EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The zinc gallate spinel (ZnGa2O4) has been widely studied for optical applications such as flat panel displays [1], in vivo bio-imaging [2], optoelectronics [3] or anti-counterfeiting applications [4].
For the first time, transparent polycrystalline ZnGa2O4 ceramics were synthesized at the IRCER laboratory, by combining high-energy ball milling, solid-state reaction and spark plasma sintering [5]. They appear transparent in both the visible and near infrared (up to 9 μm) ranges after a post-SPS annealing in air converting the raw semiconductor into an electrical insulator [6]. The maximum of transmittance, reached in the near infrared region at around 2.5 µm, appears with a value of 78 % (for a 1 mm-thick sample) close to the maximum value of transmittance previously measured for single crystals (82 % for a single crystal obtained by Czochralski method [7]).
These transparent ceramics present a classic cubic spinel ZnGa2O4 structure and a dense microstructure (> 99 %) attained without sintering aids, with an average grain size of 600 nm and a random orientation of the crystallites. TEM observations have revealed limited nanometer scale intergranular porosity which does not affect much the transparency. As a proof of success, red long-lasting luminescence arising from the entire sample volume is observed in Cr3+ doped transparent ceramics.
This innovative work is anticipated to further drive the development of transparent ZnGa2O4 ceramics towards a wider range of performing optical applications such as laser emission.
[1] T. Minami et al., J. Lumin. 1997
[2] J. Nie et al., Scientific Reports 2017
[3] E. Chikoidze et al., Crystal Growth & Design 2020
[4] C. Ma et al., Crystal Growth & Design 2020
[5] C. Mével et al., J. Eur. Cer. Soc. 2021 (doi.org/10.1016/j.jeurceramsoc.2021.03.038)
[6] Z. Galazka et al., physica status solidi (a) 2015
[7] Z. Galazka et al., APL Materials 2019