Transparent Oxyfluoride Glass Ceramics Research Articles

Tunable luminescence in transparent oxyfluoride glass–ceramics containing KY3F10: Mn2+/Eu3+ nanocrystals for highly sensitive temperature sensing

Tunable luminescence in transparent oxyfluoride glass–ceramics containing KY3F10: Mn2+/Eu3+ nanocrystals for highly sensitive temperature sensing

Color tunability and temperature sensing capabilities in Dy3+/Sm3+ co-doped transparent oxyfluoride glass ceramics containing K3YF6 nanocrystals

This paper presents the preparation and characterization of transparent oxyfluoride glass ceramics (GCs) that contain nanocrystals of K3YF6 co-doped with Dy3+ and Sm3+. The study investigates the luminescence characteristics, the process of energy transfer (ET) and the behavior of the ratio-metric temperature sensing. The formation of well-defined nanocrystals of K3YF6 in the glass substrate was confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). By varying Sm3+ concentration, a tunable emission ranging from pale yellow to orange-red was observed. Energy transfer from Dy3+ to Sm3+ ions was confirmed through fluorescence spectra and decay curves. Sample K3YF6, containing 0.5 mol%Dy3+/1.2 mol%Sm3+, showed an absolute sensitivity (Sa) of 0.635 % K−1 and relative sensitivity (Sr) of 0.401 % K−1. These findings underscore the promising applications of K3YF6: Dy3+, Sm3+ GCs in multicolor displays and high-performance temperature sensing devices.

Enabling Broadband Solar-Blind UV Photodetection by a Rare-Earth Doped Oxyfluoride Transparent Glass-Ceramic.

Oxyfluoride transparent glass-ceramics (GC) are widely used as the matrix for rare-earth (RE) ions due to their unique properties such as low phonon energy, high transmittance, and high solubility for RE ions. Tb3+ doped oxyfluoride glasses exhibit a large absorption cross section for ultraviolet (UV) excitation, high stability, high photoluminescence quantum efficiency, and sensitive spectral conversion characteristics, making them promising candidate materials for use as the spectral converter in UV photodetectors. Herein, a Tb3+ doped oxyfluoride GC isdeveloped by using the melt-quenching method, and the microstructure and optical properties of the GC sample are carefully investigated. By combining with a Si-based photo-resistor,a solar-blind UV detector is fabricated, which exhibits a significant photoelectric response with a broad detection range from 188 to 400nm. The results indicate that the designed UV photodetector is of great significance for the development of solar-blind UV detectors.

Luminescence of Nd3+-doped LaF3 glass-ceramics enhanced with Ag nanoparticles

Nd3+-doped, LaF3-based, transparent oxyfluoride glass-ceramics (GCs) containing Ag nanoparticles (NPs) have been prepared by a melt-quenching method. Different Ag-containing precursors were employed, with AgNO3 as the most suitable for obtaining Ag NPs segregated in the glassy matrix. Transmission electron microscopy and X-ray absorption spectroscopy determined the presence of Ag0 NPs, with higher concentrations in glass-ceramics produced in an inert atmosphere (N2).The spectral features of emission and excitation spectra, in addition to the different lifetimes of the 4F3/2 state in the co-doped samples with Ag NPs, demonstrate the incorporation of Nd3+ ions into the LaF3 nanocrystals. The relative contribution to the emission from Nd3+ in the nanocrystals depends on the Ag concentration and atmosphere. The glass-ceramic co-doped with 0.2 wt% Ag, thermally treated in N2, exhibits the highest contribution of emissions attributable to Nd3+ ions in the crystalline phase. The crystalline fraction is similar to that of a Ag-free sample synthesized under analogous conditions. This increase of the luminescence is likely attributable to the enhancement of the local electric field in the LaF3 nanocrystals due to the presence of Ag0 NPs.

Effect of rapid thermal annealing treatment on up-conversion luminescence in Er3+/Yb3+ co-doped NaYF4 oxy-fluoride glass-ceramics

The heat-treatment plays a decisive role in the process of crystal phase precipitation and the microscopic features of the fluoride particles, which determines the optical transmittance and up-conversion luminescence (UCL) properties. In this work, we successfully synthesized Er3+/Yb3+ co-doped UCL transparent oxy-fluoride glass-ceramics (GCs) by precipitation of NaYF4 nanoparticles using a rapid thermal annealing (RTA) treatment with ultra-high heating rate (100 K/s). The particle sizes of NaYF4 nanoprecipitation inside glass-ceramic is only 4–5 nm, which is much smaller than the 40–50 nm particle sizes obtained using normal-heating treatment. The GCs with ultra-small particle sizes provided a very high optical transmittance that is close to that of all-amorphous glass, but the intensity of UCL was similar to that of a sample prepared using a slower heating rate. Finally, under different heat treatment conditions the Er3+/Yb3+ co-doped NaYF4 transparent GCs with different particle sizes can be produced, the color and intensity of UCL were controllable.

