We report on the laser emission of the polycrystalline ceramic obtained from the full and congruent crystallization of the parent glass 1Nd 3+ :75TeO 2 -12.5Bi 2 O 3 -12.5Nb 2 O 5 composition. In particular, the current work underlines the importance of carefully controlling the heat treatment in order to solely crystallize the Bi 0.8 Nb 0.8 Te 2.4 O 8 cubic phase and consequently avoid the formation of the BiNbTe 2 O 8 orthorhombic phase that would be detrimental for optical purpose. The structure, microstructure and photoluminescence properties of the resulting transparent tellurite ceramics are characterized. The continuous-wave and gain-switching laser performances reveal that the emission remains perfectly single transversal mode in the range of pump powers explored. The maximum output power achieved was ~28.5 mW, for a pump power threshold of ~67 mW, and with associated efficiency and slope efficiency of ~22.5% and ~50%, respectively. These data definitely stand among the best results obtained so far for bulk laser tellurite materials and thus demonstrate the potential of such polycrystalline transparent ceramics as optically active materials. Finally, the laser emission characteristics in pulsed regime, at low and high repetition rates, are also provided: more than 6.5 W of peak power at a repetition rate of 728 kHz can be obtained.Tellurite based-glasses present numerous advantages, such as a large transparency window up to ~6 µm, a rather low melting point and excellent third-order non-linear optical properties . These are key parameters which will favour radiative transitions, further permitting laser emission.So far, all the literature dedicated to tellurite bulk lasers is still rather scarce, as it was recently reviewed in 5, and most of all, is limited to bulk glass lasers [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] . The most convenient way to sort all these contributions remains to classify them into three categories, which find their origin from the nature of the rare earth ions employed. Hence, papers dealing with Nd 3+ -doped tellurite glass bulk lasers are the most abundant 6-15 : except one of them which treats the lasing properties at 1.37 μm, they are all related to laser emission around 1064 nm. Then, one can find articles reporting on Ho 3+ -doped, Tm 3+ -doped and also Tm 3+ -Ho 3+ co-doped tellurite glasses for laser emission around 2 μm [16][17][18][19] . Finally, the last category regroups papers focused on Yb 3+ -doped tellurite glasses, emitting in the 0.9-1.1 μm range, like in 20 .Besides that, there is some important and recent research activity concentrated on the study of the optical properties of tellurite glass-ceramics, considered as promising materials for lasers, especially in the near and mid-infrared [21][22][23] . However, to the authors knowledge, laser emission in bulk tellurite glass-ceramics has not yet been reported.On another hand, a very interesting and innovative way of producing some transparent ceramics is the full congruent crystallization met...

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Crystallization from glass can lead to the stabilization of metastable crystalline phases, which offers an interesting way to unveil novel binary or ternary compounds and control the optical properties of obtained glass-ceramics. Here, we report on a crystallization study of the ZrF 4 -TeO 2 glass system and show that under specific synthesis conditions, a previously unreported Zr 10 Te 9 O x F y zirconium oxyfluorotellurite anti-glass phase can be selectively crystallized at the nanometric scale within the 65TeO 2 -35ZrF 4 amorphous matrix. This leads to highly transparent glass-ceramics in both the visible and near infrared ranges. Under longer heattreatment, the stable cubic ZrTe 3 O 8 phase crystallizes in addition to the previous unreported anti-glass phase. The structure, microstructure and optical properties of different 65TeO 2 -35ZrF 4 Tm 3+ -doped glass-ceramics, were investigated in detail by means of X-ray diffraction, 2 scanning and transmission electron microscopies, 19 F, 91 Zr and 125 Te NMR, Raman and photoluminescence spectroscopies.Single crystals of this novel phase could be successfully synthesized from the liquid state and their basic structure has been determined. The crystal chemistry study of several samples evidences various superstructures along a, b and c axes and likely twinning of crystals, suggesting that the novel phase corresponds to a complex series of micro-phases rather than a stoichiometric compound. These results highlight the peculiar disorder-order phenomenon occurring in tellurite materials.