Novel transparent Er3+ doped perovskite glasses fabricated by containerless solidification

Journal Pre-proof Novel transparent Er solidification

3+

doped perovskite glasses fabricated by containerless

Jinsheng Li, Xiaoyan Zhang, Huanyu Zhao, Jinrong Zhang, Hang Geng, Han Wu, Yaohang Gu, Xiwei Qi PII:

S0022-2313(19)31323-7

DOI:

https://doi.org/10.1016/j.jlumin.2019.116892

Reference:

LUMIN 116892

To appear in:

Journal of Luminescence

Received Date: 2 July 2019 Revised Date:

1 November 2019

Accepted Date: 11 November 2019

Please cite this article as: J. Li, X. Zhang, H. Zhao, J. Zhang, H. Geng, H. Wu, Y. Gu, X. Qi, Novel 3+ transparent Er doped perovskite glasses fabricated by containerless solidification, Journal of Luminescence (2019), doi: https://doi.org/10.1016/j.jlumin.2019.116892. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier B.V.

Novel transparent Er3+ doped perovskite glasses fabricated by containerless solidification Jinsheng Lia,b,c, Xiaoyan Zhanga,b,c*, Huanyu Zhaoa, Jinrong Zhanga,b, Hang Geng b,c, Han Wua,b, Yaohang Gua,b, Xiwei Qia,b,c*

a

School of materials science and Engineering, Northeastern University, Shenyang 110819, PR

China b

School of Resources and Materials, Northeastern University at QinHuangDao, QinHuangDao

066004, PR China c

Key Laboratory of Dielectric and Electrolyte Functional Material, Hebei Province,

QinHuangDao 066004, PR China

*Corresponding author: Xiwei Qi: Tel./Fax: +86 0335 8053004 E–mail: [email protected] Xiaoyan Zhang: E–mail: [email protected]

Abstract Perovskite glasses with the compositions of La0.85-xErxBi0.15Al0.5Ga0.5O3 (x = 0.025, 0.05, 0.1, 0.125, 0.15) and remarkable electrical insulation performance were synthesized by containerless solidification. The x = 0.15 amorphous material had the highest Vicker’s hardness (7.34 GPa). The transmittance reached as high as 86% in the infrared (IR) region. The absorption peaks in the UV-vis-NIR region of transmittance spectra could be attributed to the transitions of Er3+ ions from the ground state 4I15/2 to excited states. All transparent samples emitted intense green emissions when excited at 379 nm, corresponding to the 2H11/2 and 4S3/2 to 4I15/2 transitions of Er3+ ions. The average decay life-time decreased from 25.3 µs to 6.1µs with increasing Er3+ ion content, revealing the interaction within Er-Er clusters. Keywords: luminescent glass; La0.85-xErxBi0.15Al0.5Ga0.5O3; containerless method 1. Introduction Glassy materials have been widely investigated for applications in optical data storage, solid state laser host and scintillating devices, because they have facile preparation processes, as well as high chemical stability, refractive index, transmittance from the visible to infrared (IR) region and reproducibility [1-3]. The addition of rare-earth (RE) ions into glasses with various compositions has attracted widespread attention due to potential use in laser technology [4]. Erbium is an attractive dopant candidate for IR pumped visible luminescence and laser emission. In particular, lasing at the green transition 4S3/2→4I15/2 of Er3+ gives excellent results when doped in host matrices. The IR region emissions of Er3+ ions at 1.5 µm (4I13/2→4I15/2) and 860 nm (4S3/2→4I13/2) allow Er3+-doped materials to be applicable to laser devices and optical amplifiers [5]. Thus, researchers have endeavored to study the photoluminescence properties of Er3+-doped glasses,

such as up-conversion mechanisms [6], absorption spectrum [7] and Judd-Ofelt analysis [8]. However, the optical, mechanical and electric properties of Er3+-doped glasses, especially the refractive index, Vicker’s hardness and electrical insulation performance, have seldom been reported. La2O3-Al2O3- or La2O3-Ga2O3-based glasses are highly chemically and thermally stable, with outstanding mechanical and optical properties such as high Vicker’s hardnesses and transmittance [9-11]. Herein, we prepared high-purity green light- emitting Er3+-activated perovskite glasses La0.85-xErxBi0.15Al0.5Ga0.5O3 by containerless solidification using an aerodynamic levitation furnace. The Vicker’s hardnesses together with optical, electrical insulation and photoluminescence properties of these glasses were investigated. 2. Experimental

