Effect of B2O3 Content and Microstructure

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C: Plasmonics; Optical, Magnetic, and Hybrid Materials 2

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Effect of BO Content and Microstructure on Verdet Constant of TbO Doped GBSG Magneto-Optical Glass 2

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Hairong Yin, Yang Gao, Hongwei Guo, Cuicui Wang, and Chen Yang J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b04989 • Publication Date (Web): 03 Jul 2018 Downloaded from http://pubs.acs.org on July 12, 2018

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The Journal of Physical Chemistry

Effect of B2O3 Content and Microstructure on Verdet Constant of Tb2O3 Doped GBSG Magneto-Optical Glass Hairong Yin*, Yang Gao, Hongwei Guo, Cuicui Wang, and Chen Yang School of Materials Science and Engineering, Shaanxi University of Science & Technology, Xi’an 710021, China. * Email: [email protected] Abstract: Rare earth oxide Tb2O3 doped GBSG glasses with different B2O3 concentrations were prepared and studied. The Verdet constant of the GBSG glasses were measured and it was found that the Verdet constant increased greatly when the content of Tb4O7 is fixed but the B2O3 concentration increases. The XPS and EPR spectrums show that the ratio Tb3+/Tb4+ increases with the increase of B2O3. The self-reduction of Tb4+ occurred. According to the FTIR and MAS-NMR spectrums, when the B2O3 concentration increased, the depolymerization of the boron groups occurred. The [BO4] based high polymeric network decomposed into the lower ones containing [BO3], which caused the reduction in which the diamagnetic Tb4+ gradually reduce to the paramagnetic Tb3+. This is the basic reason why the Verdet constant increases with the B2O3 concentration. Finally, the schematic illustration of the position of Tb ions and the electron transfer between Tb ions and the surrounding negative boron units were discussed.

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1.

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Introduction Magneto-optical (MO) material which has been widely concerned and studied is

an indispensable element in modern optical components such as laser optics for polarization control, optical isolation, birefringence compensation, or narrow-band optical filtering in gaseous media

1-2

. One of the traditional MO materials is

magneto-optical crystals, the most widely used magneto-optical crystal is terbium gallium garnet (TGG) thanks to the high value of its Verdet constant, good thermo-optical characteristics enabling operation at high average power 3. Recently some magneto-optical ceramic materials synthesized by magneto-optical crystal powder, such as terbium aluminum garnet ceramics TAG 4, Ce:TAG 5, Ti:TAG, Si:TAG

6-7

, and single crystal TSAG 8, have also received some attention. Compared

with crystals and transparent ceramics, MO glasses could be fabricated in larger sizes, low absorption coefficient and high transmittance, making them attractive to be applied in communication and larger power laser systems

9-10

. Because of the highest

magnetic moment and paramagnetic effects of Tb3+ ion 11, we chose Tb as rare earth doped ions to prepare magneto-optical glass samples. Verdet constant is a parameter that characterizes the magneto-optical performance of a MO material. The Verdet constant of magneto-optic glass is generally lower than that of magneto-optic crystals 12, so it is very important to master the method of increasing the Verdet constant of magneto-optic glass effectively, but this is not an easy task for magneto-optical glass. Currently there are two main methods that are widely used to improve the Verdet constant of MO glasses. The first


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is to increase the content of rare earth ions. Jingxin Ding 13 prepared Tb3+ doped MO glass and found the influence of Tb3+ concentration on the optical properties and Verdet constant of the MO glass. But high content of rare earth ions will greatly increase the difficulty of glass melting and glass crystallization tendency which will make the glass unusable 14. The second is to control the Verdet constant by controlling external conditions. I.L. Snetkov

3, 15

reported the temperature characteristics and the

wavelength dependence of the Verdet constant of Tb2O3 ceramics. However, the control of external conditions is not easy to achieve. In this work, we increase the Verdet constant by adjusting the Tb2O3 doped MO glass microstructure. We know that the paramagnetic of Tb2O3 doped glass comes from the emission properties of Tb3+ 16, but Tb3+ state is not the only state in the glass. The raw material Tb2O3 contains a part of Tb4+ ions, during the melting of the glass, a portion of Tb3+ will be oxidized to Tb4+

