Influence of Al/Er ratio on the optical properties and structures of Er3+/ Al3+ co-doped silica glasses

Abstract

In this study, Er3+/Al3+ co-doped silica glasses with various Al/Er ratios ranging from 0 to 200 and a constant Er2O3 amount were prepared using the sol-gel method combined with high-temperature vacuum sintering. The absorption, emission spectra, and fluorescence lifetime of Er3+ ions were recorded and the absorption and emission cross sections were calculated. Using Raman, 27Al and 29Si magic angle spinning nuclear magnetic resonance (MAS-NMR), 27Al triple-quantum (TQ)-MAS-NMR, and electron paramagnetic resonance (EPR) spectroscopies, the physical and optical properties were correlated with the glass structural modifications due to the Al/Er ratio change. With the increase in the Al/Er ratio, the content of Al3+ ions around the Er3+ ions gradually increased. Meanwhile, the AlO5 and AlO6 polyhedrons increased at the expense of the AlO4 and SiO4 tetrahedrons, which resulted in an improved symmetry and better ionic Er–O bonds. These structural changes led to the site-to-site variations in the Er3+ local environment and the changes in the ligand field strength of the Er–O bonds. This, in turn, resulted in the inhomogeneous broadening of the absorption and emission spectra, with a blue shift of both absorption and emission peaks and a decrease in both absorption and emission at 1.53 μm. With the increase in Al/Er ratio, the full width at half maximum (FWHM) of the emission increased from 27.2 to 54.3 nm. The FWHM × emission cross section (σemi) parameter for evaluating broadband amplification behavior was 30.1 × 10−20 cm2 · nm. This work reveals the close relationship between the glass structure and the spectroscopic properties of Er3+ ions and provides an important reference for the design of broadband amplifier materials in the field of optical communication.

Near-IR Luminescence of Rare-Earth Ions (Er3+, Pr3+, Ho3+, Tm3+) in Titanate–Germanate Glasses under Excitation of Yb3+

“…In some cases, the glass modifiers have a minor influence on absorption properties but a strong impact on the emission cross-sections attributed to the 4 I 13/2 → 4 I 15/2 near-infrared transition of Er 3+ ions. Recently, it was well demonstrated for Er 3+ ions in silicate glass with various Al 2 O 3 content [ 45 ] and Er 3+ /Yb 3+ co-doped phosphate glass modified by Y 2 O 3 [ 46 ].…”

Sol–Gel Photonic Glasses: From Material to Application

“…The importance of efficient light emission by RE-doped sol–gel bulk and thin-film glasses has promoted a large number of studies of the way to improve the fluorescence yield in these materials [ 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 ]. One of the ways to enhance fluorescence is based on aluminum co-doping; its positive effect on the fluorescence properties of RE-doped glasses [ 47 ], and in particular of sol–gel glasses [ 37 , 48 , 49 , 50 ] has been known for a long time, although the physical-chemical mechanism is still an object of research.…”

“…It was suggested that the fluorescence enhancement by Al co-doping was due to different mechanisms, depending on the Al:RE ratio: at low Al concentrations, the site symmetry is lowered, and the transition probability is increased; at a high Al:RE ratio, the highest frequency phonons are of lower energy and therefore nonradiative decay rates are reduced. In another recent study, dealing with Er 3+ /Al 3+ -doped silica glasses with Al/Er ratios from 0 to 200 [ 45 ], it was shown that, as the Al/Er ratio increased, the number of Al 3+ ions around the Er 3+ ions gradually increased, too. Concurrent structural changes led to the site-to-site variations in the erbium local environment and finally to the inhomogeneous broadening of the absorption and emission spectra, with a decrease in both absorption and emission at 1.53 µm.…”

Investigation of Er3+-Doped Phosphate Glass for L+ Band Optical Amplification

“…However, the development of new generation communication demands for broadband emissions at wavelength longer than 1610 nm (L+ band) furtherly [3]. Besides, EDFA is difficult to achieve a flat and efficient gain spectrum in L+ band due to the characteristics of Er 3+ spectrum in silica glass [4].…”

“…However, the development of new generation communication demands for broadband emissions at wavelength longer than 1610 nm (L+ band) furtherly [3]. Besides, EDFA is difficult to achieve a flat and efficient gain spectrum in L+ band due to the characteristics of Er 3+ spectrum in silica glass [4].Instead, among glass hosts, phosphate glass shows many advantages such as mature manufacture technology, high transparency, high doped concentration and large-scale component adjustment [5], [6]. Meanwhile, the spectroscopic properties of Er 3+ in phosphate glass can be widely adjusted by changing the composition [7].…”