2.1 Synthesis

Er3+-activated La0.85-xErxBi0.15Al0.5Ga0.5O3 (x= 0.025, 0.05, 0.1, 0.125, 0.15) glasses were prepared by containerless processing in an aerodynamic levitation furnace. Firstly, appropriate amounts of high-purity La(NO3)3·6H2O, Bi(NO3)3·5H2O, Al(NO3)3·9H2O, Ga(NO3)3·6H2O, Er(NO3)3·6H2O and citric acid (in a molar ratio of 1.5:1 to total metal ions) were dissolved with deionized water in a beaker and magnetically stirred till a homogeneous solution formed. Then the mixture was heated to 80°C and stirred for 6-7 h, giving a yellowish wet gel. The gel was dried at 120°C and converted into a fluffy xerogel which was ground and calcined at 750°C for 2 h, yielding La0.85-xErxBi0.15Al0.5Ga0.5O3 powders. Subsequently, the powders were compacted into disks, molten by a CO2 laser device, levitated by O2 with the mass flow rate of 600 mg/min and kept in the molten state for about 20 s to ensure homogenization. Afterwards, the laser device was

turned off, and the homogeneous melts levitated by O2 were rapidly quenched to room temperature at a rate of about 300 °C/s. Finally, La0.85-xErxBi0.15Al0.5Ga0.5O3 glasses, as pink transparent glassy-spheres with the diameter of ~3 mm, were obtained. 2.2 Characterizations of samples The structures of the prepared glasses were determined by X-ray diffraction (XRD) using SmartLab X-ray diffractometer (Rigaku, Japan). Based on the Archimedes’ principle, the densities of the as-prepared amorphous spheres were measured by AL104 four-digit electronic balance and its density component (Mettler Toledo, China). The leakage current density was measured using 6517A electrometer (Keithley Instruments Inc., USA). The transmittances of the glasses in the wavelength range of 200-2500 nm were detected by Cary 5000 UV-vis spectrometer (Varian, USA), and those in the range of 2500-10000 nm were measured by Excalibur 3100 Fourier transform IR spectrometer (Varian, USA). The photoluminescence properties of the glasses were evaluated by measuring their excitation and emission spectra with F-7000 fluorescence spectrometer (Hitachi, Japan) employing a 150 W Xe lamp, and the fluorescence decay curves were plotted with FLS-920 fluorescence spectrometer (Edinburgh, Germany). Vicker’s hardness was measured three times by MHV-52 digital Vicker’s hardness tester (Sctmc, China) equipped with a diamond Vicker’s indenter at an applied load of 1 kg for 10 s, and then averaged. All the experiments were performed at room temperature. 3. Results and discussion 3.1 Structural properties Given the same structural properties of La0.85-xErxBi0.15Al0.5Ga0.5O3 glasses, the XRD patterns of x = 0.025, 0.125, 0.15 as typical samples were tested (Fig. 1). Clearly, there is no crystalline phase or peak. The broad diffraction bands confirm the glassy nature of the prepared samples.

3.2 Density, electrical insulation property and Vicker’s hardness Under an increasing applied electric field, the leakage currents (J) of La0.85-xErxBi0.15Al0.5Ga0.5O3 (x = 0.025, 0.05, 0.1, 0.125, 0.15) glasses ranged from 8×10-10 to 7×10-11 A/cm2(Fig. 2). Table 1 listed the current densities at 55 V/cm for all glasses. The change of J may be caused by the volatilization of Bi3+ and disordered state. The leakage current of x = 0.025 was minimal. As evidenced by the low leakage currents, La0.85-xErxBi0.15Al0.5Ga0.5O3 glasses had remarkable electrical insulation performance. The densities ρ and Vicker’s hardnesses of the glasses were summarized in Table 1. With rising Er2O3 content, the density increased from 5.235 to 5.603 g/cm3, which can be ascribed to the substitution of light oxide La2O3 (325.84 g/mol) by heavy oxide Er2O3 (382.52 g/mol). The Vicker’s hardness also rose as x increased, with the highest value of 7.34 GPa for x = 0.15. The value was slightly higher than that of fused silica (7 GPa) [12] and even close to that of Er3+/Yb3+-doped glass TiO2-La2O3-Ta2O5 (7.7 GPa) [13]. 3.2 Optical properties All the glasses exhibited similar transmittance spectra from the UV to IR region. Fig. 3 displayed the transmittance spectra of La0.85-xErxBi0.15Al0.5Ga0.5O3 (x = 0.05, 0.125) glasses in the UV-vis-NIR region. The transmittance of x = 0.05 was about 77% in the visible region and increases to 83% in the near-IR region, both exceeding