17

. According to the literature, in contrast to Tb3+, Tb4+ is

diamagnetic 11, its existence leads to a decrease in Verdet constant of the paramagnetic magneto-optic glass. Therefore, it is considered that the Tb3+/Tb4+ ratio is proportional to the Verdet constant of the Tb2O3 doped MO glass. But it is difficult to prevent Tb3+ from being oxidized during the glass melting process. So in this work we took some measures to promote the self-reduction of Tb4+ to Tb3+. Qing Jiao

18-19

reported the

great influence of the B2O3 configuration structure on the value state of the rare earth Eu ions and proposed that the self-reduction of Eu3+ can be achieved by controlling the content of B2O3. Qiuling Chen 11 believes that a large increase of Tb2O3 can make Tb4+ into Tb3+. But we cannot ignore the problem of increasing the difficulty of glass



melting caused by the increase of rare earth content. In this work, we have succeeded in controlling the value state of Tb ions by adjusting the B2O3 content in the Tb2O3 doped magneto-optic glass. The Verdet constant of the Tb2O3 doped magneto-optic glass was successfully increased without increasing the content of rare earth ions. At the same time, we analyzed the microstructure of the Tb2O3 doped magneto-optic glass and found out how the B2O3 content affects the Verdet constant: changes in charge in glass systems due to the depolymerization of the boron group. With the gradual increase in B2O3 content, the changes of the B2O3 configuration structure and the value state of Tb ion are clearly demonstrated by the XPS spectra and the FTIR spectra. 2.

Experimental

2.1 Materials We prepared a series of Tb3+ doped Ga2O3–B2O3–SiO2–GeO2 (GBSG) glasses by the melt-quenching technique. The molar composition of the glass samples can be written as 20Tb2O3–25Ga2O3–xB2O3–(35-x)SiO2–20GeO2 (x=20, 24, 26, 28, 30, 35). And 0.3g Sb2O3 was added into the raw materials during the melting process of every sample as a role of clarifying agent. The raw materials of the samples used for the present study includes GeO2, H3BO3, Ga2O3, Tb4O7(Tb2O3•2TbO2) and SiO2. GeO2 and Ga2O3 have a purity of 99.99%, H3BO3 and SiO2 are analytically pure. Rare earth Tb3+ is doped by the type of Tb4O7(Tb2O3•2TbO2) which has a purity of 99.99%. These appropriate amounts of these raw materials were well mixed in an agate mortar for about 10-20 min, and then melted at 1450 ℃ in a platinum crucible which had been heated to 1300 ℃ for 1 h. The resultant liquid was then poured in a graphite mould and subsequently cool slowly from 700 ℃ to room temperature at a precision


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annealing furnace to eliminate the stress of the glass. Finally, the glasses were cut and polished to be characterized performance. 2.2 Methods The influence of B2O3 contents on the Verdet constant of magneto-optical glass was measured by multi-wavelength optical rotation coefficient measuring instrument manufactured by Shanghai Daheng Optical Precision Machinery Co., Ltd. To know the valence change of Tb ions as a factor of B2O3 concentration, the electron spin state of different valence states of Tb ions was measured by a Bruker A300-9.5/12 electronic paramagnetic resonance (EPR) spectrometer and then the valance band spectra of Tb ions in different valence state present in the glass with different B2O3 contents was recorded by an AXIS supra X-ray photoelectron spectrometer (XPS). To find the change of the B2O3 configuration structure with the increasing of B2O3, the microstructure of magneto-optical glasses was analyzed by a Bruker VECTOR-22 Fourier transform infrared spectroscopy (FTIR) and a Bruker InfinityPlus 400 Nuclear Magnetic Resonance (NMR) Spectroscopy. 3.

