Abstract: One bright unusual afterglow has been observed for the first time in the Tm³⁺doped yttrium oxysulfide phosphors synthesized by flux fusion method. When the phosphors are illuminated with UV light (263 nm) or visible light, one bright orange-yellow light can be seen in the darkroom lasting for about one hour. The bright orange-yellow afterglow light is a mixture of six main emissions including 470, 495)516, 545, 588 and 626 nm, which can be attributed to the 4f-4f transition emissions of Tm³⁺in Y₂O₂S. One conclusion can be drawn from the phosphorescence spectra and the afterglow decay curve that the Tm³⁺doped yttrium oxysulfide is a new phosphor with good afterglow properties. The Tm³⁺doped yttrium oxysulfide not only shows afterglow when excited by UV light or visible light, but also create obviously upcon version afterglow emission peak located at 545 nm when it was excited by near infrared light (798 nm). This unusual afterglow phenomenon maybe finds some new application of the long-lasting phosphor and opens a new field of phosphor research.

Key words: Yttrium oxysulfide, Thulium ion, Phosphor material, Upconversion, Afterglow