those of x = 0.125. The absorption

peaks at about 451, 487, 527, 652, 797, 977 and 1540 nm represented the transitions of Er3+ ions from the ground state 4I15/2 to excited states 4F5/2, 4F7/2, 2H11/2, 4F9/2, 4I9/2, 4I11/2 and 4I13/2 respectively [14, 15]. The inset of Fig. 3 presented the magnified spectra from 280 to 400 nm. The two absorption peaks centered at 366 and 379 nm were caused by the 4I15/2 →4G9/2 and 4I15/2 →

4

G11/2 transitions of Er3+ ions respectively [6], which were clearly observable in the excitation

spectra. Fig. 4 showed the photographs and transmittance spectra of selected and well- polished La0.85-xErxBi0.15Al0.5Ga0.5O3 (x = 0.05, 0.125) glasses in the IR region. The absorptions at near 3 µm and 4.2 µm may be assigned to free hydroxyl group and ambient CO2 respectively [1, 16]. The transmittance remained above 80% up to 5 µm, and the cut-off absorption wavelength reached about 8 µm. Hence, such wide IR transmission windows makes the glasses as promising candidates for optical devices. The dependence of refractive index of La0.825Er0.025Bi0.15Al0.5Ga0.5O3 glass on wavelength was shown in Fig. 5. According to the single oscillator model from the Drude-Voigt relationship, the refractive index n can be expressed as a function of the wavelength of an applied light, and the plot of 1/(n2-1) vs. 1/λ2 was expected to be a straight line [17, 18]. The inset of Fig. 5 showed that the measured values (dotted curve) followed a good linear relationship and can be well fitted by the linear curve (red), indicating that the single oscillator model adequately described the refractive index dispersion of La0.825Er0.025Bi0.15Al0.5Ga0.5O3 glass. The composition dependence of refractive index nd at 587.6 nm and the Abbe numbers νd of La0.85-xErxBi0.15Al0.5Ga0.5O3 (x = 0.025, 0.05, 0.1, 0.125, 0.15) glasses were given in Fig. 6. The wavelength dispersion of refractive indices was evaluated by the Abbe number νd defined as

vd = (nd − 1) / (nF − nC ) , where nd, nF, and nC were the refractive indices at 587.6, 486.1 and 656.3 nm, respectively. Evidently, nd and νd show the same variation tendency with increasing Er2O3 content. The maximum refractive index was 1.97 for x = 0.025, and the highest Abbe number was 32.32for x = 0.1 respectively.

3.3 Photoluminescence properties The photoluminescence excitation spectra of La0.85-xErxBi0.15Al0.5Ga0.5O3 glasses under an excitation of 550 nm were shown in Fig. 7. The two intense peaks centered at 366 and 379 nm in the near-UV region can be attributed to the 4I15/2→4G9/2 and 4I15/2→4G11/2 4f-4f transitions of Er3+ ions. Since the strongest excitation of all phosphors is related to the transition of 4I15/2→4G11/2, the photoluminescence emission spectra in the range of 500-700 nm at the excitation wavelength of 379 nm were recorded (Fig. 8). All spectra exhibit dominant green emissions with two typical peaks at 527 and 550 nm which correspond to the 2H11/2 and 4S3/2 to 4I15/2 transitions of Er3+ ions. Besides the Stark splitting, the shoulders around the prominent peak at 550 nm indicated that there must exist multisite in corporation of Er3+ ions [5, 19]. In addition to the dominant green emissions, a weak red emission band at 662 nm appeared, representing the 4F9/2 to 4I15/2 transitions of Er3+ [15]. Notably, the green emission intensity soared for x = 0.05, and the highest red one appeared for x = 0.1. The increase of green emission intensity for x = 0.05 can mainly be attributed to the spontaneous radiation transition of increasingly excited 4S3/2 level of Er3+ ions. At the Er3+ content of >0.05, the emission intensity gradually dropped, which was usually related to the conjunction of RE ion clusters through RE-O-RE bonds [20]. Meanwhile, the interaction between Er3+ ions enhanced the cross-relaxation, allowing the transition of Er3+ ions from the excited state 4

