A new rare earth complex Tb(BSA)4 was synthesized and studied. Pure green and narrow band emission was generated from the device with structure ITO/PVK:Tb(BSA)4 /Alq3 /LiF/Al, where PVK was used to improve the film-formation and hole-transport property of the Tb(BSA)4. The absorption mechanism, and the photoluminescence and electroluminescence mechanisms are discussed. It has been proved that there exists energy transfer from PVK to Tb(BSA)4 and the mechanisms of photoluminescence and electroluminescence are different. The effect of different ratios of PVK on the device characteristics is also studied.