New TeO2-La2O3-In2O3 glasses and properties of Er3+-doped highly transparent glass-ceramics based on the crystallization of “anti-glass” micro-inclusions

New undoped TeO 2 -La 2 O 3 -In 2 O 3 glasses were synthesized by the traditional melt-quenching method. For the specific composition (85.714 TeO 2 - 4.511 In 2 O 3 - 9.775 La 2 O 3 (mol. %)), a series of undoped and Er 3+ -doped glass-ceramic samples were elaborated via a one step heat-treatment conducted at 450°C, for different dwell times. X-ray diffraction data testify to the presence of the unique La-substituted (La,In) 2 Te 6 O 15 (LITO) fluorite-type phase, frequently labelled as “anti-glass” due to the intrinsic disorder of its anionic sub-lattice. The microstructure of these glass-ceramics can be described as crystalline micro-inclusions dispersed in a residual glass phase; the two bearing the same chemical composition, as proved by Energy Dispersive X-ray Spectroscopy analyses. The disordered character of the LITO phase was evidenced by Raman spectroscopy, confirming the adapted “anti-glass” qualification. In addition, both the near infrared and visible macroscopic photoluminescence (PL) properties of Er 3+ ions were recorded for the series of doped samples. Limited spectral variations were observed and a constant lifetime value of the 4 I 13/2 excited state was measured. Fortunately, micro-PL measurements allowed discriminating the emission for Er 3+ ions located inside the micro-inclusions from that of Er 3+ ions situated in the glassy matrix. Finally, after 12h of heat treatment at 450°C and beyond, multiple cracks appear, leading to the degradation of the optical transmission. Surprisingly, adapting the heat treatment to higher temperatures (550°C) leads to reach a higher optical transparency. Such behaviour is explained by the phase transition from the “anti-glass” fluorite-type structure towards the bixbyite-type structure, characterized by some ordering of Te 4+ /In 3+ /La 3+ cations.