Relocalization of Ce3+ 5d electrons from host conduction band

Single crystal fibers of Ce3+ doped SrAl2O4 and CaAl4O7 were prepared through the laser heated pedestal growth method. Sites dependent Ce3+ emissions were found at 385 nm (427 nm) and 420 nm (325 nm) in SrAl2O4 and CaAl4O7 hosts, respectively. The Ce3+ emissions at 385 nm and 420 nm in the two hosts exhibited strong afterglows. They could persist for more than 10 h. The long persistence and sites dependence of Ce3+ emissions were originated from charge compensation of doping Ce3+ into divalent cation sites. The lifetimes of Ce3+ emissions in both hosts were found to depend on the laser excitation wavelengths. With 266 nm laser excitation, Ce3+ 5d electrons were delocalized into the host's conduction band, resulting in a prolonged decay time. The 355 nm laser excitation did not delocalize the 5d electrons and hence the measured lifetimes were the intrinsic Ce3+ emission lifetimes that were 17 and 35.5 ns in SrAl2O4 and CaAl4O7 hosts, respectively. The prolonged Ce3+ emission lifetime on 266 nm laser excitation was because of the relocalization of the 5d electrons from the host conduction band. The lifetimes of Ce3+ 5d electrons within the conduction band were found to be 34 and 44 ns in SrAl2O4 and CaAl4O7 hosts, respectively.