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Dissertation Defense

Site Specific Relaxation Dynamics of Fluorescent Centers  
Guest Speaker
Mayuri Perera  
Guest Affiliation
UGA Physics and Astronomy  
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Prof. Uwe Happek  
Friday, June 24, 2016 1:00 pm - 2:00 pm  
Room 204B, Physics Building  

The relaxation dynamics of Ce3+ ions in phosphor materials relevant to solid state lighting has been investigated. Of particular interest was the temperature dependence of the emission efficiency in heavily doped yttrium aluminum garnet (YAG) materials, which show a decreased quenching temperature compared to low concentration samples. Using site se- lective spectroscopy, we demonstrate that the lowering of the quenching temperature in high concentration samples is due to cerium ions in distorted sites. Our results can be generalized that high concentrations of cerium and/or an addition of optically mute rare earth ions to broaden the emission spectrum will lead to a lowered quenching temperature. We studied also Na2Gd2O(BO3)2 doped with Ce3+, a system where Ce3+ ions occupy two distinct lattice sites. In this case it is shown that the luminescence quenching is due to photoionization.

Index words: Lifetime Measurements, Luminescencence, Level Crossing, Rare Earth Ions, Photoionization