Magneto-optical borogermanate glasses and fibers containing Tb3

Abstract

New glass compositions containing high concentrations of Tb³⁺ ions were developed aiming at the production of magneto-optical (MO) fibers. This work reports on the structural and MO properties of a new glass composition based on (100 - x)(41GeO₂-25B₂O₃-4Al₂O₃-10Na₂O-20BaO) - xTb₄O₇. Morphological analysis (HR-TEM) of the sample with the highest concentration of Tb³⁺ ions confirmed the homogeneous distribution of Tb³⁺ ions and the absence of nanoclusters. All the samples presented excellent thermal stability against crystallization (ΔT > 100 °C). An optical fiber was manufactured by a fiber drawing process. The UV-Vis spectra of the glasses showed Tb³⁺ electronic transitions and optical windows varying from 0.4 to 1.6 μm. The magneto-optical properties and the paramagnetic behaviors of the glasses were investigated using Faraday rotation experiments. The Verdet constant (V_B) values were calculated at 500, 650, 880, 1050, 1330, and 1550 nm. The maximum V_B values obtained at 650 and 1550 nm for the glass with x = 18 mol% were -128 and - 17.6 rad T^-1 m^-1, respectively. The V_B values at 500 and 1550 nm for the optical fiber containing 8 mol% of Tb₄O₇ were - 110.2 and - 9.5 rad T^-1 m^-1, respectively, while the optical loss at around 880 nm was 6.4 dB m^-1.

Figure 1

Photograph of BGB-xTb glasses with different Tb₄O₇ contents.

Figure 2

(a) DSC curves, (b) T_g and ΔT, and (c) optical basicity, as a function of Tb₄O₇ concentration. The lines in (b) and (c) are just guides for the eyes.

Figure 3

XRD patterns for the BGB-xTb glasses.

Figure 4

(A) HRTEM micrograph of BGB-18Tb [the inset shows the fast Fourier transform (FFT)]. (B) HAADF mode (Z-contrast) image of the analyzed area (1) and elemental EDS mapping for Ba-K (2), Tb-L (3), and O-K (4).

Figure 5

Normalized Raman spectra for the BGB-xTb glasses in (a) low (~ 130–650 cm⁻¹), (b) medium (~ 650–1050 cm⁻¹), and (c) high (1050–1700 cm⁻¹) frequency regions. Deconvolution of the Raman spectra for the 0, 4, 8, and 18 Tb glasses in the low (d–g), medium (h–k), and high (l–o) frequency regions.

Figure 5

Normalized Raman spectra for the BGB-xTb glasses in (a) low (~ 130–650 cm⁻¹), (b) medium (~ 650–1050 cm⁻¹), and (c) high (1050–1700 cm⁻¹) frequency regions. Deconvolution of the Raman spectra for the 0, 4, 8, and 18 Tb glasses in the low (d–g), medium (h–k), and high (l–o) frequency regions.

Figure 6

(a) UV–Vis–NIR optical absorption, (b) transmission spectra, (c) refractive indices as a function of Tb₄O₇ content, at different wavelengths, and (d) refractive indices for BGB-xTb glasses (0 ≤ x ≤ 18), as a function of wavelength.

Figure 7

(a) PLE spectrum of the BGB-4Tb glass and (b) PL spectra of the BGB-xTb glasses at room temperature. Inset photograph: BGB-4Tb sample under excitation at 375 nm. Inset: PL spectra of the BGB-xTb glasses (x = 14, 16, and 18 mol% Tb₄O₇) in the region from 530 to 560 nm.

Figure 8

(a) Photographs of the BGB-xTb glasses and the magnetic attraction of the BGB-18Tb glass using a commercial neodymium magnet. Plots of V_B as a function of (b) Tb₄O₇ content (mol%), (c) Tb³⁺ ions density (g cm⁻³), and (d) wavelength.

Figure 9

(a) Glass preform, (b) MO fiber based on the BGB-8Tb composition, (c) SEM cross-section image of the BGB-8Tb fiber, (d) glass preform after the drawing process, and (e) optical microscopy image of the surface of the fiber.

Figure 10

(a) Variation of the Verdet constant as a function of wavelength and (b) attenuation spectrum of the BGB-8Tb fiber determined using the cut-back method, with a final length of 0.21 cm.