Contrasting role of Ca2+ on the Gd2TiO5: Eu3+ light emission under charge transfer and f-f band excitation: Interplay of oxygen vacancies and structural distortion

Abstract

The possibility of generating new lanthanide ion doped inorganic material that could work efficiently towards solid-state lighting was explored. The material studied in this work is Gd2TiO5 doped with Eu3+ which displays the lowest lattice strain, high solubility, and lacks both charge-compensating defects and structural deformation. In this study, the impacts of exchanging Gd with up to 10 mol% of Ca, an optically inactive ion, on the luminescence characteristics are investigated. Only small variations in the positron lifetimes suggest the Ca2+ doping only enhanced oxygen vacancies in the system.. Time resolved photoluminescence suggested that the emission intensity increases with Ca2+content when excited with 395 nm (f-f band) while it reduced when excited with 270 nm (charge transfer). The host to dopant energy transfer is attributed to the charge transfer from O2− to Eu3+ and the creation of oxygen vacancies due to Ca2+ doping reduced the charge transfer intensity. The intensity with excitation at 395 nm is almost doubled upon 10 % Ca doping and is attributed to enhanced distortions around the dopant favouring the direct excitation of Eu3+. The creation of oxygen vacancies via Ca substitution and the resultant distortions around Eu3+ ion have resulted in opposite variations in the emission intensity under excitation using charge transfer band and direct excitation. The study offers the possibility of exploring more methods of creating vacancies and distortions around Eu3+ to induce the spectral shifts.