Transparent Glass Ceramics Research Articles

Luminescence properties and thermal stability of Sm3+-doped Na2O–Y2O3–SiO2–P2O5 transparent glass-ceramics containing Na3YSi2O7 crystals

Sm3+-doped Na2O–Y2O3–SiO2–P2O5 precursor glasses were prepared by melting cooling and quenching methods. The optimal doping concentration of Sm3+ ions was determined by fluorescence spectrum. The thermodynamic parameters of precursor glass were determined by the DSC test. The transparent glass-ceramics containing Na3YSi2O7 crystals were obtained by proper heat treatment. The types and microstructures of Na3YSi2O7 crystals were characterized by XRD and SEM. The highest emission peak in the emission spectrum represents the transition of Sm3+: 6H5/2 → 4F7/2. Moreover, the emission intensity of the glass-ceramic is 3 times higher than the original. According to the calculation results of CIE chromaticity coordinates, the luminescence of the glass-ceramics and precursor glass were located in the orange light region. The high thermal stability of the glass-ceramic was discussed through the variable temperature fluorescence test. The thermal quenching activation energy was determined to be 0.27 eV. The results indicate that the transparent glass-ceramics containing Na3YSi2O7 crystals have potential applications in orange LED components.

Optimization of the nucleating agent content for the obtaining of transparent fluormica glass-ceramics

The crystallization behaviours, mechanical and optical properties of fluormica glass-ceramic system without and with P2O5 as nucleating agent are studied. The crystallization mechanism of fluor-phlogopite (KMg3(Si3AlO10)F2) without P2O5 oxide represented one-dimensional surface crystallization with a fixed number of nuclei, and with the addition of P2O5, the mechanism tends to two-dimensional bulk crystallization with a constant nucleation rate being the most predominant phase, forsterite crystals (Mg2SiO4). The base glasses had the spinodal phase separation, which coarsened considerably by increasing P2O5 content. P2O5 had a strong influence on the microstructure and morphology of this type of glass-ceramic. The addition of small amount of P2O5 (1.0 mol%) to these glass-ceramic changed the microstructure from dendritic growth having leaf-like feature to a flower-like morphology of the crystal phase. Glass-ceramic without P2O5 produces yellowish to colourless transparent glass-ceramic, and with the incorporation of the P2O5 (1.0 mol%), which has been found the optimum to obtain transparent glass-ceramics, the transmittance is still about 85%. As the P2O5 content increased to 3.0 mol%, besides fluor-phlogopite mica, forsterite also precipitates, the size of the crystals increase, their distributions turned to be broad due to the change of the crystallization mechanism and the transparency of glass-ceramic consequently decreases.

Preparation and luminescence of Dy3+/Tm3+ co-doped Ca3NbGa3Si2O14 glass-ceramics for w-LED

In this work, a series of Dy3+ and Dy3+/Tm3+ ion activated Ca3NbGa3Si2O14 glass-ceramics were prepared by traditional melt crystallization method, and report on the structural, optical, and energy transfer (ET)-based photoluminescence (PL) properties of glass-ceramics co-doped Dy3+/Tm3+. The preparation of glass-ceramics was studied by DTA, XRD, SEM, and UV–vis photometer technology, phase composition, transmittance, optimum heat treatment conditions, and luminescence properties. The best heat treatment procedure for obtaining transparent and well-formed glass-ceramics is crystallization at 820 °C for 5 h. The spectra excited by Tm3+ and Dy3+ have intersections at 352 nm and 365 nm, which means that CNGS: Dy3+/Tm3+ can be effectively excited by 352 nm and 365 nm ultraviolet light. Under the excitation of 352 nm ultraviolet light, four main emission peaks corresponding to 1D2 →3F4, 4F9/2 → 6H15/2, 4F9/2 → 6H13/2, 4F9/2 → 6H11/2 were found at 456 nm, 484 nm, 577 nm, and 663 nm, respectively. When the optimal concentration (4 at.%) of Dy3+ is Co-doped with a different amount of Tm3+, the luminous color can be adjusted by adjusting the doping amount of Tm3+ and changing the excitation wavelength. There is an overlapping region between the emission spectrum of Tm3+ doped glass and the excitation spectrum of Dy3+ doped glass, which indicates that there is energy transfer between Tm3+ and Dy3+. In addition, CNGS: Dy3+/Tm3+ CIE coordinates show that the color coordinates (0.3324, 0.3352) when y = 0.02 under 365 nm excitation are closest to the standard white light (0.333, 0.333), indicating that this glass has potential applications in WLED devices.

