Optical properties of tellurite glasses elaborated within the TeO2-Tl2O-Ag2O and TeO2-ZnO-Ag2O ternary systems
Résumé
The optical properties of glasses elaborated within the TeO2-Tl2O-Ag2O and TeO2-ZnO-Ag2O ternary systems are presented. The paper is articulated in two parts. The first part concerns the TeO2-Tl2O-Ag2O system, where the linear refractive index, the absorption coefficient and the optical band gap are measured as a function of the Ag2O content. From ellipsometry measurements, it is noticed that the linear refractive index n0 remains constant up to 5 mol% in AgO0.5 and then slightly increases at higher concentrations (10 mol%). Such evolution of the refractive index was related to the higher electronic polarizability of Ag+ cations compared to that of Te4+ cations, assuming that the electronic polarizability of O2 anions remains constant. The reduction in the optical band gap value is attributed for some part to the higher quantity of non-bridging oxygen atoms induced by the depolymerization of the glass. The third order non-linear optical properties (c and Re(v(3)) values) of these TeO2-Tl2O-Ag2O glasses are then extracted from Z-scan measurements. For glass compositions ranging from 0 to 10 mol% in AgO0.5, the Re(v(3)) value shifts from roughly 60 to more than 80 times that of silica, which testify to the excellent non-linear optical properties of such TeO2-Tl2O glasses containing silver (tellurite glasses possess intrinsic high optical non-linearity). The addition of Tl2O induces the depolymerization of the glass framework but, on the other hand, helps to maintain the amplitude of the optical non-linearity, through the presence of highly polarizable Tl-based entities. Here, below 5 mol% in AgO0.5, it is believed that the activity of the electronic lone pair of Tl+ ions is inhibited. Over this limit, such lone pair would become active, explaining the clear increase of the Re(v(3)) value. Finally, the second part of the paper is devoted to the study of photoluminescence properties of new TeO2-ZnO-Ag2O glasses. Indeed, probably due to the creation of Ag+-Tl+ pairs, there is absolutely no photoluminescence detected for glasses elaborated in the TeO2-Tl2O-Ag2O system. At the opposite, the temperature dependent photoluminescence properties of TeO2-ZnO-Ag2O glasses are reported. Under UV-visible excitation at 385 nm, the samples emit orange light, with a broad emission wavelength peaking around 580-585 nm. The nature of the light emitting centers is discussed and two main hypotheses are debated: the creation of Ag+-Ag+ or Ag+-Zn2+ pairs, with stronger arguments more in favor of the last one.