- Email: [email protected]
Effect of melting temperature on the structure of self-crystallized Ba2LaF7 glass-ceramics
Journal of Non-Crystalline Solids 523 (2019) 119579
Contents lists available at ScienceDirect
Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol
Effect of melting temperature on the structure of self-crystallized Ba2LaF7 glass-ceramics
T
⁎
Weihui Shena, Yong Yanga, , Zhencai Lia, Muhammad Ibrar Khanb, Enhao Caoa, Dacheng Zhoua, ⁎ Jianbei Qiua, a
Key Laboratory of Advanced Materials of Yunnan Province, School of Materials Science and Engineering, Kunming University of Science and Technology, Kunming 650093, China b School of Metallurgy and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Self-crystallization Temperature Ba2LaF7 Glass-ceramics FTIR Luminescence
The self-crystallization phenomenon in glass can provide low-phonon energy environment for the up-conversion of luminescence centers. Nevertheless, the crystallization mechanism is not clear, hence the effect of temperature on the self-crystallization of Ba2LaF7: Er3+/Yb3+ glass-ceramics via adjusting its melting temperature has investigated. The self-crystallization fraction of Ba2LaF7 has decreased with the increase in melting temperature. The Fourier transforms infrared spectra, X-ray Fluorescence analysis and differential thermal analysis revealed that the increase in temperature makes the SieO bond longer in the glass, resulting in the increase of activation energy for crystallization instead of precipitating the crystals.
1. Introduction
2. Experiment details
Recently, there is an increasing interest in optical materials doped with lanthanide (Ln3+) activators for efficient up-conversion (UC) from infrared to visible radiation that can be widely used in the field of the solid-state laser, optical fibers, W-LED illumination, three-dimensional display, etc. [1,2]. Among the UC matrix materials, the fluoride glassceramics, such as NaYF4, Ba2LnF7 (Ln = Y, La, Yb, Gd) [3–6], have attracted great attention due to their wide infrared transmittance range, excellent solubility of rare earth ions and low photon energy. Usually, the controlled nucleation and growth process in glass matrix produces the glass-ceramics [7]. In recent years, Chen and Guo et al. found the self-crystallization (or spontaneous crystallization) phenomenon in rare earth doped NaLuF4, KGd3F10, KTb2F7 and K3YF6 glass-ceramics, which is different from the conventional crystallization process in glass-ceramics [8–11]. Another article reported that selfcrystallization also exists in Nd/Eu co-doped Ba2LaF7 glass-ceramics [12]; however, the origin of self-crystallization is not clear yet [16,17]. In present work, we found that the self-crystallization phenomenon occurs at a certain specific temperature range. Therefore, the temperature-dependent experiments were designed to reveal the melting temperature effects on the self-crystallization of Yb/Er co-doped Ba2LaF7.
Reagents of SiO2 (99.99%), BaF2 (99.99%), AlF3 (99.99%), TiO2 (99.99%), LaF3 (99.99%), ErF3 (99.99%), and YbF3 (99.99%) were used as raw materials, with a composition of 50SiO2- 5TiO2-10AlF330BaF2–3.5LaF3–1.5YbF3–1ErF3. The total mass of raw materials is about 10 g for each sample which were mixed thoroughly. The mixture then melted in a covered alumina crucible in air at four different temperatures (1350 °C, 1400 °C, 1450 °C, 1500 °C) for 45 min. After natural cooling, the precursor self-crystallization glasses were prepared, named as PG1350, PG1400, PG1450, and PG1500, respectively. The X-ray diffraction (XRD) analysis was carried out to identify the crystallization phase with a power diffractometer operated at 40 Kv and 30 mA, using Cu-Kα as the radiation source. And the 2θ scan range was 20–90° with a step size of 0.02°. The thermodynamic properties of the samples were measured by differential thermal analysis (DTA) that carried out in air with a rate of 10 °C/min on DTA-60AH SHIMADZU. The microstructures of the samples were analyzed by transmission electron microscopy (TEM, JEM-2100). Fourier transforms infrared (FTIR) spectra were measured on a Bruker ALPHA infrared spectrometer. The UC luminescence properties were measured by a HITACHI F-7000 fluorescence spectrophotometer in the wavelength range of 400 nm–690 nm with a 2 W diode laser at 980 nm. The elemental contents of all samples were measured on an Axios mAX PANalytical X-
⁎
Corresponding authors. E-mail addresses: [email protected] (Y. Yang), [email protected] (J. Qiu).
https://doi.org/10.1016/j.jnoncrysol.2019.119579 Received 19 May 2019; Received in revised form 4 July 2019; Accepted 15 July 2019 Available online 24 August 2019 0022-3093/ © 2019 Elsevier B.V. All rights reserved.
