Energy transfer and multiple photoluminescence of LuNbO4 co-doped with Eu3+ and Tb3+

The energy transfer and multiple photoluminescence of LuNbO₄:Eu³⁺,Tb³⁺ powders were investigated. The photoluminescence spectra of the powders mainly consisted of green and red emission peaks. The green emission peaks (551 nm) were assigned to the ⁵D₄ → ⁷F₅ transition of Tb³⁺, and the strong red emission peaks (614 nm) originated from Eu³⁺ (⁵D₀ → ⁷F₂) via a Tb³⁺ → Eu³⁺ energy transfer. Tb³⁺–Eu³⁺ co-doping greatly enhanced the red emission under UV excitation that could rarely activate Eu³⁺ ions. The emission of the powders was tunable from green to red by adjusting the ratio of Eu³⁺/Tb³⁺, and thus warm white-light-emitting powders could be obtained. The Tb³⁺ → Eu³⁺ energy transfer mechanism was explained using the energy transfer efficiency, the critical distance for the Tb³⁺ → Eu³⁺ energy transfer, fluorescence decay curves, and multipolar interactions. The results demonstrate that LuNbO₄:Eu³⁺,Tb³⁺ powders have a high potential for use in UV-pumped white-light-emitting diodes.