Optical properties of Bi and energy transfer from Bi to Tb in MgAl2O4 phosphor

A simple combustion method was used to prepare Bi doped MgAl2O4 nanocrystals using metal nitrates as precursors and urea as fuel. The samples were characterized by x-ray diffraction, diffuse reflectance spectroscopy, scanning and transmission electron microscopy, and photoluminescence spectroscopy. Blue emission from Bi doped MgAl2O4 was found to occur in the wavelength region corresponding to the well known host independent weak f-f excitation peaks of Tb. Therefore, in addition to being used as an activator for emission of blue light, the possibility of using Bi3+ ions as a sensitizer for Tb3+ ions emitting green light was investigated. Although Tb can generally be excited efficiently using its strong f-d transitions, the possibility of exciting it through energy transfer from Bi to the normally weak f-f transitions is important, since the excitation wavelength of Bi (335 nm) is longer and more accessible than the f-d transition wavelength of Tb in MgAl2O4 (227 nm). The results suggest that Bi offers an attractive alternative to Ce which is often used to sensitize Tb in many other hosts.