Photon energy dependent appearance and disappearance of magnetic dipole transition in Gd2Hf2O7:Sm3+ nanophosphors

Tuning the light emission from rare earth ions in host materials can be controlled by relative intensity of electric and magnetic dipole transitions (EDT and MDT). This work reports an investigation on photon energy and dopant local site endowed appearance-disappearance of magnetic dipole transition in pyrochlore Gd2Hf2O7:Sm3+ (GHOS) nanophosphors. This is utilized in achieving color tunable luminescence in GHOS nanocrystals by photon energy manipulations and local site engineering. DFT calculated formation energy showed the distribution of Sm3+ at both Gd3+ and Hf4+ sites. Excitation with charge transfer band (CTB at ∼275 nm) leads to both EDT and MDT endowed by excitation of both Sm@Gd and Sm@Hf sites. On the other hand, excitation with f-f band (∼405 nm) selectively excites Sm@Hf site and completely quenches MDT leading to pure red emission. Luminescence lifetime population analysis shows that CTB excites Sm@Gd and Sm@Hf sites with equal probability leading to yellowish orange emission whereas f-f band excitation exclusively excites Sm@Hf site generating pure red light. This work represents a way forward in the areas of understanding structure-property correlation, local site/photon energy induced color tunability, and modulating local structure of lanthanide dopants of phosphors.