Non-Linear Optical Properties of Er(3+)–Yb(3+)-Doped NaGdF(4) Nanostructured Glass–Ceramics

Transparent oxyfluoride glass–ceramics containing NaGdF(4) nanocrystals were prepared by melt-quenching and doped with Er(3+) (0.5 mol%) and different amounts of Yb(3+) (0–2 mol%). The selected dopant concentration the crystallization thermal treatments were chosen to obtain the most efficient visible up-conversion emissions, together with near infrared emissions. The crystal size increased with dopant content and treatment time. NaGdF(4) NCs with a size ranging 9–30 nm were obtained after heat treatments at T(g) + 20–80 °C as confirmed by X-ray diffraction and high-resolution transmission electron microscopy. Energy dispersive X-ray analysis shows the incorporation of rare earth ions into the NaGdF(4) nanocrystals. Near-infrared emission spectra, together with the up-conversion emissions were measured. The optical characterization of the glass–ceramics clearly shows that Er(3+) and Yb(3+) ions are incorporated in the crystalline phase. Moreover, visible up-conversion emissions could be tuned by controlling the nanocrystals size through appropriated heat treatment, making possible a correlation between structural and optical properties.