Results and discussion

3.1 Verdet constant of GBSG glass with different B2O3 contents To the rare earth ions doped magneto-optical (MO) materials, the most fatal factor to measure the property is Verdet constant. According to the former study, the Verdet constant of Tb ions doped MO glasses is directly proportional to the Tb2O3 content 20. And the external factors such as temperature 21 and incident wavelength 22 both have great influence which we cannot ignore on the Faraday Effect of MO materials. This chapter focuses on the effect of the internal structure of the matrix glass—in particular, the type of boron groups—on the Faraday Effect of MO glasses.



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The black curve in Fig. 1 (a) shows the Verdet constant of the MO glasses with the same Tb2O3 content at the same wavelength (450 nm) and the same temperature (room temperature, about 23 ℃) as a function of B2O3 concentration. As we can see in Fig. 1 (a), although we did not increase the content of Tb2O3 in the glasses, the Verdet constant was significantly improved. With the B2O3 concentration increased from 20 mol.% to 35 mol.%, the Verdet constant increased by 15% (from -210 rad/T/m to -236 rad/T/m). We know that the Faraday Effect of Tb2O3 doped magneto-optic glass originates from the energy transition 4f8−4f75d of Tb3+ 23, and the Tb2O3 contents in all our six samples are fixed, so we can think that the reduction reaction in which the diamagnetic Tb4+ transfer to the paramagnetic Tb3+ has occurred in our paramagnetic magneto-optic glass system with the increase of the B2O3 concentration, which caused a rise in the Verdet constant. The optical basicity of the MO glasses we prepared was calculated using the Duffy optical basicity theory 24. Optical basicity theory is used for characterizing the non-bridge oxygen and electrons in the glasses. And it is believed that the lower the optical basicity of the glass, the lower of the non-oxygen content and thus the lower the valence state of multivalence metal ions was preferred

25

. Therefore, optical

basicity can be used to approximately determine the valence state of Tb ions in our MO glass systems. According to the theory, the optical basicity can be written as = ∑ ∙

(1)

Where is the optical basicity quantity of one composition of glass, is the


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mole fraction of the component studied. The Optical basicity of every composition of the MO glasses we prepared 26 was listed in Tab. 1. The calculation results of optical basicity of the MO glasses we prepared were listed in Tab. 2. Table 1 Optical basicity of oxides in magneto-optical glass Oxides

0.954

0.71

0.43

0.48

0.70

Optical basicity

Table 2 Optical basicity of Tb2O3 doped glasses with different B2O3 concentration Sample

B20

B24

B26

B28

B30

B35

0.674

0.669

0.666

0.664

0.661

0.656

Optical basicity

From the Tab. 2 and the blue curve in Fig. 1 (a) we can directly see the trend of optical basicity. With the addition of B2O3, the value of optical basicity decreases. So we can know that, with the increase of B2O3 content, the environment of the MO glass system is more and more favorable to the presence of Tb3+ who is in a relatively lower valence. The reason for the decrease of the optical basicity is that more non-bridge oxygen will be needed to link the high polymeric borate groups consist of [BO4] and [BO3] when the B2O3 concentration increases

27

. The decrease of the amount of the

non-bridge oxygen directly leads to the decrease of optical basicity. As the B2O3 concentration continues to increase, the amount of non-bridged oxygen is not sufficient to maintain the high polymeric borate groups and the high



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polymeric borate groups will depolymerize to some lower polymeric borate groups 18. This is also one of the important reasons that lead to the self-reduction of Tb4+. We will be discussed about it in later chapters. 3.2 Spectroscopic properties of Tb ions with different valences in GBSG glass The electronic paramagnetic resonance (EPR) and X-ray photoelectron spectrometer (XPS) test were done to investigate the mechanism of the increase of Verdet constant with increasing B2O3 concentration in GBSG glass under the precondition that the content of Tb2O3 is certain. Both Tb3+ and Tb4+ can be detected by EPR. However, their EPR spectra are rather different 28-30. Fig. 2 shows the x-band EPR spectra of GBSG glasses with four different B2O3 concentrations. From the picture we can see some trends of GBSG glass with gradually increasing B2O3 concentration. Firstly, all the four samples have a very strong peak at H≈2500 G. We calculated the g value at this position using the formula: hν = gβH

