Effect of Rare-Earth Doping on Free-Volume Nanostructure of Ga-Codoped Glassy (As/Sb)2Se3

Shpotyuk Nanoscale Research Letters (2017) 12:191 DOI 10.1186/s11671-017-1959-2 NANO EXPRESS Open Access Effect of Rare-Earth Doping on Free-Volume Nanostructure of Ga-Codoped Glassy (As/Sb)2Se3 Yaroslav Shpotyuk1,2,3 Abstract Subsequent stages of atomic-deficient nanostructurization finalizing rare-earth functionality under Pr3+-doping in Ga2(As0.28Sb0.12Se0.60)98 glass are studied employing method of positron annihilation lifetime spectroscopy. Genesis of free-volume positron trapping sites, composed of atomic-accessible geometrical holes (void cores) arrested by surrounding atomic-inaccessible Se-based bond-free solid angles (void shells), are disclosed for parent As2Se3, Ga-codoped Ga2(As0.40Se0.60)98, as well as Ga-codoped and Sb-modified Ga2(As0.28Sb0.12Se0.60)98 glasses. The finalizing nanostructurization due to Pr3+-doping (500 wppm) in glassy Ga2(As0.28Sb0.12Se0.60)98 is explained in terms of competitive contribution of changed occupancy sites available for both rare-earth ions and positrons. Keywords: Rare-earth doping, Positron annihilation lifetime spectroscopy, Atomic-deficient nanostructurization, Sb-modification Background Glassy-like compounds of chalcogens (i.e., S, Se, Te) with some elements from IV-V groups of the periodic table (typically Ge, As, Sb, Bi), also known as chalcogenide glasses (ChG) [1, 2], compose a promising class of functional media for modern optoelectronics and IR optics [2–5]. Because of wide transparency window up to 20 μm accompanied by low phonon absorption, good chemical durability, and glass-forming ability, the ChG provide an excellent platform for modern fiber-optic amplifiers and mid-IR lasers [4, 5]. To be functional in many of such active photonic applications, the ChG should successfully operate as high-efficient host matrices for embedded guest activators in the form of rare-earth (RE) ions (such as Dy3+, Er3+, Pr3+) [5]. This can be achieved by useful modification of ChG at a nanoscale level due to nanostructurization, the process stretching over both atomic-specific and atomic-deficient (free-volume) Correspondence: 1 Department of Sensor and Semiconductor Electronics, Ivan Franko National University of Lviv, 107, Tarnavskogo str., Lviv 79017, Ukraine 2 Center for Innovation and Transfer of Natural Sciences and Engineering Knowledge, Faculty of Mathematics and Natural Sciences, University of Rzeszow, 1, Pigonia str., 35-959 Rzeszow, Poland Full list of author information is available at the end of the article structural arrangement at a nanospace. From most generalized viewpoint, such nanostructurization route includes subsequent stages of glass structure modification to meet requirements of effective charge compensator, devitrification inhibitor, and low phonon energy RE hosting site. In this work, at the example of glassy arsenic selenide g-As2Se3, one of most popular ChG for waveguide optical sensing, IR lasers and telecommunication [6], we shall trace evolution of atomic-deficient glass structure during these stages (atomic-deficient or free-volume nanostructurization), employing the method of positron annihilation lifetime (PAL) spectroscopy, one of most efficient tool to study free-volume elements (FVE) in different solids (like vacancies, vacancy-type clusters, voids, pores, intrinsic cracks) at atomistic and sub-atomistic length-scales [7–10]. Methods Nanostructurization Technologies in Chalcogenide Photonics Nanostructurization is aimed to ensure high-efficient chemical environment in which RE ions reside homogeneously without clustering, crystallization, and phase separation. © The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Shpotyuk Nanoscale Research Letters (2017) 12:191 The first stage in this row of nanostructurization technologies belongs just to glass preparation owing to conventional melt-quenching route, which is described in details elsewhere [11–13]. For this research, the ChG of stoichiometric g-As2Se3 (i.e., As40Se60) were prepared from high-purity elemental precursors, e.g., As (5 N) and Se (5 N), these ingredients being specially purified by distillation with low evaporation rate to remove impurities (such as O, C, H2O, and SiO2). Appropriate amounts of ingredients with total weight close to 30 g were put into silica tube of 10 mm diameter. Then, the ampoules were sealed under a vacuum, heated up to 900 °C with 2 °C/min rate and stayed at this temperature for 10 h in a rocking furnace with further quenching into water from 700 °C. To remove mechanical strains appeared during rapid quenching, the alloys were annealed for 6 h at 10 °C less than the glass transition temperature. Then, the obtained rods were cut into ~2-mm disks and polished. The second stage in nanostructurization is to prepare the ChG with locally disturbed covalent glass-forming network possessing effective charge-compensation properties for potential RE dopants. In respect to g-As2Se3-based media, this can be achieved due to doping with small amount of Ga (or alternatively, In), allowing stabilization of optimal compound with maximal Ga content, but still in glassy state [14–18]. The procedure of such Ga codoping is realized via the same melt-quenching technological route as for gAs2Se3 using high-purity elemental Ga (7 N purity). As was shown in our preliminary research [13, 17], the Ga-codoped g-As2Se3 is optimized under chemical composition of g-Ga2(As0.40Se0.60)98. The third stage in nanostructurization is to modify the Ga-codoped ChG against possible parasitic devitrification (phase separation, crystallite nucleation, extraction, and growth), which can be activated in ChG under further RE doping. One of the best resolutions is transferring to partial As to Sb replacement in g-As-Se, allowing optimal Ga-codoped g-Ga2(As0.28Sb0.12Se0.60)98 prepared by melt-quenching route like g-As2Se3 or gGa2(As0.40Se0.60)98 [19]. The fourth stage in nanostructurization is just finalizing RE-doping technology, i.e., the process, which is also realized under conventional melt-quenching using some precursors for RE dotation, such as Pr2Se3 (3 N purity). Within row of examined glassy arsenic selenides g-As-Se, this stage results in optimal g-Ga2(As0.28Sb0.12Se0.60)98 affected by RE doping with 500 wppm of Pr3+. PAL Spectroscopy as Instrumentation Tool Tracing Atomic-Deficient Nanostructurization The PAL measurements were performed using a fast-fast coincidence system of 230 ps resolution based on two Photonis XP2020/Q photomultiplier tubes coupled to BaF2 scintillator 25.4A10/2M-Q-BaF-X-N detectors Page 2 of 7 (Scionix, Bunnik, Holland) and ORTEC® electro (...truncated)