Enhancement of up-conversion luminescent characteristics of Yb3+/Ho3+ co-doped Bi3+ based SrGd2O4 nanoparticles

In this investigation, samples of SrGd2O4 doped with different Yb3+ (2, 4, 6 at.%) ions and constant Ho3+ (1 at.%) and Bi3+ (2 at.%) concentrations were prepared. The sol-gel method with glycine as a fuel and citric acid as a chelator was chosen for sample preparation. All samples were heated in the furnace for 1.5 h at 500 °C and then thermally treated for 2.5 h at 1000 °C. The pure orthorhombic lattice of SrGd2O4, space group Pnma, was revealed by X-ray diffraction (XRD) (JCPDS Card No.:01-072-6387). Transmission electron microscopy (TEM) discovered agglomerated clusters of spherical particles measuring around 150 nm in size. Including Bi3+ ions into the structure influenced the morphology of the sample showing fine packing of pyramidal-shaped nanoparticles. The uniform distribution of constitutive elements in the samples was confirmed by energy dispersive spectroscopy (EDS). Up-conversion emission properties were evaluated from photoluminescent emission spectra and intensity dependence on excitation power after excitation at 976 nm. Dominant green (550 nm), red (671 nm), and infrared (758 nm) 5F4, 5S2 → 5I8, 5F5 → 5I8, 5F4, 5S2 → 5I7 transition emissions, respectively, are detected in all samples. The sample co-doped with Bi3+ showed the most intense photoluminescent emission