Erbium environment on Er-doped silica and alumino-silicate glass films: An EXAFS study
Introduction
The increasing demand for telecommunications and broadband services can be achieved by using optical data transfer through optical fibers [1], for which the large bandwidth of optical communication enables the development of very high rate information transmission systems. While optical fibers and fiber amplifiers are usually used for long-distance communications, the development of the optical networks requires systems able to process optical signal on a local scale. The synthesis of new materials is therefore required for the development of planar integrated optics devices. In this framework, erbium-doped glasses are interesting materials due to the optical transition at 1.54 μm shown by the Er3+ ions [2], [3]: this radiative transition falls in the range of minimum transmission loss for silica-based optical fibers [4]. The performances of erbium-doped glass materials crucially depend on both the host matrix and the doping process, since they determine the atomic scale structure around the Er3+ ions on which the characteristics of the optical transition at 1.54 μm depend. Moreover, the contemporary presence in the glass matrix of other metallic species (such us gold or silver) in the form of dimers, trimers and/or nanoparticles can enhance the out-of-resonance Er3+ absorption cross-section, thus increasing the radiative decay emission at 1.54 μm [5], [6], [7].
In literature, several papers deal with the study of the erbium environment in different Er-doped matrices, such us silica (synthesized by means of ion implantation, sol–gel routes, chemical vapour deposition (PVD) techniques, see for instance [8], [9], [10], [11]), silicate glasses (obtained by ion implantation, melt, sol–gel, or ion exchange [8], [11], [12], [13], [14], [15]), phosphate glasses (obtained by melt [16]), zinc and lead chloro-tellurite glasses (obtained by melt [17]).
In this paper, Er:SiO2 thin films on silica were prepared by radiofrequency magnetron co-sputtering deposition followed by a suitable thermal treatment to optically activate the rare-earth. Moreover, Er:SiO2–Al2O3–Na2O silicate glass films were prepared by sol–gel route and subsequently doped with silver by Ag+ ↔ Na+ field-assisted solid-state ion exchange (FASSIE) [18]. The extended X-ray absorption fine structure (EXAFS) spectroscopy, performed at the Er LIII-edge, allowed to determine the local structure around the Er ions as a function of the synthesis route and to evidence possible structural modifications of the Er environment depending on the post-synthesis treatments.
Section snippets
Experimental
Erbium-doped silica films were synthesized by simultaneous deposition of silica and erbia on fused silica slides 25 × 75 mm2, 1 mm thick, in a radiofrequency magnetron sputtering deposition apparatus. Co-depositions were performed by means of two 13.56 MHz radiofrequency sources acting in a neutral atmosphere (pure Ar), at a pressure of 0.40 Pa. The rf-power to the 2 in. diameter targets was fixed at 150 and 12 W for silica and erbia, respectively. The 75 (or 225) min co-deposition of silica and erbia
Results and discussion
In Table 1 the synthesis parameter used are reported for the two series of samples. The values of the Er concentration (not higher than 1.4 × 1020 atoms/cm3) are below the solubility limit of Er in glass: this allows to avoid concentration quenching effects for the photoluminescence signal [8], [9]. The total amount of Er was measured by Rutherford backscattering spectrometry (RBS); in all samples the rare-earth showed an almost uniform in-depth distribution. In the samples deposited by sputtering
Conclusion
Er:glass systems, synthesized with different methods and showing 1.54 μm photoluminescence emission were investigated with EXAFS to obtain information about the Er environment. In the silica samples deposited by sputtering, the Er coordinates about 4.5 O atoms at a short distance (R = 2.07–2.13 Å): this site is similar to the one observed in Er-doped glasses when the preparation conditions are far from the thermodynamical equilibrium. In alumino-silicate samples produced by sol–gel route, the first
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Cited by (6)
Structure analysis of bimetallic Co-Au nanoparticles formed by sequential ion implantation
2016, Applied Surface ScienceCitation Excerpt :The atomic force microscopy and extended X-ray absorption fine structure (EXAFS) spectroscopy have been explored to investigate the composite materials. X-Ray absorption fine structure (XAFS) spectroscopy has experienced a rapid development in the last four decades and has provided a powerful tool for structural analysis of particles of nanometer dimensions [9–11]. Furthermore, it can give unique information about the local atomic environment of the center atom, such as coordination number (N), interatomic distance (R).
Unexpected behavior of the 1.54 μm luminescence in Er-doped silica films
2014, Journal of Non-Crystalline SolidsCitation Excerpt :The photoluminescence properties of Er in silica were always thought to depend mainly on the atomic local structure around the Er ions. In spite of the existence of several published papers investigating the structure of the first neighboring atoms around Er in Er:SiO2 systems prepared by different synthesis routes (see for instance [4–10]), an exhaustive description of the correlation between the local structure of erbium ions and their photoluminescence properties is far from being completely accepted. Actually, the difficult to investigate the structure of the surrounding atoms behind the first coordination shell around Er prevents the possibility to find the characteristic distance (if any) of the neighboring atoms able to influence the luminescence emission of erbium, in particular the 1.54 μm wavelength radiation.
Temperature-driven local rearrangement in the Er environment of Er-doped silica glass films prepared by rf-cosputtering deposition
2012, Thin Solid FilmsCitation Excerpt :Indeed, this fact further indicates how the co-deposition-annealing methodology may be potentially suitable for controlling the material structure and composition, and so its optical properties. The complexity of the system structuring has been observed for the system at issue in using synchrotron radiation techniques, which investigated on the local Er environment within different silicate glass matrices [29,30]. Erbium dopant atoms in glass were observed to be structured in sites varying from an Er2O3-like one (6 O atoms at a distance of about 2.27 Å) toward a less populated state, with about 3 O atoms at shorter distances [31].
Photoluminescence optimization of Er-doped SiO<inf>2</inf> films synthesized by radiofrequency magnetron sputtering with energetic treatments during and after deposition
2011, Thin Solid FilmsCitation Excerpt :Being well-known that the local order around the erbium ions influences the optical emission properties (in primis number and distance of the first-neighbor oxygen atoms; probably also the disposition of the second- and third-shell atoms) [10,21,29–33], another possible explanation of the PL intensity behavior in Fig. 4(a) is that the Er3+ environment could be slightly different from sample to sample. A preliminary investigation of the Er first-shell environment performed with EXAFS [34] on two of our Er-doped silica films showed that, in spite of the strong difference between the PL signal intensity before and after the thermal activation, the similarity between the Er first-shell environment in the samples suggests the possibility that important mechanisms of non-radiative emission take place in the as-deposited samples (much probably related to the presence of defects in the as-deposited silica structure), or that the PL signal could be strongly influenced by Er site difference over the first-shell. The samples in which the energy was delivered to the growing film contemporaneously by heating and by ion bombardment show high values of the 1.54 μm PL signal also by using strong bias negative voltage.
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