Er/Yb co-doped LiYF4 transparent oxyfluoride glass-ceramics with up-conversion optical properties

Transparent oxyfluoride glass-ceramics doped with rare earth ions (RE3+) are promising materials for photoluminescence up- and down-conversion. In this study, glass compositions within the system 40SiO2–25Al2O3–18Li2O–7LiF–10YF3 (mol.%) doped with ErF3 and codoped with ErF3/YbF3 were prepared by melt-quenching method and subjected to thermal treatment at temperatures above glass transition (Tg + 35 °C) for long dwell times to obtain the corresponding glass-ceramics. The formation of LiYF4 and LiAlSiO4 nanocrystals was confirmed by XRD analysis after thermal treatment at 540 °C for 20 h. The increase in the treatment time up to 80 h resulted in the enhancement of the UC luminescence yield and the decrease of the Red to Green ratio (R/G) emission intensity. Due to the nano-sized crystals, the glass-ceramic products were transparent (%T) in near-infrared (NIR) and visible spectral region with %T remaining approximately 85% and 75%, respectively, after 20 h treatment. However, the visible window transparency reduced, with %T dropping to around 50% after 80 h due to the increase in crystal size and crystalline fraction. The influence of Yb3+ co-doping on the up-conversion (UC) luminescence has been investigated in the glass-ceramics and compared to the parent glasses, confirming that Yb3+ ions were also a key factor for facilitating up-conversion via energy transfer (ET), leading to a greater luminescence yield than for Er3+ single doped glass-ceramics and tuning of R/G intensities.

Optical properties of Er3+ doped NaLuF4 transparent glass-ceramics produced by spark plasma sintering

Transparent oxyfluoride glass-ceramics (GCs) containing NaLuF4 nanocrystals doped with Er3+ have been prepared by combination of glass melt-quenching and spark plasma sintering (SPS) of glass powders. The parameters, such as temperature, pressure, particle size and holding times were optimized to obtain the densification of the powdered samples together with the desired transparency. The major advantage of this technique is the shorter times (few minutes) compared with those used for the preparation of these GCs by conventional heat treatments (more than 10 h). SPS presents an important inconvenient, which is the carbon contamination coming from graphite punch, this has been improved using Pt foils.The structural study indicates the presence of nanocrystals corresponding to the crystalline phase α-NaLuF4, with a crystal size between 26 and 31 nm. The optical characterization, which includes near infrared emission and infrared-to-visible up-conversion, confirms the incorporation of Er3+ ions in the nanocrystals. The longer lifetimes of the 4I11/2 and 4I13/2 levels together with the enhancement of the upconverted green and red emissions (as well as the weak blue emission) in the SPS-GCs samples, if compared with the precursor glass, indicates the presence of Er3+ ions in a crystalline environment. Possible energy conversion mechanisms for the green and red emissions based on the temporal behavior of the upconverted luminescence are discussed.

Rare-earth doped transparent oxyfluoride glass-ceramics: processing is the key [Invited

Oxyfluoride glass-ceramics (OxGCs) are transparent materials composed by an oxide glass matrix with homogeneously distributed fluoride nanocrystals. In particular, OxGCs with RE-doped lanthanide-fluoride nanocrystals are of special interest for photonic applications. More than 600 publications including several review papers were indexed on Scopus related to “glass-ceramics” revealing the importance of the topic. Melt-quenching followed by thermal treatment, is the most used preparation method, which allows materials in bulk and fibre form to be obtained, being also a scalable industrial process. Spark plasma sintering from glass powders is showing promising results. The sol-gel process has appeared as an alternative method to avoid some of the drawbacks of the melting process such as the high temperature. It also permits to process materials with different shapes such as thin films, nano-sized powders or bulk materials at very low temperature. This paper reviews the different aspects involved in the preparation of OxGC materials by melt-quenching, spark plasma sintering and sol-gel and how the processing parameters directly affect the glass-ceramics properties from results of the GlaSS research group from CSIC. A comparison of the thermal, structural and optical properties is discussed along with some perspectives for preparing other advanced materials within this field.

