Eu³⁺ luminescence, Ce⁴⁺→Eu³⁺ energy transfer, and white-red light generation in Sr₂CeO₄

Abstract

Photoluminescence studies on pure and Eu³⁺-doped Sr₂CeO₄ compounds are presented. The pure compound displays a broad band in its emission spectrum when excited with 254 nm, which peaks at 467 nm and is due to the energy transfer between the molecular orbital of the ligand and charge transfer state of the Ce⁴⁺ ion. The excitation spectrum shows a broad band which peaks at 300 nm. From the spectral properties, it is established that Sr₂CeO₄ has good potential for application as a blue phosphor in low pressure mercury vapor lamps and in TV tubes. The Eu³⁺ spectral features, when doped at the Ce⁴⁺ site either singly or along with La³⁺, have been studied and compared with the results obtained by doping the Eu³⁺ ion at the Sr²⁺ site. At low Eu³⁺ concentrations (≤ 4 mol %), the observed excitation and emission spectra reveal excellent energy transfer between Ce⁴⁺ and Eu³⁺. This energy transfer generates white light with a color tuning from blue-white to red-white, the tuning being dependent on the Eu³⁺ concentration. At high Eu³⁺ concentrations (5-15 mol %), these compounds exhibit efficient red emission under 254, 355, and 466 nm excitations. The observed luminescence properties of these compounds are similar to those of the known Y₂O₃:Eu³⁺ red phosphor. The emission intensity of Sr₂CeO₄:Eu (>0.05) under 466 nm excitation is twice that of Y₂O₃:Eu. The results establish that the compound Sr₂CeO₄ is an efficient "single host lattice" for the generation of white and red lights under UV irradiation.