Upconversion luminescence and ratiometric temperature sensing behavior of Er3+/Yb3+-codoped CaY2Ge3O10 germanate

A new series of CaY_2–10xYb_9xEr_xGe₃O₁₀ trigermanates (space group P2₁/c, Z=4) has been synthesized using an EDTA-assisted method. Under 980nm laser diode excitation, the samples exhibit intense upconversion luminescence corresponding to the characteristic transitions ²H_9/2→⁴I_15/2 (400–420nm), ²H_11/2,⁴S_3/2→⁴I_15/2 (500–600nm) and ⁴F_9/2→⁴I_15/2 (625–725nm) in Er³⁺ ions. The CaY_1.5Yb_0.45Er_0.05Ge₃O₁₀ phosphor can be used as a good temperature sensor with high absolute and relative sensitivities S_a(max)=0.0051 K⁻¹ and S_r(max)=0.0109 K⁻¹.