Cécile Genevois

Long-lasting luminescent ZnGa2O4:Cr3+ transparent glass-ceramics

Highly transparent ZnGa2O4 glass-ceramic materials are elaborated via a simple heat treatment of a 55SiO2–5Na2O–17ZnO–23Ga2O3 parent glass composition, which presents nanoscale spinodal phase separation. This optimized glass-ceramic exhibits 50 wt% of ZnGa2O4 nanocrystals showing a homogeneous and tuneable size. To describe the crystallization process, the glass and glass-ceramic nanostructures are studied by high resolution scanning transmission electron microscopy analysis coupled with in situ high temperature X-ray diffraction and optical measurements. From these results, an original mechanism is proposed to explain the crystallization process occurring in a spinodal phase separated glass. Remarkably, red long-lasting luminescence arising from the entire sample volume is observed in the Cr3+ doped transparent glass-ceramics, opening the route to a wider range of performing applications for this famous zinc gallate persistent phosphor.

Pressureless glass crystallization of transparent yttrium aluminum garnet-based nanoceramics

Transparent crystalline yttrium aluminum garnet (YAG; Y3Al5O12) is a dominant host material used in phosphors, scintillators, and solid state lasers. However, YAG single crystals and transparent ceramics face several technological limitations including complex, time-consuming, and costly synthetic approaches. Here we report facile elaboration of transparent YAG-based ceramics by pressureless nano-crystallization of Y2O3–Al2O3 bulk glasses. The resulting ceramics present a nanostructuration composed of YAG nanocrystals (77 wt%) separated by small Al2O3 crystalline domains (23 wt%). The hardness of these YAG-Al2O3 nanoceramics is 10% higher than that of YAG single crystals. When doped by Ce3+, the YAG-Al2O3 ceramics show a 87.5% quantum efficiency. The combination of these mechanical and optical properties, coupled with their simple, economical, and innovative preparation method, could drive the development of technologically relevant materials with potential applications in wide optical fields such as scintillators, lenses, gem stones, and phosphor converters in high-power white-light LED and laser diode.Transparent YAG crystals are ubiquitous in phosphors, scintillators and lasers, but are complex and costly to make. Here, the authors use a one-step pressureless crystallization of bulk glass to make a transparent biphasic YAG nanoceramic that can be doped for optical applications.

First transparent oxide ion conducting ceramics synthesized by full crystallization from glass

We propose here to use full crystallization from glass as an innovative process to elaborate completely dense transparent oxide conductors. This is demonstrated in the case of new non-stoichiometric Ln1+xSr1−xGa3O7+δ (Ln = Eu, Gd or Tb) melilite ceramics which show bulk conductivity greater than 0.02 S cm−1 at 500 °C. Full crystallization from glass is used here as an alternative method to conventional solid state synthesis in order to elaborate new crystalline phases, i.e. melilite compositions with small rare earth elements, which could not be synthesized by a solid state reaction. The materials are stable up to 800 °C under cycled conductivity measurement conditions. Moreover, as melilite compositions show similar glass and crystalline phase densities, the process can produce fully dense ceramics with thin grain boundaries. Coupled to the limited birefringence of the melilite structure, such materials retain some of the glass transparency during crystallization, leading to the first transparent oxide ion conducting ceramics. This work may open a way to a new class of fully dense, and possibly transparent, solid state electrolytes.