Journal of Non-Crystalline Solids 523 (2019) 119579
W. Shen, et al.
Fig. 1. XRD patterns (a), TEM image of PG1350 (b), PG1400 (c), PG1450 (d), PG1500 (e), HRTEM image of PG1350 (inset of b) and UC emission spectra of Ba2LaF7 PGs under 980 nm excitation.
the TEM result of PG1500. On the whole, the TEM results are almost consistent with the XRD analysis. Fig. 1f shows the characteristic UC emission spectra of Yb/Er codoped Ba2LaF7 PGs, which are 412 nm (2H9/2 → 4I15/2), 520 nm (2H11/ 4 4 4 4 2 → I15/2), 540 nm, 548 nm ( S3/2 → I15/2), 654 nm, 668 nm ( F9/2 → 4 I15/2). The characteristic UC emission bands gradually increased with the decrease of melting temperature, which is in correspondence to the crystallinity in PGs. According to the random network theory [13], the network structure of glass is composed of ionic polyhedra (tetrahedron or triangular polyhedron), so the crystal precipitation in the glass will affect the arrangement of ionic polyhedra. The FTIR spectra (Fig. 2) of PGs confirms that the network structure of PGs mainly consisted of [SiO4] and [AlO4] tetrahedrons, as the related bending vibrations (400–560 cm−1), symmetric stretching vibrations (650–820 cm−1) and anti-symmetric stretching vibrations (820–1200 cm−1) can be obviously observed [14]. However, the SieO anti-symmetric stretching vibration that located at about 1190 cm−1, deviates towards smaller wavenumber with the increasing melting temperature, indicating increase in the bond length of SieO. This illustrates that the crystallinity inside PGs is decreasing with the increasing melting temperature. From the XRF measurements (Fig. 3), it is found that the self-crystallization disappears when the proportion of Ba2LaF7 is lower than 12.423%. The proportion of aluminum rises while that of barium and lanthanum fall when the melting temperature of PGs increases. It can be inferred that aluminum is distributed in the glass to form [AlO4] tetrahedrons, while lanthanum and barium exist in Ba2LaF7 lattices through the whole glass phase. As the melting temperature increases, the amount of lanthanum and barium in the entire glass phase is gradually lost, which is insufficient to form crystals. The DTA results of PGs were shown in Fig. 4. The areas of the
ray Fluorescence (XRF) Spectrometer. All the measurements were performed at room temperature. 3. Results and discussions The XRD pattern of PG1350 is shown in Fig. 1a, in which the diffraction peaks located at 25.346°, 29.395°, 41.968°, 49.669°, 52.004°, 60.808°, 66.924°, 68.881°, 76.588°, and 82.179°. The same diffraction peaks of the PG1400 sample show a relatively lower intensity. Correspondingly, few weak diffraction peaks can be observed from the XRD pattern of PG1450, while no distinct diffraction peak appears on that of PG1500. It demonstrates that the self-crystallization of Ba2LaF7 PGs weakened gradually with the increase of melting temperature. The average sizes of Ba2LaF7 nanocrystal in PG1350 and PG1400 samples can be calculated from Scherrer formula:
D=
kλ , β cos θ
where D is the crystal size, k = 0.89, λ (0.154056 nm) represents the Xray wavelength of Cu Kα radiation, β is the full-width at half-maximum of the diffraction peak, and θ is the Bragg diffraction angle of the XRD peak. The estimated mean sizes of PG1350 and PG1400 are 17.88 nm and 10 nm respectively. Fig. 1b shows the TEM image and the HRTEM image (inset of Fig. 1b) of PG1350. The TEM image clearly indicates the homogeneous spherical nanocrystals uniform distribution in the glass matrix. The mean size of nanocrystals is 17.7 nm, which is close to that estimated by Scherrer formula. The HRTEM image represents a welldefined lattice structure and the (200) crystalline plane of Ba2LaF7 with a corresponding inter-planar spacing of 0.304 nm. Fig. 1c and d show the TEM images of PG1400 and PG1450 with 12.61 nm and 12.12 nm mean sizes of corresponding nanocrystals respectively. Fig. 1e presents 2
Journal of Non-Crystalline Solids 523 (2019) 119579
W. Shen, et al.
Fig. 4. The DTA results of PG1350, PG1400, PG1450, PG1500.
