Optically active SrGd2O4 phase: Yb3+/Ho3+ and Yb3+/Tm3+ co-doping

Abstract

Optically active materials have a wide range of applications. The phenomenon of light conversion includes two main types: up-conversion, which is the ability of convertion lower energy photons into the ones with the higher energy, and down-conversion, which is vice versa. Orthorhorhombic SrGd2O4 doped with rare earth elements is established to have promising optical characteristics, but rarely explored until nowadays as up-converting material. Due to the phonon energy of around 475 cm-1, which is lower than in many other compounds commonly used hosts, this one has a great perspective as an optically active material. Here, for the first time two combinations of rare earth dopant ions, Yb3+/Ho3+ and Yb3+/Tm3+, with different mutual ratios were chosen as pairs for inducing up-conversion. Sol-gel assisted combustion synthesis, which comprises citric acid as chelator and glycine as fuel, was used to obtain powdered samples that are subsequently thermally treated for 3.5 h at 1100°C. X-ray powder diffraction analysis (XRPD) was performed to determine crystal structure. Morphology characteristics were observed by scanning and transmission electron microscopy (SEM/TEM). Photoluminescent up-converting properties were measured in function of laser power (976 nm) in order to define optimal doping concentration and upconversion mechanism.