Lanthanide-doped lanthanum hafnate nanoparticles as multicolor phosphors for warm white lighting and scintillators

Designing luminescent materials especially nanomaterials with multifunctional applications is highly challenging and demanding. In this work, we explored pyrochlore La₂Hf₂O₇ nanoparticles (NPs) singly and triply codoped with Eu³⁺, Tb³⁺ and Dy³⁺. Under both ultraviolet and X-ray irradiations, the La₂Hf₂O₇ NPs singly doped with Eu³⁺, Tb³⁺ and Dy³⁺ displayed red, green and yellowish-blue emission, respectively. The concentration quenching study revealed a non-radiative energy transfer in Eu³⁺ doped La₂Hf₂O₇ NPs, which takes place via dipole-quadrupole mechanism. On the other hand, a dipole-dipole interaction prevails in Tb³⁺ and Dy³⁺ doped La₂Hf₂O₇ NPs. Lifetime spectroscopy reveals the stabilization of Eu³⁺ and Dy³⁺ ions at La³⁺ site at low doping concentration whereas a fraction of them migrates to Hf⁴⁺ site at high doping concentration. For the La₂Hf₂O₇:Tb³⁺ NPs, Tb³⁺ ions are localized at Hf⁴⁺ site at all doping concentrations. Furthermore, when triply codoped with Eu³⁺, Tb³⁺ and Dy³⁺ ions, the La₂Hf₂O₇ NPs display beautiful warm white light as a new strategy for color tunability through doping percentage. To sum, our complete spectrum of studies on the structure, UV excited photoluminescence, concentration quenching, and local site spectroscopy of the La₂Hf₂O₇:Ln³⁺ NPs suggests that they are potential candidates as single-component multicolor-emitting phosphors for lighting and scintillating applications.