Microfluorescence Analysis of Nanostructuring Inhomogeneity in Optical Fibers with Embedded Gallium Oxide Nanocrystals

Abstract

A spectroscopic protocol is proposed to implement confocal microfluorescence imaging to the analysis of microinhomogeneity in the nanocrystallization of the core of fibers belonging to a new kind of broadband fiber amplifier based on glass with embedded nanocrystals. Nanocrystallization, crucial for achieving an adequate light emission efficiency of transition metal ions in these materials, has to be as homogeneous as possible in the fiber to assure optical amplification. This requirement calls for a sensitive method for monitoring nanostructuring in oxide glasses. Here we show that mapping microfluorescence excited at 633 nm by a He-Ne laser may give a useful tool in this regard, thanks to quasi-resonant excitation of coordination defects typical of germanosilicate materials, such as nonbridging oxygens and charged Ge-O-Ge sites, whose fluorescence are shown to undergo spectral modifications when nanocrystals form into the glass. The method has been positively checked on prototypes of optical fibers-preventively characterized by means of scanning electron microscopy and energy dispersive spectroscopy-fabricated from preforms of Ni-doped Li 2 O-Na 2 OSb 2 O 3 -Ga 2 O 3 -GeO 2 -SiO 2 glass in silica cladding and subjected to heat treatment to activate gallium oxide nanocrystal growth. The method indeed enables not only the mapping of the crystallization degree but also the identification of drawing-induced defects in the fiber cladding.

Native amorphous nanoheterogeneity in gallium germanosilicates as a tool for driving Ga2O3nanocrystal formation in glass for optical devices

“…As shown in Fig. 9, the typical red-light emission of NBO sites in oxides [33][34][35][36][37] is much higher in asquenched glass than in treated samples, except when the treatment temperature approaches the crystallization point. The high NBO PL in as-quenched glass suggests a structure with a large fraction of Ga ions in sites coordinated with NBOs.…”

Nucleation-controlled vacancy formation in light-emitting wide-band-gap oxide nanocrystals in glass

“…Energy-dispersive X-ray fluorescence microanalysis (Bruker, Artax 200) was carried out on as-quenched glass, providing evidence of the uniform dispersion of the main elements (Ga, Ge, Si), consistent with analogous results obtained using a scanning electron microscope equipped with a microprobe (Edax, Genesis 4000 XMS) on similar glass prepared by an identical route for the production of optical fibre prototypes. 23 The as-quenched glass was cut with a low-speed diamond saw or grinding disc using water as a coolant. Samples were then polished for optical measurements or ground for XRD or TEM analysis.…”

Formation and applications of nanoparticles in silica optical fibers

“…In the case of a nickel-and antimony-codoped gallo-germano-silicate core rod, the formation of nanoparticles is obtained by applying a heat treatment for 1.5 h at 840 °C [42].According to studies on the bulk material, phases are precipitated as LiGa 5 O 8 and γ-Ga 2 O 3 , with an average size of about 6 ± 2 nm. One note that in this case, crystallites preferably formed at the interface between the core and the silica cladding: it shows that the post-heat treatment approach does not always provide a beneficial transformation to the bulk of the core volume.…”