Fig. 2. The FTIR spectra of PG1350, PG1400, PG1450, PG1500 that measured at room temperature.
Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests. Acknowledgements This work was supported by the National Natural Science Foundation of China (No. 11774138, 11664022) and Foundation of Yunnan Province (2016FA021 and 2016FB081) and the project for personnel training fund supported by Kunming University of Science and Technology (KKSY201632046). References [1] X. Li, D. Chen, F. Huang, G. Chang, J. Zhao, X. Qiao, X. Xu, J. Du, M. Yin, Phaseselective nanocrystallization of NaLnF4 in aluminosilicate glass for random laser and 940 nm LED-excitable upconverted luminescence, Laser Photonics Rev. 12 (7) (2018) 1800030. [2] M. Clara Gonçalves, Luís F. Santos, Rui M. Almeida, Rare-earth-doped transparent glass ceramics, C. R. Chimie 5 (2002) 845–854. [3] Y. Gao, Y. Hu, D. Zhou, J. Qiu, Effect of heat treatment mechanism on upconversion luminescence in Er3+/Yb3+ co-doped NaYF4 oxyfluoride glass-ceramics, J. Alloys Compd. 699 (2017) 303–307. [4] H.K. Dan, D. Zhou, R. Wang, T.M. Hau, Q. Jiao, X. Yu, J. Qiu, Up-conversion of Er3+/Yb3+ co-doped transparent glass-ceramics containing Ba2LaF7 nanocrystals, J. Rare Earths 31 (9) (2013) 843–848. [5] P.P. Fedorov, A.A. Luginina, A.I. Popov, Transparent oxyfluoride glass ceramics, J. Fluor. Chem. 172 (2015) 22–50. [6] F. Wang, X. Liu, Recent advances in the chemistry of lanthanide-doped upconversion nanocrystals, Chem. Soc. Rev. 38 (4) (2009) 976–989. [7] W. Höland, G.W. Greenwood, A.L. Greer, D.M. Herlach, K.F. Kelton, V. Rheinberger, M. Schweiger, Control of nucleation in glass ceramics, Philos. Trans. R. Soc. London, Ser. A 361 (1804) (2003) 575–589. [8] D. Chen, Z. Wan, Y. Zhou, P. Huang, Z. Ji, Ce3+ dopants-induced spectral conversion from green to red in the Yb/Ho: NaLuF4 self-crystallized nano-glass-ceramics, J. Alloys Compd. 654 (2016) 151–156. [9] Y. Peng, D. Chen, J. Zhong, X. Li, Q. Mao, F. Chi, Lanthanide-doped KGd3F10 nanocrystals embedded glass ceramics: self-crystallization, optical properties and temperature sensing, J. Alloys Compd. 767 (2018) 682–689. [10] J. Cao, L. Chen, W. Chen, D. Xu, X. Sun, H. Guo, Enhanced emissions in self-crystallized oxyfluoride scintillating glass ceramics containing KTb2F7 nanocrystals, Opt. Mater. Expr. 6 (7) (2016) 2201–2206. [11] J. Cao, X. Li, Z. Wang, Y. Wei, L. Chen, H. Guo, Optical thermometry based on upconversion luminescence behavior of self-crystallized K3YF6: Er3+ glass ceramics, Sensors Actuators B Chem. 224 (2016) 507–513. [12] Z. Zhao, F. Hu, Z. Cao, F. Chi, X. Wei, Y. Chen, C. Duan, M. Yin, Self-crystallized Ba2LaF7 : Nd3+/Eu3+ glass ceramics for optical thermometry, Ceram. Int. 43 (17) (2017) 14951–14955. [13] R.J. Bell, P. Dean, The structure of vitreous silica: validity of the random network
Fig. 3. The analyzed XRF results of Al, Ba, La, Ba2LaF7 in PG1350, PG1400, PG1450, PG1500.
