Enhanced energy transfer in Nd3+/Cr3+ co-doped Ca3Ga2Ge3O12 phosphors with near-infrared and long-lasting luminescence properties

Abstract

The phosphors of Ca₃Ga₂Ge₃O₁₂ (CGGG) co-doped with Nd³⁺ and Cr³⁺ ions were synthesized using conventional solid-state reaction techniques. Steady-state and time-resolved near-infrared (NIR) photoluminescence (PL) and long-lasting phosphorescence (LLP) properties are investigated in the Nd³⁺-doped CGGG samples. An increase in NIR luminescence traps can be realized in Nd³⁺/Cr³⁺ co-doped samples. Energy transfer from Cr³⁺ to Nd³⁺ with an efficiency of up to 57.5% is evident for Ca_3−xNd_xGa_1.99Cr_0.01Ge₃O₁₂ at x = 0.09. A cross relaxation scheme related to ⁴T₂–⁴A₂ of Cr³⁺ and ⁴I_9/2–⁴F_3/2 transitions of Nd³⁺ is discussed. We have presented the luminescence mechanism involving the competing processes of NIR PL and LLP, which is in accordance with our measurements. The results show that the NIR persistent luminescence of CGGG co-doped with Nd³⁺ and Cr³⁺ is more efficient compared to the single Nd³⁺ ion doped CGGG.