Thermal and structural analysis of germanate glass and thin films co-doped with silver nanoparticles and rare earth ions with insights from visible and Raman spectroscopy

This paper reports on the thermal and optical properties of germanate glasses GeO2-PbO co-doped with silver nanoparticles and rare earth ions (Tm3+, Er3+ and Yb3+) with a focus on the thermal diffusivity (D). The presence of rare earth ions and nanoparticles is evidenced by absorption spectra and TEM images, respectively. Additionally, a structural comparison between thin films and bulk glass with the same nominal composition is given. It is found that D increases up to 20% in samples where nanoparticles are present, although their quantity corresponds only to a volume fraction of 1.7%. Therefore, such enhancement could be associated with the nanoparticles. Nevertheless, a Raman analysis revealed a structural change after the thermal treatment used for the nucleation of the nanoparticles. A decrease in the intensity of the band at 534 cm−1 in the Raman spectra is interpreted as the disruption of the 3-membered rings of the GeO4 tetrahedra. The Raman analysis also revealed the formation of small crystals of α-GeO2 type quartz and the adsorption of carbon dioxide on the surface of the silver nanoparticles inserted in the germanate thin film.