crystallization exothermic peaks were calculated as 85.4 J/g (PG1350), 101.1 J/g (PG1400), 105.8 J/g (PG1450) and 114.9 J/g (PG1500), which represent the crystallization activation energy of PGs. As the melting temperature increases, the crystallization activation energy also increases, therefore a higher melting temperature means that selfcrystallization in the glass matrix is more difficult to occur [15]. 4. Conclusions The effect of temperature on the self-crystallization of Ba2LaF7 glass-ceramics by adjusting the melting temperature has investigated. As the melting temperature increases, the silica bond becomes longer, meanwhile the content of barium and lanthanum decreases, which leads to the increase of crystallization activation energy. Therefore, the self-crystallization disappears at last. We doped Yb/Er into Ba2LaF7 PGs by decreasing the melting temperature to achieve an enhancement of UC luminescence. Our study offers a reference for controlled self-crystallization. 3
Journal of Non-Crystalline Solids 523 (2019) 119579
W. Shen, et al.
Ceram. Soc. 37 (2) (2017) 763–770. [16] M.O. Prado, E.D. Zanotto, Glass sintering with concurrent crystallization, Comptes Rendus Chimie 5 (2002) 773–786. [17] Edgar Dutra Zanotto, A bright future for glass-ceramics, Am. Ceram. Soc. Bull. 89 (8) (2010).
theory, Philos. Mag. 25 (6) (1972) 1381–1398. [14] A. Goel, D.U. Tulyaganov, V.V. Kharton, A.A. Yaremchenko, S. Eriksson, J.M.F. Ferreira, Optimization of La2O3-containing diopside based glass-ceramic sealants for fuel cell applications, J. Power Sources 189 (2) (2009) 1032–1043. [15] Y. Gao, Y. Hu, D. Zhou, J. Qiu, Effect of crystalline fraction on upconversion luminescence in Er 3+ /Yb 3+ Co-doped NaYF4 oxyfluoride glass-ceramics, J. Eur.
4
Contents lists available at ScienceDirect
Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol
Effect of melting temperature on the structure of self-crystallized Ba2LaF7 glass-ceramics
T
⁎
Weihui Shena, Yong Yanga, , Zhencai Lia, Muhammad Ibrar Khanb, Enhao Caoa, Dacheng Zhoua, ⁎ Jianbei Qiua, a
Key Laboratory of Advanced Materials of Yunnan Province, School of Materials Science and Engineering, Kunming University of Science and Technology, Kunming 650093, China b School of Metallurgy and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Self-crystallization Temperature Ba2LaF7 Glass-ceramics FTIR Luminescence
The self-crystallization phenomenon in glass can provide low-phonon energy environment for the up-conversion of luminescence centers. Nevertheless, the crystallization mechanism is not clear, hence the effect of temperature on the self-crystallization of Ba2LaF7: Er3+/Yb3+ glass-ceramics via adjusting its melting temperature has investigated. The self-crystallization fraction of Ba2LaF7 has decreased with the increase in melting temperature. The Fourier transforms infrared spectra, X-ray Fluorescence analysis and differential thermal analysis revealed that the increase in temperature makes the SieO bond longer in the glass, resulting in the increase of activation energy for crystallization instead of precipitating the crystals.
1. Introduction
2. Experiment details
Recently, there is an increasing interest in optical materials doped with lanthanide (Ln3+) activators for efficient up-conversion (UC) from infrared to visible radiation that can be widely used in the field of the solid-state laser, optical fibers, W-LED illumination, three-dimensional display, etc. [1,2]. Among the UC matrix materials, the fluoride glassceramics, such as NaYF4, Ba2LnF7 (Ln = Y, La, Yb, Gd) [3–6], have attracted great attention due to their wide infrared transmittance range, excellent solubility of rare earth ions and low photon energy. Usually, the controlled nucleation and growth process in glass matrix produces the glass-ceramics [7]. In recent years, Chen and Guo et al. found the self-crystallization (or spontaneous crystallization) phenomenon in rare earth doped NaLuF4, KGd3F10, KTb2F7 and K3YF6 glass-ceramics, which is different from the conventional crystallization process in glass-ceramics [8–11]. Another article reported that selfcrystallization also exists in Nd/Eu co-doped Ba2LaF7 glass-ceramics [12]; however, the origin of self-crystallization is not clear yet [16,17]. In present work, we found that the self-crystallization phenomenon occurs at a certain specific temperature range. Therefore, the temperature-dependent experiments were designed to reveal the melting temperature effects on the self-crystallization of Yb/Er co-doped Ba2LaF7.
