, a phase transition from distorted metastable fluorite to ordered rhombohedral Ba4Gd3F17 was observed and resulted in the enhancement of the efficiency of UCL.

Enhanced near‐infrared to green upconversion from Er3+‐doped oxyfluoride glass and glass ceramics containing BaGdF5 nanocrystals

AbstractIn this work, effect of glass composition as well as ceramization on visible and near‐infrared (NIR) luminescence properties along with their decay dynamics of Er3+ ions has been compared considering two different oxyfluoride glasses yielding BaF2 and BaGdF5 nanocrystals. Both the glass systems have exhibited an intense normal and upconversion green emission under ultraviolet (378 nm) and NIR (978 nm) excitations, respectively. A remarkable enhancement of these emission intensities is observed for gadolinium‐(Gd) containing glasses. Interestingly, NIR fluorescence intensity from Er3+ ions at 1540 nm has showed marginal decrease in gadolinium‐containing glass which is attributed to occurrence of strong excited‐state absorption (ESA) due to higher fluorine content ensuing an augmentation of upconversion green emission with a concomitant decrease in NIR emission. The quadratic dependence of upconversion green emission intensity on its pump power for all the samples revealed biphotonic absorption process from ground‐state 4I15/2 to the excited‐state 4I11/2 followed by ESA of second photon to the 4F7/2 level. The intense green upconversion emission as well as enhanced NIR fluorescence lifetimes indicate the suitability of these glass/glass ceramics for upconversion lasers and amplification in the third telecom window.

Synthesis and characterization of BaLuF5: Tb3+ oxyfluoride glass ceramics as nanocomposite scintillator for X-ray imaging

Tb3+-dopedoxy-fluoride glass ceramics (GC) containing BaLuF5 nanocrystals were manufactured successfully by melt-quenching method with further thermal treatment. Their micro-structural and optical properties were investigated systemically by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM) techniques, transmittance spectra, photoluminescence (PL), luminescence lifetime measurements and X-ray excited luminescence (XEL). PL and XEL from BaLuF5:Tb3+ GC are both highly enhanced after further thermal treatment benefiting from the preferential incorporation of Tb3+ ions into the crystallized BaLuF5 nanocrystals with low phonon energy. Impressively, the integrated XEL intensity for GC640 is about 26% of the commercial BGO scintillator. Our investigation indicates that such Tb3+-doped transparent BaLuF5 GC are potential candidates of X-ray scintillators for slow event detection.

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.

New insight into two-step near-infrared quantum cutting in Pr^3+ singly doped oxyfluoride glass-ceramics

Efficient near-infrared (NIR) quantum cutting (QC) in RE3+/Yb3+ requires the UV-blue photon excited RE3+ donor has intermediate energy level to separate the energy gaps (~10000 cm−1) resonant to Yb3+absorption. Thus the unique Pr3+/Yb3+ resonant QC at low Yb3+content (room temperature) essentially requires Pr3+-doping features distinctive NIR radiative transitions: in our prepared Pr3+-doped oxyfluoride glass-ceramics containing CaF2 nanocrystals, a two-photon NIR-QC from blue-photon excited 3Pj (j = 0, 1, 2) states takes place efficiently with 1G4 acting as an intermediate level. The underlying energy transfer mechanisms involving the two-step sequential transitions of 3P0→1G4 ~915 nm and 1G4→3H4 ~990 nm (crucial resonant routes for the further 1Pr3+→2Yb3+), as well as the 1D2→3F2 ~873 nm and 1D2→3F3,4 ~1040 nm, are rationally distinguished by means of photoemission, excitation, and time-resolved fluorescence spectra.

Upconversion luminescence in erbium doped transparent oxyfluoride glass ceramics containing hexagonal NaYF4 nanocrystals

In this work transparent erbium doped oxyfluoride glass ceramics containing hexagonal NaYF4 nanocrystals has been prepared by melt-quenching and subsequent heat treatment of the precursor glass. The formation of β-NaYF4 was confirmed by X-ray diffraction measurements. The overall intensity of the upconversion luminescence of the glass ceramics sample is 2 orders of magnitude higher than that of the precursor glass. The observed enhancement of the efficiency is explained by the incorporation of Er3+ into low-phonon β-NaYF4 crystalline phase.

Near-infrared quantum cutting platform in transparent oxyfluoride glass–ceramics for solar sells

This study investigated the photoluminescent properties of Er3+/Yb3+ and Ce3+/Er3+/Yb3+ -doped oxyfluoride glass–ceramics. The transparent oxyfluoride glass–ceramics were prepared by high temperature melting method and subsequent heat treatment. Effect of heat treatment schedules on crystallization behavior and microstructure were analyzed by differential scanning caborimetry, X-ray diffraction, infrared spectrum and scanning electron microscopy. The structure of fluoride nanocrystals indicates that the main phase in the oxyfluoride glass ceramics is CaF2 nanocrystal sized at 25nm at the optimal crystallization temperature 600°C for 8h. The Ce3+/Er3+/Yb3+ tri-doped oxyfluoride glass–ceramics shows wider absorption bands comparing with Er3+/Yb3+ co-doped oxyfluoride glass–ceramics. The effective energy transfer processes from Ce3+ to Yb3+, Er3+ to Yb3+ and Ce3+ to Er3+ all can take place simultaneously. The idea of using Ce3+ together with Er3+ and Yb3+ ions could enhance the ultraviolet visible light absorption and the 960–1040nm near infrared emission. Results of this study demonstrate that the tri-activator Ce3+/Er3+/Yb3+ materials are promising for practical application to enhance the energy efficiency of crystalline Si solar cells via spectrum modification.

Enhanced emissions in Tb3+-doped oxyfluoride scintillating glass ceramics containing BaF2 nanocrystals

Transparent Tb3+-doped glass ceramics containing BaF2 nanocrystals were prepared by melt-quenching method with subsequent heat treatment. The XRD and EDS results showed the precipitated crystalline phase in the glass matrix was BaF2. Under 376nm light, Tb3+ doped oxyfluoride glass ceramics containing BaF2 nanocrystals showed more intense green emission than the as-made glass, and the emission intensity increased with increasing heat treatment temperature and time. The lifetimes of 541nm emission of Tb3+ doped oxyfluoride glass ceramics were longer than that of as-made glass, which are in the range from 3.00ms to 3.55ms. Under X-ray excitation, the green emission was enhanced in the glass ceramics compared to the as-made glass. The results indicate Tb3+ doped oxyfluoride glass ceramics containing BaF2 nanocrystals could be a material candidate for X-ray glass scintillator for slow event detection.

Eu2+/Eu3+-doped oxyfluoride glass ceramics with LaF3 for white LED color conversion

SiO2–Na2O–Al2O3–LaF3 glasses doped with Eu2+ and Eu3+ were synthesized to realize an inorganic color converter for white LED using 400nm UV LED. Among various rare earth ions, Eu2+ and Eu3+ showed prominent emission under 400nm LED excitation. Carbon and EuF3 content were varied to control the ratio of Eu2+ and Eu3+ during the melting process. When the ratio of Eu2+ and Eu3+ within the glass matrix was properly controlled, color coordinates of the photoluminescence spectra could be adjusted to make white colors under 400nm LED excitation. The emission intensity was increased with subsequent heat treatment which led to the formation of LaF3 nano-crystals. However, almost no conversion was observed when the glasses were actually mounted on UV-LED to make a white LED. Heavy crystallization of the oxyfluoride glasses was thus investigated to improve its scattering of the light source and color conversion efficiency, and its practical feasibility as an inorganic UV-LED color converter was demonstrated.