Relocalization of Ce 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.