Upconversion Luminescence of Yttrium Oxysulfide Co-doped with Rare Earth Elements

Rare earth ions doped upconversion phosphors have been used in many applications such as infrared laser detecting, anti-counterfeit protection and solid state display. In this study, yttrium oxysulfide (Y2O2S) compounds co-doped with rare earth elements, ytterbium (Yb), and one of the following elements, erbium (Er), thulium (Tm), europium (Eu) or holmium (Ho) were synthesized from doped rare earth oxides using sulfide fusion method with pelletization pretreatment. The doping was carried out with the mixing of yttrium nitrate and rare earth nitrate solutions to obtain homogeneous mixture. The mixed nitrate solution was precipitated with oxalic acid and calcined to doped oxide precursors. Doping of Yb was 2.5 mol% and the other minor doping was 0.10 and 0.25 mol%. The structure and the morphology of the oxysulfide samples were examined by X-ray diffractometer (XRD) and scanning electron microscope (SEM). The upconversion luminescent characteristic of the synthesis phosphors was investigated with spectrofluorometer and IR laser pen. It was found that, under 980 nm excitation radiation, most of the phosphors exhibited green emission band of 541-552 nm wavelengths except the phosphor co-doped with Yb and Tm (Y2O2S:Yb, Tm) exhibited infrared emission band of 787-810 nm wavelength and slight blue color. Yttrium oxysulfide co-doped with Yb and Ho (Y2O2S:Yb, Ho) showed the highest brightness upconversion luminescence. The luminescence efficiency was seen to increase with the increasing of the dopants.