Wide colour tunability through cross relaxation and energy transfer in a Eu3+/Tb3+:ZnGa2O4 phosphor

Abstract

In this article, the Tb3+, Eu3+ activated/co-activated ZnGa2O4 phosphors were synthesized using solid state reaction method to study the structural and optical characteristics. The XRD and SEM techniques, were used to study the crystallinity, phase purity and particles size whereas the EDS measurement approved the existence of different elements present in the phosphor samples. The FTIR and diffuse reflectance spectra of phosphor samples were studied to know the phonon frequency and the optical band gap. The PLem spectra of Tb3+ activated ZnGa2O4 phosphor contain blue, green and orange red emissions on 378 nm excitation. A colour tunability from blue to green regions was seen to arise due to cross relaxation on increasing the concentrations of Tb3+ ion. The Eu3+ activated ZnGa2O4 phosphor exhibited a strong red emission under 393 nm excitation. Further, the Eu3+ activated ZnGa2O4:Tb3+ phosphor showed colour tunability from blue to bluish white and from green to red under 260 and 378 nm excitations, respectively. Moreover, an energy-transfer (ET) has been observed from Tb3+ to Eu3+ ions with energy transfer mechanism as dipole-dipole interaction. The ET efficiency for 0.8 mol% Eu3+ in ZnGa2O4:0.05 Tb3+ phosphor has been found 97%. Under 260 nm excitation, the Eu3+/Tb3+ co-activated ZnGa2O4 phosphor also emits blue, green and red bands. Thus, the Tb3+, Eu3+ co-activated ZnGa2O4 phosphor may be useful for solid-state lighting applications.