Light emission of Lu2Sn2O7 pyrochlore driven by oxygen vacancy and local site engineering

Abstract

This work manifested the crucial role played by defect and dopant ion local structure in maneuvering light emission characteristics of optical materials. We have harnessed the full gamut of visible light emission from green to yellow to orange-red endowed by oxygen vacancies (OVs) in undoped Lu2Sn2O7 (LSO) pyrochlore and Sm3+/Dy3+ doping in LSO pyrochlore. The energy required to create a OVs at 48f position is lowered with respect to VO8b, hence VO48f defects are expected to present at a larger fraction and are responsible for green emission in the LSO. Though Dy3+ ion is distributed at both Lu3+ and Sn4+ site, the contribution of asymmetric Dy@Sn ion is more than that of symmetric Dy@Lu in PL process of Lu2Sn2O7:Dy3+ leading to intense yellow light compared to blue light and is consistent with the DFT calculations. On the other hand, Sm3+ substitution at the Sn lattice site is thermodynamically more favorable in Lu2Sn2O7:Sm3+ (LSOS) by 1.38 eV with respect to Lu lattice site. Based on time-resolved photoluminescence spectroscopy, it is postulated that Sm@Sn with far-off OVs leads to magnetic dipole (MDT) and the one with nearby OVs leads to electric dipole transition (EDT) in LSOS. This concept of defect induced emission and role of defect and dopant local structure can be applicable to various luminescent phosphors which provides a unique approach for tuning other properties of optically multifunctional crystals that are highly sensitive to defect and dopants local site engineering.