Tuneable Nanostructuring of Highly Transparent Zinc Gallogermanate Glasses and Glass‐Ceramics

Abstract

routes [ 9,10 ] have been recently reported. Technical challenges remain to produce these transparent ceramic materials (complicated and time-consuming procedures to avoid porosity, [ 11 ] limited compositions, segregation of doping agents, etc.). Many of these obstacles can be avoided via the use of glass-ceramic technology. [ 12 ] Therefore, the development of transparent glassceramics is of great interest for many promising optical applications [ 13 ] (solar concentrators, [ 14 ] optical memory media, [ 15 ] telescope mirrors, [ 16 ] amplifi ers, [ 17 ] electrooptical devices [ 18 ] ). Unlike single crystals and polycrystalline sintered ceramics, glass-ceramic materials offer considerable advantages such as a wider range of accessible chemical compositions, fabrication of complex shapes, and largescale production by fast and cost-effi cient glass-forming processes. The absence of porosity, control of the microstructure, and high transparency allow a large variety of optical glass-ceramics to be designed and commercialized.Glass-ceramic technology is generally based on the controlled crystallization of glass. [ 12 ] According to the Rayleigh-GansDebye [ 19 ] and Hendy theories, [ 20 ] the retention of transparency during glass crystallization typically requires a homogeneous distribution of nanoscale crystals in the glass-ceramic material to minimize light scattering. Nucleating agents (such as ZrO 2 and TiO 2 ) are thus often added in the parent glass to produce, by heat treatment, uniformly dispersed nanocrystals. [ 21 ] Nevertheless, a few exceptions with large crystal sizes (β-quartz- [ 16 ] and Na 2 O-CaO-SiO 2 -based glass-ceramics [ 22 ] ) have been reported, and their transparency is directly linked to a very small refractive index difference between the amorphous and crystalline phases. Much attention has been devoted to transparent silicate glass-ceramics, which often present low thermal expansion, thermal stability, and high transparency in both visible and near-infrared ranges. [ 12,16 ] However, silicatebased glass-ceramics present a high phonon energy, which considerably limits their transparency in the infrared range and therefore their applications in this domain. The development of oxyfl uoride [23][24][25][26] and chalcogenide [ 27,28 ] glass-ceramics has extended the transparency toward the infrared range. These materials offer a real alternative allowing access to applications in telecommunications [ 25,26,29 ] (up-conversion devices, waveguide amplifi ers), although their poor chemical durability and complex fabrication (synthesis under a controlled New nanostructured gallogermanate-based glass materials exhibiting high transparency in the visible and infrared regions are fabricated by conventional melt-quenching. These materials can accommodate wide oxide compositions and present nanoscale phase separation, in the form of droplets well separated from the germanate matrix. The size of the nanostructures can be tailored depending on the composition. A single heat treatment then allows select...

Selective doping of Ni2+ in highly transparent glass-ceramics containing nano-spinels ZnGa2O4 and Zn1+x Ga2−2x Ge x O4 for broadband near-infrared fiber amplifiers

“…Additionally, transparent GCs containing Zn 1+ x Ga 2−2 x Ge x O 4 nanocrystals have been recently fabricated 21, 22 . Selective doping of Ni 2+ in Zn 1+ x Ga 2−2 x Ge x O 4 nanocrystals embedded in GCs has been reported; however, the NIR luminescence properties were not clearly identified in this case 22 . To date the authors of this article are not aware of any study relating to the luminescence properties of ZnGa 2 O 4 : Ni 2+ GCs, although GCs containing ZnGa 2 O 4 : Cr 3+ nanocrystals, showing persistent luminescence and temperature sensing properties, have recently been extensively studied 12, 23 .…”

Preparation of dense amorphous Al2O3–ZrO2–Y2O3 by two-step hot pressing

“…5(b), but no lattice fringes were detected and the SAD exhibited faint rings representing the amorphous structure, which proved amorphous structure with phase separation. Phase separation has been also reported in various glasses [1,18], and can be regarded as a transition from amorphous to crystalline phase. It is reasonable that, phase separation occurs with densification during hot pressing, and crystallization emerges once phase separation reaches a critical value.…”

“…Bulk amorphous ceramics, metastable in thermodynamics with short-range ordering and long-range disordering structure, have exhibited interesting and useful properties, such as optical transmittivity [1], dielectricity [2], and semiconductivity [3]. In addition to these functional properties, bulk amorphous oxides were reported to display unusual plastic deformation at moderate temperature.…”

Infrared-transparent glass ceramics: An exploratory study

“…Additionally, nucleating agents may be added to increase bulk crystallization. Phase-separation could also be used deliberately to nucleate crystallization such as has been proposed for oxide systems precipitating cordierite [15], spinel [16,65], fresnoite [66], and fluorides [67]. This method is likely to result in a reasonably low to moderate total crystal fraction, perhaps at b 50 vol.%.…”