Influence of annealing temperature on persistent luminescence in BaAl₂O₄:Eu²⁺/Eu³⁺ nanocrystals and its application for latent fingerprint detection

Abstract

The luminescent properties of europium (Eu) doped BaAl₂O₄ phosphors were strongly influenced by post-annealing temperatures for blue-green persistent luminescence and latent fingerprints (LFPs). The X-ray powder diffraction patterns of the BaAl₂O₄: 1 mol% Eu nanophosphor, annealed between 1000 and 1300 °C, indicated a hexagonal ferroelectric phase. The X-ray photoelectron spectroscopy (XPS) revealed that the Ba atoms occupied two different sites in the BaAl₂O₄. The XPS and photoluminescence (PL) results revealed the presence of Eu³⁺ and Eu²⁺ states. The Eu-doped BaAl₂O₄ showed the characteristic red emission of Eu³⁺ at 251 and 464 nm excitations, while excitations at 340 and 380 nm showed yellowish-green emission. Strong evidence of energy transfer between a charge transfer band and the different energy levels of Eu²⁺ and Eu³⁺ ions was obtained. The existence of the Cr ion impurity in the aluminates was confirmed with UV-VIS diffuse reflectance and PL spectroscopy. The present results suggested that and O''_i defects have introduced electron and hole traps in the host that acted as luminescent centers for persistent luminescence. LFPs detection using BaAl₂O₃:Eu²⁺/Eu³⁺ phosphor showed an excellent marking agent for applications in forensic science.