(2)

Where h and β are constant, g is the g factor, H is magnetic field strength. According to the result from Formula (2), the g factor at 2500 G is 2.19, which is consistent with the previous studies’ conclusion that the g value of Tb3+ is approximately equal to 2, so we know that the strong peak at H=2500 G is belong to the Tb3+ who have an electronic configuration of 4f8. Secondly we can find a faint peak at approximately 1400 G which is believed to be the characteristic peak of Tb4+ (4f7) 31, the calculated g value at this position is 3.74. From the four spectra curves we


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can directly find that the characteristic peak of Tb3+ at 2500 G gradually enhanced with the increase of B2O3 content. However, the Tb4+ characteristic peak at 1400G is very weak and almost can only be found in sample B20 with a relatively low B2O3 content. To a certain extent, this can prove the occurrence of the reduction reaction. The presence of Tb4+ ions gets complicated by the very intense signal at g=2. Because of this limitation the EPR test may not provide accurate evidence for the decrease of Tb4+ 31. XPS spectra can show Tb ions in all different statements in the GBSG glass samples, so we did an XPS test to find the quantitative evidence for the reduction reaction in which Tb4+ transfer to Tb3+. X-ray photoelectron spectrometer (XPS) test can determine the status of the Tb ion (such as the valence state of Tb ions what we focus on) by detecting the electronic arrangement on the 4d or 3d electronic orbit. However, the spectrum of the 3d orbit of Tb is too complex. It contains multiple peaks and is difficult to analyze. Therefore, we choose the 4d orbit as the object of analysis. Fig. 3 shows the XPS spectra of Tb 4d in Tb2O3 doped glasses with three different B2O3 concentrations. As we can see in the picture, there are two main peaks of Tb ions in Tb 4d spectra. One appears at about binging energy 147 eV and the other one is at approximately 150 eV. According to the former researches, the peak at 147 eV (the red curve in Fig. 3) is the characteristic peak of Tb3+ and the peak at 150 eV (the blue curve in Fig. 3) is the characteristic peak of Tb4+

32

. The peak area of each

characteristic peak can indicate the relative content of the corresponding ion. To find



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the trend directly, we calculated the percentages of the peak area of Tb3+ and Tb4+, the results could be found in the insert table of Fig. 3 (a), (b) and (c). And then, using the data obtained above, we get the ratios of the area of Tb3+ and Tb4+ in XPS spectra of the glasses with different B2O3 dopants. The results were listed in Tab. 3 and Fig. 1 (b). Table 3 Ratios of the area of Tb3+ and Tb4+ in XPS spectra of the glasses with different B2O3 dopants Concentration of B2O3

20 (mol.%)

24 (mol.%)

26 (mol.%)

28 (mol.%)

30 (mol.%)

35 (mol.%)

Ratio of Tb3+/Tb4+

1.667

1.755

1.768

1.777

2.096

2.606

As we can see in Tab. 3 and the blue curve in Fig. 1 (b), the ratio of the area of Tb3+ and Tb4+ increases significantly with the increase of B2O3 concentration. And we can clearly see from the two curves in Fig 1 (b), the Tb3+/Tb4+ ratio and Verdet constant both increase with the increasing of B2O3 concentration, the two trends are the same. This is consistent with previous studies that Tb3+ ions favor the Verdet constant of paramagnetic glass, while Tb4+ ions negatively affect it. Fig. 3 (d) shows the contrast between the peak areas of the glasses with the above three different B2O3 concentrations. From the picture we can see more intuitively that the content of Tb3+ gradually increases and the content of Tb4+ gradually decreases, which is consistent with the trend in the Tb3+/Tb4+ ratio calculated above. Combining the results and trends of EPR and XPS spectra, we have proved very well that some change had happened to the microstructure of the Tb2O3 doped GBSG glass with the B2O3 content increasing which caused the reduction reaction in which Tb4+ transfer to Tb3+.


