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Photo-Bleaching Eect in Divalent Samarium-Doped Alkaline-Earth Fluorohalides
Weiping Qin,Kiwan Jang,Changdae Kim,Hynngab Cho,Seongtae Park,Yonghwa Chung,Yong-ill Lee 한국물리학회 2004 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.45 No.2
When a CW laser was focused on a sample of divalent samarium-doped alkaline-earth uorohalides (Mg0:5Sr0:5FCl0:5Br0:5 : Sm2+ or BaFCl0:5Br0:5 : Sm2+), the uorescence intensity of Sm2+ ions decreased rapidly. Under irradiation from a 488-nm laser with a power density of 10 W/cm2, the intensity of the 5D0 ! 7F0 (Sm2+) emission decreased as much as 96 % of its initial intensity in 30 minutes (for an X-ray-reduced sample). The so-called photo-bleaching eect can be in uenced by the processes used for sample synthesis, such as the reduction method, the grinding process or X-ray irradiation. The decreasing curves obtained in the photo-bleaching experiments were tted, a biexponential decreasing mode was found, which included a fast decrease (time constant tens of seconds) and a slow decrease (time constant hundreds of seconds). There was no evidence to support the divalent samarium ions being photo-ionized into trivalent samarium ions in the photobleaching process. The most probable mechanism for the photo-bleaching eect involves structural defects and color centers in the samples.