Insights into the mechanism and kinetics of dissolution of aluminoborosilicate glasses in acidic media: Impact of high ionic field strength cations

Achieving thinner and higher performance display/substrate glasses and transparent glass-ceramics with tunable properties requires a precise control of acid-etching process, thus necessitating a comprehensive understanding of glass composition–structure–dissolution behavior relationships in acidic medium. Unfortunately, the literature on this subject has been focused only on a narrow set of glass chemistries. Therefore, consensus on the mechanisms that govern the acidic dissolution of multicomponent silicate glasses over a broad compositional space is still lacking. The present work employs a suite of state-of-the-art spectroscopic techniques, including 1D and 2D NMR, TEM-EELS, ICP-OES, and XPS, to provide an insight into the mechanism and kinetics of corrosion of alkali/alkaline-earth aluminoborosilicate glasses (comprising high field strength cations – HFSCs, i.e., La3+, Ti4+, Zr4+ and Nb5+) in acidic media (HCl; pH = 2). Incorporating the HFSCs into the glasses induces significant structural changes in their network, thus, impacting the forward rate dissolution kinetics. Based on the results, we hypothesize that the glasses dissolve at pH = 2 through an ‘interfacial dissolution – re-precipitation mechanism (IDPM)’ and ‘in-situ recondensation’ coupled pattern, wherein the IDPM results in a Si-rich alteration layer, followed by local recondensation occurring due to limited kinetics near the interfacial solution between the uncorroded glass surface and the outer alteration layer.

Highly transparent bismuth borotellurite glass-ceramics: Comprehension of crystallization mechanisms

Understanding the mechanism at play during the partial crystallization of a parent glass remains crucial for controlling the optical properties of the final glass-ceramics. In this work, we study the crystallization of bismuth borotellurite glasses, where a specific investigation on the 60TeO2–20B2O3–20Bi2O3 composition is reported. Under adapted heat treatment conditions, highly transparent glass-ceramics can be obtained: the crystallization of the unique anti-glass Bi2Te4O11 phase is evidenced by X-ray diffraction and Raman spectroscopy data confirm its disordered nature. While the quenched glass appears homogeneous, the observation of the early stages glass-ceramic samples by transmission electron microscopy reveals the formation of isolated polycrystalline Bi2Te4O11 entities scattered in a predominant glassy matrix. However, longer heat-treatment of samples induce some chemical demixtion of the residual glass matrix, where two separate amorphous regions of a different composition coexist. The resulting material is finally constituted of the aforementioned Bi2Te4O11 polycrystalline clusters dispersed within a majority of regions with a Te/Bi ratio larger than the nominal 1.5 ratio, separated by tiny “venules” strongly impoverished in tellurium and also likely containing boron element. Photoluminescence properties of Eu3+-doped samples indicate that tiny spectral and temporal modifications happen with the crystallization, reflecting the persistent disordered surrounding of the rare-earth ions.

Enhanced up-conversion luminescence of Tb3+-Yb3+ doped glass ceramics by doping Li+

Tb3+-Yb3+ co-doped transparent glass ceramics (GCs) containing Y2Ti2O7 crystal phases were synthesized by the melt crystallization. The light transmittance of GCs in the visible region reached 78%, and the average grain size was 278 nm under the optimal heat treatment conditions (720 °C/2 h). The GCs exhibited greater up-conversion luminescence intensity than precursor glass, and the reason for this result was explained in accordance with the Judd-Ofelt theory. Moreover, the introduction of Li+ did not change the crystalline phase of GCs. The emission intensity of the green light of the 8% Li + doped GCs was significantly enhanced by nearly 4.48 times under 980 nm excitation. The XRD refinement results suggest that the enhanced luminescence intensity is correlated with the change of the Y2Ti2O7 crystal lattice caused by Li+ doping. The relevant luminescence mechanism was elucidated. The results suggest that Li+ doped transparent GCs open novel avenues for green UC applications.

