Near-infrared rechargeable glass-based composites for green persistent luminescence

Abstract

<p>The fabrication of Yb<sup>3+</sup>, Tm<sup>3+</sup> co-doped oxyfluorophosphate glass-based composites, with green persistent luminescence after being charged with near-infrared light, is demonstrated. The mechanism responsible for the green afterglow after near-infrared illumination is unveiled. The composite is prepared using a modified melting process to limit the evaporation of fluorine during melting. Intense (blue and ultraviolet) up-conversion emission is obtained by optimizing the Yb<sub>2</sub>O<sub>3</sub> and Tm<sub>2</sub>O<sub>3</sub> concentrations. A heat treatment promotes volume precipitation of Yb<sup>3+</sup>, Tm<sup>3+</sup> co-doped CaF<sub>2</sub> crystals. Although the intensity of the blue up-conversion emission from the Tm<sup>3+</sup> <sup>1</sup>G<sub>4</sub> level is lower in the highly Yb<sup>3+</sup>-concentrated glass-ceramic due to reverse energy transfer from Tm<sup>3+</sup> to Yb<sup>3+</sup>, the heat treatment leads to an increase of the intensity of the emissions around 346 nm, 361 nm nm and 450 nm coming from the Tm<sup>3+</sup> <sup>1</sup>I<sub>6</sub> and <sup>1</sup>D<sub>2</sub> levels. By combining the Yb<sup>3+</sup> and Tm<sup>3+</sup> ions with SrAl<sub>2</sub>O<sub>4</sub>:Eu<sup>2+</sup>,Dy<sup>3+</sup>crystals, green afterglow can be obtained after charging with near-infrared light.</p>