Conjugation of TEM-EDX and optical spectroscopy tools for the localization of Yb3+, Er3+ and Co2+ dopants in laser glass ceramics composed of MgAl2O4 spinel nano-crystals embedded in SiO2 glass

The main goal of this work is to conjugate two independent techniques of TEM-EDX and optical spectroscopy, which is rare, for the localization of Yb3+ and Er3+ rare earth ions and Co2+ transition metal ions as dopants in a compact self-Q-switched microchip laser glass ceramic composed of MgAl2O4 spinel nano-crystals of 10-20 nm size embedded in SiO2 glass. The use of the TEM-EDX technique associated with both the elemental mapping of each dopant and the direct visualization of the heavier rare earth ions has led to the result that Er3+ and Yb3+ rare earth ions are preferentially located in the spinel nano-crystals. Regarding the low Co2+ concentration this technique was not accurate enough for characterization and finally we have used absorption spectroscopy to probe the main presence of Co2+ ions in the spinel nano-crystals. The use of Yb3+ ions as structural probes allows the identification of the 0-phonon broad line at 977 nm as both that of the disordered glass and that of the spinel inverted phases. A new Yb3+ radiationless center has been pointed out by the presence of a strong absorption line at 970 nm which has been assigned to the strongly perturbed area of the spinel nano-crystallite surface. This dopant characterization is worthwhile to be shown as a special case where characterization of rare earth and transition metal ions needs the use of both TEM and spectroscopic techniques.