Achieving perfect white light, color tunability and X-ray scintillation in nanocrystalline La2Hf2O7:Eu3+,Bi3+ by photon energy and doping engineering

Materials which can demonstrate multifunctional lighting efficacy could be boon towards sustainable and developed economy owing to large materials crunch and huge electricity demands. In this work, we have hit three birds with one stone by judicious choice of photon energy and dopant composition engineering in bismuth sensitized Eu3+-doped La2Hf2O7 nanoparticles prepared by a molten salt synthesis method. Bismuth is found to stabilized at both La3+ and Hf4+ sites with Bi@La get excited at high photon energy whereas both Bi@La and Bi@Hf get co-excited at low photon energy to produce perfect amalgam of blue and green Bi3+ emissions upon excitation at 365 nm which couples with Eu3+ red emission and produces white light with (0.31, 0.32) color coordinate. Also, color tunability from violet-blue-purple-pink to orangish red is successfully achieved by effi-cient Bi3+ -> Eu3+ energy transfers via electric multipolar interaction. Density functional theory (DFT) calcu-lations for defect formation energy and density of state (DOS) supported distribution of Bi3+ at both La3+ and Hf4+ sites as well as high feasibility of Bi3+ -> Eu3+ energy transfers. Moreover, the La2Hf2O7:0.5%Bi3+,x%Eu3+ NPs demonstrated excellent Eu2+/Eu3+ radioluminescence properties. These characteristics of the La2Hf2O7:0.5%Bi3+,x%Eu3+ NPs described above indicate that these phosphors can be used as potential radio-luminescent materials for phosphor converted light emitting diodes and X-ray screen.