S3/2 to the lower 4F9/2 level by nonradiative relaxation. As a result, the 4S3/2→4I15/2 emission

intensity reduced and the red one increased for x = 0.1. The

normalized

decay

curves

for

the

4

S3/2→4I15/2

transition

of

Er3+

ions

in

La0.85-xErxBi0.15Al0.5Ga0.5O3 glasses at 550 nm when excited at 379 nm were displayed in Fig. 9. All curves were fitted by the double exponential function. The decay curve of

La0.8Er0.05Bi0.15Al0.5Ga0.5O3 glass and the fitted curve with a double exponential decay equation were exhibited in Fig. 10. The effective decay life time (τ) can be calculated by Equation (1) [21] (inset of Fig. 10).

A1τ 12 + A2τ 2 2 τ= A1τ 1 + A2τ 2

(1)

The average decay life time (τ) decreased from 25.3 µs to 6.1 µs with increasing Er3+ ion content, which may be related to the interaction between Er3+ ions. With rising Er3+ content, the distance between Eu3+ ions reduced, thereby enhancing the energy transfer among Er3+ ions and decreasing the fluorescence lifetime [22, 23]. The life time values of the glasses herein were comparable with those of previously reported Er3+-doped systems [19]. 4. Conclusions In summary, we successfully prepared a series of transparent luminescent glasses La0.85-xErxBi0.15Al0.5Ga0.5O3 (x = 0.025, 0.05, 0.1, 0.125, 0.15) by aerodynamic levitation technique. Their amorphous nature was confirmed by XRD. The samples had high transmittance (over 80%) and outstanding electrical insulation performance (J: 8×10-10 - 7×10-11 A/cm2). All glasses exhibited two strong green emissions centered at 527 and 550 nm, corresponding to the 2

H11/2→4I15/2 and 4S3/2→4I15/2 transitions of Er3+ ions, respectively. Elevating the content of Er3+

ions augmented the green emissions first and then reduced from x = 0.1, proving the concentration quenching effect. The average decay life-time (τ) decreased from 25.3 µs to 6.1 µs with rising Er3+ ion content, indicating the interaction between Er3+ ions. Therefore, the perovskite glasses have feasible optical applications. Acknowledgments This work was financially supported by the National Nature Science Foundation of China

(No.51602042) and the Natural Science Foundation of Heibei Province (No. E2018501042, B2018407058). References [1] X. G. Ma, Z. J. Peng, J. Q. Li, Effect of Ta2O5 Substituting on Thermal and Optical Properties of High Refractive Index La2O3-Nb2O5 Glass System Prepared by Aerodynamic Levitation Method, J. Am. Ceram. Soc. 98 (2015) 770-773. [2] S. X. Peng, F. J. Yang, L. B. Wu, Y. W. Qi, S. C. Zheng, D. D. Yin, X. S. Wang, Y. X. Zhou, Tm3+/Ho3+/Yb3+ codoped tellurite glass for multicolor emission- Structure, thermal stability and spectroscopic properties, J. Alloy. Compd. 609 (2014) 14-20. [3] A. Tumuluri, M. S. S. Bharati, S. V. Rao, K. C. J. Raju, Structural, optical and femtosecond third-order nonlinear optical properties of LiNbO3 thin films, Mater. Res. Bull. 94 (2017) 342-351. [4] J. A. Caird, A. J. Ramponi, P. R. Staver, Quantum efficiency and excited-state relaxation dynamics in neodymium-doped phosphate laser glasses, J. Opt. Soc. Am. B 8 (1991) 1391-1403. [5] R. Sosa, I. Foldvari, A. Wattericha, A. Munozb, R. S. Maillardc, G. Kugel, Photoluminescence of Er3+ ions in Bi2TeO5 single crystals, J. Lumin. 111 (2005) 25-35. [6] T. Castro, D. Manzani, S. J. L. Ribeiro, Up-conversion mechanisms in Er3+-doped fluoroindate glasses under 1550 nm excitation for enhancing photocurrent of crystalline silicon solar cell, J. Lumin. 200 (2018) 260-264. [7] P. Kostka, Z. G. Ivanova, M. Nouadji, E. Cernoskova, J. Zavadil, Er-doped antimonite Sb2O3-PbO-ZnO/ZnS glasses studied by low-temperature photoluminescence spectroscopy, J. Alloy. Compd. 780 (2019) 866-872. [8] A. L. Martins Jr., C. A. C. Feitosa, W. Q. Santos, C. Jacinto, C. C. Santos, Influence of BaX2

