Long-lasting phosphorescent （LLP） materials have attracted considerable attention since green and blue emitting persis- tent Eu2＋ doped alkaline earth phosphors were reported in the mid-1990s [1-3]. Over the past few decades, a consid- erable effort has been made to design novel LLP materials for a wide range of applications such as emergency lighting, interior decoration, road signs, and in vivo bioimaging [4-6]. For these applications, long persistence times are often desir- able. Two types of active center involved are： emitters and traps in LLP phosphors. Emitters are capable of emitting ra- diation after being excited, and their color is determined by the emission wavelength of the LLP phosphor. Traps states usually do not emit radiation, but store the excitation energy later releasing it to the emitters under thermal disturbance. Thus, traps play an important role in photo-energy storage of LLP phosphors. The trap type and trap distribution are gen- erally associated with lattice defects and/or co-dopants. The overall nature of the trap states determines the persistence in- tensity and time. Thus, design of LLP phosphors focuses on generating suitable trap levels and trap densities.
Yan CongYangYang HeDaPeng DongLiMei WangZhen ZhangZiWen WangBin Dong
