Terbium Ion-Mediated Energy Transfer In Wo3:Tb3+ And Eu3+ Phosphors For Uv-Sensitized White Light Emission

Incorporation of suitable lanthanide (Ln(3+)) ions into semiconducting WO3 can be useful to produce host-sensitized luminescence for solid-state lighting applications. Codoping of another Ln(3+) ion can assist in transferring energy from the host to the activator Ln(3+) ion to produce bright luminescence depending upon the electronic structure of the doped system. As a case study, Eu3+ and Tb3+ ion-doped WO3 phosphors (WO3:Tbx3+Euy3+, x = 0-0.05 and y = 0-0.20) have been prepared over a wide range of doping concentrations to investigate the role of the Tb3+ ion as a sensitizer and realize host-sensitized emission from Eu3+ ions. The steady-state and time-resolved photoluminescence (TRPL) data for WO3:Tbx3+Euy3+ (x = 0-0.05 and y = 0-0.10) samples confirm that Tb3+ ions assist in excitation of Eu3+ ions via sequential energy transfers from the host to Tb3+ ions followed by Tb3+ to Eu3+ ions. The energy transfer process is controlled by optimizing their doping concentrations, and a single-phase white-light-emitting phosphor with a composition WO3:Tb0.053+Eu0.00053+ has been developed. The electronic band structures and projected density of state plots for the WO3:Tb0.031253+Eu00.031253+ system obtained using density functional theory (DFT)-based simulations confirm the formation of impurity states due to Eu3+ and Tb3+ ions within the forbidden gap of WO3. Based on the TRPL and DFT data, it is confirmed that the Tb3+ ions act as a bridge between the conduction band edge of WO3 and excited states of Eu3+ ions to transfer energy and facilitate characteristic emission from europium species.