Enhancement of yellow emission and afterglow in Sr 3 SiO 5 : Eu 2+ , Dy 3+ by adding alkaline earth metal fluorides

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guo Xiao,a) Xiaoliang Yang, and Jian Wen Ding Department of Physics, Institute for Nanophysics and Rare-earth Luminescence, and Key Laboratory of Low Dimensional Materials & Application Technology, Xiangtan University, Xiangtan, Hunan 411105, People’s Republic of China (Received 22 March 2012; accepted 24 July 2012)

Yellow-emitting long afterglow phosphors Sr3 xSiO5, xMF2: Eu21, Dy31 (0 # x # 0.15, M: Ba, Sr, Ca) have been prepared by high-temperature solid-state reaction method followed with rapid cooling process. Photoluminescence measurement reveals that the main emission of the phosphors locates at 575 nm, corresponding to the 4f 65d1–4f 7 transition of Eu21. The introduction of alkaline earth metal fluoride effectively enhances the luminescence intensity and prolongs the afterglow time. Especially, the afterglow of the Sr2.95SiO5, 0.05BaF2: Eu21, Dy31 phosphor can last for 12 h. Thermal luminescence measurement shows that the trap density of Sr3SiO5: Eu21, Dy31 phosphor can be adjusted by adding different alkaline earth metal fluorides, which offers a feasible way to improve the afterglow properties of silicate phosphors.

I. INTRODUCTION

Long-lasting phosphors have experienced more than 100 years of development, from sulfides to aluminates and then to silicates. As novel functional materials, the rare earth-doped long afterglow phosphors attract increasing attention in recent years for their wide applications in emergency light, traffic signs, multidimensional optical memory, luminous paint, etc. Due to their excellent performance in luminescence intensity, afterglow time, and chemical stability, many blue and green afterglow phosphors of silicates and aluminates are commercially available, while the red and yellow long-lasting phosphors are still in a relatively backward situation. Especially, the present yellow afterglow phosphors are far away from practical application for their weak luminescence intensity, short afterglow duration time, and bad chemical stability.1–7 Recently, Sun et al.8 reported a new yellow-emitting phosphor Sr3SiO5: Eu21, Dy31 with broadband emission peaked at 570 nm, of which the afterglow can be observed for several hours in darkness after removal of the excitation source. Unfortunately, the brightness and persistent time cannot satisfy the practical application yet. In this work, the luminescence intensity and afterglow time of the Sr3SiO5: Eu21, Dy31 phosphor are effectively improved with introduction of alkaline earth metal fluorides. It shows that the density of trap at different depth for the a)

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.291 J. Mater. Res., Vol. 27, No. 19, Oct 14, 2012

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phosphor can be adjusted, making the afterglow properties tunable. II. EXPERIMENTAL

All the powder samples were prepared by hightemperature solid-state reaction. Analytical reagents SrCO3, SiO2, CaF2, SrF2, BaF2, Eu2O3, and Dy2O3 were used as raw materials. The nominal concentrations of Eu21