Study on X-ray Absorption Near Edge Structure of Eu Centers in CaAl₂O₄:Eu Phosphor Thin Films Prepared by Pulsed Laser Deposition

X-ray absorption fine structure and photoluminescence studies of CaAl2O4:Eu phosphor thin films prepared by pulse laser deposition have been carried out. The ratio of the Eu2+/Eu3+ =1 content is estimated from the Eu-L-III edge X-ray absorption near-edge structure spectra. It has been found that Eu2+ predominates in the as-deposited films. The ratio of Eu2+ is further increased to 95% by post-annealing only for the films deposited under an almost stoichiometric condition in the laser-induced plasma, which is crystallized as CaAl2O4 and emits blue light due to Eu2+ in CaAl2O4 crystal. For the film deposited under a non-stoichiometric condition, The Eu3+ ratio is increased by post-annealing even in a reducing atmosphere, resulting in poor luminescence intensity and a color shift of Eu2+.