High polarizability enhanced EPR, optical linear & nonlinear and electric conductivity: Role of NiFe2O4 nanocrystals in transparent tellurite glass-ceramics

Glass containing magnetic nanocrystals is attractive to obtain high nonlinear and high polarizability. In this study, for the first time, 10 nm cubic NiFe2O4 (NFO) nanocrystals doped tellurite glass was studied in terms of the influence on glass structure, chemical bonds, EPR spectra, optical linear and nonlinearity, complex impedance, and dielectric constant. X-ray diffraction, FT-IR, and X-ray photoelectron spectroscopy revealed the single phase and chemical energy of NFO NCs and NFO- doped glasses. The introduction of NFO modified the glass structure through conversion of TeO4→TeO3, and PO4→PO3 units and producing non-bridging oxygen, which in turn enhanced the polarizability according. EPR analysis revealed the super-exchange interaction between multi-valence states of Ni and Fe ions, contributing to the deformation of NFO lattice and NBO defects in the glass network. The energy band gap of glass was red-shifted by NFO due to the multi-valence states of 3d ions. In addition, the linear and nonlinear refractive index, third-order absorption coefficient, and susceptibility were significantly enhanced because of the high polarizability. 3%NFO glass demonstrated huge third-order nonlinear susceptibility of 9.37 × 10−7 esu and giant DC electric conductivity of 8.84 × 10−4 S/cm at room temperature. The values obtained in the present study were much superior to values from the literature, and the obtained glasses are promising for high ultra-fast laser, supercontinuum generation, and holography applications.

Effects of Al2O3 addition on microstructure and luminescence of transparent germanosilicate glass-ceramics with incorporated spinel Ga-oxide nanocrystals

Ga-oxide spinel nanocrystals are wide band gap systems, which can be incorporated in a glass matrix by phase separation mechanisms. In suitable conditions, this kind of processes can give rise to transparent nanostructured glass-ceramics with UV excitation and luminescence properties potentially interesting in several technological areas. Nanophase size dispersion and volume fraction have been demonstrated to be controllable, at some extent, by suitable thermal treatments for nucleation and nano-crystallization in low-alkali gallium germanosilicate system. Here we report the results on the role of Al2O3 additions on the microstructure and optical response of the glass-ceramics fabricated in this system. Data of differential scanning calorimetry, X-ray diffraction, transmission electron microscopy, absorption and fluorescence spectroscopy show that Al2O3 addition, up to 4.5 mol%, turns out to have a considerable impact on the size and number density of precipitated nanocrystals, which are solid solutions of γ-Ga2-xAlxO3 resulting from the partial incorporation of Al3+ ions into the crystalline phase. We show that the use of Al2O3 as an additive in the composition of gallium germanosilicates facilitates glass melting and leads to glass-ceramics with significantly modified photoluminescence characteristics such as decay lifetime and integrated intensity of light emission. The possible reasons are discussed.

Tb4O7-Sm2O3 co-doped glass ceramics containing Ba3Gd(PO4)3: Preparation, tunable emission and temperature sensing properties

Tb4O7-Sm2O3 co-doped transparent glass ceramics (GCs) containing Ba3Gd(PO4)3 crystalline phase were prepared by melt crystallization. The heat treatment condition for GCs was determined to be 740 ℃/2 h by differential scanning calorimetry, X-ray diffraction, scanning electron microscopy and transmittance curves. The optical energy bandgap value of glass ceramics is smaller than that of glass. The fluorescence lifetime and Dexter theory demonstrated the energy transfer from Tb3+ to Sm3+. The luminescence color can be adjusted in the white range when the Sm2O3 doping concentration is changed. At 473 K, the luminous intensity of Tb3+ and Sm3+ can be maintained 86.63 % and 89.36 % of that at room temperature, respectively. The maximum values of the absolute and relative sensitivity of the glass ceramics are 0.00525 K−1 and 2.33 % K−1, respectively. This study shows that the obtained luminescent glass ceramics have potential applications in ultraviolet excited white light emitting diodes and optical thermometry.

