Efficient energy transfer and photoluminescent characteristics in SrAl ₁₂O₁₉:Eu²⁺,Cr³⁺ nano-rods

Cr³⁺ singly doped and Eu²⁺, Cr³⁺ co-doped SrAl₁₂O₁₉ nano-rods with different diameters have been prepared by a combustion method. A new emission band of Cr³⁺ centered at 704 nm on the low energy side of the R-line at 688 nm originating from the ²E-⁴A₂ transition of Cr³⁺ is observed. This band enhances with decreasing diameter of the nano-rods, implying its origin in the Cr³⁺ ions on the surface of the nano-rods. Photoluminescence study and fluorescence lifetime measurements demonstrate efficient energy transfer from Eu²⁺ to Cr³⁺ in SrAl ₁₂O₁₉ nano-rods in comparison with the corresponding bulk materials. This result is attributed to a large spectral overlap between the Eu²⁺ emission band and the ⁴A₂- ⁴T₁ (F) absorption band of Cr³⁺ on the surface of the nano-rods.