Suppressing disorder-order phase transition of Gd2Zr2O7 pyrochlore by Dy3+ doping and their impact on luminescence

Abstract

The functionality of the Gd2Zr2O7 matrix is dictated by ordering at the cationic lattice (pyrochlore or defective fluorite) and associated local manifestations. In this work, we have synthesized nano and bulk undoped Gd2Zr2O7 (GZO) and Gd2Zr2O7:Dy3+ (GZOD) by molten salt synthesis adopting a crystal engineering approach and investigated their impact on photoluminescence properties. DFT calculations along with the higher intensity of yellow emission in the bulk GZOD confirm that the presence of Dy3+ is energetically favorable in defect fluorite structure compared to ordered pyrochlore counterpart. Increase/adjustments in the Zr–O bond distances in Dy3+ surroundings facilitate the release of local strain/stress in defective fluorite structure, which is not feasible in the perfectly ordered pyrochlore structure. Overall, the preference of defective fluorite structure by the GZO NCs, GZOD NCs, and bulk GZOD has been attributed to inherent flexibility in local structure with varying coordination numbers and polyhedral arrangements that assist in reducing the strain arising due to smaller particle size and/or by Dy3+ doping. It is believed that the present work provides simplistic pathways to control the order-disorder transformation, and in turn, the functionality of the Gd2Zr2O7 matrix for better hosting of nuclear waste and phosphor centers.