Synthesis and Spectroscopic Properties of GdAl₃(BO₃)₄ Poly-crystals Codoped with Yb³⁺ and Eu³⁺

Abstract

GdAl₃(BO₃)₄ polycrystals co-doped with Yb³⁺ and Eu³⁺ has been synthesised by combustion method with urea. Upon the excitation at 465 nm (Eu³⁺/⁷F₆ → ⁵D₂ transition), emission bands centered at 590, 613, 697 and 702 nm in the wavelength region of 550–750 nm have clearly been observed, assigned to the electronic transitions of ⁵D₀ → ⁷F _J (J = 1, 2, 4 and 5) of Eu³⁺ ions, respectively. Meanwhile, an intense emission centred at 980 nm along with a shoulder at 1,040 nm has also been observed by exploiting a cross-relaxation process between the transitions of Eu³⁺/⁵D₀ → ⁷F₆ and Yb³⁺/²F_7/2 → ²F_5/2. On the contrary, an intense red up-conversion emission centred at 613 nm originated from the ⁵D₀ → ⁷F₂ transition of Eu³⁺ has been observed upon excitation with 980 nm laser diode. The quadratic dependence of the red up-conversion intensity on the pump-laser power reveals a cooperative energy transfer mechanism from a pair of Yb³⁺ ions to one Eu³⁺ ion.