Effects of Er3+ and/or Cr3+ doping on crystallization activation energy and fluorescence properties of transparent ZnGa2O4 glass-ceramics

Er3+ and/or Cr3+ doped transparent ZnGa2O4 glass-ceramics were successfully obtained by one-step heat treatment. The results showed that Er3+ ions can enrich around ZnGa2O4 crystal to reduce the crystallization activation energy and promote the growth of ZnGa2O4 crystal. Cr3+ ions may successfully occupy the Ga3+ sites in the ZnGa2O4 lattice but will increase crystallization activation energy and inhibit the growth of the ZnGa2O4 crystal. Before and after crystallization, the coordination-field intensity of Cr3+ ions increased from 2.17 to 2.86, resulting in the peak position of its emission spectra moving from 850 to 688 nm. By excitation at 378 nm, the precursor glass co-doped with Er3+ and Cr3+ ions only showed the characteristic emission peaks belonging to Er3+ ions. After heat treatment, the characteristic emission peaks belonging to Er3+ and Cr3+ ions existed simultaneously, and the emission color changed from green to yellow. By excitation at 980 nm, there were only characteristic emission peaks belonging to Er3+ ions of the Er3+/Cr3+ co-doped glasses before and after heat treatment. The results showed that the Er3+ and/or Cr3+ doped ZnGa2O4 glass-ceramics have adjustable luminescence ability and show potential application value in the field of luminescence display.

Effects of coordination field environment on the fluorescence properties of transparent ZnGa2O4 glass-ceramics doped with Mn2+ and Cr3+ ions

The transparent ZnGa2O4 glass-ceramics doped with Mn2+/Cr3+ ions were prepared by a one-step crystallization method. The visible light fluorescence properties of Mn2+ ions in 6-coordination and 4-coordination environments and the visible light fluorescence properties of Mn2+/Cr3+ ions co-doped in transparent ZnGa2O4 glass-ceramics were studied. The results manifest that in the parent glass, Mn2+ ions mainly occupy the network former in the form of Hexa-coordination, and the luminescence center can emit orange-yellow light at ~600 nm. In transparent ZnGa2O4 glass-ceramics, Mn2+ ions and Cr3+ ions appear at the four-coordination site (Zn site) and six-coordination site (Ga site) in ZnGa2O4 spinel, respectively, and they can radiate green (510 nm) and red light (688 nm), respectively. An energy transfer mechanism of Mn2+→Cr3+ exists in ZnGa2O4: Mn2+/Cr3+ and different colors of luminescence can be produced by changing the molar ratios of components and test conditions. CIE results show that Mn2+-single-doped parent glass and glass-ceramics can be used in orange-yellow and green light displays, while Mn2+/Cr3+ co-doped transparent ZnGa2O4 glass-ceramics can be used as ideal materials for the green and red light displays.

Luminescence and energy transfer of Sm3+/Eu3+ co-doped transparent glass ceramics

Luminescence and energy transfer of Sm3+/Eu3+ co-doped transparent glass ceramics

Up-conversion luminescence transparent CaNb2O6 glass ceramics for temperature monitoring

To explore new up-conversion luminescent materials with high sensitivity for optical thermometry, Yb3+/Tm3+ co-doped transparent CaNb2O6 glass ceramics are successfully prepared using the traditional melting and controlling crystallization. Its structure, micro-morphology and luminescence characteristics are studied comprehensively by means of XRD, Raman, TEM and a fluorescence spectrometer. The results show that the luminescence intensity of glass ceramics is significantly higher than that of glasses under 980 nm laser excitation. A dual-mode temperature measurement based on fluorescence intensity ratios (FIR, I690/I796 and I690/I651) is realized by using the different temperature dependence of emission peaks of Tm3+. In a wide temperature range (298 − 573 K), the highest absolute sensitivity (Sa-max) of 0.42‰ K−1 and the supreme relative sensitivity (Sr-max) of 2.65% K−1 based on thermal coupling energy levels (TCELs) are gained. Furthermore, using non-thermal coupling energy levels (NTCELs), Sr-max and Sa-max reach 0.23% K−1 and 20.49% K−1, respectively. This work indicates that the CaNb2O6 glass ceramics as a new type of up-conversion luminescent material have great application prospects in the field of optical thermometry.