Reagents of SiO2 (99.99%), BaF2 (99.99%), AlF3 (99.99%), TiO2 (99.99%), LaF3 (99.99%), ErF3 (99.99%), and YbF3 (99.99%) were used as raw materials, with a composition of 50SiO2- 5TiO2-10AlF330BaF2–3.5LaF3–1.5YbF3–1ErF3. The total mass of raw materials is about 10 g for each sample which were mixed thoroughly. The mixture then melted in a covered alumina crucible in air at four different temperatures (1350 °C, 1400 °C, 1450 °C, 1500 °C) for 45 min. After natural cooling, the precursor self-crystallization glasses were prepared, named as PG1350, PG1400, PG1450, and PG1500, respectively. The X-ray diffraction (XRD) analysis was carried out to identify the crystallization phase with a power diffractometer operated at 40 Kv and 30 mA, using Cu-Kα as the radiation source. And the 2θ scan range was 20–90° with a step size of 0.02°. The thermodynamic properties of the samples were measured by differential thermal analysis (DTA) that carried out in air with a rate of 10 °C/min on DTA-60AH SHIMADZU. The microstructures of the samples were analyzed by transmission electron microscopy (TEM, JEM-2100). Fourier transforms infrared (FTIR) spectra were measured on a Bruker ALPHA infrared spectrometer. The UC luminescence properties were measured by a HITACHI F-7000 fluorescence spectrophotometer in the wavelength range of 400 nm–690 nm with a 2 W diode laser at 980 nm. The elemental contents of all samples were measured on an Axios mAX PANalytical X-
⁎
Corresponding authors. E-mail addresses: [email protected] (Y. Yang), [email protected] (J. Qiu).
https://doi.org/10.1016/j.jnoncrysol.2019.119579 Received 19 May 2019; Received in revised form 4 July 2019; Accepted 15 July 2019 Available online 24 August 2019 0022-3093/ © 2019 Elsevier B.V. All rights reserved.
Journal of Non-Crystalline Solids 523 (2019) 119579
W. Shen, et al.
Fig. 1. XRD patterns (a), TEM image of PG1350 (b), PG1400 (c), PG1450 (d), PG1500 (e), HRTEM image of PG1350 (inset of b) and UC emission spectra of Ba2LaF7 PGs under 980 nm excitation.
the TEM result of PG1500. On the whole, the TEM results are almost consistent with the XRD analysis. Fig. 1f shows the characteristic UC emission spectra of Yb/Er codoped Ba2LaF7 PGs, which are 412 nm (2H9/2 → 4I15/2), 520 nm (2H11/ 4 4 4 4 2 → I15/2), 540 nm, 548 nm ( S3/2 → I15/2), 654 nm, 668 nm ( F9/2 → 4 I15/2). The characteristic UC emission bands gradually increased with the decrease of melting temperature, which is in correspondence to the crystallinity in PGs. According to the random network theory [13], the network structure of glass is composed of ionic polyhedra (tetrahedron or triangular polyhedron), so the crystal precipitation in the glass will affect the arrangement of ionic polyhedra. The FTIR spectra (Fig. 2) of PGs confirms that the network structure of PGs mainly consisted of [SiO4] and [AlO4] tetrahedrons, as the related bending vibrations (400–560 cm−1), symmetric stretching vibrations (650–820 cm−1) and anti-symmetric stretching vibrations (820–1200 cm−1) can be obviously observed [14]. However, the SieO anti-symmetric stretching vibration that located at about 1190 cm−1, deviates towards smaller wavenumber with the increasing melting temperature, indicating increase in the bond length of SieO. This illustrates that the crystallinity inside PGs is decreasing with the increasing melting temperature. From the XRF measurements (Fig. 3), it is found that the self-crystallization disappears when the proportion of Ba2LaF7 is lower than 12.423%. The proportion of aluminum rises while that of barium and lanthanum fall when the melting temperature of PGs increases. It can be inferred that aluminum is distributed in the glass to form [AlO4] tetrahedrons, while lanthanum and barium exist in Ba2LaF7 lattices through the whole glass phase. As the melting temperature increases, the amount of lanthanum and barium in the entire glass phase is gradually lost, which is insufficient to form crystals. The DTA results of PGs were shown in Fig. 4. The areas of the
