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 Ca₃₋ₓNdₓGa₁.₉₉Cr₀.₀₁Ge₃O₁₂ at x = 0.09. A cross relaxation scheme related to ⁴T₂-⁴A₂ of Cr³⁺ and ⁴I₉/₂-⁴F₃/₂ 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.