Correction to: Transparent oxyfluoride glass-ceramics obtained by different sol-gel routes

Correction to: Transparent oxyfluoride glass-ceramics obtained by different sol-gel routes

Color-tunable luminescence and temperature sensing in Ce3+/Tb3+ co-doped transparent oxyfluoride glass-ceramics containing Na1.5Y2.5F9 nanocrystals

Transparent glass-ceramics (GCs) containing Na1.5Y2.5F9 nanocrystals doped with Ce3+/Tb3+ were synthesized by melt-quenching approach. The nanocrystal structure was determined by X-ray diffraction, and its distribution and morphology were observed by transmission electron microscope. Luminous characteristics, energy transfer, and temperature sensing performance were investigated. Under 312 nm light excitation, the Ce3+/Tb3+ co-doped Na1.5Y2.5F9 GCs exhibited a blue emission (Ce3+: 424 nm) and sensitized a green emission (Tb3+: 546 nm). The emission color can be adjusted from blue (0.1643, 0.0826) to green (0.2891, 0.5243) via adding Tb3+ ions. The energy transfer efficiencies from Ce3+ to Tb3+ can reach 33.3%. The temperature sensitivity of sample Na1.5Y2.5F9: 0.5Ce3+, 0.1 Tb3+ and sample Na1.5Y2.5F9: 0.5Ce3+, 1.0 Tb3+ were compared. Based on the fluorescence intensity ratio of the Ce3+ and Tb3+ emission, the absolute sensitivity, relative sensitivity, temperature resolution, and thermal repeatability were estimated to be 0.768% K−1, 0.603% K−1, 0.049 K, and 0.993, respectively. The results indicate that Na1.5Y2.5F9: Ce3+, Tb3+ GCs have immense application prospects for multicolor displays and temperature sensors.

Transparent oxyfluoride glass-ceramics obtained by different sol-gel routes

Transparent oxyfluoride glass-ceramics obtained by different sol-gel routes

Intense and broadband mid-infrared emission by nano-crystallization of rare‐earth doped oxyfluoride glass-ceramic

Transparent oxyfluoride glass ceramics (GCs) comprised of a uniform oxide glass phase and a well-distributed fluoride crystal phase are regarded as suitable optical gain materials because of the combination of facile fabricability of glass and low phonon energy of nanocrystals. Here, oxyfluoride GCs containing NaYF4: Er3+/Ho3+/Dy3+ nanocrystals were controllably prepared. Due to the preferential incorporation of rare-earth ions into NaYF4 nanocrystals with low phonon energy and the efficient energy transfer between active ions, enhanced and broadband mid-infrared (MIR) emission at 2.5–3.3 µm was obtained from the GCs, which was nearly unobserved in precursor glass (PG) because of the high phonon energy of glass matrix. Compared with Er3+ singly-doped sample, the full width at half maximum (FWHM) is more than 3 times broader in Er3+/Ho3+/Dy3+ triply-doped sample. Furthermore, by the match of the refractive index of glass with NaYF4 nanocrystal, transparent GCs with average crystal size of 80 nm and high transmittance over 80% were achieved simultaneously. The desirable optical properties endow the GCs with potential applications in MIR broadband tunable lasers.

KLaF4:Nd3+doped transparent glass-ceramics processed by spark plasma sintering

Transparent oxyfluoride glass-ceramics (GCs) containing KLaF4 nanocrystals (NCs) doped with Nd3+were prepared by Spark Plasma Sintering (SPS). Glass powder pellets were sintered under a vacuum atmosphere, optimizing the processing parameters such as particle size, pressure, temperature, and holding time to obtain full densification. Transparency decreased when decreasing the particle size due to higher carbon contamination from the die. The α-KLaF4 crystalline phase was identified by X-ray diffraction (XRD) and its average crystal size was 10–20 nm. High-resolution transmission electron microscopy (HR-TEM) confirmed the presence of KLaF4 nanocrystals with incorporated Nd3+ions. Low-temperature site-selective emission and excitation spectra of Nd3+ions confirmed that α- KLaF4 was the predominant polymorph, although a minor presence of β- KLaF4 was also demonstrated.

In Situ Synthesis of β-Na1.5Y1.5F6: Er3+ Crystals in Oxyfluoride Silicate Glass for Temperature Sensors and Their Spectral Conversion and Optical Thermometry Analysis.

Transparent oxyfluoride glass-ceramics (GCs) with embedded β-Na1.5Y1.5F6 crystals doped with Er3+ ions were fabricated by a melt-quenching method with subsequent heat-treatment. The structural characterizations and spectroscopic techniques were performed to verify the precipitation of β-Na1.5Y1.5F6 crystals and partition of the Er3+ dopant into the crystals. Bright green up-conversion (UC) emission was achieved in Er3+-doped glass-ceramic (Er-GC). Furthermore, the temperature-dependent visible UC behavior based on thermally coupled energy levels (TCLs) and non-thermally coupled energy levels (NTCLs) was also examined in the temperature range 298 k to 823 K with maximum relative sensitivity (Sr) of 1.1% K−1 at 298 K for TCLs in Er-G and Er-GC samples.

