On the unusual photoluminescence of Eu3+ in α-Zn2P2O7: a time resolved emission spectrometric and Judd–Ofelt study

Abstract

Zn₂P₂O₇:Eu³⁺ was synthesized and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM); Fourier transformed infrared spectroscopy (FTIR) and photoluminescence (PL) techniques. Based on the time resolved emission spectroscopic investigations (TRES), it was inferred that two different types of Eu³⁺ ions were present in the zinc pyrophosphate. The first type was a long lived species (∼τ = 1.77 ms) present at relatively few symmetric ‘5-coordinated Zn’ sites, while the second was a short lived species (∼τ = 620 μs) present at symmetric ‘6-coordinated Zn’ sites. This unusual behavior of the trivalent rare earth species could be explained with the help of Judd–Ofelt (J–O) calculations. From the calculations, the radiative (τ_R) and non radiative (τ_NR) life times were evaluated for both species. It was observed that the radiative life time of the Eu³⁺ species present in symmetric environment was higher than that of the species present in the asymmetric environment, which is consistent with the selection rules governing the transition. It was observed that the presence of a very strong non-radiative component at the symmetric site brings down the overall lifetime value. The J–O intensity parameters for all the Eu³⁺ species present in the pyrophosphate system were calculated adopting standard procedure. Ω₄ > Ω₂ was found that for short lived species; while for the long lived species, the reverse trend was observed further confirming the correlation between the asymmetry and bonding.