Luminescence properties of Eu³⁺ and Ti^IV/Zr^IV doped yttrium oxysulfides (Y₂O₂S:Eu³⁺,Ti^IV/Zr^IV)

The red emitting Y₂O₂S:Eu³⁺,Ti^IV (or Zr^IV, x_Eu: 0.01, x_Ti/Zr: 0.003/0.015/0.03) materials were prepared with a flux method. According to X-ray powder diffraction, the materials have the hexagonal crystal structure. The UV excited (λ_exc: 250 nm) emission maximum was observed at 628 nm due to the ⁵D₀→⁷F₂ transition of Eu³⁺. The excitation spectra (λ_em: 628 nm) consist of broad bands centered at 240 and 320 nm due to the charge transfer transitions O²⁻→Eu³⁺ and S²⁻→Eu³⁺, respectively. Red persistent luminescence was observed with a maximum at 628 nm, as well. Persistent luminescence was the strongest with the Ti^IV co-doping though the intensity of persistent luminescence decreased with the increasing amount of both the Ti^IV and Zr^IV co-dopants. The thermoluminescence (TL) glow curves of the Y₂O₂S:Eu³⁺,Ti^IV materials consist of bands at ca. 110 and 200 °C. In Y₂O₂S:Eu³⁺,Zr^IV, similar bands are observed at lower temperatures viz. at ca. 100 and 180 °C. TL weakens when the amount of co-dopants is increased. The Ti^IV co-doped materials have stronger TL than the Zr^IV co-doped materials. The deconvolution of TL glow curves revealed three distinct traps with depths ranging from 0.6 to 1.0 eV.