ray Fluorescence (XRF) Spectrometer. All the measurements were performed at room temperature. 3. Results and discussions The XRD pattern of PG1350 is shown in Fig. 1a, in which the diffraction peaks located at 25.346°, 29.395°, 41.968°, 49.669°, 52.004°, 60.808°, 66.924°, 68.881°, 76.588°, and 82.179°. The same diffraction peaks of the PG1400 sample show a relatively lower intensity. Correspondingly, few weak diffraction peaks can be observed from the XRD pattern of PG1450, while no distinct diffraction peak appears on that of PG1500. It demonstrates that the self-crystallization of Ba2LaF7 PGs weakened gradually with the increase of melting temperature. The average sizes of Ba2LaF7 nanocrystal in PG1350 and PG1400 samples can be calculated from Scherrer formula:
D=
kλ , β cos θ
where D is the crystal size, k = 0.89, λ (0.154056 nm) represents the Xray wavelength of Cu Kα radiation, β is the full-width at half-maximum of the diffraction peak, and θ is the Bragg diffraction angle of the XRD peak. The estimated mean sizes of PG1350 and PG1400 are 17.88 nm and 10 nm respectively. Fig. 1b shows the TEM image and the HRTEM image (inset of Fig. 1b) of PG1350. The TEM image clearly indicates the homogeneous spherical nanocrystals uniform distribution in the glass matrix. The mean size of nanocrystals is 17.7 nm, which is close to that estimated by Scherrer formula. The HRTEM image represents a welldefined lattice structure and the (200) crystalline plane of Ba2LaF7 with a corresponding inter-planar spacing of 0.304 nm. Fig. 1c and d show the TEM images of PG1400 and PG1450 with 12.61 nm and 12.12 nm mean sizes of corresponding nanocrystals respectively. Fig. 1e presents 2
Journal of Non-Crystalline Solids 523 (2019) 119579
W. Shen, et al.
Fig. 4. The DTA results of PG1350, PG1400, PG1450, PG1500.
Fig. 2. The FTIR spectra of PG1350, PG1400, PG1450, PG1500 that measured at room temperature.
Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests. Acknowledgements This work was supported by the National Natural Science Foundation of China (No. 11774138, 11664022) and Foundation of Yunnan Province (2016FA021 and 2016FB081) and the project for personnel training fund supported by Kunming University of Science and Technology (KKSY201632046). References [1] X. Li, D. Chen, F. Huang, G. Chang, J. Zhao, X. Qiao, X. Xu, J. Du, M. Yin, Phaseselective nanocrystallization of NaLnF4 in aluminosilicate glass for random laser and 940 nm LED-excitable upconverted luminescence, Laser Photonics Rev. 12 (7) (2018) 1800030. [2] M. Clara Gonçalves, Luís F. Santos, Rui M. Almeida, Rare-earth-doped transparent glass ceramics, C. R. Chimie 5 (2002) 845–854. [3] Y. Gao, Y. Hu, D. Zhou, J. Qiu, Effect of heat treatment mechanism on upconversion luminescence in Er3+/Yb3+ co-doped NaYF4 oxyfluoride glass-ceramics, J. Alloys Compd. 