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.

Crystallization behavior and enhanced fluorescence properties of Yb3+/Ho3+/Tb3+ co-doped transparent glass-ceramics containing oxyapatite-type Na3YSi2O7 crystals

The Yb3+/Ho3+/Tb3+ co-doped Na2O-Y2O3-SiO2 system transparent glass-ceramics containing oxyapatite-type Na3YSi2O7 (NYS) crystals were prepared. The structure of the crystal was characterized by XRD and TEM. The most suitable heat treatment process was confirmed by DSC and TEM results. The strongest emission peak in the fluorescence spectra relates to the Tb3+: 5D4→7F5 transition. In the CIE chromaticity diagram, the luminescence is concentrated in the green area. The emission intensity of the glass-ceramic is increased by 7 times compared with the precursor glass. The increase in emission intensity is caused by the entry of rare-earth ions into the Na3YSi2O7 grains to replace the positions of Y3+ ions. The fluorescence properties of the glass-ceramics containing Na3YSi2O7 crystals were tested at different temperatures. It is demonstrated that the luminescent materials show good thermal stability. The obtained glass-ceramic would be a candidate material for green diode elements.

Mechanoluminescence from highly transparent ZGO:Cr spinel glass ceramics

Light emission in response to mechanical stimulation-termed mechanoluminescence (ML)-enables the optical detection and visualization of mechanical strain. In particular, materials with ML response in the transmission window of aqueous media or biological tissue enable in situ stress level monitoring, biophysical imaging or mechanically induced light delivery. However, most of today’s ML materials are polycrystalline ceramics or ceramic particle composites, which puts constraints on their bulk processability, material homogeneity and optical transparency. Here, we demonstrate ML from highly transparent glass ceramics comprising of a high-volume fraction of extraordinarily small Cr3+-doped ZnGa2O4 (ZGO) crystals embedded in a binary potassium germanate glass matrix. The ZGO phase is precipitated directly from the precursor glass by homogeneous nucleation in a narrow temperature window; entropic phase separation and a self-limited crystal growth rate yield a crystal number density above 1023 m-3. The residual glass matrix encapsulates these crystals in a dense, highly homogeneous material, whereby the microstructural stability and the extended supercooling range of the glass enable glass-like processing, for example, in the shapes of fiber, beads or microspheres.

Reproducible X-ray excited luminescence performance with transparent Tb3+-doped NaGd2F7 scintillating glass ceramics

Oxyfluoride glass ceramics with low toxicity, high stability and strong X-ray excited luminescence intensity are introduced as scintillating material. Herein, a series of novel NaGd2F7:xTb3+ (x = 0, 0.1, 0.2, 0.3, 0.4) were synthesized through in situ growth self-crystallization. X-ray diffraction, fourier transform infrared spectrometer and transmission electron microscopy were measured to investigate the structure and morphology of NaGd2F7 glass ceramics. These investigations demonstrate that NaGd2F7 nanocrystals are uniformly distributed in glass matrix with 20–30 nm diameter. Photoluminescence and X-ray excitation spectra are greatly enhanced after further thermal treatment which verify better crystallization of NaGd2F7 glass ceramics. The X-ray excited luminescence of the GC2–640 sample can reach 143.8% of the commercial BGO. More importantly, the damaged material can be completely repaired by annealing at 350 °C for 30 min. Our investigation indicates that Tb-doped transparent NaGd2F7 glass ceramics are potential candidates of X-ray scintillating material.

