Exploiting valence band mapping and select blue-green and red phosphorescence decay of γ-irradiated nanoscale Eu3+: Gd2O3 below concentration quenching

Abstract

We report on manifested blue-green and red emission features in Eu 3+ doped Gd 2 O 3 nanophosphors, subjected to 1.3 MeV gamma ( γ ) -irradiation and up to a dose of 2.4 kGy. While Eu 3+ states can be predicted at the core, occurrence of divalent species (Eu 2+ ) at the nanoparticle surfaces was revealed from the X-ray photoelectron spectroscopy (XPS) studies. Characteristic Eu 3+ activated orange-red emissions (590–650 nm) were revealed, and the nature of the corresponding transitions assigned. Moreover, time resolved photoluminescence (TR-PL) technique was employed to evaluate the lifetime of carriers participating in specific recombination emission events with and without specimens being exposed to γ -rays. The lifetime decay of our nanophosphor ranges between ∼1.6–1.3 ms, for electrically driven (ED: 5 D 0 → 7 F 2 ) and ∼1.98–1.56 ms, for magnetically driven (MD: 5 D 0 → 7 F 1 ) emissions. The modulation of ED and MD transitions in a suitable nanophosphor will have immense scope in next generation smart windows, display panels and bioimaging prospects. • XPS analysis reveals near surface Eu 2+ (divalent) states and dominant Eu 3+ (trivalent) at the core. • Modulation of PL emissions accompanied via 5 D 0 . → 7 F 1 (magnetic) and 5 D 0 → 7 F 2 (electric) transitions has been realized with dopant concentration andγ-dose. • TR-PL study offers decay parameters that seem to vary with dopant concentration and radiation exposure. • Two possible excitation pathways can populate the 5 D 0 level, one via 5 D 1 level and the other directly into 5 D 0 at higher dose.