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3.3 Microstructure of Tb2O3 GBSG glass with different B2O3 concentration According to the research of Qing Jiao

18

, the type of boron units in borate

glasses has a very great effect on the valence state of dopant ions. In order to find what happened in the structure of Tb2O3 GBSG glass when B2O3 concentration increased, a series of tests for the type of boron group were conducted. We know that the boron exists as polymerized network units in B2O3-containing glass

33

. Such as

boroxol rings, tetraborate groups, pentaborate groups, and triborate groups

34

. And

these boron groups can be divided into two types: the high polymerized network units mainly consist of [BO4] and the low polymeric states containing only [BO3] units 18. Firstly, a 11B MAS-NMR test was used to find the trend in the ratio of ⅢB and

Ⅳ

B as

the B2O3 content increases. The 11B MAS-NMR test can determine the content of tricoordinated BⅢ ions and four-coordinated BⅣ ions in the samples by detecting the energy-level difference of B ions when an energy level transitions occurs under a strong magnetic field. The content is expressed in peak intensity in the spectrum. Paramagnetism in the Tb2O3 MO glass may affect the test data to a certain extent, such as the peak position

35

.

However, the ratio of B ions in the two coordination states will not be affected. As we can see in Fig. 4, a strong peak representing B ions appeared at 0~20 ppm, and it was divided into two lower peaks at 9 ppm and 15 ppm. According to the research of Peidong Zhao 36, the peak at about 9 ppm is the characteristic peak of BⅣ which is the main components of [BO4], the peak at 15 ppm is the characteristic peak of BⅢ which is the main components of [BO3]. In the picture, obviously, as the content of B2O3



increases, the content of BⅣ gradually decreases, and the content of BⅢ gradually increases. So we can think that the addition of B2O3 makes some changes to the microstructure of GBSG glasses, the low polymeric network containing [BO3] gradually replaced the higher polymeric network containing [BO4]. In other words, the depolymerization of the boron unit network occurs. In order to more specifically understand the depolymerization process of the boron unit network, we conducted the FTIR spectrum test. FTIR spectroscopy determines the type of groups in the samples by detecting the vibration different units in GBSG glasses. As we can see in Fig. 5 (a), samples with different B2O3 content have peaks at essentially the same wavelength but the peak intensities are different. It is believed that the vibration of B-O bonds stretching of the [BO4] units appears between 800 and 1200 cm-1, which can correspond to the peak at 980 cm-1 in Fig. 5; and the peaks at 1200–1600 cm-1 belong to the asymmetric stretching relaxation of the B-O bands of triangles [BO3] units, which can correspond to the peak at 1210 and 1420 cm-1 in Fig. 5 characteristic peak of B3O63-

37

. The peak at 1210 cm-1 is the

38

. And the peaks at 520 and 710 cm-1 are the

deformation modes of the glass network 39, in particular, the peak at 710 cm-1 belongs to the bond-bending motion of B-O-B groups. With the increase of the concentration of B2O3, the characteristic peak of [BO4] at 980 cm-1 is weakening and is almost invisible in the sample with 30 % B2O3 and 35 % B2O3, at the same time, the characteristic peaks of [BO3] and B3O63- at 1210 and 1420 cm-1 are continuously enhanced. No significant change occurs in the peaks which are