Effect of Mg2+/Sr2+ addition on luminescence properties of Dy3+ doped glass ceramics containing Ca2Ti2O6

Dy2O3-doped transparent glass-ceramics containing Ca2Ti2O6 crystal phase were synthesized by melting crystallization method. The optimum heat treatment condition was determined to be 710 °C/1.5 h by differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmittance curves. The optimal doped concentration of Dy2O3 is 0.4 mol%. The effects of doping with different concentrations of Mg2+ and Sr2+ on the fluorescence intensity of glass-ceramics were discussed. In comparison to Sr2+, the addition of Mg2+ effectively increased the luminescence intensity of 0.4 mol% Dy2O3-doped glass-ceramics. Since Mg2+ has a smaller ionic radius, it has a larger Coulomb potential and is more attractive to O2−, which makes the three-dimensional skeleton of BO6 tilt, and the symmetry of the structure deteriorates, resulting in enhanced luminescence. Comparison of 0.4 mol%Dy2O3-doped glass-ceramic and 8 mol%MgF2-0.4 mol%Dy2O3 co-doped glass-ceramic, the fluorescence intensity increased by 56.8% at 484 nm and 83.5% at 577 nm, the optical band gap value was reduced from 2.7824 eV to 2.4341 eV. The findings suggest that Dy3+-doped glass-ceramics containing Ca2Ti2O6 crystal phase will be used in white light-emitting diodes (W-LEDs).

Up-conversion luminescence, temperature sensitive and energy storage performance of lead-free transparent Yb3+/Er3+ co-doped Ba2NaNb5O15 glass-ceramics

In this work, a new type of Yb 3+ /Er 3+ co-doped lead-free glass-ceramics (GCs) containing Ba 2 NaNb 5 O 15 nanocrystals was synthesized via traditional melt-quenching and controlled crystallization. The research results illustrate that a transparency of GCs can reach 50% at wavelength of 600 nm and the up-conversion (UC) luminous performance of GCs has been improved obviously compared with precursor glass (PG). And the dual-mode temperature measurement was carried out by fluorescence intensity ratio technology. Using thermally/non-thermally coupled energy levels (TCELs/non-TCELs), the maximum absolute sensitivities of S a-max (TCELs) and S a-max (non-TCELs) are 0.65% K −1 and 0.68% K −1 , and the maximal relative sensitivities of S r-max (TCELs) and S r-max (non-TCELs) are 1.19% K −1 and 0.90% K −1 , respectively. Furthermore, the discharge energy density (W d ) of 1.53 J cm −3 and the instantaneous discharge power density of 370 MW cm −3 with ultra-fast discharge time of 7 ns are simultaneously achieved in the GCs. These findings reveal the potential applications of new lead-free transparent Yb 3+ /Er 3+ co-doped Ba 2 NaNb 5 O 15 GCs for optical temperature measurement and energy storage. • Multi-function RE-doped Ba 2 NaNb 5 O 15 transparent glass ceramics were first fabricated. • Realizing dual-mode Up-conversion optical thermometry in the glass ceramics. • The maximum S r-max and S a-max can reach 1.19% K −1 and 0.68% K −1 . • Achieving high W d of 1.53 J cm − 3 and high P d of 370 MW cm − 3 at 600 kV/cm.

Highly sensitive optical thermometry based on Tm3+/Yb3+ doped NaGd2F7 glass ceramics

Developing transparent glass ceramics (GC) with high stability and good repeatability for reliable and accurate optical fiber temperature sensing is significant. In this study, a sequence of transparent Tm3+/Yb3+ doped oxyfluoride NaGd2F7 GC were successfully produced through self-crystallization. By precisely controlling the heat treatment time and temperature, the obtained NaGd2F7 nanocrystals (NCs) were evenly dispersed in glass host with particle size in tens of nanometers. The enhanced up-conversion intensity, noticeable Stark splitting and prolonged lifetime of Tm3+ emission manifest better crystallization of NaGd2F7 GC by heat treatment. More importantly, optical temperature performance of NaGd2F7 GC based on the splits of thermally coupled energy level was explored through fluorescence intensity ratio. The maximum relative sensitivity for 3F2 → 3H6 (679 nm) and 1G4 → 3F4 (644 nm) attains 3.33% K−1 at 313 K. Moreover, temperature resolution of GC20 is 0.03 K at 573 K and repeatability is high up to 99.5%. Our investigations above demonstrate that NaGd2F7 GC with high sensitivity, superior precision and stability are potential materials in the field of temperature measurement.