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

摘要

A new zirconate-based pyrochlore-type red phosphor, Nd2Zr2O7: Eu3+, was synthesized using the gelcombustion 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 D-5(0)-F-7(0) 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 C-4. The red purity and high quantum efficiency of (NdZrO7)-Zr-2-O-2: Eu3+ projects it to be a new materials for commercial application in white light emitting diodes.