699 (2017) 303–307. [4] H.K. Dan, D. Zhou, R. Wang, T.M. Hau, Q. Jiao, X. Yu, J. Qiu, Up-conversion of Er3+/Yb3+ co-doped transparent glass-ceramics containing Ba2LaF7 nanocrystals, J. Rare Earths 31 (9) (2013) 843–848. [5] P.P. Fedorov, A.A. Luginina, A.I. Popov, Transparent oxyfluoride glass ceramics, J. Fluor. Chem. 172 (2015) 22–50. [6] F. Wang, X. Liu, Recent advances in the chemistry of lanthanide-doped upconversion nanocrystals, Chem. Soc. Rev. 38 (4) (2009) 976–989. [7] W. Höland, G.W. Greenwood, A.L. Greer, D.M. Herlach, K.F. Kelton, V. Rheinberger, M. Schweiger, Control of nucleation in glass ceramics, Philos. Trans. R. Soc. London, Ser. A 361 (1804) (2003) 575–589. [8] D. Chen, Z. Wan, Y. Zhou, P. Huang, Z. Ji, Ce3+ dopants-induced spectral conversion from green to red in the Yb/Ho: NaLuF4 self-crystallized nano-glass-ceramics, J. Alloys Compd. 654 (2016) 151–156. [9] Y. Peng, D. Chen, J. Zhong, X. Li, Q. Mao, F. Chi, Lanthanide-doped KGd3F10 nanocrystals embedded glass ceramics: self-crystallization, optical properties and temperature sensing, J. Alloys Compd. 767 (2018) 682–689. [10] J. Cao, L. Chen, W. Chen, D. Xu, X. Sun, H. Guo, Enhanced emissions in self-crystallized oxyfluoride scintillating glass ceramics containing KTb2F7 nanocrystals, Opt. Mater. Expr. 6 (7) (2016) 2201–2206. [11] J. Cao, X. Li, Z. Wang, Y. Wei, L. Chen, H. Guo, Optical thermometry based on upconversion luminescence behavior of self-crystallized K3YF6: Er3+ glass ceramics, Sensors Actuators B Chem. 224 (2016) 507–513. [12] Z. Zhao, F. Hu, Z. Cao, F. Chi, X. Wei, Y. Chen, C. Duan, M. Yin, Self-crystallized Ba2LaF7 : Nd3+/Eu3+ glass ceramics for optical thermometry, Ceram. Int. 43 (17) (2017) 14951–14955. [13] R.J. Bell, P. Dean, The structure of vitreous silica: validity of the random network
Fig. 3. The analyzed XRF results of Al, Ba, La, Ba2LaF7 in PG1350, PG1400, PG1450, PG1500.
crystallization exothermic peaks were calculated as 85.4 J/g (PG1350), 101.1 J/g (PG1400), 105.8 J/g (PG1450) and 114.9 J/g (PG1500), which represent the crystallization activation energy of PGs. As the melting temperature increases, the crystallization activation energy also increases, therefore a higher melting temperature means that selfcrystallization in the glass matrix is more difficult to occur [15]. 4. Conclusions The effect of temperature on the self-crystallization of Ba2LaF7 glass-ceramics by adjusting the melting temperature has investigated. As the melting temperature increases, the silica bond becomes longer, meanwhile the content of barium and lanthanum decreases, which leads to the increase of crystallization activation energy. Therefore, the self-crystallization disappears at last. We doped Yb/Er into Ba2LaF7 PGs by decreasing the melting temperature to achieve an enhancement of UC luminescence. Our study offers a reference for controlled self-crystallization. 3
Journal of Non-Crystalline Solids 523 (2019) 119579
W. Shen, et al.
Ceram. Soc. 37 (2) (2017) 763–770. [16] M.O. Prado, E.D. Zanotto, Glass sintering with concurrent crystallization, Comptes Rendus Chimie 5 (2002) 773–786. [17] Edgar Dutra Zanotto, A bright future for glass-ceramics, Am. Ceram. Soc. Bull. 89 (8) (2010).
theory, Philos. Mag. 25 (6) (1972) 1381–1398. [14] A. Goel, D.U. Tulyaganov, V.V. Kharton, A.A. Yaremchenko, S. Eriksson, J.M.F. Ferreira, Optimization of La2O3-containing diopside based glass-ceramic sealants for fuel cell applications, J. Power Sources 189 (2) (2009) 1032–1043. [15] Y. Gao, Y. Hu, D. Zhou, J. Qiu, Effect of crystalline fraction on upconversion luminescence in Er 3+ /Yb 3+ Co-doped NaYF4 oxyfluoride glass-ceramics, J. Eur.
4