Effect of gadolinium on europium luminescence and its in-situ valence conversion in SrBPO5 host

Abstract

Gadolinium/europium-activated strontium borophosphate (SrBPO5) phosphors were synthesized through solid-state reaction route in air atmosphere. Morphology and particle size were analyzed using scanning electron microscopy (SEM). Both europium and gadolinium were observed to emit strongly in this host. Interestingly, photoluminescence (PL) of both Eu2+ and Eu3+ was also observed. In the co-activated SrBPO5: Eu, Gd phosphors, the PL intensity of Eu3+ was enhanced significantly with simultaneous quenching of Eu2+ luminescence. The excitation and emission profiles of europium indicated the valence conversion (VC) of Eu2+ to Eu3+ in the presence of gadolinium. In addition to the VC, the luminescence of Eu3+ was also enhanced due to the energy transfer (ET) from Gd3+ to Eu3+. The ET was maximum for SrBPO5: Eu0.01, Gd0.075 phosphor at a critical distance of 2.76 Å. The co-activated phosphors exhibited a high color rendering index for Eu3+, suggesting it to be an efficient orange-red phosphor. PL lifetime decay studies suggested a single site occupancy for Eu2+ though the number of sites for Gd3+ and Eu3+ varied depending on their concentrations. The time-resolved emission spectroscopy (TRES) revealed different emission profiles for Eu3+ in varying time domains corroborating its different site occupancies. Strong thermoluminescence (TSL) was observed from these phosphors, though Eu2+ and Eu3+ PL were quenched following γ-irradiation. The calculated trap parameters and dose-response of γ-irradiated Eu, Gd-coactivated phosphor, suggested it to be a good thermoluminescent phosphor.