Effect of Bi3+co-doping on the up-converting and photocatalytic properties of SrGd2O4:Yb3+/Ho3+ phase

In this investigation, samples of strontium-gadolinium-oxide (SrGd2O4) doped with different Yb3+ (2, 4 and 6 at%) and constant Ho3+ (1 at%) contents and co-doped with Bi3+ (2 at%) were prepared using the glycine-assisted sol-gel method. The pure orthorhombic SrGd2O4 phase, space group Pnma, was revealed using X-ray diffraction in all samples. Transmission electron microscopy discovered agglomerated clusters of spherical particles measuring approximately 150 nm in size. The inclusion of Bi3+ ions into the structure influenced the morphology since the formation of larger grains was observed, with sizes reaching up to similar to1.7 mu m. The uniform distribution of all constitutive elements was confirmed by energy-dispersive X-ray spectroscopy. In all samples, up-conversion emission spectra revealed two dominant green (540 and 550 nm), red (671 nm), and infrared (758 nm) emission lines, due to the F-5(4),S-5(2)-> I-5(8), F-5(5)-> I-5(8,) and F-5(4),S-5(2) -> I-5(7) transitions, respectively. The sample co-doped with Bi3+ showed the most intense photoluminescent emissions, shorter luminescence decay, and the highest quantum yield. Additionally, a significant decrease in the energy band gap value was detected using diffuse reflectance spectroscopy for this sample. Methylene blue was used as a test pollutant to investigate its photocatalytic efficiency under simulated sunlight irradiation. The results show that Bi3+ co-doping deteriorates the photocatalytic efficiency of the SrGd2O4:Yb3+/Ho3+ phase by reducing hydroxyl radical formation.

Automated summary

In this study, strontium-gadolinium-oxide (SrGd2O4) samples doped with different Yb3+ concentrations and co-doped with Bi3+ were prepared. The inclusion of Bi3+ improved the photoluminescent properties, but decreased the photocatalytic efficiency of the samples.