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Figure captions Fig.1 XRD patterns of La0.85-xErxBi0.15Al0.5Ga0.5O3 ( x= 0.025, 0.125, 0.15) glasses. Fig. 2 Leakage currents of La0.85-xErxBi0.15Al0.5Ga0.5O3 (x= 0.025, 0.05, 0.1, 0.125, 0.15) glasses. Fig. 3 Transmittance spectra of La0.85-xErxBi0.15Al0.5Ga0.5O3 ( x= 0.05, 0.125) glasses in the UV–VIS-NIR region. The inset gives the zoom of the spectra ranging from 280 to 400 nm. Fig. 4 Transmittance spectra of La0.85-xErxBi0.15Al0.5Ga0.5O3 (x = 0.05, 0.125) glasses in the IR region. Fig. 5 Refractive index dispersion of La0.825Er0.025Bi0.15Al0.5Ga0.5O3 glass. The dotted curve in the inset is obtained using the Drude–Voigt relationship, and the red curve is the fitted linear curve. Fig. 6 The composition dependence of the refractive index nd and the Abbe numbers νd of La0.85-xErxBi0.15Al0.5Ga0.5O3 glasses. Fig. 7 Photoluminescence excitation spectra of La0.85-xErxBi0.15Al0.5Ga0.5O3 glasses under an excitation of 550 nm. Fig. 8 Photoluminescence emission spectra of La0.85-xErxBi0.15Al0.5Ga0.5O3 glasses (λex = 379 nm). Fig. 9 Decay curves of the 4S3/2 emitting level of Er3+ ions in La0.85-xErxBi0.15Al0.5Ga0.5O3 glasses. Fig.10 The dotted curve is the obtained decay curve for x = 0.05, and the red curve is the fitted results of the experimental data to a double exponential decay equation. Inset shows the variation of life time with Er3+ ion concentration.

Table

1

Density,

Current

density

(at

55

V/cm)

and

La0.85-xErxBi0.15Al0.5Ga0.5O3 (x= 0.025, 0.05, 0.1, 0.125, 0.15) glasses

Vicker’s

hardness

of

Fig. 1

Fig. 2

Fig. 3

Fig. 4

Fig. 5

Fig. 6

Fig. 7

Fig. 8

Fig. 9

Fig. 10

Table 1

Density x

3

g/cm

current density

Vicker’s hardness

(×10-10A/cm2)

(GPa)

0.025

5.235

1.26

6.18

0.05

5.312

3.37

6.64

0.1

5.424

3.40

6.96

0.125

5.487

2.50

7.12

0.15

5.603

3.05

7.34

Highlights 1. Er3+ doped perovskite glasses were synthesized. 2. These glasses have intense emissions. 3. These glasses exhibited high transmittance.

Dear Editor: We have read and understood your journal’s policies, and we confirm that the manuscript, or its contents in some other form, has not been published previously by any of the authors and is not under consideration for publication in another journal at the time of submission. We state there is no conflict of interests in our manuscript. Thank you for your consideration. I look forward to hearing from you. Sincerely yours, Xiwei Qi