Crystallization Process and Site-Selective Excitation of Nd3+ in LaF3/NaLaF4 Sol–Gel-Synthesized Transparent Glass-Ceramics

In this study, transparent oxyfluoride glass-ceramics (GCs) with NaLaF4 nanocrystals (NCs) were prepared by the sol–gel method for the first time. Three different molar ratios of La(CH3COO)3/Na(CH3COO) were used to obtain the GCs, which were sintered at 450, 550 and 650 °C for 1 min. X-ray diffraction (XRD) was employed to follow the evolution of the xerogel during the heat treatments and to study crystal growth for the three temperatures. In all cases, the LaF3 crystalline phase was present, but crystallization of NaLaF4 was only promoted at 650 °C. Thermogravimetric and thermodifferential analysis (TGA-DTA) and Fourier transform infrared spectroscopy (FTIR) were used to analyze the crystallization process. High-resolution transmission electron microscopy (HRTEM) was employed to confirm NaLaF4 crystallization and determine the size distribution. The incorporation of Nd3+ ion into NaLaF4 and LaF3 nanocrystals was confirmed by site-selective emission and excitation spectra. The Nd3+ emission intensities in both phases depend not only on the NaLaF4/LaF3 ratio but also on their emission efficiencies.

Non-Linear Optical Properties of Er3+-Yb3+-Doped NaGdF4 Nanostructured Glass-Ceramics.

Transparent oxyfluoride glass–ceramics containing NaGdF4 nanocrystals were prepared by melt-quenching and doped with Er3+ (0.5 mol%) and different amounts of Yb3+ (0–2 mol%). The selected dopant concentration the crystallization thermal treatments were chosen to obtain the most efficient visible up-conversion emissions, together with near infrared emissions. The crystal size increased with dopant content and treatment time. NaGdF4 NCs with a size ranging 9–30 nm were obtained after heat treatments at Tg + 20–80 °C as confirmed by X-ray diffraction and high-resolution transmission electron microscopy. Energy dispersive X-ray analysis shows the incorporation of rare earth ions into the NaGdF4 nanocrystals. Near-infrared emission spectra, together with the up-conversion emissions were measured. The optical characterization of the glass–ceramics clearly shows that Er3+ and Yb3+ ions are incorporated in the crystalline phase. Moreover, visible up-conversion emissions could be tuned by controlling the nanocrystals size through appropriated heat treatment, making possible a correlation between structural and optical properties.

Temperature sensing behavior of Tm3+: 1G4(a), 1G4(b) in oxyfluoride glass ceramics containing BaYbxY(1-x)F5 nanocrystals

Tm3+-doped transparent oxyfluoride glass ceramics containing BaYbxY(1-x)F5 nanocrystals were prepared via high temperature solid phase melting method, of which up-conversion emission is achieved by the Yb3+-mediated energy transfer process. The required photon number of Tm3+ ions emissions in BaYbxY(1-x)F5 nanocrystals was calculated through the luminescence spectra, revealing the strong dependence of energy transfer mechanism on Yb3+ ions concentration. Meanwhile, based on the fluorescence intensity ratio technology, the effect of different energy transfer mechanism on the temperature sensitivity was investigated by the temperature-dependent luminescence intensity of thermally coupled energy levels of Tm3+: 1G4(a), 1G4(b). The obtained sensitivity decreases with the increase of Yb3+ ions content, which is mainly attributed to the changes in photon absorption process of Tm3+: 1G4(b).

A transparent and dual-functional oxyfluoride glass ceramics with color-tunable up-conversion luminescence and high thermosensitivity

Transparent and dual-functional Er3+/Tm3+/Yb3+ tri-doped β-PbF2 glass ceramics (GCs) were synthesized successfully by the conventional melting-quenching method. Under 976 nm laser excitation, intense and typical emissions of Tm3+ and Er3+ with good signal discriminability were simultaneously observed. Just through regulating Er3+ concentration, a color-tunable emission over a large range of “purplish blue→cool white→green→reddish orange” was achieved in Er3+/Tm3+/Yb3+ tri-doped β-PbF2 GCs upon 976 nm laser excitation. Additionally, besides two pairs of conventional thermally coupled energy levels (TCELs) of Er3+ and Tm3+, temperature sensing property of the Er3+/Tm3+/Yb3+ tri-doped β-PbF2 GCs was investigated based on a novel coupled energy levels, 3F2,3 (Tm3+)/4S3/2 (Er3+). Fortunately, the relative sensitivity Sr of the novel coupled energy levels of 3F2,3 (Tm3+)/4S3/2 (Er3+) with the maximum value of 2.70 %K−1 at 288 K is improved tempestuously than the conventional TCELs, even larger than many other rare earth ion doped temperature sensors. The results presented in this work indicate that the transparent Er3+/Tm3+/Yb3+ tri-doped β-PbF2 GCs is a competitive dual-functional candidate with large range of color-tunable UCL and high thermosensitivity.

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.

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.