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due to the deformation modes of the glass network at 520 and 710 cm-1 (due to a large increase in the content of B2O3, the peak at 720 cm-1 which belongs to the motion of B-O-B groups of the sample with 35 % B2O3 became more intense). Fig. 5 (b) shows the ratio of [BO3] and [BO4] as a function of B2O3 concentration using the data from the FTIR spectrogram in Fig. 5 (a). It is obviously that the [BO3]/[BO4] ratio was gradually increasing, which proves that the high polymeric network containing [BO4] constantly transformed into the lower polymeric network containing [BO3]. In other words, the depolymerization of boron groups occurred. This is consistent with the conclusion drawn by the optical basicity theory above. Qing Jiao reached the same conclusion in the study 18. This is the fundamental reason that leads to the reduction of Tb4+ ions in the GBSG glass and thus raises the Verdet constant. According to the results of the NMR and FTIR test, the schematic illustration of structure depolymerization process with introduction of B2O3 concentration in Tb2O3 doped glasses was shown in Fig. 6. In summary, as shown in Fig. 6, the complicated high polymeric network gradually decomposed into dispersed low polymeric network, such as [BO3] based B3O63- and B2O54- who have negative charge. It makes Tb ions much easier to enter the boron polymer groups of the glasses and be surrounded by plenty of negative groups (as shown in Fig. 7 (a)), which leads to the reduction reaction of Tb4+ 20. In addition, because of the consuming of the free oxygen with the B2O3 increasing, plenty of the boron oxygen hole centers (BOHCs) may be generated in the glass matrix during the depolymerization process of the boron group. These hole centers



accompanied with the low polymeric groups will also greatly enhance the chance of the reduction reaction of Tb4+ 19. Finally, as the diamagnetic Tb4+ gradually transfer to the paramagnetic Tb3+, the Verdet constant of the Tb2O3 doped GBSG glass has been significantly improved. Fig. 7 shows the schematic illustration of the position of Tb ions in the boron polymer groups of the glasses and the electron transfer between Tb ions and the surrnuding negative boron units mentioned above. 4.

Conclusions We prepared Tb2O3 doped GBSG glass with different B2O3 concentration (20

mol.%, 24 mol.%, 26 mol.%, 28 mol.%, 30 mol.%, 35 mol.%) and successfully increased the Verdet constant without increasing the Tb2O3 content, and analyzed the mechanism through a series of tests. As B2O3 content gradually increases from 20% to 35%, the Verdet constant increases by almost 15% (from -210 rad/T/m to -236 rad/T/m). From the results of XPS and EPR analysis, it is proved that the increase in the Verdet constant of our paramagnetic MO GBSG glass is due to the reduction reaction in which the diamagnetic Tb4+ gradually reduced to the paramagnetic Tb3+. Then, the change of the microstructure of Tb2O3 doped GBSG with the increase of B2O3 was studied by FTIR and MAS-NMR test. We found that the increase of B2O3 leads to the depolymerization of the boron group. Specifically, when the B2O3 concentration continues to increase, the complicated high polymeric network containing [BO4] gradually decomposed into dispersed [BO3] based low polymeric network. At the same time, a large amount of the boron oxygen hole centers (BOHCs) which can react with Tb4+ generated in the glass matrix. It makes Tb4+ be surrounded by plenty of negative units, which leads to the reduction of Tb4+ and eventually leads


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to an increase in the Verdet constant.

Acknowledgments This work was supported by the Natural Science Foundation of China (NO. 51472151), Science and Technology Research Project of Xianyang (NO. 2016K02-28), Science and Technology R & D Program Focused on Special Project (NO. 2017YFB0310201-02), Science and Technology Planning Project of Weiyang District of Xi'an (NO. 201706).

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and

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Heavily

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TOC graphic


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Table captions (1) Table 1 Optical basicity of oxides in magneto-optical glass (2) Table 2 Optical basicity of Tb2O3 doped glasses with different B2O3 concentration (3) Table 3 Ratios of the area of Tb3+ and Tb4+ in XPS spectra of the glasses with different B2O3 dopants



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Table 1 Optical basicity of oxides in magneto-optical glass Oxides

0.954

0.71

0.43

0.48

0.70

Optical basicity


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Table 2 Optical basicity of Tb2O3 doped glasses with different B2O3 concentration Sample

B20

B24

B26

B28

B30

B35

0.674

0.669

0.666

0.664

0.661

0.656

Optical basicity



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Table 3 Ratios of the area of Tb3+ and Tb4+ in XPS spectra of the glasses with different B2O3 dopants Concentration of B2O3

20 (mol.%)

24 (mol.%)

26 (mol.%)

28 (mol.%)

30 (mol.%)

35 (mol.%)

