Eu3+ local site analysis and emission characteristics of novel Nd2Zr2O7:Eu phosphor: insight into the effect of europium concentration on its photoluminescence properties

Abstract

A new zirconate-based pyrochlore-type red phosphor, Nd₂Zr₂O₇:Eu³⁺, was synthesized using the gel-combustion method. The un-doped sample showed visible emission due to the presence of oxygen vacancies. On doping with europium ions, it was found that Eu was distributed into both Nd³⁺ as well as Zr⁴⁺ sites based on emission and lifetime spectroscopy with a lifetime value of 3.35 and 1.14 ms, respectively, although the population at the Zr⁴⁺ site is more than that at the Nd³⁺ site. This is also justified by the presence of two stark components in the ⁵D₀–⁷F₀ transition. The presence of host emission in the spectrum of Nd₂Zr₂O₇:Eu³⁺ indicated incomplete energy transfer process at low levels of europium doping. Moreover, the efficiency of energy transfer increased as the doping percentage increased, and complete host-dopant energy transfer took place at 5.0% Eu³⁺ doping. Based on time resolved emission spectroscopy (TRES), the emission spectrum of europium into the Nd³⁺ sites as well as at Zr⁴⁺ sites was elucidated. Calculation of the Judd–Ofelt parameter illustrated that at all europium concentration, the local surrounding area lacks inversion symmetry (asymmetric environment) and the exact point group symmetry was found to be C₄. The red purity and high quantum efficiency of Nd₂Zr₂O₇:Eu³⁺ projects it to be a new materials for commercial application in white light emitting diodes.