Ratio of Tb3+/Tb4+

1.667

1.755

1.768

1.777

2.096

2.606


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Figure captions (1) Fig. 1 Verdet constant and optical basicity of the Tb2O3 glasses with different B2O3 concentration (a), Verdet constant and Tb3+/Tb4+ ratio of the Tb2O3 glasses with different B2O3 concentration (b). (2) Fig. 2 EPR spectra of Tb2O3 doped glasses with four different B2O3 concentrations. (3) Fig. 3 XPS spectra of Tb2O3 doped glasses with 20 mol.% B2O3 (a), 30 mol.% B2O3 (b), 35 mol.% B2O3 (c) and the contrast between the peak areas of the glasses with the above three B2O3 concentration (d). (4) Fig. 4

11

B MAS-NMR spectra of the Tb2O3 doped glasses with different B2O3

concentration. (5) Fig. 5 FTIR spectra of the Tb2O3 doped glasses with different B2O3 concentration (a) and the ratio of BO3 and BO4 as a function of B2O3 concentration (b). (6) Fig. 6 Schematic illustration of structure depolymerization process with increasing of B2O3 concentration in Tb2O3 doped glasses. (7) Fig. 7 Schematic illustration of the position of Tb ions in the boron polymer groups of the glasses (a) and the energy level diagram of Tb3+ (b).



Fig. 1 Verdet constant and optical basicity of the Tb2O3 glasses with different B2O3 concentration (a), Verdet constant and Tb3+/Tb4+ ratio of the Tb2O3 glasses with different B2O3 concentration (b).


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Fig. 2 EPR spectra of Tb2O3 doped glasses with four different B2O3 concentrations.



Fig. 3 XPS spectra of Tb2O3 doped glasses with 20 mol.% B2O3 (a), 30 mol.% B2O3 (b), 35 mol.% B2O3 (c) and the contrast between the peak areas of the glasses with the above three B2O3 concentration (d).


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Fig. 4

11

B MAS-NMR spectra of the Tb2O3 doped glasses with different B2O3

concentration.



Fig. 5 FTIR spectra of the Tb2O3 doped glasses with different B2O3 concentration (a) and the ratio of BO3 and BO4 as a function of B2O3 concentration (b).


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Fig. 6 Schematic illustration of structure depolymerization process with increasing of B2O3 concentration in Tb2O3 doped glasses.



Fig. 7 Schematic illustration of the position of Tb ions in the boron polymer groups of the glasses (a) and the energy level diagram of Tb3+ (b).


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Fig. 1 Verdet constant and optical basicity of the Tb2O3 glasses with different B2O3 concentration (a), Verdet constant and Tb3+/Tb4+ ratio of the Tb2O3 glasses with different B2O3 concentration (b). 147x62mm (300 x 300 DPI)



Fig. 2 EPR spectra of Tb2O3 doped glasses with four different B2O3 concentrations. 201x141mm (300 x 300 DPI)


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Fig. 3 XPS spectra of Tb2O3 doped glasses with 20 mol.% B2O3 (a), 30 mol.% B2O3 (b), 35 mol.% B2O3 (c) and the contrast between the peak areas of the glasses with the above three B2O3 concentration (d). 181x150mm (300 x 300 DPI)



Fig. 4 11B MAS-NMR spectra of the Tb2O3 doped glasses with different B2O3 concentration. 201x141mm (300 x 300 DPI)


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Fig. 5 FTIR spectra of the Tb2O3 doped glasses with different B2O3 concentration (a) and the ratio of BO3 and BO4 as a function of B2O3 concentration (b). 139x77mm (300 x 300 DPI)



Fig. 6 Schematic illustration of structure depolymerization process with increasing of B2O3 concentration in Tb2O3 doped glasses. 201x138mm (300 x 300 DPI)


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Fig. 7 Schematic illustration of the position of Tb ions in the boron polymer groups of the glasses (a) and the energy level diagram of Tb3+ (b). 190x142mm (300 x 300 DPI)


Effect of B2O3 Content and Microstructure

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